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# Spherical tokamak

Not to be confused with the spheromak, another topic in fusion research.
A plasma in the MAST reactor. Note the almost spherical shape of the outside edge of the plasma. The high "elongation" is also evident, notably the filaments extending off the top and bottom near the central conductor.

A spherical tokamak is a type of fusion power device based on the tokamak principle. It is notable for its very narrow profile, or "aspect ratio". A traditional tokamak has a toroidal confinement area that gives it an overall shape similar to a donut, complete with a large hole in the middle. The spherical tokamak reduces the size of the hole almost to zero, resulting in a plasma shape that is almost spherical, often compared with a cored apple. The spherical tokamak is sometimes referred to as a spherical torus and often shortened to ST.

The spherical tokamak is an offshoot of the conventional tokamak design. Proponents claim that it has a number of practical advantages over these devices, some of them dramatic. For this reason the ST has seen considerable interest since it was introduced in the late 1980s. However, development remains effectively one generation behind mainline efforts like JET. Major experiments in the field include the pioneering START and MAST at Culham in the UK, the US's NSTX, and numerous others.

Further theoretical work has cast some doubt on the use of spherical tokamaks as a route to lower cost power producing reactors. Further research is needed to better understand the "scaling laws" associated with this design. Even in the event that spherical tokamaks do not lead to lower cost approaches to generation, they are still lower cost in general; this makes them attractive devices for general plasma physics uses, or as concentrated high-energy neutron sources.

## History

### Aspect ratio

Fusion reactor efficiency is based on the amount of power released from fusion reactions compared with the power needed to keep the plasma hot. This can be calculated from three key measures; the temperature of the plasma, its density, and the length of time the reaction is maintained. The product of these three measures is the "fusion triple product", and in order to be economic it must reach the Lawson criterion, ≥3 • 1021  keV • seconds / m³.[1][2]

Tokamaks are the leading approach within the larger group of magnetic fusion energy (MFE) designs, all of which attempt to confine a plasma using powerful magnetic fields. In the MFE approach, it is the time axis that is considered most important for ongoing development. Tokamaks confine their fuel at low pressure (around 1/millionth of atmospheric) but high temperatures (150 million Celsius), and attempt to keep those conditions stable for increasing times on the order of seconds to minutes.[3]

A key measure of MFE reactor economics is "beta", β, the ratio of plasma pressure to the magnetic pressure.[4][5] Improving beta means that you need to use, in relative terms, less energy to generate the magnetic fields for any given plasma pressure (or density). The price of magnets scales roughly with β½, so reactors operating at higher betas are less expensive for any given level of confinement. Tokamaks operate at relatively low betas, a few %, and generally require superconducting magnets in order to have enough field strength to reach useful densities.

The limiting factor in reducing beta is the size of the magnets. Tokamaks use a series of ring-shaped magnets around the confinement area, and their physical dimensions mean that the hole in the middle of the torus can be reduced only so much before the magnet windings are touching. This limits the aspect ratio, A, of the reactor to about 2.5; the diameter of the reactor as a whole could be about 2.5 times the cross-sectional diameter of the confinement area. Some experimental designs were slightly under this limit, while many reactors had much higher A.

### Reducing A

During the 1980s, researchers at Oak Ridge National Laboratory (ORNL), led by Ben Carreras and Tim Hender, were studying the operations of tokamaks as A was reduced. They noticed, based on magnetohydrodynamic considerations, that tokamaks were inherently more stable at low aspect ratios. In particular, the classic "kink instability" was strongly suppressed. Other groups expanded on this body of theory, and found that the same was true for the high-order ballooning instability as well. This suggested that a low-A machine would not only be less expensive to build, but have better performance as well.[6]

One way to reduce the size of the magnets is to re-arrange them around the confinement area. This was the idea behind the "compact tokamak" designs, typified by the Alcator C-Mod, Riggatron and IGNITOR. The later two of these designs place the magnets inside the confinement area, so the toroidal vacuum vessel can be replaced with a cylinder. The decreased distance between the magnets and plasma leads to much higher betas, so conventional (non-superconducting) magnets could be used.[7] The downside to this approach, one that was widely criticized, is that it places the magnets directly in the high-energy neutron flux of the fusion reactions.[8] In operation the magnets would be rapidly eroded, requiring the vacuum vessel to be opened and the entire magnet assembly replaced after a month or so of operation.

Around the same time, several advances in plasma physics were making their way through the fusion community. Of particular importance were the concepts of elongation and triangularity, referring to the cross-sectional shape of the plasma. Early tokamaks had all used circular cross-sections simply because that was the easiest to model and build, but over time it became clear that C or (more commonly) D-shaped plasma cross-sections led to higher performance. This produces plasmas with high "shear", which distributed and broke up turbulent eddies in the plasma.[6] These changes led to the "advanced tokamak" designs, which include ITER.[9]

### Spherical tokamaks

In 1984,[10] Martin Peng of ORNL proposed an alternate arrangement of the magnet coils that would greatly reduce the aspect ratio while avoiding the erosion issues of the compact tokamak. Instead of wiring each magnet coil separately, he proposed using a single large conductor in the center, and wiring the magnets as half-rings off of this conductor. What was once a series of individual rings passing through the hole in the center of the reactor was reduced to a single post, allowing for aspect ratios as low as 1.2.[5][11] This means that ST's can reach the same operational triple product numbers as conventional designs using one tenth the magnetic field.

The design, naturally, also included the advances in plasma shaping that were being studied concurrently. Like all modern designs, the ST uses a D-shaped plasma cross section. If you consider a D on the right side and a reversed D on the left, as the two approach each other (as A is reduced) eventually the vertical surfaces touch and the resulting shape is a circle. In 3D, the outer surface is roughly spherical. They named this layout the "spherical tokamak", or ST. These studies suggested that the ST layout would include all the qualities of the advanced tokamak, the compact tokamak, would strongly suppress several forms of turbulence, reach high β, have high self-magnetism and be less costly to build.[12]

The ST concept appeared to represent an enormous advance in tokamak design. However, it was being proposed during a period when US fusion research budgets were being dramatically scaled back. ORNL was provided with funds to develop a suitable central column built out of a high-strength copper alloy called "Glidcop".[13] However, they were unable to secure funding to build a demonstration machine, "STX".[12][14]

### From spheromak to ST

Failing to build an ST at ORNL, Peng began a worldwide effort to interest other teams in the ST concept and get a test machine built. One way to do this quickly would be to convert a spheromak machine to the ST layout.[11]

Spheromaks are essentially "smoke rings" of plasma that are internally self-stable. They can, however, drift about within their confinement area. The typical solution to this problem was to wrap the area in a sheet of copper, or more rarely, place a copper conductor down the center. When the spheromak approaches the conductor, a magnetic field is generated that pushes it away again. A number of experimental spheromak machines were built in the 1970s and early 80s, but demonstrated performance that simply was not interesting enough to suggest further development.

Machines with the central conductor had a strong mechanical resemblance to the ST design, and could be converted with relative ease. The first such conversion was made to the Heidelberg Spheromak Experiment, or HSE. Built at Heidelberg University in the early 1980s, HSE was quickly converted to a ST in 1987 by adding new magnets to the outside of the confinement area and attaching them to its central conductor.[15] Although the new configuration only operated "cold", far below fusion temperatures, the results were promising and demonstrated all of the basic features of the ST.

Several other groups with spheromak machines made similar conversions, notably the rotamak at the Australian Nuclear Science and Technology Organisation and the SPHEX machine.[16] In general they all found an increase in performance of a factor of two or more. This was an enormous advance, and the need for a purpose-built machine became pressing.

Peng's advocacy also caught the interest of Derek Robinson, of the United Kingdom Atomic Energy Authority (UKAEA) fusion center at Culham.[17] What is today known as the Culham Centre for Fusion Energy was set up in the 1960s to gather together all of the UK's fusion research, formerly spread across several sites, and Robinson had recently been promoted to running several projects at the site.

Robinson was able to gather together a team and secure funding on the order of 100,000 pounds to build an experimental machine, the Small Tight Aspect Ratio Tokamak, or START. Several parts of the machine were recycled from earlier projects, while others were loaned from other labs, including a 40 keV neutral beam injector from ORNL.[18] Before it started operation there was considerable uncertainty about its performance, and predictions that the project would be shut down if confinement proved to be similar to spheromaks.

Construction of START began in 1990, it was assembled rapidly and started operation in January 1991.[14] Its earliest operations quickly put any theoretical concerns to rest. Using ohmic heating alone, START demonstrated betas as high as 12%, almost matching the record of 12.6% on the DIII-D machine.[11][19] The results were so good that an additional 10 million pounds of funding was provided over time, leading to a major re-build in 1995. When neutral beam heating was turned on, beta jumped to 40%, beating any conventional design by 3 times.[19]

Additionally, START demonstrated excellent plasma stability. A practical rule of thumb in conventional designs is that as the operational beta approaches a certain value normalized for the machine size, ballooning instability destabilizes the plasma. This so-called "Troyon limit" is normally 4, and generally limited to about 3.5 in real world machines. START improved this dramatically to 6. The limit depends on size of the machine, and indicates that machines will have to be built of at least a certain size if they wish to reach some performance goal. With START's much higher scaling, the same limits would be reached with a smaller machine.[20]

### Rush to build STs

START proved Peng and Strickler's predictions; the ST had performance an order of magnitude better than conventional designs, and cost much less to build as well. In terms of overall economics, the ST was an enormous step forward.

Moreover, the ST was a new approach, and a low-cost one. It was one of the few areas of mainline fusion research where real contributions could be made on small budgets. This sparked off a series of ST developments around the world. In particular, the National Spherical Torus Experiment (NSTX) and Pegasus experiments in the US, Globus-M in Russia, and the UK's follow-on to START, MAST. START itself found new life as part of the Proto-Sphera project in Italy, where experimenters are attempting to eliminate the central column by passing the current through a secondary plasma.[21]

## Design

Tokamak reactors consist of a toroidal vacuum tube surrounded by a series of magnets. One set of magnets is logically wired in a series of rings around the outside of the tube, but are physically connected through a common conductor in the center. The central column is also normally used to house the solenoid that forms the inductive loop for the ohmic heating system (and pinch current).

The canonical example of the design can be seen in the small tabletop ST device made at Flinders University,[22] which uses a central column made of copper wire wound into a solenoid, return bars for the toroidal field made of vertical copper wires, and a metal ring connecting the two and providing mechanical support to the structure.

### Stability within the ST

Advances in plasma physics in the 1970s and 80s led to a much stronger understanding of stability issues, and this developed into a series of "scaling laws" that can be used to quickly determine rough operational numbers across a wide variety of systems. In particular, Troyon's work on the critical beta of a reactor design is considered one of the great advances in modern plasma physics. Troyon's work provides a beta limit where operational reactors will start to see significant instabilities, and demonstrates how this limit scales with size, layout, magnetic field and current in the plasma.

However, Troyon's work did not consider extreme aspect ratios, work that was later carried out by a group at the Princeton Plasma Physics Laboratory.[23] This starts with a development of a useful beta for a highly asymmetric volume:

$\beta=\frac{\mu_{0}p}{\langle B^2\rangle}.$

Where $\langle B^2\rangle$ is the volume averaged magnetic field $\scriptstyle\langle B^2\rangle = \langle B_{\theta}^2 + B_{\rho}^2\rangle$ (as opposed to Troyon's use of the field in the vacuum outside the plasma, $\scriptstyle B_0$). Following Freidberg,[24] this beta is then fed into a modified version of the safety factor:

$q_\star= \frac{2\pi B_0 a^2}{\mu_0 R_0 I} \left( \frac{1+\kappa^2}{2} \right).$

Where $\scriptstyle B_0$ is the vacuum magnetic field, a is the minor radius, $\scriptstyle R$ the major radius, $\scriptstyle I$ the plasma current, and $\scriptstyle \kappa$ the elongation. In this definition it should be clear that decreasing aspect ratio, $\scriptstyle a/R,$ leads to higher average safety factors. These definitions allowed the Princeton group to develop a more flexible version of Troyon's critical beta:

$\beta_\text{crit} = 5\langle B_N\rangle \left( \frac{1+\kappa^2}{2}\right) \frac{\epsilon}{q_\star}.$

Where $\epsilon$ is the inverse aspect ratio $1/A$ and $\langle B_N\rangle$ is a constant scaling factor that is about 0.03 for any $q_\star$ greater than 2. Note that the critical beta scales with aspect ratio, although not directly, because $q_\star$ also includes aspect ratio factors. Numerically, it can be shown that $q_\star$ is maximized for:

$q_\star = 1 + \left(\frac{3}{4}\right)^{4/5} \approx 1.8.$

Using this in the critical beta formula above:

$\beta_\text{max} = 0.072 \left(\frac{1+\kappa^2}{2}\right)\epsilon.$

For a spherical tokamak with an elongation $\kappa$ of 2 and an aspect ratio of 1.25:

$\beta_\text{max} = 0.072 \left(\frac{1+2^2}{2}\right)\frac{1}{1.25} = 0.14.$

Now compare this to a traditional tokamak with the same elongation and a major radius of 5 meters and minor radius of 2 meters:

$\beta_\text{max} = 0.072 \left(\frac{1+2^2}{2}\right)\frac{1}{5/2} = 0.072.$

The linearity of $\beta_\text{max}\,$ with aspect ratio is evident.

### Power scaling

Beta is an important measure of performance, but in the case of a reactor designed to produce electricity, there are other practical issues that have to be considered. Among these is the power density, which offers an estimate of the size of the machine needed for a given power output. This is, in turn, a function of the plasma pressure, which is in turn a function of beta. At first glance it might seem that the ST's higher betas would naturally lead to higher allowable pressures, and thus higher power density. However, this is only true if the magnetic field remains the same – beta is the ratio of magnetic to plasma density.

If one imagines a toroidal confinement area wrapped with ring-shaped magnets, it is clear that the magnetic field is greater on the inside radius than the outside - this is the basic stability problem that the tokamak's electrical current addresses. However, the difference in that field is a function of aspect ratio; an infinitely large toroid would approximate a straight solenoid, while an ST maximizes the difference in field strength. Moreover, as there are certain aspects of reactor design that are fixed in size, the aspect ratio might be forced into certain configurations. For instance, production reactors would use a thick "blanket" containing lithium around the reactor core in order to capture the high-energy neutrons being released, both to protect the rest of the reactor mass from these neutrons as well as produce tritium for fuel. The size of the blanket is a function of the neutron's energy, which is 14 MeV in the D-T reaction regardless of the reactor design, Thus the blanket would be the same for a ST or traditional design, about a meter across.

In this case further consideration of the overall magnetic field is needed when considering the betas. Working inward through the reactor volume toward the inner surface of the plasma we would encounter the blanket, "first wall" and several empty spaces. As we move away from the magnet, the field reduces in a roughly linear fashion. If we consider these reactor components as a group, we can calculate the magnetic field that remains on the far side of the blanket, at the inner face of the plasma:

$B_{0}= ({1 - \epsilon_B - \epsilon}) {B_\text{max}}.\,$

Now we consider the average plasma pressure that can be generated with this magnetic field. Following Freidberg:[24]

${\langle p \rangle} = \beta_\text{max}\left (1 + \kappa^2\right) \epsilon \left({1 - \epsilon_B - \epsilon}\right)^2 G(\epsilon) \left(B_\text{max}\right)^2.$

In an ST, where were are attempting to maximize $B_0$ as a general principle, one can eliminate the blanket on the inside face and leave the central column open to the neutrons. In this case, $\epsilon_0$ is zero. Considering a central column made of copper, we can fix the maximum field generated in the coil, $B_\text{max}$ to about 7.5 T. Using the ideal numbers from the section above:

${\langle p \rangle} = 0.14 \left(1 + 2^2\right) \left(\frac{1}{1.25}\right) \left(1 - \frac{1}{1.25}\right)^2 2.5 \cdot 7.5^2 = 2.6 \text{ atmospheres}.$

Now consider the conventional design as above, using superconducting magnets with a $B_\text{max}$ of 15 T, and a blanket of 1.2 meters thickness. First we calculate $\epsilon$ to be 1/(5/2) = 0.4 and $\epsilon_b$ to be 1.5/5 = 0.24, then:

${\langle p \rangle} = 0.072 \left(1 + 2^2\right) \left(\frac{1}{0.4}\right) \left(1 - \frac{1}{0.24} - \frac{1}{0.4}\right)^2 1.2 \cdot 15^2 = 7.7 \text{ atmospheres}.$

So in spite of the higher beta in the ST, the overall power density is lower, largely due to the use of superconducting magnets in the traditional design. This issue has led to considerable work to see if these scaling laws hold for the ST, and efforts to increase the allowable field strength through a variety of methods. Work on START suggests that the scaling factors are much higher in ST's, but this work needs to be replicated at higher powers to better understand the scaling.[25]

ST's have two major advantages over conventional designs.

The first is practical. Using the ST layout places the toroidal magnets much closer to the plasma, on average. This greatly reduces the amount of energy needed to power the magnets in order to reach any particular level of magnetic field within the plasma. Smaller magnets cost less, reducing the cost of the reactor. The gains are so great that superconducting magnets may not be required, leading to even greater cost reductions. START placed the secondary magnets inside the vacuum chamber, but in modern machines these have been moved outside and can be superconducting.[26]

The other advantages have to do with the stability of the plasma. Since the earliest days of fusion research, the problem in making a useful system has been a number of plasma instabilities that only appeared as the operating conditions moved ever closer to useful ones for fusion power. In 1954 Edward Teller hosted a meeting exploring some of these issues, and noted that he felt plasmas would be inherently more stable if they were following convex lines of magnetic force, rather than concave.[27] It was not clear at the time if this manifested itself in the real world, but over time the wisdom of these words become apparent.

In the tokamak, stellarator and most pinch devices, the plasma is forced to follow helical magnetic lines. This alternately moves the plasma from the outside of the confinement area to the inside. While on the outside, the particles are being pushed inward, following a concave line. As they move to the inside they are being pushed outward, following a convex line. Thus, following Teller's reasoning, the plasma is inherently more stable on the inside section of the reactor. In practice the actual limits are suggested by the "safety factor", q, which vary over the volume of the plasma.[28]

In a traditional circular cross-section tokamak, the plasma spends about the same time on the inside and the outside of the torus; slightly less on the inside because of the shorter radius. In the advanced tokamak with a D-shaped plasma, the inside surface of the plasma is significantly enlarged and the particles spend more time there. However, in a normal high-A design, q varies only slightly as the particle moves about, as the relative distance from inside the outside is small compared to the radius of the machine as a whole (the definition of aspect ratio). In an ST machine, the variance from "inside" to "outside" is much larger in relative terms, and the particles spend much more of their time on the "inside". This leads to greatly improved stability.[25]

It is possible to build a traditional tokamak that operates at higher betas, through the use of more powerful magnets. To do this, the current in the plasma must be increased in order to generate the toroidal magnetic field of the right magnitude. This drives the plasma ever closer to the Troyon limits where instabilities set in. The ST design, through its mechanical arrangement, has much better q and thus allows for much more magnetic power before the instabilities appear. Conventional designs hit the Troyon limit around 3.5, whereas START demonstrated operation at 6.[19]

The ST has three distinct disadvantages compared to "conventional" advanced tokamaks with higher aspect ratios.

The first issue is that the overall pressure of the plasma in an ST is lower than conventional designs, in spite of higher beta. This is due to the limits of the magnetic field on the inside of the plasma, $B_\text{max}.$ This limit is theoretically the same in the ST and conventional designs, but as the ST has a much higher aspect ratio, the effective field changes more dramatically over the plasma volume.[29]

The second issue is both an advantage and disadvantage. The ST is so small, at least in the center, that there is little or no room for superconducting magnets. This is not a deal-breaker for the design, as the fields from conventional copper wound magnets is enough for the ST design. However, this means that power dissipation in the central column will be considerable. Engineering studies suggest that the maximum field possible will be about 7.5 T, much lower than is possible with a conventional layout. This places a further limit on the allowable plasma pressures.[29] However, the lack of superconducting magnets greatly lowers the price of the system, potentially offsetting this issue economically.

The lack of shielding also means the magnet is directly exposed to the interior of the reactor. It is subject to the full heating flux of the plasma, and the neutrons generated by the fusion reactions. In practice, this means that the column would have to be replaced fairly often, likely on the order of a year, greatly affecting the availability of the reactor.[30] In production settings, the availability is directly related to the cost of electrical production. Experiments are underway to see if the conductor can be replaced by a z-pinch plasma[31] or liquid metal conductor[32] in its place.

Finally, the highly asymmetrical plasma cross sections and tightly wound magnetic fields require very high toroidal currents to maintain. Normally this would require large amounts of secondary heating systems, like neutral beam injection. These are energetically expensive, so the ST design relies on high bootstrap currents for economical operation.[29] Luckily, high elongation and triangularity are the features that give rise to these currents, so it is possible that the ST will actually be more economical in this regard.[33] This is an area of active research.

## References

Citations
1. ^ John Lawson, "Some Criteria for a Power Producing Thermonuclear Reactor", Proceedings of the Physical Society B, Volume 70 (1957), p. 6
2. ^ Sykes 2008, pg. 41
3. ^ Many advanced tokamak designs routinely hit numbers on the order of ~ 1 × 1021 keV • seconds / m³, see "Fusion Triple Product and the Density Limit of High-Density Internal Diffusion Barrier Plasmas in LHD", 35th EPS Conference on Plasma Phys. Hersonissos, 9–13 June 2008
4. ^ John Wesson and David Campbell, "Tokamaks", Clarendon Press, 2004, pg. 115
5. ^ a b Sykes 1997, pg. B247
6. ^ a b Sykes 2008, pg. 10
7. ^ D.L. Jasby, "Selection of a toroidal fusion reactor concept for a magnetic fusion production reactor", Journal of Fusion Energy, Volume 6 Number 1 (1987), pg. 65
8. ^ "Evaluation of Riggatron Concept", Office of Naval Research
9. ^ Charles Kessel, "What's an Advanced Tokamak", Spring APS, Philadelphia, 2003
10. ^ Y-K Martin Peng, "Spherical Torus, Compact Fusion at Low Yield"., ORNL/FEDC-87/7 (December 1984)
11. ^ a b c Braams and Scott, pg. 225
12. ^ a b Y-K Martin Peng, "Compact DT Fusion Spherical Tori at Modest Fields", CONF-850610-37 (December 1985)
13. ^ T.J. McManamy et all, "STX Magnet Fabrication and Testing to 18T", Martin Marietta Energy Systems, December 1988
14. ^ a b Sykes 2008, pg. 11
15. ^ Alan Sykes et all, "First results from the START experiment", Nuclear Fusion, Volume 32 Number 4 (1992), pg. 694
16. ^ Sykes 1998, pg. 1
17. ^ "Derek Robinson: Physicist devoted to creating a safe form of energy from fusion" The Sunday Times, 11 December 2002
18. ^ Sykes 1997, pg. B248
19. ^ a b c Sykes 2008, pg. 29
20. ^ Sykes 1998, pg. 4
21. ^ Sykes 2008, pg. 18
22. ^ See images in Sykes 2008, pg. 20
23. ^ Freidberg, pg. 414
24. ^ a b Freidberg, pg. 413
25. ^ a b Sykes 2008, pg. 24
26. ^ See examples, Sykes 2008, pg. 13
27. ^ Robin Herman, "Fusion: The Search for Endless Energy", Cambridge University Press, 1990, pg. 30
28. ^ Freidberg 2007, p. 287.
29. ^ a b c Freidberg, pg. 412
30. ^ Sykes 2008, p. 43.
31. ^ Paolo Micozzi et all, "Ideal MHD stability limits of the PROTO-SPHERA configuration", Nuclear Fusion, Volume 50 Number 9 (September 2010)
32. ^ Yican Wu et all, "Conceptual study on liquid metal center conductor post in spherical tokamak reactors", Fusion Engineering and Design, Volumes 51-52 (November 2000), pg. 395-399
33. ^ Sykes 2008, p. 31.
Bibliography


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# Astronomy and Planetary Science Thread

#### Flyaway

##### ACCESS: Above Top Secret
Senior Member
Venus’ clouds too dry, acidic for life

Here’s the related paper:

They also ruled out life in the Martian atmosphere and the upper atmosphere of Earth. But not some places in Jupiter’s atmosphere.

#### FighterJock

##### ACCESS: Top Secret
Venus’ clouds too dry, acidic for life

Here’s the related paper:

They also ruled out life in the Martian atmosphere and the upper atmosphere of Earth. But not some places in Jupiter’s atmosphere.

A shame about Venus’s atmosphere not being suitable for life, it is also interesting about the possibility of life in some parts of Jupiter’s atmosphere.

Senior Member

#### Grey Havoc

##### ACCESS: USAP
Senior Member
They also ruled out life in the Martian atmosphere and the upper atmosphere of Earth.

On the other hand: 'It's life Jim, but not as we know it.'

Senior Member

#### Flyaway

##### ACCESS: Above Top Secret
Senior Member
An Extreme Supernova Lit The Skies 1,000 Years Ago. We May Finally Know Its Type

Based on an analysis of a more recent supernova labeled SN 2018zd, astronomers think both SN 2018zd and the 1054 CE supernova are electron-capture supernovae – a rare third type of supernova alongside type I (thermonuclear) and type II (core collapse).

Experts have hypothesized about this third type of exploding star for decades at this point, though actual physical evidence of electron-capture supernovae has been difficult to come by. The unusual characteristics of SN 2018zd – a mere 31 million light-years away – may be the first one we've actually properly identified.

Here’s the related paper:

The electron-capture origin of supernova 2018zd

Abstract
In the transitional mass range (~8–10 solar masses) between white dwarf formation and iron core-collapse supernovae, stars are expected to produce an electron-capture supernova. Theoretically, these progenitors are thought to be super-asymptotic giant branch stars with a degenerate O + Ne + Mg core, and electron capture onto Ne and Mg nuclei should initiate core collapse1,2,3,4. However, no supernovae have unequivocally been identified from an electron-capture origin, partly because of uncertainty in theoretical predictions. Here we present six indicators of electron-capture supernovae and show that supernova 2018zd is the only known supernova with strong evidence for or consistent with all six: progenitor identification, circumstellar material, chemical composition5,6,7, explosion energy, light curve and nucleosynthesis8,9,10,11,12. For supernova 2018zd, we infer a super-asymptotic giant branch progenitor based on the faint candidate in the pre-explosion images and the chemically enriched circumstellar material revealed by the early ultraviolet colours and flash spectroscopy. The light-curve morphology and nebular emission lines can be explained by the low explosion energy and neutron-rich nucleosynthesis produced in an electron-capture supernova. This identification provides insights into the complex stellar evolution, supernova physics, cosmic nucleosynthesis and remnant populations in the transitional mass range.

#### Flyaway

##### ACCESS: Above Top Secret
Senior Member
It’s Time To Retire The Super-Earth, The Most Unsupported Idea In Exoplanets

What came as a bit of a surprise to many, however, was where that transition point occurred. Many scientists working on exoplanets — based on no physical motivation in particular — had drawn an imaginary line at about two Earth radii in their minds: below that, and you’re likely to be rocky, above that, and you’re likely to be gas-rich. The simplest way to tell, of course, would be to look at the density of your planet. In our own Solar System, the rocky planets and the gas-rich planets possess enormously different densities, so if you’re two Earth radii and still rocky, you’d expect such a planet to have about eight times the mass of Earth.

But when the data came in, it showed something remarkable: there is a transition between rocky planets and gas-rich planets, but it occurs much, much earlier, at about two Earth masses, or just 1.2 to 1.3 Earth radii. There appears to be some variety in exoplanets above that size/mass, with most of them appearing to be miniature versions of Neptune, but with a few of them, perhaps all the way up to 1.5 or even 1.6 Earth radii, still being rocky. (The majority of those, interestingly enough, are extremely hot as well.)

There is no need, and in fact it’s harmful, to remain wedded to erroneous assumptions that were made in the early days of exploring a new scientific field. As it stands today, it’s already been some ~5 years since we recognized how exoplanet populations were actually distributed; we now have PhDs who entered graduate school when it was already known that almost everything we currently call a “super-Earth” is not a rocky planet at all. Although there’s still much to learn about these exoplanets, including what’s underneath those atmospheres, we know enough about them to know which worlds are rocky and which ones are more like the gas giants we have. Based on that, now is absolutely the proper time to retire the archaic, inaccurate term, “super-Earth.”

#### Flyaway

##### ACCESS: Above Top Secret
Senior Member
Characteristics of the Basal Interface of the Martian South Polar Layered Deposits

Using radio waves, we investigated the properties of materials lying below the surface of Mars’ south polar regions (South Polar Layered Deposits; “SPLD”). We made maps of the buried surface below the SPLD (“basal interface”) and measured the radar energy reflected by this interface. From these maps, we measured the SPLD volume as 1.6 million cubic kilometers. Additionally, we found that there are multiple areas throughout the south polar region where the energy reflected from the basal interface is unexpectedly higher than that of the surface. Previous analyses of one such region suggested that these stronger reflections could be caused by the presence of an underground lake.

#### Flyaway

##### ACCESS: Above Top Secret
Senior Member
Astronomers Thrill at Giant Comet Flying into Our Solar System

Efforts to study the object since it was announced have been swift. Already a team of astronomers has been able to detect signs of activity, most likely melting ices forming an atmosphere, or “coma,” around its solid nucleus, confirming it to be a comet. “Its brightness has increased a lot, which means that it’s active,” says Rosita Kokotanekova of the European Southern Observatory, who led the observations using a network of telescopes in the Southern Hemisphere. Getting continued rapid observations will be crucial in learning more about the comet. “There might still be a possibility we can see a rotational signal from the nucleus,” Kokotanekova says. “When the activity gets stronger, it will be completely obscured.”
Observing that activity will be enlightening, too, “because we’ve never observed a comet being active so far out [from the sun],” Kokotanekova says. This will allow researchers to probe the regions of the solar system where cometary activity begins. From the object’s initial apparition in DES optics in 2014 to 2018, it did not appear to show activity, meaning it likely “switched on” at some point in the past three years, Fitzsimmons says. “It’s going to give us a really nice ability to study what happens in this transition region—from being a frozen ice ball out in the Oort cloud to a fully active comet in the solar system.”

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#### Flyaway

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A highly magnetized and rapidly rotating white dwarf as small as the Moon

Abstract
White dwarfs represent the last stage of evolution of stars with mass less than about eight times that of the Sun and, like other stars, are often found in binaries1,2. If the orbital period of the binary is short enough, energy losses from gravitational-wave radiation can shrink the orbit until the two white dwarfs come into contact and merge3. Depending on the component masses, the merger can lead to a supernova of type Ia or result in a massive white dwarf4. In the latter case, the white dwarf remnant is expected to be highly magnetized5,6 because of the strong magnetic dynamo that should arise during the merger, and be rapidly spinning from the conservation of the orbital angular momentum7. Here we report observations of a white dwarf, ZTF J190132.9+145808.7, that exhibits these properties, but to an extreme: a rotation period of 6.94 minutes, a magnetic field ranging between 600 megagauss and 900 megagauss over its surface, and a stellar radius of 2140+160−230
2140

230
+
160
kilometres, only slightly larger than the radius of the Moon. Such a small radius implies that the star’s mass is close to the maximum white dwarf mass, or Chandrasekhar mass. ZTF J190132.9+145808.7 is likely to be cooling through the Urca processes (neutrino emission from electron capture on sodium) because of the high densities reached in its core.

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#### Flyaway

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Alien Technosignature? The Mysterious Star VVV-WIT-08:

As he says with trying to fit an alien explanation you’re always going to run in the issue of “aliens of the gaps”.

View: https://youtu.be/OgZtPIo-hKE

#### Flyaway

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Did ancient astronomers set a message in stone for us?

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#### Flyaway

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Observational Evidence for a Thick Disk of Dark Molecular Gas in the Outer Galaxy

Abstract
We present the serendipitous discovery of an extremely broad (ΔVLSR ~ 150 km s−1), faint (Tmb < 10 mK), and ubiquitous 1667 and 1665 MHz ground-state thermal OH emission toward the second quadrant of the outer Galaxy (Rgal > 8 kpc) with the Green Bank Telescope. Originally discovered in 2015, we describe the redundant experimental, observational, and data quality tests of this result over the last five years. The longitude–velocity distribution of the emission unambiguously suggests large-scale Galactic structure. We observe a smooth distribution of OH in radial velocity that is morphologically similar to the H i radial velocity distribution in the outer Galaxy, showing that molecular gas is significantly more extended in the outer Galaxy than previously expected. Our results imply the existence of a thick (−200 pc < z < 200 pc) disk of diffuse (${n}_{{{\rm{H}}}_{2}}$ ~ 5 × 10−3 cm−3) molecular gas in the outer Galaxy previously undetected in all-sky 12CO surveys.

#### publiusr

##### I really should change my personal text
Alien Technosignature? The Mysterious Star VVV-WIT-08:

As he says with trying to fit an alien explanation you’re always going to run in the issue of “aliens of the gaps”.

View: https://youtu.be/OgZtPIo-hKE
The Great Daylight Fireball of 1972 (Teton event) stayed in atmosphere for 1,500 km. The grainy Super-8 film of it showed no fragmentation like that from Chelyabinsk or Peekskill. The de facto aerobrake was such that it was to make a resonant return in the 1990’s. In 1993, SMU recorded a linear earthquake that suggested the passage of a strangelet through the Earth. I wonder if there has been any trajectory works suggesting a link, and/or if another return might be had. Seismologists and volcanologists don’t often talk to each other—as per Galeras—so I expect seismologists and astronomers cross pollinate even less. But calculating the orbit of such contraterrene objects might give us potential new missions. Vela, Tunguska are still being looked at…but the SMU linear earthquake.. could that have been Teton?

#### Flyaway

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Study Projects a Surge in Coastal Flooding, Starting in 2030s

In the mid-2030s, every U.S. coast will experience rapidly increasing high-tide floods, when a lunar cycle will amplify rising sea levels caused by climate change.

#### Flyaway

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The problem with this theory isn’t just that it requires active volcanoes on Venus, but explosive active ones at a high level in the recent past to get the phosphides in the amounts where they need to be in the atmosphere.

Biosignature Spotted on Venus Could Be From Volcanoes, Not Life

“The phosphine is not telling us about the biology of Venus,” said Jonathan Lunine, a planetary scientist at Cornell University and co-author of the paper, in a university press release. “It’s telling us about the geology. Science is pointing to a planet that has active explosive volcanism today or in the very recent past.”

But the mystery of whether Venus has phosphine or not, and what might have produced it, is far from settled. “I sadly remain unconvinced by this latest argument,” said Clara Sousa-Silva, a quantum astrochemist at the Center for Astrophysics | Harvard and Smithsonian, in an email. “The reaction of mineral phosphides with concentrated sulfuric acid will not necessarily generate phosphine. ... A likely outcome of reacting phosphides with concentrated sulfuric acid would be an oxidation reaction and not production of phosphine.”

Sousa-Silva’s previous work has examined the atmospheres of Venus and other planets for potential signs of life like phosphine. She added, “we have known (and stated as much, repeatedly) that there are abiotic routes for the formation of phosphine, including volcanism. It’s just that these routes are extremely rare and inefficient.”

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#### Flyaway

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A Single-Year Cosmic Ray Event at 5410 BCE Registered in 14C of Tree Rings

Plain Language Summary
The 14C data of tree rings register extreme storms of solar energetic particles (SEPs), far larger than the largest SEP event ever observed in the Space Era. So far, three extreme SEP events have been reported as a rapid 14C increase in tree rings and 10Be and 36Cl increases in ice cores. In this study, we found a new rapid 14C increase in 5410 BCE using annual 14C content in ring samples from California, Switzerland, and Finland. The 14C signature of 5410 BCE event ties the origin of this 14C excursion to an extreme SEP event similar to three other extreme SEP events (774/775 CE, 992/993 CE, and ∼660 BCE) confirmed with radionuclides of ice cores.

Source: https://phys.org/news/2021-07-tree-newly-extreme-solar-event.html

#### Flyaway

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A hot subdwarf–white dwarf super-Chandrasekhar candidate supernova Ia progenitor

Abstract
Supernovae Ia are bright explosive events that can be used to estimate cosmological distances, allowing us to study the expansion of the Universe. They are understood to result from a thermonuclear detonation in a white dwarf that formed from the exhausted core of a star more massive than the Sun. However, the possible progenitor channels leading to an explosion are a long-standing debate, limiting the precision and accuracy of supernovae Ia as distance indicators. Here we present HD 265435, a binary system with an orbital period of less than a hundred minutes that consists of a white dwarf and a hot subdwarf, which is a stripped core-helium-burning star. The total mass of the system is 1.65 ± 0.25 solar masses, exceeding the Chandrasekhar limit (the maximum mass of a stable white dwarf). The system will merge owing to gravitational wave emission in 70 million years, likely triggering a supernova Ia event. We use this detection to place constraints on the contribution of hot subdwarf–white dwarf binaries to supernova Ia progenitors.

Source: http://www.sci-news.com/astronomy/hd-265435-type-ia-supernova-progenitor-09857.html

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#### Rhinocrates

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Not sure if I've posted this before, but its Shostakovich and I'll take any excuse to bring him up. I like the rough imagery - this one's all editing, no CGI. As a young man, DSCH earned money playing the piano at cinemas, so I can imagine him under the flickering black and white imagery. The Kubrickian reference is canny too - in the original drafts of 2001, Discovery was to go to Saturn (the monolith would be on Iapetus) and this remained so in the novel, but Mr K was not happy with the special effects. Doug Trumbull later went on to use Saturn as a backdrop for Silent Running. As for the waltz, Kubrick used it in Eyes Wide Shut. So it goes, round and round.

#### Flyaway

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Methane in the plumes of Saturn's moon Enceladus: Possible signs of life?

An unknown methane-producing process is likely at work in the hidden ocean beneath the icy shell of Saturn's moon Enceladus, suggests a new study published in Nature Astronomy by scientists at the University of Arizona and Paris Sciences & Lettres University.

Related paper:

Bayesian analysis of Enceladus’s plume data to assess methanogenesis

Abstract
Observations from NASA’s Cassini spacecraft established that Saturn’s moon Enceladus has an internal liquid ocean. Analysis of a plume of ocean material ejected into space suggests that alkaline hydrothermal vents are present on Enceladus’s seafloor. On Earth, such deep-sea vents harbour microbial ecosystems rich in methanogenic archaea. Here we use a Bayesian statistical approach to quantify the probability that methanogenesis (biotic methane production) might explain the escape rates of molecular hydrogen and methane in Enceladus’s plume, as measured by Cassini instruments. We find that the observed escape rates (1) cannot be explained solely by the abiotic alteration of the rocky core by serpentinization; (2) are compatible with the hypothesis of habitable conditions for methanogens; and (3) score the highest likelihood under the hypothesis of methanogenesis, assuming that the probability of life emerging is high enough. If the probability of life emerging on Enceladus is low, the Cassini measurements are consistent with habitable yet uninhabited hydrothermal vents and point to unknown sources of methane (for example, primordial methane) awaiting discovery by future missions.

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EHT Pinpoints Dark Heart of the Nearest Radio Galaxy

In a new paper published Monday in Nature Astronomy, data from the 2017 Event Horizon Telescope (EHT) observations have been analyzed to image Centaurus A in unprecedented detail.

"This allows us for the first time to see and study an extragalactic radio jet on scales smaller than the distance light travels in one day. We see up close and personal how a monstrously gigantic jet launched by a supermassive black hole is being born,” says astronomer Michael Janssen of the Max Planck Institute for Radio Astronomy and Radboud University.

The researchers predict that future observations at an even shorter wavelength and higher resolution will be able to photograph the central black hole of Centaurus A. This will require the use of space-based satellite observatories.

“These data are from the same observing campaign that delivered the famous image of the black hole in M87. The new results show that the EHT provides a treasure trove of data on the rich variety of black holes and there is still more to come”, says Heino Falcke, EHT board member and professor for astrophysics at Radboud University.

Event Horizon Telescope observations of the jet launching and collimation in Centaurus A

Abstract
Very-long-baseline interferometry (VLBI) observations of active galactic nuclei at millimetre wavelengths have the power to reveal the launching and initial collimation region of extragalactic radio jets, down to 10–100 gravitational radii (rg ≡ GM/c2) scales in nearby sources1. Centaurus A is the closest radio-loud source to Earth2. It bridges the gap in mass and accretion rate between the supermassive black holes (SMBHs) in Messier 87 and our Galactic Centre. A large southern declination of −43° has, however, prevented VLBI imaging of Centaurus A below a wavelength of 1 cm thus far. Here we show the millimetre VLBI image of the source, which we obtained with the Event Horizon Telescope at 228 GHz. Compared with previous observations3, we image the jet of Centaurus A at a tenfold higher frequency and sixteen times sharper resolution and thereby probe sub-lightday structures. We reveal a highly collimated, asymmetrically edge-brightened jet as well as the fainter counterjet. We find that the source structure of Centaurus A resembles the jet in Messier 87 on ~500 rg scales remarkably well. Furthermore, we identify the location of Centaurus A’s SMBH with respect to its resolved jet core at a wavelength of 1.3 mm and conclude that the source’s event horizon shadow4 should be visible at terahertz frequencies. This location further supports the universal scale invariance of black holes over a wide range of masses5,6.

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Chunk of an ancient supercontinent discovered under New Zealand

As the California heat blazed outside in the summer of 2018, Rose Turnbull sat in the cool confines of a windowless basement sorting through grains of fine sand. A geologist based in New Zealand, Turnbull was in a colleague’s lab at California State University, Northridge, trying to find tiny crystals of zircon, which she hoped would help unravel secrets of the mysterious eighth continent of Zealandia, also known by its Māori name Te Riu-a-Māui.

The task required a practiced hand and a bit of elbow grease—or rather, nose grease. Turnbull demonstrates over Zoom, raising the closed tweezers to the outside of her nose to pick up a bit of oil, which prevents the grains from zinging across the room when plucked.

The crystals hailed from rocks that were collected from the islands of New Zealand, which are among the few bits of Zealandia's nearly two million square miles that poke above the sea. Only recently recognized by scientists, Zealandia is the most submerged, thinnest, and youngest continent yet found. Turnbull, who works at the research and consulting group GNS Science in New Zealand, and her colleagues wanted to know more about the processes that shaped this unusual landmass.

A hidden Rodinian lithospheric keel beneath Zealandia, Earth’s newly recognized continent

We present a data set of >1500 in situ O-Hf-U-Pb zircon isotope analyses that document the existence of a concealed Rodinian lithospheric keel beneath continental Zealandia. The new data reveal the presence of a distinct isotopic domain of Paleozoic–Mesozoic plutonic rocks that contain zircon characterized by anomalously low δ18O values (median = +4.1‰) and radiogenic εHf(t) (median = +6.1). The scale (>10,000 km2) and time span (>>250 m.y.) over which plutonic rocks with this anomalously low-δ18O signature were emplaced appear unique in a global context, especially for magmas generated and emplaced along a continental margin. Calculated crustal-residence ages (depleted mantle model, TDM) for this low-δ18O isotope domain range from 1300 to 500 Ma and are interpreted to represent melting of a Precambrian lithospheric keel that was formed and subsequently hydrothermally altered during Rodinian assembly and rifting. Recognition of a concealed Precambrian lithosphere beneath Zealandia and the uniqueness of the pervasive low-δ18O isotope domain link Zealandia to South China, providing a novel test of specific hypotheses of continental block arrangements within Rodinia.

### NASA's InSight Reveals the Deep Interior of Mars

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#### Flyaway

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A peculiarly short-duration gamma-ray burst from massive star core collapse

Abstract
Gamma-ray bursts (GRBs) have been phenomenologically classified into long and short populations based on the observed bimodal distribution of duration1. Multi-wavelength and multi-messenger observations in recent years have revealed that in general long GRBs originate from massive star core collapse events2, whereas short GRBs originate from binary neutron star mergers3. It has been known that the duration criterion is sometimes unreliable, and multi-wavelength criteria are needed to identify the physical origin of a particular GRB4. Some apparently long GRBs have been suggested to have a neutron star merger origin5, whereas some apparently short GRBs have been attributed to genuinely long GRBs6 whose short, bright emission is slightly above the detector’s sensitivity threshold. Here, we report the comprehensive analysis of the multi-wavelength data of the short, bright GRB 200826A. Characterized by a sharp pulse, this burst shows a duration of 1 second and no evidence of an underlying longer-duration event. Its other observational properties such as its spectral behaviours, total energy and host galaxy offset are, however, inconsistent with those of other short GRBs believed to originate from binary neutron star mergers. Rather, these properties resemble those of long GRBs. This burst confirms the existence of short-duration GRBs with stellar core-collapse origin4, and presents some challenges to the existing models.

Discovery and confirmation of the shortest gamma-ray burst from a collapsar

Abstract
Gamma-ray bursts (GRBs) are among the brightest and most energetic events in the Universe. The duration and hardness distribution of GRBs has two clusters1, now understood to reflect (at least) two different progenitors2. Short-hard GRBs (SGRBs; T90 < 2 s) arise from compact binary mergers, and long-soft GRBs (LGRBs; T90 > 2 s) have been attributed to the collapse of peculiar massive stars (collapsars)3. The discovery of SN 1998bw/GRB 980425 (ref. 4) marked the first association of an LGRB with a collapsar, and AT 2017gfo (ref. 5)/GRB 170817A/GW170817 (ref. 6) marked the first association of an SGRB with a binary neutron star merger, which also produced a gravitational wave. Here, we present the discovery of ZTF20abwysqy (AT2020scz), a fast-fading optical transient in the Fermi satellite and the Interplanetary Network localization regions of GRB 200826A; X-ray and radio emission further confirm that this is the afterglow. Follow-up imaging (at rest-frame 16.5 days) reveals excess emission above the afterglow that cannot be explained as an underlying kilonova, but which is consistent with being the supernova. Although the GRB duration is short (rest-frame T90 of 0.65 s), our panchromatic follow-up data confirm a collapsar origin. GRB 200826A is the shortest LGRB found with an associated collapsar; it appears to sit on the brink between a successful and a failed collapsar. Our discovery is consistent with the hypothesis that most collapsars fail to produce ultra-relativistic jets.

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A neighbouring Planetary system reveals its secrets (ESO cast 242 Light):

View: https://youtu.be/BfnlIoapky0
A team of astronomers have used ESO’s Very Large Telescope in Chile to shed new light on planets around a nearby star that resemble those in the inner Solar System. This video summarises what they found about the planetary system, called L 98-59.

#### Flyaway

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One Year in the Life of Young Suns: Data Constrained Corona-Wind Model of kappa1 Ceti

The young magnetically active solar-like stars are efficient generators of ionizing radiation in the form of X-ray and Extreme UV (EUV) flux, stellar wind and eruptive events. These outputs are the critical factors affecting atmospheric escape and chemistry of (exo)planets around active stars. While X-ray fluxes and surface magnetic fields can be derived from observations, the EUV emission and wind mass fluxes, Coronal Mass Ejections and associated Stellar Energetic Particle events cannot be directly observed. Here, we present the results of a three-dimensional magnetohydrodynamic (MHD) model with inputs constrained by spectropolarimetric data, HST/STIS Far UV, X-ray data data and stellar magnetic maps reconstructed at two epochs separated by 11 months. The simulations show that over the course of the year, the global stellar corona had undergone a drastic transition from a simple dipole-like to a tilted dipole with multipole field components, and thus, provided favorable conditions for Corotating Interaction Events (CIRs) that drive strong shocks. The dynamic pressure exerted by CIRs are 1300 times larger than those observed from the Sun and can contribute to the atmospheric erosion of early Venus, Earth, Mars and young Earth-like exoplanets. Our data-constrained MHD model provides the framework to model coronal environments of G-M planet hosting dwarfs. The model outputs can serve as a realistic input for exoplanetary atmospheric models to evaluate the impact of stellar coronal emission, stellar winds and CIRs on their atmospheric escape and chemistry that can be tested in the upcoming JWST and ground-based observations.

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text:
# Q6. In a model of a ship, the mast is 9 cm high, while the mast of the actual ship is 12 m high. If the length of the ship is 28 m, how long is the model ship?

Given that the mast of the model ship is 9 m high, while the mast of the actual ship is 12 m.

If the length of the ship given is 28m then,

Length of the model ship can be obtained from the direct proportion relation of mast height and length of ship.

We obtained the relation:

$\frac{height\ of\ mast(model)}{height\ of\ mast (actual)} = \frac{length\ of\ ship(model)}{length\ of\ ship(actual)}$

So, by the relation we have;

Let us assume that the length of model ship is 'x

$\frac{9cm}{1200cm} = \frac{x}{2800cm}$                                                                $\because (1m = 100cm)$

after solving this relation we get,

$x=\frac{9cm\times 2800cm}{1200cm}= 21cm$,

Length of the model ship is 21cm.

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text:
Setting the SSDIR environment variable in Microsoft Visual Source Safe

July 27, 2008

I have this problem crop up every once in awhile with using the command
line of Visual Source Safe 2005. I attempt to perform a task and I receive and error back saying “No VSS database (srcsafe.ini) found. Set the SSDIR environment variable to the path of srcsafe.ini for your VSS database.”

To correct this problem, open the command window and go to C:\Program Files\Microsoft Visual SourceSafe

Execute the following command:

set ssdir=\\yourserver\VSS\VSProjects

This should work, of course, verify where your srcsafe.ini file is located before setting the variable.

-Flea#


text:
• Corpus ID: 119119022

# The Hot QCD White Paper: Exploring the Phases of QCD at RHIC and the LHC

@article{Akiba2015TheHQ,
title={The Hot QCD White Paper: Exploring the Phases of QCD at RHIC and the LHC},
author={Yasuyuki Akiba and Aaron Angerami and Helen Caines and A. D. Frawley and Ulrich Heinz and Barbara Jacak and Jiangyong Jia and T. Lappi and Wei Li and Abhijit Majumder and David Morrison and M. Płoskoń and Joern Putschke and Krishna Rajagopal and Ralf Rapp and G Roland and Paul Richard Sorensen and Urs Achim Wiedemann and Nu Xu and William A. Zajc},
journal={arXiv: Nuclear Experiment},
year={2015}
}
• Published 9 February 2015
• Physics
• arXiv: Nuclear Experiment
The past decade has seen huge advances in experimental measurements made in heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) and more recently at the Large Hadron Collider (LHC). These new data, in combination with theoretical advances from calculations made in a variety of frameworks, have led to a broad and deep knowledge of the properties of thermal QCD matter. Increasingly quantitative descriptions of the quark-gluon plasma (QGP) created in these collisions have…
61 Citations
Jet measurements in heavy ion physics
• Physics
Reviews of Modern Physics
• 2018
A hot, dense medium called a quark gluon plasma (QGP) is created in ultrarelativistic heavy ion collisions. Early in the collision, hard parton scatterings generate high momentum partons that
Open Heavy Flavor in QCD Matter and in Nuclear Collisions
• Physics
• 2016
We review the experimental and theoretical status of open heavy-flavor (HF) production in high-energy nuclear collisions at RHIC and LHC. We first overview the theoretical concepts and pertinent
Jet quenching tests of the QCD Equation of State.
• Physics
• 2019
After almost two decades of investigation, jet quenching has become a fundamental tool to study the properties of the QCD matter produced in high-energy nuclear collisions. Despite the large progress
Trajectory of the cosmic plasma through the quark matter phase diagram
Experimental studies of the Quark-Gluon Plasma (QGP) focus on two, in practice distinct, regimes: one in which the baryonic chemical potential $\mu_B$ is essentially zero, the other in which it is of
INFN What Next: Ultra-relativistic Heavy-Ion Collisions
• Physics
• 2016
This document was prepared by the community that is active in Italy, within INFN (Istituto Nazionale di Fisica Nucleare), in the field of ultra-relativistic heavy-ion collisions. The experimental
Full resummation analysis of jet quenching and tests of the QCD Equation of State
• X. Feal
• Physics
Proceedings of 10th International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions — PoS(HardProbes2020)
• 2021
Jet quenching has become a fundamental tool to study the hot QCD matter produced in heavy ion collisions. While important theoretical and experimental advances have been made in the last two decades,
Heavy-flavour and quarkonium production in the LHC era: from proton–proton to heavy-ion collisions
• Physics
The European physical journal. C, Particles and fields
• 2016
This report reviews the study of open heavy-flavour and quarkonium production in high-energy hadronic collisions, as tools to investigate fundamental aspects of Quantum Chromodynamics, from the
Hadron-quark phase transition: the QCD phase diagram and stellar conversion
• Physics
Journal of Cosmology and Astroparticle Physics
• 2019
Different extensions of the Nambu-Jona-Lasinio model, known to satisfy expected QCD chiral symmetry aspects, are used to investigate a possible hadron-quark phase transition at zero temperature and

## References

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Heavy flavor puzzle at LHC: a serendipitous interplay of jet suppression and fragmentation.
This paper uses the recently developed energy loss formalism in a finite-size dynamical QCD medium to analyze the "heavy flavor puzzle at LHC", and shows that this puzzle is a consequence of an unusual combination of the suppression and fragmentation patterns and does not require invoking the same energy loss for light partons.
D(s) meson as a quantitative probe of diffusion and hadronization in nuclear collisions.
• Physics
Physical review letters
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The effects of diffusion in the hadronic phase are introduced and it is suggested that an increase of the D-meson elliptic flow compared to the D(s) can disentangle the transport properties of hadronic and QGP liquids.
The order of the quantum chromodynamics transition predicted by the standard model of particle physics
• Physics
Nature
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Finite-size scaling analysis shows that the finite-temperature QCD transition in the hot early Universe was not a real phase transition, but an analytic crossover (involving a rapid change, as opposed to a jump, as the temperature varied).
Strongly interacting low-viscosity matter created in relativistic nuclear collisions.
• Physics
Physical review letters
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It is shown that the transition from hadrons to quarks and gluons has behavior similar to helium, nitrogen, and water at and near their phase transitions in the ratio eta/s, and suggests that experimental measurements can pinpoint the location of this transition or rapid crossover in QCD.
Thermal Dileptons from Hot and Dense Strongly Interacting Matter
The NA60 experiment at the CERN SPS has studied muon-pair production in 158A GeV In-In collisions. The unprecedented precision of the data has allowed to isolate a strong excess of pairs above the
Is there still any Tc mystery in lattice QCD? Results with physical masses in the continuum limit III
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The present paper concludes our investigations on the QCD cross-over transition temperatures with 2+1 staggered flavours and one-link stout improvement. We extend our previous two studies [Phys.
Physics probed by the P T dependence of the nuclear suppression factor
The nuclear suppression factor R_AA of single inclusive hadrons measured in ultrarelativistic heavy-ion collisions was the first observable to study jet quenching, i.e. the final state interaction of