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depending on the operating parameters , fractions of @xmath5 , @xmath0 and @xmath1 are generated in the hydrogen gas plasma .
@xmath0 and @xmath1 beams are used at fixed velocity heavy ion linacs like unilac to get more beam intensity at a given space charge limit ( @xmath6 ) . at an energy above a few mev
the molecular ion beam can be converted into a proton beam at very high efficiency and with negligible loss in beam quality by passage through a thin carbon stripping foil .
actually , @xmath0 and @xmath1 beams can be produced very efficiently by hot cathode driven volume plasma sources at modest operation parameters @xcite .
applications might be at medical ion beam facilities for cancer treatment .
if @xmath7 and @xmath5 beams are needed , both beams are generated in identical electron cyclotron resonance ecr - sources @xcite .
the sources and injector settings have to be changed due to the @xmath8 difference between @xmath5 and @xmath2 . moreover , this type of ecr source was optimized for heavy ion beams .
this paper explains , why it might be reasonable to add a third source to the injector complex , which can produce @xmath9 efficiently .
the source is cheap , compact , and easy in maintainance .
it allows a factor @xmath10 higher @xmath5 beam current at injector parameters identical to @xmath2 operation down to the stripper foil - due to the space charge limit of a multicell linac .
another application are high current @xmath11 and @xmath12 beam facilities @xcite .
as these beams show a high activation potential it is very important to have a `` start up '' beam for finding operation parameter settings .
this could be done very nicely with intense @xmath13 and @xmath9 beam , respectively .
as shown in fig.[source_cross ] the source consists of a plasma chamber with a hot tungsten filament and a triode extraction system .
the cathode emits electrons which are accelerated to the cylindrical plasma chamber wall .
electrons are forced into cycloidal paths by an external solenoidal field , increasing their path lengths to the wall , and thereby , increasing the probability of an ionizing collision with neutrals .
fig.[source_mag ] shows the block diagram of the source with power supplies and the on axis magnetic field produced by the solenoid .
one can see , that almost a @xmath14 magnetic field level is present at the extraction system .
magnetic field levels at the plasma chamber centre up to @xmath15 were applied by coil currents up to @xmath16 .
the heating filament as well produces a comparable magnetic field of around @xmath17 by heating current upto @xmath18 .
this magnetic force does not have a significant effect on the ion beam , but does change the plasma properties significantly .
a triode extraction system was used . at normal settings the plasma electrode
is held at positive potential , the screening electrode is held at a negative @xmath19 level of the plasma electrode potential . the space charge dominated beam current is given by the child langmuir law , @xmath20 @xmath21 is the current density , @xmath22 is the accelerating potential and @xmath11 is the acceleration gap length . in the source
used @xmath11 was @xmath23 .
fig.[setup ] shows the experimental setup used for a characterization of the ion source .
the source was mounted on a differential pumping chamber equipped with three turbo molecular pumps .
a faraday cup was installed in the same tank for beam current measurements .
an emittance scanner of the grid slit type was mounted and a momentum analyzer was installed downstream .
the helium beam consists of a single specie , singly charged ion beam for this source type , generated by the reaction @xmath25
fig.[he_example ] shows an example of a @xmath24 beam with current @xmath26 extracted at @xmath27 beam energy .
a gas filling pressure of @xmath28 and @xmath29 arc potential were used as standard settings .
the terminal can supply voltage levels up to @xmath30 .
the current extracted was measured by a faraday cup .
the proton beam is extracted from a plasma fed by @xmath33 .
the key reactions involved are , @xmath34 the last two processes are assumed to be important for an efficient production of protons in a small source@xcite@xcite@xcite . it was figured out that the proton fraction depends upon plasma parameters .
the whole parameter space of arc current and magnetic field was scanned at three different values of arc potential ( @xmath35 ) and three different values of source filling pressure ( @xmath36 ) to find the maximum fraction of individual species . to get a clear contrast in the plots for identifying the optimum settings for the production of the species of interest , for example for protons , the _ relative occurrence _
( @xmath37 ) was defined as @xmath38 where @xmath39 is the relative percentage at that perticular set of parameters . in a similar way ,
the @xmath37 for @xmath40 and @xmath41 were defined .
fig.[rel_occ_max ] shows the relative occurrence of @xmath42 , @xmath40 and @xmath41 as function of arc current ( @xmath43 ) and magnetic field at the gas filling pressure of @xmath44 and @xmath45 arc potential . at particular values of magnetic field and plasma density
the relative occurrence of particular species is very high .
thus the graph shows an _ island _ kind structure .
fig.[mass_spectra_max ] shows the mass spectra at the optimum values of relative occurrences . as optimum ratios at each of the separate _ island
_ positions , about @xmath46 of proton corresponding to @xmath47 , about @xmath48 of @xmath40 corresponding to @xmath49 and about @xmath50 of @xmath41 corresponding to @xmath3 current were extracted at @xmath4 beam energy respectively .    when these graphs were plotted for different filling pressure or arc potential the island positions moved ( see fig.[rel_occ_vary_p ] and [ rel_occ_vary_ubogen ] ) and the intensity decreased while retaining the island structure .
typically , the used version of heating cathode should be changed after around @xmath51 of operation .
a proton beam containing @xmath52 of @xmath42 was extracted routinely for the beam transport experiments at frankfurt university .
especially , this ion source provides @xmath0 and @xmath1 beams with individual ratios up to @xmath50 .
the source can be tuned in a wide range of operating parameters to optimize the beam .
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recently , there is an increasing need for @xmath0 and @xmath1 ion sources . 
 one example are ion therapy facilities , where @xmath2 and @xmath1 ion beams along the linac are of great interest . 
 another example is a @xmath0 test beam for linacs finally operated with intense deuteron beams . at frankfurt 
 , a simple proton ion source is needed to test a new kind of beam injection into a magnetic storage ring@xcite@xcite . 
 this article describes a volume type ion source which can deliver upto @xmath3 beam current at @xmath4 in stable dc operation . 
 it is a hot filament driven ion source which can provide high fractions of @xmath5 , @xmath0 or @xmath1 , depending on the operation settings .    ,    ,    ,    .