P.Spädtke, J.Bossler, H.Emig, K.D.Leible, M.Khaouli,
C.Mühle,
S.Schennach, H.Schulte, K.Tinschert
GSI Darmstadt
At GSI different ion beams are delivered to the UNILAC, the synchrotron SIS or to the storage ring ESR. For that purpose three different injectors are in use for the UNILAC, equipped with different ion sources. The standard injector with a Penning ion source and the high current injector (with CHORDIS or MEVVA ion source) supply the Wider”e accelerator (pre-stripper section of UNILAC) with an injection energy of 11.7 keV/u. The newly built high charge state injector HLI is equipped with an ECR ion source (CAPRICE). The injection energy for the succeeding RFQ and IH accelerator is 2.5 keV/u. Both beams are further accelerated in the Alvarez accelerator (post-stripper section of UNILAC) with an injection energy of 1.4 MeV/u. For ion source tests and developments additional test benches are available. The specific advantages of each injector, recent improvements and specific operating modes are described.
The regular injector is equipped with a Penning ion source (fig.1). This source is operated in a pulsed mode, typically 50Hz with pulse length from 2 to 6ms. Extraction voltage is between 10 and 15kV. For SIS-operation such a high repetition rate is not necessary, and the extracted ion current within the pulse can be increased by reducing the duty cycle allowing higher peak discharge power.
Typical ion currents measured in front of the Wider”e are listed in Tab.1.
The absolute acceptance of the analyzing and transport
system is about 100 
mmmrad.
Table 1: Ion currents from the PIG source. Different operation modes
are not distinguished.
We hope to increase the available intensities, especially in the low repetition mode for SIS, by further development of the PIG ion source. These investigations and developments will be carried out at the newly built PIG test bench in close collaboration with the JINR in Dubna. The following modifications are planned:
To increase the available ion currents for the synchrotron
the Wider”e pre-stripper section will be replaced by a RFQ/IH accelerator in
the near future [2].
The injection energy will be reduced from 11.7 keV/u to 2.2 keV/u. This
implies the use of lower charge states from the ion source (design ion
U 
, el.current 15 mA). The total extracted current from the ion
source will be in the range of 100 mA.
To minimize beam transport problems at low energies,
there is no charge or mass separation on the high voltage platform.
To preserve the beam quality during post-acceleration, the acceleration
column is equipped with a movable single gap and a screening
electrode[3].
The present 320 kV high voltage power supply limits the current to 40mA.
It will be replaced by a new one with a maximum voltage of 150kV and
maximum load current of 150mA in 1997.
Like the PIG source, the CHORDIS (shown in fig.2) is regularly operated in a pulsed mode up to 50Hz and pulse length from 0.5 to 5ms. Extraction voltage is between 20 and 40kV.
Typical ion currents from the CHORDIS for D and Ne are given in table 2. The currents are measured at the same location as for the PIG source.
For high current investigations at the UNILAC and SIS we use the Ne-beam delivered by the CHORDIS. The molecular deuterium beam has been used instead of the atomic one for two reasons:
Figure 2: Gas version of CHORDIS.
For all beams from metallic elements we are using the MEVVA ion source [4]. Our version of that source type (see fig.3) is operated in a pulsed mode with a repetition frequency of up to 5Hz and pulse length from 0.5 to 2ms [5],[6]. Extraction voltage is between 20 and 40kV. The same extraction system as for the CHORDIS is used.
Typical ion currents for the MEVVA ion source are listed in table 3.
Table 3: Ion currents from the MEVVA.
beam has been measured at the UNILAC injector, whereas
all other data have been taken
at the high current test bench (analyzed current after 5m beam transport).
For the Ti-beam the maximum of the charge state distribution is at the required charge state, for other elements special measures are necessary to get the maximum current in the desired charge state. Higher charge states can be achieved by applying a high magnetic field close to the cathode region. To decrease the charge state (1+ desired for the Mg-beam) additional gas is fed into the discharge chamber. This is shown in fig.4.
The development of the MEVVA ion source is made in close collaboration between TASUR in Tomsk, LBL in Berkeley and GSI. After achieving the desired currents, the main activity is now to decrease the noise level on the beam as well as the pulse-to-pulse reproducibility.
Figure 4: Mg spectra from MEVVA ion source. I: no additional gas,
II: nitrogen pressure at the gas inlet is 
mbar,
III: 
mbar.
The extraction voltage from the ECR source (shown in fig.5) is chosen to match the specific input energy of the RFQ (2.5keV/u). Because of the high charge states available from this source no high voltage platform is necessary. The most important features of the ECR ion source are the stable production without interruptions for weeks and the low material consumption for the desired element. Typical ion currents are listed in table 4. These ion currents are not always the maximum achievable currents, but they were sufficient for the specific experiment.
Table 4: Ion currents from the ECR ion source. Enriched isotopes
are marked by an asterisk.
The main activity for that source is to develop different techniques to create ions from solid materials [7].
Tests at the ECR test bench revealed that for Se (vapor pressure
10 
mbar at 
200 
C) the regularly used oven
did not yield stable operating
conditions, even with some modifications to minimize the influence
of the discharge on the sample temperature.
For such high vapor pressure materials we built a new low temperature
evaporator (fig.6) in which the sample is placed outside the source and the vapor
is guided to the standard quartz gas feeding system through a long heated
quartz capillary.
Thus the source operation is very similar to that for normal gases
with the supplementary condition that a minimum microwave power
of around 200W should be applied to the source to avoid condensation
of the material in the front part of the feeding system.
Figure 5: ECR ion source CAPRICE.
Figure 6: Evaporator for ECR ion source CAPRICE.
