Participants: Fredrik Wenander,
1. GENERAL ISSUES
- At the last meeting of the MINIBALL steering committee it was decided to address the issue of the slow extraction from the EBIS to the REX upgrade group (which will meet in November), because we do not have a manpower and expertise solution to the problem right now.
- The plans to keep the MINIBALL at GSI until mid May next year have been changed. It will arrive now earlier (April) at ISOLDE. In total 10 REX runs are foreseen for next year.
- Georgi Gregoriew presented two detectors, which could be very suitable for REX to improve the beam diagnostics at the REX target (and behind the trap) with respect to particle identification and detection of very low intensities (100 particles/s). The detectors are a gas filled wire detector and an ionization chamber in connection with silicon detector, which were produced at GANIL. Some of them might still be available for REX. The REX team – supported by Georgi - will try to find out about the availability and check if there are mechanical solutions to install them in the beam line. The instrumentation group of the AB division should be involved in any developments in that field.
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Oliver Kester has a diploma
student who is interested in working at ISOLDE on ion sources, in particular on
the REXEBIS. He could start in the beginning of next year, financed by the
- Thomas has finished the list of spare parts for the budget of next year. He will send a copy to all people involved. Discussion at next meeting.
2. TRAP
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- During tests before the run he could reach a cooling efficiency of 50%, which is the regular value and shows that the rf-excitation is working properly now.
- While injecting the F1+ ions, NH3 molecules and a large fraction of S2+ saturated the trap and the efficiency went down to about 35%.
- Losses of F might also have occurred due to charge exchange with the Sulfur ions.
- We do not exactly know the efficiency of the trap for trapping and cooling the F ions, because we could not clearly separate the F from the S2+ in the TOF spectra.
- Due to space charge effects in the trap, the beam size increased and the injection into the EBIS was not very efficient.
3. EBIS
- The EBIS showed the regular efficiency for the different charge states during the run.
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Fredrik estimated the overall efficiency of REX to
0.5%. He agrees with
- Before the run Fredrik could achieve a trapping and breeding efficiency of 18% for a Na7+, which is the record for this ion species so far.
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Glyn Kirby from AT/MEL was in
contact with
- Two old cathodes, which had to be replaced, were sent for diagnostics to the supplier company. One of the cathodes could be remounted and will be sent back. Yet two more fresh cathodes will be purchased this year.
4. LINAC
- During the run no major problems with the rf-system occurred. A faulty Feedback Ctrl. module has been replaced beforehand and the power levels were quite low(A/q = 3.4). For that reason the system was running very stable.
- The preamplifier of the RFQ still runs with a bridged temperature interlock. We will get the spare part/drawing from Dressler soon. It will be repaired as soon as there is a break in the runs.
- The operation with the stripping foil worked out well. We finally used a 50 mm/cm2 foil, provided by G. Bourgeois from AB/ABP. The efficiency and energy loss fitted very good to our SRIM calculations. Overall efficiency through the accelerator was 30% (linac 75%, stripping 40%).
- From counting scattered particles at the MINIBALL target, we learned during the run that the detection limit of our beam observation system is about 100 particles/s.
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At the moment,
5. CONTROL SYSTEM
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Minutes by Thomas