Participants: Fredrik Wenander,
1. TRAP
- The trap VME crate is working stable now since it has been repaired with the help from GSI (Frank Herfurth).
- Due to the interruption of the REX runs, some tests are performed at the moment with noble gases to check the charge exchange in the trap.
- It was decided not to test the injection of AlF due to the bad efficiency. Other F-molecules (Barium, Lanthanum) will be used instead.
- If the radioactive beam is available there might be a test of the Si detector in front of the trap.
2. EBIS
- Fredriks summer student is now calculating mass spectra, using different restgas pressures to get a consistent model of the distribution of extracted ions and charge states and to learn something about possible contaminations in the radioactive beam. The OPERA calculations which he was supposed to do could not be performed due to a missing space charge routine in the program.
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Next week Fredrik will go to
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There are problems with the GFAS modules for the power
supplies on the high voltage side.
- After heating up the EBIS to investigate the big liquid He consumption, it has to filled each 4 days now (was 5 days before).
- The pulsed high voltage supply for the EBIS platform voltage is broken. The recent run and also the following experiment have been cancelled, also due to problems with the LINAC (see below). The power supply will be shipped to FUG tomorrow (23.07.) and shall return – if a quick repair is possible - by the end of next week (30.07.). The FUG will be in Holidays from 02.08. So we must hope and push that the repair is finished next week. The power supply group provided us with a static 30 kV power supply which allows to work with stable beam on the LINAC meanwhile.
- If the repair is delayed there might be a solution using a 30 kV pulsed lens power supply for the platform voltage and run ISOLDE target, trap and EBIS at 30 kV. But this would be a lot of effort and less efficient than having the 60 kV.
3. LINAC
- The LINAC has been optimized with beams of A/q=4 and A/q=3.5. Settings were found for a reasonable transmission (75%) and a good beam spot (5mm x 5mm) at 2.2 MeV/u and also for the A/q=3.5 beam at 2.9 MeV/u (transmission ~70%, spot size 3mm x 3mm) to the MINIBALL target. The measurements of the 2.9 MeV/u were done at 75 kW. They were difficult to perform due to instabilities of the amplifier.
- There are some restrictions concerning the beam energy, resp. the A/q of the ions for REX running at 3 MeV/u. 1. At the moment the rf-power is limited to 90 kW, this means 3 MeV/u are only possible for A/q≤3.5. An energy of 2.9 MeV/u would be available for A/q≤3.85. We hope to increase the rf-power to the nominal value of 100 kW (or a bit more) soon, but this does not change the situation very much, so a compromise has to be found to do the charge breeding in a way that we end up at “lighter” ions. 2. The big bending magnet in the end of the beamline has, looking at its specifications, a maximum field of 1140 mT. We reach this limit at 3 MeV/u for an A/q of 4.3. Keeping a safety margin to the complete saturation of the magnet, we see 3 MeV/u for A/q=4 as a limit. This limit can definitely not be exceeded whatever rf-power we might have in the 9-gap resonator in the future.
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2 weeks ago the tube in the 200 MHz amplifier has been
changed. It turned out, that the instabilities during the test measurements
mentioned above were a result of voltage breakdowns on the tube. Traces of
sparking could be found, which already occurred during tests in
- When switching on the amplifier for the Kr run, unfortunately a shortcut between anode and ground occured (damaged capton insulator). As a result the grid 2 power supply was strongly damaged. This has to be repaired now together with the anode circuit by Berdermann. It was agreed between the AB-RF-LR group and Berdermann that the repairs shall be done until 02.08.
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Matteo Pasini
from
4. Control System
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- There are some problems remaining with the FECs. The beam diagnostic FEC is still very sensitive when it is accessed from different terminals at the same time, or even when to FCs are active simultaneously. The beam optics FEC works good. The EBIS FEC has been replaced with the old NT machine in connection with the above mentioned difficulties to set values via the GFAS modules. It turned out that the problems are still there when using the old FEC, so they are not a result of the XP upgrade.