Participants: Fredrik Wenander,
1. GENERAL ISSUES
- Mats proposed to have a “REX-day” in the future. Staying somewhere over night and spent two days with discussions around REX in a relaxed atmosphere. The idea was appreciated by all. First date could be in January.
- Luis reported that the physics group account has been charged for an amplifier which should have been paid already from the 2003 budget. Actually there is no money left. We planned to use it for the most urgent items on our spare part list to disencumber our own budget for next year.
- Thomas has started to produce this list.
- Mats had a meeting with the vacuum group. There will be two more technicians in 2005, which are trained to work at ISOLDE, but there will be no Piquet Service in that year. Mats was asking for more support for REX reminding that REX is a CERN facility since 01.01.2004.
- The effort to get some support also from the BD group will be relaunched by Mats during an upcoming meeting of the group leaders.
- Fredrik has sent three roughing pumps for repair. The repair will be paid from the physics group budget. REX keeps one pump as a spare.
- G. Giorgiev is a new Fellow at ISOLDE. He might act as a MINIBALL contact person. Giorgiev had some ideas how to improve the beam diagnostics in the target chamber. Fredrik has invited him for the meeting in two weeks to present them.
- Romain Savreux shall get a “Werksvertrag” with the LMU Munich for ½ year, similar to the contract JPA had. Thomas will take care for this.
- It was brought up, that the users should include time for beam development in their proposals (like time for calibration with stable beam), because the last runs have shown that in particular for molecular beams and heavy masses, a lot of time is needed to get the beam from ISOLDE to the trap and to set up the charge breeder.
- Thomas will give a talk about the REX machine at the workshop in December.
2. TRAP
-
- Fredrik and Pierre have written the following summary:
Zn run
isotopes
run: 74,76,78Zn run, charge states:
74Zn20+,76Zn20+,78Zn21+
breeding time: 78 ms
efficiencies: 2-3% EBIS; 50% trap; 70% Linac
currents after trap and ebis: ??? à beam
detection will work up to 80Zn
technical problems: running GPS at 30
kV, complete re-setup of REX for this voltage
comments: used 39 K for setting up the low energy part
used 66Zn for testing
(not stable since it's laser ionised)
lesson: a well outgassed
produces very little beam, mass marker important
don't mess around / tune a REX system setup with high intensity beam
Cd run
isotopes run: 122Cd, 124Cd, 126Cd, charge states: 122Cd30+, 124Cd30+, 126Cd31+
breeding time: 148 ms
efficiencies: almost the same than with
the Zn, lower for the EBIS
currents after trap and ebis: beam detection limit reached with 126Cd
122Cd 9 pA on inj plate, 4 pA out of trap, 3.5 pA out of EBIS, 2.8% breeding eff,
43% linac eff
124Cd 6 pA after the
trap, 1% efficiency in the EBIS
126 Cd
<1 pA on inj
plate, BTS.FC20=1 pA (peak value), RFQ.FC20=0.7 pA (peak value)
technical problems: repetitious rebooting of srv1_isolde,
RF server switched off over weekend
database problems (disappearing database)
difficulties setting up the linac (steering in the
end, low transmission)
comments: used 133Cs for stable beam setup
many mass changes in
small amount of time for REX
SeCO run
isotope run 70Se17+
breeding time: 33 ms
currents after trap and ebis: 70SeCO 10% of 0.5 pA out of
trap
efficiency: 40% trap EBIS unknown for
molecular injection - awaiting MINIBALL results
comments: breakup of
molecule in EBIS and not in trap
the molecule breakup in the trap had too low efficiency to work, drowned
in background
no Coulex excitations were seen - something wrong in the
on-line analysis or too few particles
technical problems:
control for the REX mass
separator failing (operate in manual mode)
no mass marker;
resetting the HRS (new beam transport every time)
unknown beam composition
(stable and radioactive beams) out of the primary target
lesson:
with present scheduling
all runs become test runs, need two days dedicated beam setup
mass
marker, yield measurement, target characterisation (stable and radioactive),
GPS instead of HRS
3. EBIS
-
Fredrik was in
Notes from MSL meeting
30/7-2004
Present Leif Liljeby (MSL), Örjan Skeppstedt (MSL), Fredrik Wenander
(CERN)
At a strategy discussion a
number topics were raised and the following ‘agreements’ was reached.
1. MSL workshop should
manufacture two electron guns with post acceleration. One to
be tested at CERN in November when Leif comes down for a visit.
2. Fredrik should order LaB6
cathodes from Kimball Physics to be tested at CERN in November (if possible)
together with Leif.
3. MSL acquires an IrCe cathode from
(The number of cathodes that
can be tested at CERN depends on the planning for the solenoid repair. If the
EBIS solenoid is not available the tests have to be carried out at MSL.)
4. Workshop time could be
available at MSL. They could produce a spare collector for the REXEBIS.
5. Leif comes for a visit in
November (if possible).
6. Leif provides Fredrik with
ACAD drawings of the REXEBIS. Important for future
modifications.
7. We should apply for a postdoc; to be based at MSL. This is important for
REX-ISOLDE if one wants to go to heavier elements. A doctoral student was ruled
out for several reasons. The postdoc should carry
out:
Electron beam simulations (Opera
available at MSL)
Cathode tests
Improve the gun design of the
REXEBIS
How to finance the position?
Fredrik has made inquires to Oliver Kester, but he
has no funding apart from already allocated EURONS money. Örjan
investigates possibilities for Swedish funding. With a well described physics
case, that needs post acceleration of elements heavier than A=150, could one
write an application to The Swedish Research Council or find some international
funding?
Thereafter Leif and Fredrik
had a discussion about different technical issues. The outcome of the
discussion will be presented at a weekly REX meeting in the near future.
High LqHe consumption for
REXEBIS magnet
Opera simulations of EBIS electron gun
N2 liquifier
Construction concepts of the electron gun test bench a
CERN
Improvement of the REX-ISOLDE mass separator vacuum
- Fredrik measured quite strong fluctuations of the EBIS electron current. Since the beforehand noticed leakage current at the extractor electrode has almost vanished, it was decided NOT to open the EBIS to change cathode and check the extractor electrodes (3 weeks work). However, the cathode responds to the heating current in a correct way, and even changing to a new cathode will not guarantee a flawless run.
- The EBIS steerer voltages are not stable. Fredrik will ask Nicolas to look at this.
- Concerning the AlF run in the end of September, for the stripping to 9+ in the EBIS an efficiency of 30% has been calculated (time: 100ms).
4. LINAC
- The high voltage breakdown problems at the 200 MHz amplifier (anode capacitor and rf-filter broken) could be solved right at the beginning of the Zn-run.
- The amplifier was running most of the time at 85 kW, producing final energies at REX between 2.7 and 2.9 MeV/u. The operation was quite stable (had to be restarted about 2 times per night).
- There were again problems with the low level modules. In particular during the Se-run, where the read-out value of the pickup signal changed after the scaling by ~40mV and the HRPS of 7-gap2 changed the phase by more than 80° without any reason. Due to this the whole machine had to be readjusted, what took half a day. The HRPS module will be tested by the rf-group, the IH setup will be checked in general.
- Also during the Se-run, we ended up in controlling the separator lenses manually (!) due to permanent failures of the Wago modules. Since the problem occured because of inaccurate installation and grounding, the module will be rebuilt and completely recabled. Also the r/w connectors at the high voltage modules will be changed (Nicolas takes care).
-
Thomas will ask
- Thomas wants to buy a multicusp source from IAP Frankfurt to replace the test source at the separator. Price ~5k€.
- The tests with a A/q=2 beam (preparation for the AlF run) start beginning of next week.
-
Richard found various C-foils, but all 100ug or
thicker. Thomas will try to get some lighter ones in
- Concerning the next steps of the REX energy upgrade Thomas was asking once more for some input from the physics side to decide how energy variable the machine should be. A decision will be made now at the upgrade group meeting in October.
GSI is willing to give four 20° bending magnets for the high energy beam line after the 4.2 MeV/u upgrade. They want to have a detailed request until October.
4. CONTROL SYSTEM
- The board for the new control system expert has been held. The chosen candidate is Nicolai Trofimov whose contract will start on 1. October.
-
Mats will ask
Minutes by Thomas