Participants: Luis FrailePierre
Delahaye,
1. General Issues
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A summary of the 138Xe run has been written. It can be found attached to these minutes. Starting on Tuesday 17.05.,
we will have a daily short REX meeting at 16.00 in the ISOLDE kitchen to
discuss the startup and the status of the running Xe experiment.
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2. TRAP
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PierreDue to the problems with the trap controls during the last run, Romain is at the moment reinstalling all programs of the trap CS.
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For
the rest of the week and beginning of next week, Romain
and Ivan will continue with the emittance
measurements at the trap during daytime. In the evenings the beam is given to WITCH.
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On
Thursday/Friday the setup for the Se beamtime will start.
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The
trap ion source has been changed. It shows a better stability but, a high
power consumption.
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By
the end of the week Fredrik will check beam position at the entrance of the
EBIS, using beam
from the offline
source (injection tests).
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and Fredrik had the problem of discharges in
the trap, means there was more current measured at the exit than injected from
the test source. Nicolas David found a broken cable at a transfer element. The
bad contact was responsible for the discharges.
-The test ion source ’runs stable now after the
regulation has been improved.
-The application for the frequency scan of the trap
has to be improved.
3. EBIS
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The
noise on the EBIS drifttubes, which made dry
injection tests difficult, will be checked by Fredrik on Friday.
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The
work on the time of flight measurements at the EBIS has started. Cabling of the mass scan
diagnostic box has been changed to allow for easy switching between beam
monitoring and TOF.
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The
bakeout, which was planned for the time between the
first and second REX run has been postponed.
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There
is still sparking observed in the extractor region. A new flange will be produced to have better
insulation there.
-The bad transmission through
the mass separator, which has been observed on Thursday, was partially caused
by two switched cables in one of the steerers.
-There was again a problem
with the cabling of the Wago module for the high voltage cassettes, which could
be repaired by Nicolas.
-The transmission through the
separator is at the moment 70- 80%, due to the
high residual gas pressure, the current is about a factor 10 higher than usual.
-Stable beam for Linac
optimization will be available on Monday.
-The baking after the run will
be done now with the old NEG strips.
-One day is needed to optimize
beam transport through the BTS.
-Dry injection (without
electron beam and magnetic field) into the EBIS is still problematic because of
the high noise level on the electrodes.
4. Linac
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The
experts from AB-RF, supported by BERTRONIX, managed to do a fast repair of the two 100 MHz amplifiers right before the run. The two broken high voltage transformers were replaced by our own
spare transformer and a spare part from Linac3. Therefore (besides the constant problems with the 200 MHz
system) the duty cycle of the machine is at the moment limited to 1%. The broken transformers have
been shipped to
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There is still one HV transformer of the weak
type left in the RFQ amplifier. It will be replaced as soon as the repaired
transformers arrive
from
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Due
to the (almost) completed improvement of the low level control modules, the 100 MHz part showed during the Xe run for the first time a reliability which is
comparable to the other CERN Linacs.
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The
200 MHz system still requires a modification of its rf cavity. The problem seems to be, that at duty
cycles above ~1% the ferrites in the cavity loose their properties (due to the high
temperature). A parasitic mode – at low duty cycles damped by
these ferrites – causes unstable operation and breakdowns at the anode. If
better thermal contact of the ferrites and better cooling will solve the problem
will be checked in the break we have in June.
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There
is also a relevant certain number of switch offs
due to power reflected from the 9-gap cavity. This is not in connection with the amplifier, but a
problem of sparking in the cavity. Since the
cavity went back to operation only one week before the run, this is considered to be a
conditioning effect, which should vanish with time. We plan to install a circulator to make
operation more stable concerning at least this problem.
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BERTRONIX could not solve the
principle problem of the limited power level of the 200 MHz amplifier. Also the
unstable operation at 10% duty cycle is still a problem. The amplifier could be
tuned to ~100kW output power on a dummy load. It is running quite stable now at
30Hz, 600us. So we can expect closed loop operation on the cavity at about 85
kW.
4. Control System and Power Supplies
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There
has been a meeting with CO to discuss the work on the migration of the REX
Control System. The REX team will publish the results together with the minutes
of next week, after re-discussing some details.
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The
tests for control of the Danfysik supplies with the new front end developed by Nikolai have
been finished successfully. The response time turns out to be similar than what we have at the
moment.
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Nicolas
has reconnected the power supplies to the old CS to allow for beam optimization on Thursday
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There
were problems with a
jitter on the GFAS
timing pulse (EBIS)
which is used as a trigger pulse for the Linac (caused beam losses). Fredrik managed to find a
temporarily solution for this, but claims that the REX timing scheme should - in connection with the issue
of a “slow extraction” - be investigated in general by an expert from CO. He will also contact Joakim Cederkall (who starts working at ISOLDE 1. July) to help with this.
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-The BD FEC is still stopping
from time to time, Sylvestre Catin has been
informed about this.
-Nikolai found that there are
not enough Ethernet connections in the network rack, where he wants to connect
his Front end computer.
Minutes by Thomas