M.J. Barnes
CERN TE-ABT
Acknowledgements:
W. Bartmann, G. Bellotto, D. Comte, L. Ducimetière, B. Goddard,
N. Magnin, V. Namora, J. Uythoven, J. Wenninger
M.J. Barnes
14/06/2016 - LIBD Meeting
1
Example 1 of IPOC Analysis for MKI8
MS MKI8A checked – OK. But changed for other reasons
IPOC data filtered on delay (>79 μs)
TS
Δ0.45% (Δ0.11%
average for system)
MKI8A IPOC of TMR waveform
degraded from 26/05/2016 to
01/06/2016. No report of
increased beam losses or
oscillations.
Specification for system includes
field ripple of ≤ ±0.5%.
Immediate intervention not
demanded as degradation < 1%
(0.25% average for system).
- Entry-box or cable connection problem postulated at time (entry-box of MKI8A changed
during March 2015);
- Main Switch MKI8A changed 06/06/2016 (afternoon);
- During TS Entry-Box of magnet MKI8A changed. “Pince” on one HV cable adjusted too,
but no sign of erosion.
M.J. Barnes
14/06/2016 - LIBD Meeting
2
Example 2 of IPOC Analysis for MKI8
MS MKI8A checked – OK. But changed for other reasons
IPOC data filtered on delay (>79 μs)
TS
Δ6.5ns
MKI8A IPOC of TMR
waveform degraded from
26/05/2016 to 01/06/2016
then (mysteriously)
recovered (almost fully)
before TS…. Small
change after TS too.
- MS MKI8A changed 06/06/2016 (pm).
- During TS Entry-Box of magnet MKI8A changed. “Pince” on one HV cable adjusted
too, but no sign of erosion.
M.J. Barnes
14/06/2016 - LIBD Meeting
3
Example 3 of IPOC Analysis for MKI8
MS MKI8A checked – OK. But changed for other reasons
IPOC data filtered on delay (>79 μs)
TS
Δ26ns
MKI8A IPOC of TMR
waveform degraded from
26/05/2016 to 01/06/2016
then (mysteriously)
recovered (almost fully)
before TS…. “Full”
recovery after TS.
- MS MKI8A changed 06/06/2016 (pm).
- During TS Entry-Box to magnet MKI8A changed. “Pince” on one cable adjusted too.
- During TS Entry-Box of magnet MKI8A changed. “Pince” on one HV cable adjusted
too, but no sign of erosion.
M.J. Barnes
14/06/2016 - LIBD Meeting
4
MKI8A waveforms
New feature in IPOC allows data to be extracted, for comparison outside analyser:
TMR waveforms show “degradation”
to 01/06/2016. Waveform of
13/06/2016 is almost identical to that
of 18/05/2016.
TMR only affected, could be due to
Acquisition card? (e.g. slow
temperature change): to be carefully
monitored and understood.
MS current doesn’t show any
“degradation” between 18/05/2016 and
01/06/2016. Hence issue with TMR
waveforms/IPOC could be a
measurement problem.
M.J. Barnes
14/06/2016 - LIBD Meeting
5
Conclusions re Degradation of MKI8A TMR IPOC
 TMR waveform slowly degraded from 26/05/2016 to 01/06/2016 – but
substantially recovered from 01/06/2016 to 06/06/2016;
 Resistance measurements on MKI8A connectors etc., on day before TS,
showed no abnormality. But MS changed for other reasons;
 During change of MKI8A entry-box, during TS, one “Pince”, at entry-box
end of RG220 cables slightly outside specification – readjusted. But
showed no erosion, so not suspected as cause of problem;
 Performance of MKI8A TMR waveform now fully recovered;
 Reason for apparent TMR waveform degradation not understood –
probably a measurement issue (MS current showed no change and no
report of increased beam losses or oscillations) - to be studied to
identify reason;
 Capacitive pickups, at magnet input and output, connected – signals
available on local scope, but are not logged. MKI8A pickups presently
displayed on local scope.
M.J. Barnes
14/06/2016 - LIBD Meeting
6
Pulse Length Reduction
MKI8B breakdown on
05/06/2016 @ 17:52hrs, during
injection.
Present flattop  ~7.9 μs
72 bunches, 25 ns  1.8 μs.
Breakdown ~3.9 μs into flattop.
Potentially:
2x72 bunches, 25ns  ~4 μs.
Since we are operating with shorter trains right now, a reduction of the MKI pulse length:
• Is beneficial for the kicker to reduce the probability of flashovers and potential kicker damage;
• A mistiming of an MKI system would potentially miskick less circulating beam (however
reduced pulse length does not decrease quantity of miskicked beam due to an MS erratic).
To reduce the MKI pulse length, protection in the SPS has to be set up to prevent sending a
longer pulse to the LHC. This requires setting up a new cycle with reduced flat bottom and
therefore dumping high intensity beam on the TIDVG….
Reduction in pulse length agreed upon in the LMC of 08/06/2016, because a shorter cycle will be
setup in the SPS anyway and then can serve as protection.
M.J. Barnes
14/06/2016 - LIBD Meeting
7
Other MKI Notes
Analysis of the occasional flashovers/breakdowns in the MKIs during Run 2, seems to
show a correlation with recent operation with high intensity beam and relatively long
periods of stable beam.
Hence, to ensure reliable operation of the MKIs, it would be good practice to recondition the
MKIs by running an “Extended SoftStart” following operation with high intensity beam for
relatively long periods (or after every beam dump?). However, in order to ensure minimal
impact on LHC operation:
a) Extended SoftStarts would be routinely run immediately following beam dump (i.e. during
ramp down of the superconducting magnets)
b) Prior to injection a normal SoftStart is run, as per the present situation (if the Extended
SoftStart is no longer valid? - reduces both number of MKI pulses and turnaround time).
The Extended SoftStart will also potentially give additional statistical data for analysing beam
induced heating of the MKI's.
Sequencer = During every ramp-down of superconducting magnets;
Procedure = We define previous beam conditions for an Extended SoftStart.
Jorg does not foresee a problem of the Sequencer automatically running an Extended
SoftStart following a beam dump (Laurette presently looking at this). The sequencer would
then also reload the normal SoftStart parameters (to ensure that only a normal SoftStart is run
before injection).
M.J. Barnes
14/06/2016 - LIBD Meeting
8