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MP3 Meeting
MP3 Meeting (03 Feb 2010)
1. Tests with 600A power converter on RCBYHS5.R8B1 (Y. Thurel) :
(Refer to slides). The test put in evidence that the instabilities shown on the powering of the circuit are not depending on the power converter that was changed for the test (a 600 A with the DCCT on the “good side” instead of a nominal 120 A PC). Instabilities seems always present even when not evidently visible in the graphs (depends by the resolution).
Hypothesis of Yves is that only when stored energy is higher of a critical value we see a macroscopic effect; below this threshold in energy, the instabilities are probably naturally re-absorbed without quenching the magnet but they are still present.
In order to correct the instabilities even with the 600 A PS it was necessary to insert a parallel resistance of 70 Ohm.
ELQA (Nuria) confirm that the transfer function measured for this circuit is different from the other RCBY; anyway Yves noted that the inductance of the magnet is the expected one.
General agreement to perform a test on cryogenic working conditions (over-filling the cold mass) to see if problem is linked to cryo aspects. Action: S. Claudet , K. Brodzinski, Y. Thurel
Andrzej underline that, in his opinon, the situation is quite worrying and that is better to start to discuss with BE the possible back-up solutions from the point of you of machine operation.
2. RRR type test measurements results ( M. Koratzinos) :
(Refer to slides). Mike described and showed the first results of the RRR measurement test done in the Sector 8-1 last week.
The test found some problems to measure the voltage drops across the bus-bar. He focused the presentation on the measurement of the magnet cable RRR easier to measure and to crosscheck with the measurement done at SM18.
Results are as expected with a “hysteresis-like” curve on resistance as function of the temperature that can be easily explained by the physics of the thermal diffusion and by the presence of the TT821 not in contact with the cables but with the yokes lamination. The measurements obtained for the different magnets are mainly divided in two families; it will be interest to check coherency of these measurements with the measurement done at SM18 and eventually during cable production (even if these measurements were done before curing of the coils).
Data for busbar RRR are more complicate to be analyzed and this will take still few weeks.
3. RCBXH1.L2 cryo leads stability tests (N. Catalan Lasheras) :
Nuria showed the status of the investigation and last test performed. The regulation of the current leads seems good up to the 7A/s measurement.It is not possible to increase the ramp rate in such a short current interval without increasing the acceleration. As soon as the acceleration is increased, the circuit trips on the QPS due to the error in acceleration.
Two possible solutions are today envisageable:
a) To implement “intelligent” and asymmetric thresholds on U_res: Reiner confirm this possible but with a “firmware update” so it will took a little bit of time.
b) Bob propose another simpler (temporary?) solution that is to decrease the integration time on U_res. This should permit to pass across the perturbation observed during the rams and to not trigger the circuit.
Both solutions need to be quantified in terms of time and feasibility. ACTION: R. Denz. Note that in principle we could expect for similar problem in the following 8 locations (one per magnet on H1 or V1 corrector):
RPMBB.UJ14.RCBXH1.L1
RPMBB.UJ16.RCBXH1.R1
RPMBB.UA23.RCBXH1.L2
RPMBB.UAJ27.RCBXH1.R2
RPMBB.USC55.RCBXV1.L5
RPMBB.UJ56.RCBXV1.R5
RPMBB.UA83.RCBXV1.L8
RPMBB.UA87.RCBXV1.R8
The requirements from ABP are still unknown to MPP. The parameters needed would be the strength variation and total time interval in order to optimize the QPS integration, cryo control and FGC function together. ACTION: G. Arduini
AOB: Jean-Philippe mentioned that a tomography investigation could be done on the three excess resistance splices mentioned in Chamonix by Mike Koratzinos. The impact on planning will be relevant, mainly due cryogenic logistic (half sector must be empty) and safety aspects.
Impact on planning is today realistically estimated to about 2 weeks.
After discussion, the position of MP3 is to recommend the investigation but not in th e near future as the results of it are still uncertain.
Insulation fault in sector 78 was localised inside the magnet 1007. There is a stable breakdown over 1.6 kV. The fault is not degrading. ELQA team is doing further investigation to exclude that this is on the warm part. The minimum required withstand voltage for 3.5 TeV run needs to be determined. Action: ElQA team
M. Modena, N. Catalan Lasheras
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