MPP meeting (13 Aug 2008)
Present: Marta Bajko; Amalia Ballarino; Boris Bellesia; Francesco Bertinelli; Nuria Catalan Lasheras; Knud Dahlerup-Petersen; Sandor Feher; Robert Henry Flora; Glyn Kirby, Vittorio Remondino; Stephan Russenschuck; Rüdiger Schmidt; Nikolai Schwerg; Andrzej SIEMKO; Pierre Strubin; Antonio Vergara Fernandez; Louis Walckiers; Rob Wolf; Markus Zerlauth
Chaired by: Dr. Andrzej Siemko
General information.
A. Siemko presented the results of the injection test for beam 1 from TI2 to point 3. You can find a short summary in the following link. http://lhc-injection-test.web.cern.ch/lhc-injection-test/
The beam was injected in the LHC tunnel just before the inner triplet in point 2R around 19:00 on Friday. The first trial to inject the beam up to point three was successfully done at 21:00. The strength of the dipoles was found corrrect up to about 1.5 per mil.
Tests during the weekend included orbit correction, aperture scans and instrumentation tests.
The first beam induced quench occurred early Saturday during the aperture scans. The QPS detector signal shows a very sharp peak that recovers in less than 20 ms. The quench heater did not quench the magnet either. After the quench all correctors went down except for two of them (to be checked). The nature of the trip for each circuit has not been analyzed yet.
A quench heater power supply had a fault and was changed on Saturday morning. K. Dahlerup added that this fault is known and has a one per mil probability. There is no risk of damage outside the power supply. In such an event, the QPS-ok is lost but not the power permit. However the loss of two of the quench heaters will trigger a fast power abort.
RQT13. B2 tripped and was switched off as it was not needed.
In the RQD circuit several heater discharged. It was due to some testing system that was left in place. It has been now removed.
G. Kirby added that two correctors in the inner triplet tripped during the slow power abort at the end of the test.
The injection test for beam 2 from TI8 to point 7 will take place on the weekend 22-24 August. The beam will stop in point 7 and not in the beam dump to allow work in CMS.
P. Strubin informed that after the discussions about AT support to operation, a mandate has been defined for the magnets activities (see slides). The team will be chaired by A. Siemko and co-chaired by R. Wolf and E. Todesco. A kick-off meeting will take place this Friday at 14:00.
ECR for improvement of dependability of 60A software interlock. M. Zerlauth
Last year an interlock was added to take into account the cooling of the beam screen and normal conducting leads of the 60 A orbit correctors in the arc. The interlock can not be hardwired and is a software solution. There has been some failures due to utilities problem that have brought all the correctors down. This failure could be critical in the presence of beam. The new ECR aims to Increase the reliability of this interlock specially in the presence of beam.
The proposal is to leave things as they are when there is no beam. When beam is on, the software interlock will not be enabled. If the conditions are not right, the powering will not be possible. However if the conditions are lost during beam operation nothing will happen. The correctors are always protected by the power converter over-voltage. In a near future, the beam screen cooling conditions will be integrated in the cryogenic interlocks and in the general power permit.
The proposal was endorsed by MPP. The ECR will be re-written and circulated for approval. (Action: M. Zerlauth)
Quench simulation of an LHC main bending magnet. N. Schwerg
The quench simulation model included in ROXIE has been gaged for dipoles and uses measurements from SM18 of high field quench heater delay.The heater delay for low field heaters is taken as 25 ms longer.
All the possible configurations to substitute a missing quench heater have been compared with the nominal. The solution applied up to now consist on substituting a HF heater by one or two LF heaters in one aperture. The two LF heaters in parallel seem to be inefficient at low current. Peak voltage however is very dependent on quench location. The maximum voltage should be under 1kV and there could be a bias to ground of 500 V coming from the circuit grounding scheme.
The case where the LF heaters are connected in both apertures still needs to be investigated as it has advantages from the peak voltage.
A test should be done in September at 1.9 K in Sm18 to measure the heater delay of LF quench heaters.
600 A
W. Venturini prepared the list of corrector circuits with the commissioned ramp rate and acceleration parameters compared to the requirements. In the cases where this requirements are not reached, the last PNO test should be repeated with the right parameters. (Action: A. Vergara)
Matters arising
R. Schmidt pointed out that a quench in a main magnet generates a global power abort in the whole powering sub-sector. This may be risky with beam and it is not justified at low current. A small group will analyze this and come to a conclusion for early September. In the coming weeks the global power abort should be disabled. (Action: M. Zerlauth)