1. AT-MEI Group, CERN, 1211 Geneva 23 MPP 18-6-2008 1 Unbalance between apertures of MB B30R7 MPP meeting 18/06/2008 Unbalance between apertures of Dipole B30R7 in S78 (MB 1007) R. Wolf

2. AT-MEI Group, CERN, 1211 Geneva 23 MPP 18-6-2008 2 Obervations  Quench detected in MB B30 (MB 1007) during fast discharge at 7000A => dI/dt =-70A/s  Reason. There is no real quench. There is a voltage diiference between the two apertures which grows with dI/dt and exceeded 100mV. Maybe a short?  Detailed measurements made with oscilloscopes in the tunnel showed however that there was no unbalance between upper and lower poles. Short therefore unlikely, except if symmetric around the midplane(decided to make interturn test in tunnel to make sure)  Magnetic measurement in SM18 during ramp had also shown a different dynamic behaviour of the aperture with a unusually high sextupole in one aperture. Also no particular asymmetry between upper and lower poles.  The behaviour in the machine seems therefore identical to the behaviour in SM18, where this magnet was trained to 12KA as usual.

3. AT-MEI Group, CERN, 1211 Geneva 23 MPP 18-6-2008 3 Magnetic Measurement during Ramp  EDMS No: 357674. HCLBBR_000-CR001007, Magnetic Measurement Test Report, S. Sanfilippo, L. Bottura, V. Granata, R.K. Mishra / LHC-MTA

4. AT-MEI Group, CERN, 1211 Geneva 23 MPP 18-6-2008 4 Conclusion  Based on the similar behaviour in SM18 and the tunnel and the unlikelyhood of a short it would seem reasonable to continue training (if interturn test OK), with higher threshold at 200mV.  The origin of the phenomenon is not clear (Cable Rc?, external loop?). Further study to understand the origin of these large unbalances and to predict them seems useful.  Could the QPS system measure the unbalance before we start the training?