Quench test at millisecond timescale

In order to investigate the quench margin at the millisecond timescale a loss of this duration must be generated. Such a loss is generated by the wire scanner during its normal operation. Therefore a quench test using this device has been performed.

The test conditions were the following: beam with energy 3.5 TeV and intensity of $\rm 1.53\cdot 10^{13}$ protons. The MBRB magnet is situated 32 meters downstream the wire scanner. The magnet quenched when the wire speed reached $\rm 5~cm/s$. The overlapped post-mortem data from the BLM monitor and QPS system are shown in Figure 10. The irregular BLM signal (blue points) shows that the carbon fiber was vibrating during this scan. The electron microscope picture of the fiber made after the test has shown that about 50% of the wire diameter sublimated due to heating from the beam.

The raise of the QPS signal started about 10 ms after the start of the beam scan seen by the BLM system. Therefore the probed time scale was longer than the one characteristic for UFO events (about 1 ms).

Figure 10: BLM post-mortem signals (blue) overlapped with QPS voltage readout (red) during the wire scan which led to quench of MBRB magnet.

The preliminary results of the quench analysis using the QPS and BLM post-mortem data [9] and QP3 code [10] suggest that the quench limit for the 10-ms perturbation is in the range $\rm 35-42~mJ/cm^3$. The preliminary results of FLUKA simulations have been presented [11], and the final conclusions from this experiment are expected soon.

A repetition of this test during 2011 run is strongly suggested. The conditions should be modified, especially the beam intensity should be increased by about factor of 4.