E-cloud meeting with V. Baglin, D. Schulte, F. Zimmermann --------------------------------------------------------- 07.01.2004 Discussion on WAMPAC measurements and simulations. Simulated heat load of WAMPAC3 at 25 ns spacing for delta_max=1.8 agrees roughly with measurements (1.74 W/m in 4 batches). Simulated WAMPAC3 heat load at 75 ns spacing is about 7 times lower, while measured heat load is only 2 times lower than at 25 ns. There is little agreement for WAMPAC1: At 25 ns no multipacting is found in the simulation, even if intensity, beam size and bunch length are varied, while 0.2 W/m was observed in 2 batches. At 75 ns, the simulation shows strong multipacting, whereas no heat load was observed with 3 batches. Based on the dependence of yield on dose found in EPA (V. Baglin at Chamonix 2001), Vincent computed the expected scrubbing effect for different doses. for the simulated flux, above 30 eV a large scrubbing would be expected. Taking the observed heat load and an average electron energy of 50 eV, the estimated flux is even 3-4 times larger than the simulated. In this the expected scrubbing effect would be even larger. To have no scrubbing using the EPA data, a flux 100-1000 less than simulated or estimated would be needed. A possible explanation of this discrepancy is that the measured heat load is not due to multpacting. Another possible explanation could be that, in the SPS, the majority of the heat is dissipated by the low energy electrons which does not reduce effectively the delta max and, therefore, the heat load. He observed the same absolute slope in heat load versus Ah beam for three different detectors. An absolute slope of ~ - 30 mW/m/A/h is estimated. This slope is not sufficient to sensibly reduce the heat load for COLDEX or WAMPAC3. The four detectors are WAMPAC 1, WAMPAC3, COLDEX and a Pick-up calorimeter (operated by Noel Hilleret) located in an MBA SPS vacuum chamber. This pick up calorimeter exhibits a non linear decrease of the power versus beam time in A.h. But, after 2 A.h i.e 10 h operation with 4 batches, it behaves linearly like the other 3 detectors. He pointed out that in WAMPAC2 the measured heat load was a factor 2 higher with field than without a field. Suggestions for further simulations and studies: (1) Simulate WAMPAC3 at delta_max=2.2 and 2.4, as the discrepancy between 25 and 75 ns might decrease. (2) Exchange sigmax and sigmay for WAMPAC1 (3) Scan bunch length, intensity, emittance for WAMPAC1 (4) Change field (no field, 1 G, 10 G)? (5) Change energy distribution of true secondaries (wider!?) (6) check beam position in the detectors