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239th HiLumi WP2 Meeting
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Europe/Zurich
Description
Chair: Rogelio Tomas
no Minutes
HiLumi WP2 Meeting Room
Daniel presents that intertrain cleaning has been demonstrated with about 1000 nominal bunches.
Previous studies on optimal excitation for cleaning:
https://cds.cern.ch/record/1199758/files/CERN-ATS-2009-016.pdf
Wolfgang mentions that adding vertical cleaning could help. Sofia mentions that if excitation is at various tunes instead of a sweep could also help.
Emittance growth was not closely looked but did not seem problematic. Rogelio asks if there will be a follow-up of this MD with higher intensity, improved cleaning, and more accurate measurements.
There is the request from RF to identify the best excitation.
Michail presents the RF noise cleaning test. Injecting phase noise caused larger unbunched population since unintentionally there was noise being put in all buckets. This needs to be fixed for future MDs.
For the RF capture with HL beams maximum voltage was found to be 5.9 and 6.1 MV in Beam 1 and Beam 2. Currently we have 6.5MV in operation and in Run 4 we expect 7.9 MV with high efficiency klystrons (7.5-7.9MV). 4x72 bunches should be tried in MD2. 8b4e will be tested in MD2 as requested by Sofia (in the past 8b4e was tested only up to 1.8e11ppb). Sofia comments that when 2e13 is reached as debunched beam the beam would be dumped at start of ramp.
Sofia presents the emittance growth and noise studies. It was demonstrated that blow-up can be performed without losses by combining with ADT damping. PU of 160 was reached. Bunches with q=1.5 clearly lose more intensity during collapse and in the ~2 following hours. At injection the extra 0.2um/h emittance growth was confirmed. However, the bunch length evolution is not reproduced as well as in the past. The 8kHz appear at the end of the ramp (5.5 TeV). Integrated luminosity loss between q=1 and q=1.5 was 3% in first 4 hours. Concerning emittance growth collisions tend to make bunches more Gaussian. Comparing BSRT and WS at injection shows very good agreement even for tails. At flat top this agreement is not observed already for emittances and specially for B1.
Plan for MD2: collide 8b4 with 2.3e11ppb. 1 Indiv at 3 TeV. 4x72. Cleaning. Synergies with RF, e-cloud and OP.
Ewen presents corrections of LRBB with IR magnets with measurements with AC dipole. Flat optics inherently have reduced 3Qy resonance than round and could be corrected with IR skew sextupoles. The 4Qx and 4Qy resonance can be corrected with octupolar correctors. The 2Qx-2Qy resonance cannot be corrected with IR octupoles. beta-beating was also shown to reach above 20% in some pushed configurations. Sofia asked about putting these corrections in operation, which should be explored.
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