RF improvements over the weekend Giulia on behalf of Delphine, Philippe, Andy and many other people in the RF team LHC Beam Commissioning Working Group, 16 th Nov 2010

giulia papotti (BE/OP/LHC) voltage reduction at injection – 1 similar to SPS 4 inj cycle –dip to 2MV from 3MV problems: –for clean capture (no tails) voltage should be ~ matched to the SPS bucket –~ MHz –bunch grows quickly during the very long filling (IBS) - > loss from the bucket solution: –flat bottom at 7MV –reduction to 3.5MV for each inj –adiabatic descent from F1K, 1s long –adiabatic rise back to 7MV, 1s long total length: 5s Delphine’s art… and SPS experience then linear acceleration ramp from 7 to 12MV SPS TOTAL VOLTAGE LHC TOTAL VOLTAGE conserve longitudinal emittance larger momentum spread reduces IBS larger bucket reduces losses

giulia papotti (BE/OP/LHC) voltage reduction at injection – 2 transmission much improved – almost no losses at start of ramp Bunch length 19% L increase at each V reduction Capture loss

giulia papotti (BE/OP/LHC) emittance blow up during ramp – 1 rectangular phase noise power spectral density that excites only the core –avoid tails and losses –hit: 0.87 f s < f < 1.1 f s corresponds to a 1.2 ns window in the core –follow f s along the ramp from 57 Hz to 28 Hz method developed by Joachim and RF studies section for the SPS algorithm: adjust the amplitude of the excitation x n from a measurement of the instantaneous bunch length (mean) L n and comparison to target L 0 target bunch length L 0 1 ns for ions –was 1.2 ns for protons Phase noise spectrum Part of the bunch excited

giulia papotti (BE/OP/LHC) emittance blow up during ramp – 2 LSA functions: synchrotron frequency f s, f max and f min blow up time constant, gains, max excitation amplitude blow up system hardware armed with sequencer tasks blow-up is then initiated by the ramp timing event BLOW UP GAIN SYNCH FREQUENCY Controls developed by Delphine and Michael Jaussi

giulia papotti (BE/OP/LHC) emittance blow up during ramp – 3 excitation amplitude bunch lengths ramp

giulia papotti (BE/OP/LHC) emittance blow up during ramp – 4 at injection –slow lengthening, up to 1.5 ns BQM vetoes the SPS extraction if length >1.6ns at flat top –bunch lengths nicely equalized –some equalization takes place during the ramp even without blow-up though...but less