1. Bunch Flattening with RF Phase Modulation T. Argyropoulos, C. Bhat, A. Burov, J. F. Esteban Müller, S. Jakobsen, G. Papotti, T. Pieloni, T. Mastoridis, E. Metral, N. Mounet, B. Salvant, E. Shaposhnikova, H. Timko, +… Thanks to the OP crew!

2. Motivation 15/02/2013LSWG2  Heating depends on the beam spectrum and therefore bunch distribution  Modifying the bunch distribution can help to reduce the heating in some devices  The bunch distribution in the LHC can be changed by:  Installing a higher harmonic RF system (LMC open action)  Flattening the bunches by applying a sinusoidal RF phase modulation at a frequency slightly below the synchrotron frequency (~ 97% f s )  Already done in SPS and in Tevatron and checked in simulations

3. MD plan 15/02/2013LSWG3  Flat bottom  Single bunches  Synchrotron frequency distribution with PD Schottky  Synchrotron frequency shift by scanning the modulation frequency  Check parameters for RF phase modulation  Nominal beam  Test RF phase modulation  4 TeV  Ramp with nominal beam and controlled emittance blow-up  Voltage variation for transverse instability studies  RF phase modulation

4. (I) Phase Modulation Test at 450 GeV 15/02/2013LSWG4 I.a) Test with 8 bunches with intensities in range (0.65-2.3) x 10 11 scanning from above the modulation frequency  Bunch phase was monitored to see effect on each bunch  Difference in synchrotron frequency between low and high intensity bunches with length ~1.3 ns is ~ 0.2 Hz/10 11  For impedance Im(Z/n) = 0.1 Ω and parabolic amplitude distribution df s ~0.27 Hz/10 11 is expected I.b) Test with nominal Beams 1 and 2:  RF modulation at f rev ± 0.97 f s with PL ON, led to a weak bunch length variation at f rev  Visible effect on beam spectrum and bunch profiles  Beneficial effect on ALFA heating observed online

5. (II) 4 TeV : Phase Modulation 15/02/2013LSWG5

6. (II) 4TeV: Beam Induced Heating 15/02/2013LSWG6  Voltage variation in 0.5 MV steps (10-6-10 MV) to study transverse stability:  No improvement observed  Reduction in heating as expected  With flat bunches - heating reduced in many devices:  Immediate reduction in temperature of TCTVB and ALFA Roman Pots  Reduction in the BSRT, but indirect temperature monitoring  For the MKI the test was not long enough compared to the characteristic thermal time  No temperature monitoring for the TDI Temperature [ºC] UTC Time Bunch lengths ALFA TCTVB

7. Peak-Detected Schottky 15/02/2013LSWG7  Two bunches of B1 with similar length and intensities of 0.65 x 10 11 and 1.65 x 10 11 were monitored at 450 GeV during ~20 min (following the BL increase)  Advanced analysis needed to estimate accurately tiny frequency shift (~1Hz at 2fs)

8. Conclusions 15/02/2013LSWG8  Flat bunches with RF phase modulation:  Very promising method to control heating below 1.2 GHz (no show-stopper found), but it needs more checks after LS1 with better diagnostics for heating in the 1.2-1.6 GHz range  If OK above 1.2 GHz, can be used in operation after usual controlled emittance blow-up (with smaller target BL) with PL off (during this manipulation); at the end of the ramp or beginning of the flat top  Inductive impedance estimation  Data from PD Schottky and excitation  f s shift is 100 times less than in SPS  Needs advanced analysis  No improvement for transverse instability with 0.2 ns longer bunches