Chopping Simulations Results M. Garcia Tudela, JB. Lallement, PA. Posocco, A. Lombardi, G.Bellodi, M. Eshraqi, E. Sargsyan, L. Hein 1 17/06/2010

Chopper Line - Introduction  Placed between the RFQ and DTL. Figure 1.- MEBT Scheme.  Aim: Modify the time structure of the pulse, avoiding losses at high energy.  Removes the bunches that would fall outside the bucket of the PSB at injection. (133/355)  Removes the bunches during the rising time of the distributor (1µs gap) in the TL.  Generate low intensity beams.  Allow the matching to the DTL.  Beam Dynamics chopper ON, fate of the particles  Simulations with code PathManager[3]  Field maps from the electromagnetic simulations [5] to have a realistic approach. 2 17/06/2010

Chopper Line ON – 700V  Nominal case. Losses in the MEBT. Figure 2.- Beam power loss map [watts per element] in the MEBT.  Input beam: 10 6 macro particles  0.04 % Duty cycle  PSB rep. rate 1Hz, 400 µs pulse.  ~ % Beam current after the MEBT. ( From 63.5 mA to 41µA) 3 17/06/2010

Chopper Line ON – 700V  Tracking the beam up to the PSB Figure 3.- Beam power loss map [watts per meter] in the DTL.  No beam loss in the CCDTL or PIMS.  Worst case in the transfer line is 0.25 W/m.  77% of the partially chopped beam (at the output of the dump) is transmitted along the LINAC up to the end of the transfer line. 4 17/06/2010

 Figure 5.- TL beam energy. Chopper OFF. Figure 4.- TL output beam (Nominal beam and deflected beam superimposed).  Transmission, chopper ON: 0.06 % Figure 6.- TL beam energy. Chopper ON. Chopper Line ON – 700V 5 17/06/2010 Chopper OFF Chopper ON

Chopper Line ON – Other approaches  Chopping efficiency applying different voltages to the plates for the same input beam.  Chopper OFF :  Transmission after the MEBT 96.3%  Transmission to PSB 89.4% 6 17/06/2010 Voltage [V]Chopper efficiency % Input beam stopped by the dump Input beam to PSB Extinction ratio x x x x 10 -4

Some numbers 7 17/06/2010  Beam pulse 0.4 ms  Beam pulse per ring 0.1 ms  Repetition rate 1Hz  Bunch frequency MHz  Number of bunches per pulse (0.4 ms): 3.5 x 10 4  Number of bunches per pulse per ring (0.1 ms) : x 10 4  Number of particles per pulse to PSB: 1x10 14  Number of particles per bunch 1.14 x10 9  N f : Number of bunches filled in a pulse ( chopper OFF )  N e : Number of bunches empty in a pulse( chopper ON ) Extinction ratio criterion:  Other commissioning scenarios:  pulse 10 ns per ring ~ 3 bunches  F e < 0.34 x10 -3  700 v : F e = 0.6 x 10-3  Number of particles chopper on is comparable to the number of particles during the pulse.  pulse 30 ns per ring ~ 10 bunches  F e < 0.87 x µs... NfNf NeNe Ring 3Ring 2Ring 1

 If chopper driver rise/fall time > 2ns  Partially deflected bunches Partially deflected bunches 8 17/06/2010 Voltage [V] Chopper efficiency % Input beam stopped by the dump Input beam to PSB Extinction ratio x x x V300 V 400 V 5 * RMS Emittance, superimposed  The level of the losses along the linac is in the order of mW. Figure 7.- TL output deflected beams for every voltage (X-Y).

Conclusions  The percentage of particles at the end of the TL decreases exponentially with the voltage.  The larger the pulse required in a ring, the less strict the extinguish factor required.  For the nominal case: 700 v  0.6 % o particles of the input beam transmitted to the PSB.  For some commissioning scenarios requiring very low intensity beam this value could be not enough. 9 17/06/2010

References 17/06/  [1] F. Gerigk, M. Vretenar editors, “LINAC4 Technical Design Report”, CERN-AB ABP/RF  [2] N.V Mokhov and W.Chou editors, “Beam Halo and scraping”, Proc. 7th ICFA mini-workshop on high intensity and high brightness hadron beams, Interlaken resort, Wisconsin, United States, 1999  [3] A. Perrin and J.F Amand, Travel v4.07, users manual,CERN (2003).  [4] R.Duperrier, N. Pichoff, D. Uriot, “CEA Saclay codes review”, ICCS Conference 2002, Amsterdam  [5] T. Kroyer, F. Caspers, E. Mahner, “The CERN SPL Chopper Structure: A Status Report”, CERN-AB , CARE-Report HIPPI  [6] M. Garcia Tudela, JB. Lallement, A. Lombardi, “Chopper Line Studies”, CERN- sLHC-Project-Note-0012