Linac 4 Beam Characteristics Alessandra M Lombardi Giulia

Linac 4 Beam Characteristics Alessandra M. Lombardi Giulia Bellodi, Mohammad Eshraqi, Jean-Baptiste Lallement, Sara Lanzone, Edgar Sargsyan. Nominal LINAC 4 beam at the PSBooster Generation of energy modulation Tunability and uncertainties

Linac 4 Layout 45 ke. V H- RFQ RF volume source (DESY) 45 k. V 1. 9 m LEBT 3 Me. V CHOPPER Radio Frequency Quadrupole 352 MHz 3 m 1 Klystron 0. 6 MW Chopper 352 MHz 3. 6 m 11 EMquad 3 cavities Total Linac 4: 80 m, 19 klystrons Ion current: 40 m. A (avg. in pulse), 65 m. A (bunch) DTL Drift Tube Linac 352 MHz 18. 7 m 3 tanks 3 klystrons 4 MW 111 PMQuad 50 Me. V 102 Me. V CCDTL PIMS Cell-Coupled Drift Tube Linac 352 MHz 25 m 21 tanks 7 klystrons 6. 5 MW 24 EMQuads Pi-Mode Structure RF Duty cycle: 0. 1% phase 1 (Linac 4) 3 -4% phase 2 (SPL) (design: 10%) 160 Me. V 352 MHz 22 m 12 tanks 8 klystrons ~12 MW 12 EMQuads 4 different structures, (RFQ, DTL, CCDTL, PIMS)

Beam OUT of Linac 4 Transverse phase space , scale: 20 mm X 2 mrad Beam pulse length = 400 µsec Repetion rate = 1 Hz Microbunch freq. = 352 MHz (2. 8 nsec) Current per microbunch = 65 m. A Current per pulse = 40 m. A (chopping) Transverse emitt =0. 35 μm Energy = 159 Me. V (± 1 Me. V modulation) Energy spread rms = 80 ke. V Energy jitter 1 σ = 78 ke. V (assuming 0. 5 deg 0. 5% klystron stability) Longitudinal phase space , scale 1 Me. V X 180 deg at 352 MHz NB : betalambda = 440 mm , beam is 3 mm long

Energy modulation PSBooster asked for a linear energy variation over 10 + 10 µsec (20 turns) to better fit the 100 µsec pulse to the booster bucket The field in the last two tanks of the PIMS is linearly increased /decreased from 2. 6 to 3. 28 MV/m over 20 µsec to vary the beam energy by ± 1 Me. V /160 Me. V Nominal field in the 1 tanks of the PIMS structure (100 -160 Me. V)

Energy modulation Eo. T (n=11, 12)=3. 28 MV/m DE=+1 Me. V Eo. T (n=11, 12)=2. 93 MV/m nominal E=159. 4 Me. V Eo. T (n=11, 12)=2. 6 MV/m DE=-1 Me. V Longitudinal phase space at LINAC 4 output for nominal and extreme setting of the last PIMS tank. The beam transverse and longitudinal phase space is practically identical in the three cases

Transfer line to the booster About 170 meter long New part : 70 m , debuncher (0. 7 MV), 17 quads and 4 bends (35 deg H, 28 deg V) Existing line : 100 m, 18 quads and 2 bends (22 and 24 deg), distribution system. Beam dynamics Issues : 1) space charge with dispersion 2) uncompensated space charge forces (increase of energy spread) 3) limited aperture in distributor and septum ( 50 x 25 mm ; 15 X 34 mm) Side View Top View

Transfer line to the booster

Nominal beam at the injection foil Transverse Phase planes , scale 20 mm X 2 mrad Alpha=-0. 4 Beta = 3 m Emittx =0. 39 μm Alpha=-0. 8 Beta = 23 m Emitty = 0. 45 μm

Longitudinal Plane at the injection foil Current per microbunch = 65 m. A Current per pulse = 40 m. A (chopping) Transverse emitt =0. 4 μm Energy = 159 Me. V (± 1 Me. V modulation) Energy spread rms = 160 ke. V Energy jitter 1σ = 20 ke. V Scale 1 Me. V X 180 deg at 352 MHz

Nominal beam at the injection foil Beam transverse size rms = 1. 4 x 4. 3 mm Dispersion = -1. 4 m Jitter in x position 1 σ = 0. 1 mm scale : 20 mm X 20 mm

Tunability - Dispersion at BHZ 40 (handover point) when varying QFN 50 QDN 55 QFN 60 QDN 65 QFW 70 QDN 75 by 10% Randomly around their nominal value In all cases : • Emittx, y increase is limited to 5% • Full transmission

Tunability – alphas and betas Transverse alphas and beta at BHZ 40 (handover point) when varying QFN 10 QDN 20 QFW 30 QDW 40 QFW 50 QDW 60 by 10% Randomly around their nominal value 2 (X, X') Alpha 1 0 -1 0 50 100 150 200 250 300 -2 -3 -4 -5 (Y, Y') Alpha 6 4 2 0 -4 (X, X') Beta [m/rad] 0 50 100 150 200 250 300 In all cases : • Emittx, y are constant • Full transmission 0 8 -2 40 35 30 25 20 15 10 5 0 180 160 140 120 100 80 60 40 20 0 50 100 150 200 250 300 (Y, Y') Beta [m/rad] 0 50 100 150 200 250 300 • Dispersion almost unchanged

Conclusions The beam from LINAC 4 can be successfully transported and matched to the PSB ¡ Optics parameters in the injection region can be tuned in a sufficiently (? ) wide range ¡ A lower current, higher emittance and a higher energy jitter should be expected during initial operation. ¡

Reserve-energy spread in TL 3. 00 E-04 Kinetic Energy Standard Deviation [Ge. V] vs. lenght [m] 2. 50 E-04 2. 00 E-04 1. 50 E-04 1. 00 E-04 5. 00 E-05 0. 00 E+00 0 20 40 60 80 100 120 140 160 180 200

Reserve – dispersion in TL

Reserve-emittances in LINAC 4