Background, IBS, gas scattering halo, collimation and etc. * Alexander Temnykh Cornell University Laboratory for Elementary-Particle Physics * Work supported by the National Science Foundation under contract PHY 0202078

ERL review, Aug 2 2007, A. Temnykh Beam Hallo Impact The particle losses from the beam halo cause Additional Cryogenic heat load Equipment radiation damage Elevated radiation level in user area … November 19, 2018 ERL review, Aug 2 2007, A. Temnykh

ERL review, Aug 2 2007, A. Temnykh Outline Intra-beam scattering (IBS) and residual gas scattering (RGS) basic formulas and simulation technique. IBS and RGS simulation results and insertion devices radiation protection. Two other sources of the beam halo. Electron gun dark current SRF field emission current Conclusion/Summary Appendix – ID life time criteria November 19, 2018 ERL review, Aug 2 2007, A. Temnykh

Scattering on residual gas (basic formulas) Single Coulomb (elastic) scattering In simulation Using Monte-Carlo method 500 particles per 1m of orbit were scattered in range between qmin=0.1mrad and qmax=10mrad with distribution ~1/q3. qx=q x cos(2pr), qy=q x sin(2pr), r – random number between 0 and 1. They have been tracked along ERL structure to the location where they hit the beam pipe wall and been lost or to the ERL dump. The tracking particle loss distribution scaled according to (1) gives the beam loss along ERL. * Handbook of Accelerator Physics and Engineering. Alexander Chao and Maury Tigner, p.212 November 19, 2018 ERL review, Aug 2 2007, A. Temnykh

Scattering on residual gas (basic formulas) Bremsstrahlung (inelastic) Scattering * In simulation 500 particles per 1m of orbit were started with energy deviation in range between umin= 0.001 and umax=0.1 with distribution ~ u-1. They have been tracked along ERL structure to the location where they hit the beam pipe wall and been lost or to the ERL dump. The tracking particle loss distribution has been scaled according to (1). * Handbook of Accelerator Physics and Engineering. Alexander Chao and Maury Tigner, p.213 November 19, 2018 ERL review, Aug 2 2007, A. Temnykh

Intra Beam Scattering (basic formulas) Intra Beam Scattering (Touschek Effect) Number of particles scattered with momentum deviation more than Dp per 1m of orbit: In simulation 500 particles per 1m of orbit were started with momentum deviation Dp/p in range between 0.002 and 0.05 with distribution: They have been tracked along ERL structure to the location where they hit the beam pipe wall and been lost or to the dump. The tracking particle loss distribution has been scaled according to (1). * Handbook of Accelerator Physics and Engineering. Alexander Chao and Maury Tigner, p.125 November 19, 2018 ERL review, Aug 2 2007, A. Temnykh

ERL optics, general view Aperture used in model Beam pipe: round 25.4mm (1”) ID. LINAC: round, 39mm diameter Insertion device: rectangular, 5mm x 40mm Collimators: rectangular 7mm x 25.4mm 5mm x 25.4mm South arc North arc November 19, 2018 ERL review, Aug 2 2007, A. Temnykh

Intra Beam Scattering beam loss distribution Mode A (maximum flux) operation: F = 1300MHz, 77pC/bunch, 100mA – total beam current 0.3mrad x mm – normalized emittance Power deposition 0.5nA x 5GeV = 2.5Watt 25nA x 0.25GeV = 6.25Watt 90% of the IBS beam loss at the end of deacceleration. November 19, 2018 ERL review, Aug 2 2007, A. Temnykh

Intra Beam Scattering beam loss, momentum aperture hs- dispertion at scattering location. Xb – betatron amplitude at scattering energy Xdump betatron at the end of deacceleration. Xb~(Dp/p)*hs; Xdump~sqrt(Es/Edump)*Xb For Es = 5GeV; Edump = 10MeV; 1.0” DIA beam pipe, hs = ~0.5m, Xdump max ~ 19mm dpmax/p = Xdump max/ hs * Xdump~sqrt(Edump/Es) = = 1.1e-3 !!! hs= 0 hs> 0 November 19, 2018 ERL review, Aug 2 2007, A. Temnykh

Residual gas scattering beam loss November 19, 2018 ERL review, Aug 2 2007, A. Temnykh

Insertion device life time without collimators i l[m] Life_time[A-year] 1.0000 25.000 0.14612 2.0000 5.0000 15.666 3.0000 5.0000 10.011 4.0000 5.0000 6.8349 5.0000 5.0000 9.4894 6.0000 5.0000 8.1089 7.0000 5.0000 11.068 8.0000 5.0000 6.5086 9.0000 5.0000 6.5386 10.000 5.0000 17.143 11.000 5.0000 11.113 12.000 5.0000 44.407 13.000 5.0000 57.083 14.000 5.0000 39.969 15.000 5.0000 13.662 16.000 5.0000 8.6472 17.000 25.000 0.25129 18.000 5.0000 3.6896 19.000 2.5000 8.6015 20.000 2.5000 0.82313 21.000 5.0000 1.8458 22.000 5.0000 13.179 23.000 5.0000 11.977 24.000 5.0000 11.443 25.000 5.0000 12.056 26.000 5.0000 9.4615 27.000 5.0000 7.2853 28.000 25.000 0.28698 November 19, 2018 ERL review, Aug 2 2007, A. Temnykh

RG Scattering beam loss, collimator locations Collimators in the South Arc Collimators in the North Arc November 19, 2018 ERL review, Aug 2 2007, A. Temnykh

Insertion device life time with collimators i l[m] Life_time[A-year] 1.0000 25.000 21.602 2.0000 5.0000 16.162 3.0000 5.0000 9.9180 4.0000 5.0000 49.145 5.0000 5.0000 19.768 6.0000 5.0000 32.649 7.0000 5.0000 7.5905 8.0000 5.0000 6.4786 9.0000 5.0000 6.0453 10.000 5.0000 16.244 11.000 5.0000 10.967 12.000 5.0000 79.636 13.000 5.0000 32.136 14.000 5.0000 46.618 15.000 5.0000 12.926 16.000 5.0000 9.6032 17.000 25.000 4.4054 18.000 5.0000 4.1807 19.000 2.5000 43.134 20.000 2.5000 30.858 21.000 5.0000 4.0879 22.000 5.0000 12.628 23.000 5.0000 11.533 24.000 5.0000 20.592 25.000 5.0000 8.6091 26.000 5.0000 8.9323 27.000 5.0000 8.8655 28.000 25.000 3.7537 November 19, 2018 ERL review, Aug 2 2007, A. Temnykh

Another source of halo: Electron gun dark current ERL Photo-cathode DC gun POISSON calculation Anode Electrode 20 16 25 13.3 13.5 8.5 Cathode Electrode 4 13.0 Photo-cathode Numbers indicate field gradient in MV/m at 500kV of gun voltage November 19, 2018 ERL review, Aug 2 2007, A. Temnykh

Another source of halo: Electron gun dark current ERL DC gun dark current (measured in beam line with Farday Cup) Fowler-Nordheim type approximation, I=m1*E2*exp(-m2/E), predicts 13nA of dark current at 500kV of gun voltage. b (field enhancement factor) ~ 188.5 (assumed electron work function ~1eV) November 19, 2018 ERL review, Aug 2 2007, A. Temnykh

Another source of halo: Electron gun dark current Dark current dynamics simulation for ERL injector prototype Solenoids Cryo-module DC gun Quadrupole magnets Bending Z[cm] Model Dark current uniform emission from 8.2mm DIA cathode 500kV gun voltage Focusing elements optimized for 77pC/bunch current. PARMELA simulation November 19, 2018 ERL review, Aug 2 2007, A. Temnykh

Another source of halo: Electron gun dark current Dark current transport through ERL injector prototype C1 (7mm DIA) Cryo-module DC gun Solenoid magnets Quadrupole Bending Buncher C2 (10mm DIA) C1 C2 Cryo-module ~ 35% of dark current loss in the first cryo-module will result in additional, 0.35 x 13nA x 10MV = 4.5E-4W heat load. November 19, 2018 ERL review, Aug 2 2007, A. Temnykh

Another source of halo: Electron gun dark current Dark current at the exit of ERL injector prototype Normalized emmitance, 99%: ems_x = 35.6 cm*mrad, ems_y = 15.7 cm*mrad, Energy spread: rms(de/e) = 0.45% ------------------------------ It results in 1.3mm beam envelope size at 5GeV and 50m beta function November 19, 2018 ERL review, Aug 2 2007, A. Temnykh

Another source of halo: SRF field emission current TTF (FLASH) experience* 8 x 9cell cavities / module … All … cavities produced an integrated dark current of about 25 nA at 25 MV/m average gradient. (Measured at the exit of cryo-module) At 17.5 MV/m the dark current 100 times less, i.e., 0.25nA Expectation for ERL: Operational field gradient 17.5MV/m Field emission (dark) current at the cryo-module exit ~0.25nA for a 10 x 7cell cavity module. Total current ~ 0.25nA x 40 modules = 10nA with momentum distribution (if it can propagate through the LINAC): 5000 50 E [MeV] dI/dE SRF field emission current ERL ring energy acceptance ~50MeV Electrons emitted in the last module Electrons emitted in the first module 1% ( ~ 0.10nA) will be contributed to ERL beam hallo. 99%, i.e., 9.9nA will probably be lost in LINAC adding ~ 25 Watt to cryogenic heat load. Sources: “EXPERIENCE WITH THE TTF L. Lilje#, DESY, Hamburg, Germany, in Proceedings of 2005 Particle Accelerator Conference, Knoxville, Tennessee Maury Tigner, Private communication November 19, 2018 ERL review, Aug 2 2007, A. Temnykh

Conclusion/Summary Source Contribution Effect Intra-beam scattering (IBS) Total loss ~ 27nA (Mode “A” operation*) ~0.5nA will be lost at 5GeV and ~25nA will be lost at the end of deacceleration at ~250MeV or less energy. Residual gas scattering Total loss ~ 0.03nA Without collimators, it will reduce ID life time to unacceptable level. With collimators, ID lifetime will be satisfactory. Electron gun dark current Presently ~13nA. For higher field gradients on the photo-cathode, the dark current would be bigger. ~ 80% will be lost in the first cryo-module and near by located collimators. The rest 20% will propagate without loss through ERL. SRF field emission current Total current ~ 25nA ~99% will be lost in LINAC adding ~25W to cryogenic load. The rest 1% (0.25nA) will be propagated to the dump or lost in ERL main loop. * Mode “A” operation: 77pC/bunch, 1.3GHz, 100mA of total beam current November 19, 2018 ERL review, Aug 2 2007, A. Temnykh

ERL review, Aug 2 2007, A. Temnykh Acknowledgements Author would like to thank Georg Hoffstaetter and Maury Tigner for motivation and useful discussions. November 19, 2018 ERL review, Aug 2 2007, A. Temnykh

Appendix 1, Permanent magnet material demagnetization by radiation NeFeB permanent material demagnetization as function of accumulated radiation dose For PPM structure where “H” and “V” blocks contribution equaly to the field strength, 1% demagnetization dose will be 2.07Mrad Source: MEASUREMENT OF PERMANENT MAGNET MATERIAL DEMAGNETIZATION DUE TO IRRADIATION BY HIGH ENERGY ELECTRONS, A. Temnykh,,CLASS, in Proceedings of PAC 2007, Albuquerque, USA, November 19, 2018 ERL review, Aug 2 2007, A. Temnykh

Appendix 1, Permanent magnet material demagnetization by radiation Undulator model: PPM, 5m length, 25mm period, 5mm gap. Brilliance loss as function of demagnetization (SPECTRA simulation) 20% brilliance loss criteria gives requirement on dK/K < 0.2%. It implies critical accumulated radiation dose = 0.4Mrad. November 19, 2018 ERL review, Aug 2 2007, A. Temnykh

Appendix 1, Permanent magnet material demagnetization by radiation Model: ~40cm for Fe 0.4Mrad of accumulated radiation dose corresponds to ~ 1.4x1013 electrons absorbed per meter of ID structure. Damaging dose for 5m long ID ~ 7.0x1013 electrons for 25m long ID ~ 3.5x1014 electrons November 19, 2018 ERL review, Aug 2 2007, A. Temnykh