1. 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

2. 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 , A. Temnykh

3. 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 , A. Temnykh

4. 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 , A. Temnykh

5. 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= 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 , A. Temnykh

6. 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 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 , A. Temnykh

7. 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 , A. Temnykh

8. 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 , A. Temnykh

9. 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 , A. Temnykh

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

11. Insertion device life time without collimators
i l[m] Life_time[A-year]
November 19, 2018
ERL review, Aug , A. Temnykh

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

13. Insertion device life time with collimators
i l[m] Life_time[A-year]
November 19, 2018
ERL review, Aug , A. Temnykh

14. 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 , A. Temnykh

15. 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) ~ (assumed electron work function ~1eV)
November 19, 2018
ERL review, Aug , A. Temnykh

16. 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 , A. Temnykh

17. 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 , A. Temnykh

18. 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 , A. Temnykh

19. 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 , A. Temnykh

20. 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 , A. Temnykh

21. 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 , A. Temnykh

22. 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 , A. Temnykh

23. 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 , A. Temnykh

24. 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 , A. Temnykh