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H  Transport and Stripping

H  Transport and Stripping. Weiren Chou March 15 , 2005. Outline. Introduction Mini-workshop on H  transport and stripping 8 GeV H  stripping losses during transport Magnetic field Blackbody radiation Residual gas Foil stripping of 8 GeV H  at injection Conclusions.

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H  Transport and Stripping

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  1. H Transport and Stripping Weiren Chou March 15 , 2005 W. Chou - Proton Driver Director's Review

  2. Outline • Introduction • Mini-workshop on H transport and stripping • 8 GeV H stripping losses during transport • Magnetic field • Blackbody radiation • Residual gas • Foil stripping of 8 GeV H at injection • Conclusions Reference: Fermilab-TM-2285 W. Chou - Proton Driver Director's Review

  3. Introduction • Transport and stripping of 8 GeV H ions is a major technical issue concerning an SCRF linac proton driver. • Today’s highest H beam energy is 800 MeV at LANL, an order of magnitude lower than 8 GeV. • H has two electrons, one tightly bound (13.6 eV), another loosely bound (0.75 eV). • Problems when H energy goes higher: • Easier to lose the 2nd electron during transport (by blackbody radiation or magnetic field) • But harder to strip both electrons by a foil at injection Both are not what we want and have to be addressed seriously • Higher energy also means more difficult to correct energy and phase jitters of the linac beam prior to injection W. Chou - Proton Driver Director's Review

  4. Mini-Workshop on H Transport and Stripping • Dec 9-10, 2005 at Fermilab. Ten physicists from other labs and a dozen from Fermilab attended. • ANL: P. Ostroumov, L. Teng • BNL: J. Wei, YY Lee, D. Raparia • LANL: R. Macek, T. Spickermann, A. Jason • U. New Mexico: H. Bryant • ORNL: R. Shaw • Fermilab: D. Bogert, B. Brown, A. Drozhdin, B. Foster, G. Jackson (consultant), C. Hill, S. Holmes, M. Kostin, J. Lackey, F. Ostiguy, Z. Tang, W. Chou, etc. • Purpose: Feasibility of transporting and stripping 8 GeV H ions • Three topics: • Stripping losses of 8 GeV H ions • Stripping foil • Jitter correction of 8 GeV H beam W. Chou - Proton Driver Director's Review

  5. Magnetic Field Stripping Scherk’s formula Can J. Phys. v. 57, p. 558 (1979):  = a/E  exp (b/E) E = 3.197 p(GeV/c) B 500 G  Hloss rate = 109 m1 W. Chou - Proton Driver Director's Review

  6. Blackbody Radiation Stripping • A newly discovered loss mechanism, dominant for 8 GeV H • First pointed out and calculated by H. Bryant, also independently analyzed by C. Hill. Results in agreement. • Illustration of how this becomes a problem: photon distribution cross section 0.75 eV W. Chou - Proton Driver Director's Review

  7. Blackbody Radiation Stripping (cont…) Energy Dependence Temperature Dependence At 305 K (90 F) and 8 GeV, Hloss rate = 0.8  106 m1 W. Chou - Proton Driver Director's Review

  8. Residual Gas Stripping Energy dependence of total electron loss cross section for H incident on atoms W. Chou - Proton Driver Director's Review

  9. Residual Gas Stripping (cont…) Total electron loss cross section for H (unit 1018 cm2) H2 Measurement of A150 line vacuum by T. Anderson (similar to PD line) N2 Ar O2 Hloss rate = 0.1  106 m1 He W. Chou - Proton Driver Director's Review

  10. Summary of H Stripping Losses • Transport line ~ 1 km Loss on the beam line ~ 103 • H Beam intensity = 1  1014 s1 Loss rate ~108m1s1 • At 8 GeV  0.13 W/m • When MI operates at lower energy E with same beam power, loss will increase: W. Chou - Proton Driver Director's Review

  11. Discussion of H Stripping Losses • 1999 ICFA mini-workshop at Lake Como, Wisconsin, established the allowable loss for hands-on maintenance at 1 W/m • But this criterion assumes the losses are distributed unevenly around the machine and mostly shielded by the magnet • This does not apply to our case, where the losses are continuous along the whole beam line • MARS shows high dose on the beam pipe between two magnets • Observations on the MI pipe hot spots support this calculation • Possible solutions to suppress BR: • H0 intercepts (jaws) inside magnets (under investigation) • Cryogenic beam screen at 77 K 1000 mR/h (no jaw) 100 mR/h (w/ jaw) W. Chou - Proton Driver Director's Review

  12. Carbon Foil Stripping Efficiency Webber & Hojvat, 1979 Fermilab linac, 200 MeV Gulley et al., 1996 LANL linac, 800 MeV H+ H+ H- H- 11.2% H0 H0 0.4% H0 H0 W. Chou - Proton Driver Director's Review

  13. Electron Loss Cross Section Scaling (unit 10-18 cm2) 800 MeV 200 MeV 400 MeV 8 GeV (, 0) 0.676±0.009 1.49 0.942 0.484 (1.56±0.14) (0, +) 0.264±0.005 0.584 0.368 0.189 (0.60±0.10) (, +) 0.012±0.006 0.026 0.0167 0.0086 (0.08 ±0.13) scaling blue: measured red: scaled W. Chou - Proton Driver Director's Review

  14. Energy Dependence of H(0) Yield W. Chou - Proton Driver Director's Review

  15. Energy Dependence of H(0) Yield W. Chou - Proton Driver Director's Review

  16. Energy Dependence of H(0) Yield W. Chou - Proton Driver Director's Review

  17. Energy Dependence of H(0) Yield W. Chou - Proton Driver Director's Review

  18. Energy Dependence of H(0) Yield 8 GeV, 0.5% H0 W. Chou - Proton Driver Director's Review

  19. Lifetime of Stark States • In an electric field, each energy level n of H0 split into n(n+1)/2 Stark states • Lifetime formula given by R.J. Damburg and V.V. Kolosov in 1983 • Calculation for 8 GeV H0 in a magnetic field • Gap between n = 3 & 4 or n = 4 & 5 can be used for H0 loss control W. Chou - Proton Driver Director's Review

  20. Discussion of Stripping Foil • Total thickness 600 g/cm2 • Use two foils, each 300 g/cm2 • Carbon foil o.k. for 1 ms beam pulse • Diamond foil needed for 3 ms beam pulse • Issues concerning thick foils: • Multiple Coulomb scattering • Large angle Coulomb scattering • Energy straggling • Heating • Stress and buckling • Lifetime • Radiation • More to be presented by Lackey, Drozhdin and Kostin in breakout session 3 • Note added: TRIUMF 500 MeV Hfoil stripping efficiency data (G. Mackenzie) shows anomalous behavior. Reason unknown. W. Chou - Proton Driver Director's Review

  21. Conclusions • To go from 800 MeV (today’s highest energy of H ) to 8 GeV is a big leap forward • There are a number of technical challenges to transport and strip 8 GeV H ions • An intensive study in the past months gave us the basic understanding of the problems, including some new phenomena (e.g., blackbody radiation loss) • The bottom line is: To every problem we can find a solution • We found no show stoppers – which was also the conclusion of the Dec 2005 Fermilab mini-workshop W. Chou - Proton Driver Director's Review

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