M. Furman, “ecloud at the MI and LHC” p. 1ECLOUD07 Electron-Cloud Build-up in the FNAL Main Injector and the LHC Complex Miguel Furman LBNL ECLOUD07 Daegu, April 9-12, 2007

M. Furman, “ecloud at the MI and LHC” p. 2ECLOUD07 Outline Motivation POSINST code features Initial results Ongoing work Conclusions My gratitude to: A. Adelmann, G. Arduini, V. Baglin, M. Blaskiewicz, O. Brüning, Y. H. Cai, C. Celata, R. Cimino, R. Cohen, I. Collins, F. J. Decker, A. Friedman, O. Gröbner, K. Harkay, P. He, S. Heifets, N. Hilleret, U. Iriso, J. M. Jiménez, R. Kirby, M. Kireef-Covo, G. Lambertson, R. Macek, A. Molvik, K. Ohmi, S. Peggs, M. Pivi, C. Prior, A. Rossi, G. Rumolo, D. Schulte, K. Sonnad, P. Stoltz, J.-L. Vay, M. Venturini, S. Y. Zhang, X. Zhang, A. Zholents, F. Zimmermann and R. Zwaska.

M. Furman, “ecloud at the MI and LHC” p. 3ECLOUD07 ecloud at FNAL: background Proposed High Intensity Neutrino Source (HINS) —MI upgrade: Increase bunch intensity N b from ~6e10 to ~3e11 RFA electron detectors installed (one in the MI and one in the Tevatron) —See R. Zwaska’s talk (session B) We’ve been simulating ecloud effects at the MI for >~1 yr —Goal: assess ecloud effects on the operation —ecloud build-up (this talk) —ecloud effects on the beam —simulations of microwave transmission through ecloud (Caspers-Kroyer diagnostic technique) —see Kiran Sonnad’s talks (sessions D & E)

M. Furman, “ecloud at the MI and LHC” p. 4ECLOUD07 “POSINST” simulation code features Code development started ~1994 (PEP-II design stage) —essential contributions by M. Pivi since 2000 —this is a “build-up type” code Formation of an ecloud by a prescribed (non-dynamical) beam —Based on Ohmi’s original simulation approach —Similar to other codes (e.g., “ECLOUD”, …) —2D —incorporates a detailed model of SEE both SE yield  (E 0 ) and SE emission energy spectrum d  /dE —incorporates approximate models of primary electron emission —validated against measurements at APS and PSR (~2000) good agreement with RFA measurements required peak SEY ~2 both for PSR and APS SEY is an essential ingredient in most cases; however: —many SEY parameters not well known —can trade off one for another

M. Furman, “ecloud at the MI and LHC” p. 5ECLOUD07 Initial results Preliminary assessment for MI upgrade: —Uniform fill (504 bunches out of 588 buckets) —Injection energy (K.E.=8 GeV) —Bunch population N b =(6–30)x10 10 —Elliptical chamber cross-section (~2:1) —Field-free or dipole bending magnet Conclusions: —Sharp threshold at N b ~1.25x10 11 for  max =1.3 —above threshold: EC ~neutralizes beam —  ~ 0.06 (assuming uniform EC density around the ring ) The assumed value  max =1.3 was a first step N b below thr. N b above thr. M. Furman, LBNL-57634/FERMILAB-PUB AD

M. Furman, “ecloud at the MI and LHC” p. 6ECLOUD07 Initial results:  z dependence Lower d e for shorter bunches Possibly due to higher electron-wall impact energy aver. d e 1-  d e e – flux at wall e – energy SEY

M. Furman, “ecloud at the MI and LHC” p. 7ECLOUD07 Recent simulations at RFA location MI ramp: KE b =8  120 GeV in ~0.9 s (~100,000 turns) Transition at t~0.2 s (KE b ~20 GeV) train=(82 H) + 5x(82 L) + gaps, N b =10.3x10 10 for H N b =5.7x10 10 for L RFA detector location: field-free region We typically simulate only one turn CPU~3.3 hrs (Mac G5, 1.8 GHz)  max =1.3 KE b =20 GeV line density vs. time

M. Furman, “ecloud at the MI and LHC” p. 8ECLOUD07 Recent simulations: 1-turn averages From Bob Zwaska’s e – detector observations, infer e – flux ~1  A/m 2 at transition —this assumes 30% area efficiency and 100% e – energy efficiency Then these simulations imply  max >~ 1.3–1.4 But direct measurements of chamber samples by R. Kirby show  max ~ 2 (R. Zwaska, session B) Caveats: —Several variables not yet adequately investigated —Ongoing work; need to reconcile simulations and measurements e – density vs.  max e – wall flux vs.  max

M. Furman, “ecloud at the MI and LHC” p. 9ECLOUD07 Discussion Other simulation exercises carried out: —Time development of ecloud —Dependence on  z, N b and  max but not in all combinations —Sensitivity to SE energy spectrum —Dependence on transverse beam size —Simulation parameters (e.g.,  t=1.4x10 –11 s, # of macroparticles=20,000,…) Incidentally, find empirical relation between e – flux at the wall J e and e – aver. line density e : — J e =  e, where  =6x10 7 m –1 s –1 Fairly robust (independent of  max,  z and E b ; even valid during the build-up stage, but not tested against all possible parameter variations)

M. Furman, “ecloud at the MI and LHC” p. 10ECLOUD07 Conclusions Extensive (but still ongoing) build-up simulations of the MI If interpret RFA measurements with these simulations, conclude that  max ~1.3–1.4; then d e ~(1–10)x10 10 m –3 Even if RFA detector is seeing only 10% of the incident electrons, would conclude that  max ~1.4–1.5 But direct chamber sample measurements show  max ~2 —This is a significant discrepancy! —Need to reconcile simulations and measurements Simulations results qualitatively stable against several simulation conditions —eg., E max, SE spectrum composition, no. of macroparticles,  t,… Not yet done, or partially done: —Sensitivity to  (0) (thus far, assumed  (0)=0.3x  max ) NB: if  (0) is assumed higher, then would conclude that  max is lower —Further sensitivity to SE spectrum composition (elastics, rediffused, true secondaries) —Clarify simulation issues at high  max : appearance of “virtual cathodes” near the wall dependence of SEY on space-charge forces (no such dependence in POSINST) Ultimate goal: assess effects on the beam (see K. Sonnad’s talk session E)

M. Furman, “ecloud at the MI and LHC” p. 11ECLOUD07 References M. A. Furman, "A preliminary assessment of the electron cloud effect for the FNAL main injector upgrade," LBNL-57634/CBP-Note-712/FERMILAB- PUB AD, June 28, Revised: June 26, An abbreviated version is published in: New Journal of Physics Focus Issue: Accelerator and Beam Physics, New J. Phys. 8 (2006) 279, M. A. Furman, "Studies of e-cloud build up for the FNAL main injector and for the LHC," LBNL-60512/CBP Note-736, June 15, 2006, Proc. 39th ICFA Advanced Beam Dynamics Workshop on High Intensity High Brightness Hadron Beams "HB2006" (Tsukuba, Japan, May 29-June 2nd, 2006), paper TUAX05. M. A. Furman, "HINS R&D Collaboration on Electron Cloud Effects: Midyear Progress Report," CBP-Technote-364/FERMILAB-TM-2369-AD, 22 September M. A. Furman, K. Sonnad and J.-L. Vay, "HINS R&D Collaboration on Electron Cloud Effects: Midyear Report," LBNL-61921/CBP-761/FERMILAB- TM-2370-AD, Nov. 7, M. A. Furman, "HINS R&D Collaboration on Electron Cloud Effects: MI ecloud build-up simulations at the electron detector location," CBP Technote- 367, Dec. 5, Kiran G. Sonnad, Miguel A. Furman and Jean-Luc Vay, "A preliminary report on electron cloud effects on beam dynamics for the FNAL main injector upgrade," CBP Technote-369, January 16, 2007.

M. Furman, “ecloud at the MI and LHC” p. 12ECLOUD07 Backup material

M. Furman, “ecloud at the MI and LHC” p. 13ECLOUD07 Electron-wall energy spectrum  max =1.7, KE=20 GeV,  z =0.06 m

M. Furman, “ecloud at the MI and LHC” p. 14ECLOUD07 Three components of secondary emission: sample spectrum at E 0 =300 eV from M. F. and M. Pivi, PRST-AB 5, (2002) E0E0 E

M. Furman, “ecloud at the MI and LHC” p. 15ECLOUD07 Secondary emission spectrum Depends on material and state of conditioning —St. St. sample, E 0 =300 eV, normal incidence, (Kirby-King, NIMPR A469, 1 (2001)) st. steel sample  = 2.04  e = 6%  r = 37%  ts =57%  e +  r =43% – Hilleret’s group CERN: Baglin et al, CERN-LHC-PR 472. – Other measurements: Cimino and Collins, 2003) Cu sample  = 2.05  e = 1%  r = 9%  ts =90%  e +  r =10%

M. Furman, “ecloud at the MI and LHC” p. 16ECLOUD07 Sample simulated LHC heat load vs. N b arc dipole, nominal beam energy Code POSINST (M. Furman, LUMI06 wkshp. et. seq.) NB: ACC calculation has been recently revised. See LUMI06 proc.  max =1.7  max =1.5  max =1.3 solid: CERN simulations (code ECLOUD) dotted: available cooling capacity for ecloud (ACC) We don’t know what peak SEY  max will be at start-up – but need to stay within cryogenic cooling capacity Simulation gives an idea of where the LHC will be able to operate during run-in Also: excellent agreement between LBNL and CERN simulations dashed: LBNL simulations (codePOSINST)

M. Furman, “ecloud at the MI and LHC” p. 17ECLOUD07 Sample assessment of two PS upgrade options: heat load vs. peak SEY  max PS2: E b =50 GeV PS+: E b =75 GeV Bunch spacings: t b =25, 50, 75 ns Conclusion: —PS2 and PS+ comparable —75 ns slightly better than 50 ns —50 ns much better than 25 ns t b [ns] N b [10 11 ] N b depends on t b : (Similar assessments carried out for SPS and LHC upgrades)

M. Furman, “ecloud at the MI and LHC” p. 18ECLOUD07 Sample simulated heat load vs.  max LHC and upgraded injectors: Cu vs. St.St. Effect of different emission spectra: —Smaller rediffused component in SE energy spectrum —Subtle mechanism; explained in detail in Sec. IV-B of Caveat: Cu and StSt emission parameters need to be re-measured to confirm Cu advantage! W/m for St.St. “PS2”, t b =25 ns “PS2”, t b =50 ns LHC nom., t b =25 ns SPS nom., t b =25 ns “SPS+”, t b =25 ns

M. Furman, “ecloud at the MI and LHC” p. 19ECLOUD07 Conditioning Peak SEY  max vs e – dose:  max ~1 when D~1 C/cm 2 —under vacuum and steady e – current ECE is a self-conditioning effect —Beam conditioning observed at SPS, PSR, PEP-II, RHIC…  max vs. dose for TiN/Al Kirby & King, NIMPR A469, 1 (2001)  max vs. dose for Cu Hilleret, 2stream2001 (KEK) 1 C/cm 2 ~1 C/cm 2

M. Furman, “ecloud at the MI and LHC” p. 20ECLOUD07 EC detectors installed recently RFA e – detectors (ANL design; Rosenberg-Harkay) measure flux and energy spectrum Main InjectorTevatron RFA ion gauge ion pump beam separator

M. Furman, “ecloud at the MI and LHC” p. 21ECLOUD07 What is the ECE Step 1: beam produces primary electrons —Photoelectrons, ionization of residual gas, stray beam particles striking the chamber, … Step 2: electrons get rattled around the chamber —Amplification by secondary electron emission Particularly intense for positively-charged beams Possible consequences: —dipole multibunch instability —emittance blowup —gas desorption from chamber walls —excessive energy deposition on the chamber walls (important for superconducting machines, eg. LHC) —particle losses, interference with diagnostics,… The ECE is a consequence of the interplay between the beam and the vacuum chamber —beam intensity, bunch shape, fill pattern, photoelectric yield, photon reflectivity, secondary emission yield (SEY), vac. chamber size and geometry, …

M. Furman, “ecloud at the MI and LHC” p. 22ECLOUD07 Importance PEP-II and KEKB: —controlling the EC was essential to achieve luminosity performance ECE limits performance of PSR at high current RHIC: vacuum pressure instability a high current Possibly serious in future machines: LHC: potentially large energy deposition from electrons — need to dissipate it otherwise, less-than-nominal performance ILC DR’s: potential for instability and/or emittance growth — main concern: wiggler regions MI upgrade: — N b x5; recently begun to investigate

M. Furman, “ecloud at the MI and LHC” p. 23ECLOUD07 Observations ECE has been observed at many machines: — PF, PEP-II, KEKB, BEPC, PS, SPS, APS, PSR, RHIC, Tevatron(?), MI(?), SNS(?) undesirable effects on performance, and/or dedicated experiments “Old” effects: — two-stream instabilities (BINP, mid 60’s) — beam-induced multipacting (ISR, mid 70’s) multibunch effect –pressure rise instability — trailing-edge multipacting (PSR, since mid 80’s) single-long-bunch effect –beam loss and instability

M. Furman, “ecloud at the MI and LHC” p. 24ECLOUD07 Controlling the ECE Add weak solenoidal fields (~20 G) — confines electrons near the chamber, away from the beam used in PEP-II and KEKB RHIC tests Tailor the bunch fill pattern (gaps in train) — used at PEP-II for a while, before solenoids Modify vacuum chamber geometry — antechamber (eg., PEP-II) — antigrazing ridges (tests at RHIC) — grooves (LHC arcs; tests at SLAC) Lower the SEY — coatings (TiN, TiZrV,…) PEP-II, LHC, SNS, RHIC, … — conditioning

M. Furman, “ecloud at the MI and LHC” p. 25ECLOUD07 EC at FNAL: background Proposed proton driver to replace booster Proposed MI upgrade: —Increase bunch intensity from present 6e10 to 3e11 —New RF system f RF not yet chosen (range considered= MHz), vs. 53 MHz at present Bunch intensity and bunch frequency are essential ingredients for EC Parameter regime has high potential for a significant EC

M. Furman, “ecloud at the MI and LHC” p. 26ECLOUD07 EC at FNAL: indirect evidence At present: indirect evidence for an EC exists —But no direct electron measurements yet Tevatron: Fast pressure rise (X. Zhang, Dec. 02; May 05) —  P seen at some of the warm straight sections (ion pump measurements) —Threshold ~4e10 p/bunch for 30 consecutive bunches —No good way to measure P in cold regions Fast emittance growth (flying wire technique) —d  /dt~28  mm-mr/hr (95%, normalized, vertical, averaged over 30 bunches) this is for E=150 GeV and N=82e10 in 30 bunches this is much faster growth than estimated IBS growth rate —d  /dt sensitive to N above threshold —Unfortunately, no BBB measurements

M. Furman, “ecloud at the MI and LHC” p. 27ECLOUD07 EC at FNAL: indirect evidence Main Injector: Fast pressure rise (R. Zwaska, Jan. 06) —82 bunches of ~9e10 p/bunch, or 418 bunches of ~5e10 p/bunch —  P seen at 24 of 523 pumps  P/P typically 5-50% but reached 600%-700% at 2 pumps: uncoated ceramic chamber –NB: ceramic has a high SEY, therefore high  P/P is consistent with e-cloud hypothesis Maximum effect at transition (short  z )