Electron Clouds at SLAC Johnny Ng ILC Damping Rings Collaboration Meeting March 4, 2009

ILC Damping Rings Collaboration Mtg, 3/4/09 Page 2 Electron Cloud R&D Program at SLAC *Goal: Reduce the SEY below instability threshold: SEY < 1.1 *Important for accelerators at the energy (LHC,ILC) as well as intensity frontiers (Project-X, Super-B factory) *Surface Treatment: –Coatings –Conditioning: reduce SEY via photon/electron/ion irradiation –Grooved chamber walls: trap low energy electrons –Clearing electrodes (KEK) *Experiments in PEP-II: –ECLOUD1 (Jan – Apr. 2008): Conditioning effect on SEY –ECLOUD2 (Jan – Apr. 2008): Test grooved chambers –ECLOUD3 (Dec Apr. 2008): Effect in dipole magnetic field *Simulation and benchmarking

ECLOUD Experiments at PEP-II ECLOUD1: SEY Station ECLOUD2: grooved chambers ECLOUD3: Uncoated and TiN-coated aluminum chamber in chicane

sample surface exposed to SR PEP-II LER side (Stainless steel chamber) Expose samples to PEP-II LER synchrotron radiation and electron conditioning. Then, measure Secondary Electron Yield (SEY) in laboratory. Samples transferred under vacuum. Complementary to CERN and KEK studies 20 mm ECLOUD1 – Conditioning and SEY

ILC Damping Rings Collaboration Mtg, 3/4/09 Page 5 Recap: ECLOUD1 Results *Goal: monitor the reduction in-situ of the SEY due to conditioning *Results: –TiN coating: SEY reduced to 1000 h) recontamination exposure to H and CO under vacuum. –Uncoated aluminum: SEY > 2 with/without conditioning. –Other preliminary findings: Activated NEG coating: SEY ~ 1.1 Copper: SEY reduced to < 1.2 Stainless steel: SEY reduced to < 1.2, but increased to 1.5 after recontamination exposure in vacuum *References: –F. Le Pimpec et al. Nucl. Inst. and Meth., A564 (2006) 44; –F. Le Pimpec et al. Nucl. Inst. and Meth., A551 (2005) 187; –M. Pivi et al. SLAC-PUB-13284

ILC Damping Rings Collaboration Mtg, 3/4/09 Page 6 ECLOUD2 – Grooved Chambers in PEP-II Standard (flat) chambers also installed as reference. All aluminum with TiN coating installed in straight sections. Rectangular groove (or “fin”) chambers fabricated by extrusion. e+ Grooved chamber Flat chamber Electron detectors

ILC Damping Rings Collaboration Mtg, 3/4/09 Page 7 Recap: ECLOUD2 Results *Goal: Measure performance of electron cloud suppression using grooved chambers *Electron cloud signal is ~ factor of 20 smaller in grooved TiN chambers compared to flat TiN chambers *Confirmed reduced electron cloud build-up in TiN coated chambers compared with uncoated stainless steel chambers. *References: –M. Pivi et al. SLAC-PUB –M. Pivi et al. accepted for publication in J. of Appl. Phys. 2008

ILC Damping Rings Collaboration Mtg, 3/4/09 Page 8 ECLOUD3 – Electron Cloud in a Dipole Retarding Field Analyzer (RFA): - electron flux at the wall - energy spectrum - lateral distribution e+

ILC Damping Rings Collaboration Mtg, 3/4/09 Page 9 ECLOUD3: Electron cloud in a dipole Uncoated aluminum chamber L. Wang et al, SLAC TiN-coated aluminum chamber Lateral distribution consistent with simulation.

ILC Damping Rings Collaboration Mtg, 3/4/09 Page 10 ECLOUD3: Magnetic field strength Electron flux peaks (and valleys) separated by integer values of n. Phase of cyclotron motion with respect to bunch crossing affects energy gain, possibly leading to the observed modulation in electron flux at the chamber wall.

ILC Damping Rings Collaboration Mtg, 3/4/09 Page 11 ECLOUD3: New resonance effect in a dipole ECLOUD signal vs. B-field, summed over all strips Uncoated AlTiN-coated Al TiN-coated chamber shows orders of magnitude lower signal Resonances expected from simulation (C. Celata et al., LBNL) Data analysis continuing, with simulation efforts.

ILC Damping Rings Collaboration Mtg, 3/4/09 Page 12 ECLOUD3: Summary *Goal: mitigation of electron clouds in a dipole magnetic field region *Preliminary results: –Demonstrated TiN-coating is effective in a dipole –Characterized electron cloud dynamics in a dipole –Observed new resonance: modulation in electron flux as field strength is varied *References: –M. Pivi, J. Ng et al., EPAC 2008; –paper submitted for publicatoin

ILC Damping Rings Collaboration Mtg, 3/4/09 Page 13 ECloud Experiments Redeployed at Cesr-TA *ECloud 1, 2, & 3 have been relocated to Cesr-TA (See Mark Palmer’s talk for current status) *Grooved chamber for dipole: Chamber fabricated,  Machining and cleaning done  Leak check this week,  then welding and coating, etc.. Expect completion early May Morrison, Pivi, Wang, SLAC

ILC Damping Rings Collaboration Mtg, 3/4/09 Page 14 Summary & Outlook *TiN coating has been demonstrated to have an SEY reliably below the instability threshold. *Continue to investigate remaining issues at SLAC: –TiN long term durability (measure PEP-II TiN chamber samples) –SEY measurement in magnetic field –Continue on-going simulation efforts *SLAC is a key collaborator with other labs to develop complementary mitigation techniques.

ILC Damping Rings Collaboration Mtg, 3/4/09 Page 15 Acknowledgement The SLAC E-Cloud Team: M. Pivi, D. Arnett, G. Collet, F. Cooper, D. Kharakh, F. King, R. Kirby, B. Kuekan, M. Munro, J. Ng, J. Olszewski, B. Smith, C. Spencer, T. Raubenheimer, L. Wang, W. Wittmer Thanks to PEP-II colleagues: M. Sullivan, J. Seeman, K. Burrows, S. De Barger, U. Wienands Also thanks to dedicated efforts of the PEP-II operations crew, and support of the staff at our magnetic measurements, vacuum, and fabrication facilities.