Electron Cloud R&D at SLAC Johnny Ng SLAC DOE HEP Review July 7 – 9, 2008

SLAC DOE HEP Review July 7 - 9, 2008 Page 2 Outline *Overview *Electron Cloud R&D at SLAC –Overview of R&D program –Recent experimental results *Future Directions –Current status of the field –What next? *Summary & Conclusion

SLAC DOE HEP Review July 7 - 9, 2008 Page 3 The Electron Cloud Problem *Electron Cloud: –Low energy electrons inside beam chamber receive momentum kicks from passing positively-charge particle bunch –Create more electrons via surface secondary electron yield (SEY) –Repeated bunch crossings lead to build-up and formation of the cloud *Beam-cloud interaction can cause beam instability and vacuum pressure rise, limiting luminosity performance *Effect observed at a variety of accelerators: –Positron storage rings (PEP-II, KEK-B,…) –Hadron machines (SPS, RHIC, …) *This problem must be resolved for future accelerators such as the LHC, and the damping rings of linear colliders such as the ILC.

SLAC DOE HEP Review July 7 - 9, 2008 Page 4 Beam instability due to electron cloud ILC Reference Design Report. Instability threshold sets maximum allowed SEY at 1.2 according to simulations for 6 km positron ring. [K.Ohmi, M. Pivi, F. Zimmerman] Beam size growth and electron cloud densities [e - /m 3 ]

SLAC DOE HEP Review July 7 - 9, 2008 Page 5 Overview of Electron Cloud Work at SLAC *Electron cloud-induced instability at PEP-II; solenoid installed in field-free regions to recover luminosity loss. *R&D program focused on Linear Collider designs –Simulation studies on electron cloud build-up and beam instability –Development of mitigation techniques (coatings, grooves) –Simulation campaigns: Significant redesign of ILC damping ring and reduction in cost Validate mitigation techniques (grooves, clearing electrodes) *Experiments at PEP-II *Key to solving this problem is the suppression of cloud build-up

SLAC DOE HEP Review July 7 - 9, 2008 Page 6 Current 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

SLAC DOE HEP Review July 7 - 9, 2008 Page 7 Selected List of Publications *Journal of Applied Physics May SLAC-PUB SLAC-PUB *Physical Review Letters 100, (2008) *Physical Review ST Accel. Beams 11, (2008). *Nuclear Instruments and Methods NIM A 571 (2007) *Journal of Applied Physics 102, (2007) *Nuclear Instruments and Methods in Physics Research, A, 564 (2006) 44–50. *Journal of Vac. Sci. Technol. A 23(6), Nov/Dec (2005). *Nuclear Instruments and Methods NIM A 551 (2005) *Physical Review Letters 93, (2004). SLAC-PUB *Physical Review ST Accel. Beams 7, (2004). *Plus numerous contributions to conference proceedings.

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

PEP-II LER e+  Transfer system at 0 o Transfer system at 45 o Isolation valves ILC tests, M. Pivi et al. – SLAC 2 samples facing beam pipe are irradiated by SR ECLOUD1 –SEY Station in PEP-II

SLAC DOE HEP Review July 7 - 9, 2008 Page 10 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

SLAC DOE HEP Review July 7 - 9, 2008 Page 11 M. Pivi et al. – SLAC Before installation in beam line After conditioning e- dose > 40mC/mm**2 ECLOUD1 – TiN Coating in PEP-II SEY reduced to < 1 after conditioning in the beam line. Surface analysis indicate significant reduction in carbon content.

SLAC DOE HEP Review July 7 - 9, 2008 Page 12 M. Pivi, R. Kirby – SLAC ECLOUD1 – Uncoated Aluminum in PEP-II SEY remain > 2 after conditioning in beam line.

SLAC DOE HEP Review July 7 - 9, 2008 Page 13 ECLOUD1 – Summary *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

SLAC DOE HEP Review July 7 - 9, 2008 Page 14 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

SLAC DOE HEP Review July 7 - 9, 2008 Page 15 ECLOUD2 – Grooved Chambers Performance M. Pivi et al, SLAC

SLAC DOE HEP Review July 7 - 9, 2008 Page 16 ECLOUD2 – Summary *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

SLAC DOE HEP Review July 7 - 9, 2008 Page 17 ECLOUD3 – Electron Cloud in a Dipole Retarding Field Analyzer (RFA): - electron flux at the wall - energy spectrum - lateral distribution e+

SLAC DOE HEP Review July 7 - 9, 2008 Page 18 ECLOUD3: Electron cloud in a dipole Uncoated aluminum chamber L. Wang et al, SLAC TiN-coated aluminum chamber Lateral distribution consistent with simulation.

SLAC DOE HEP Review July 7 - 9, 2008 Page 19 ECLOUD3: Electron energy spectrum Integrated and differential spectra: sum of all channels.Differential energy spectra for each RFA channel. Features in energy spectrum characteristic of chamber geometry, bunch charge and bunch spacing Consistent with previous simulations. [L. Wang, ECLOUD04, SLAC-PUB-10751]

SLAC DOE HEP Review July 7 - 9, 2008 Page 20 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.

SLAC DOE HEP Review July 7 - 9, 2008 Page 21 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.

SLAC DOE HEP Review July 7 - 9, 2008 Page 22 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 being prepared for submission to Phys. Rev. Lett.

SLAC DOE HEP Review July 7 - 9, 2008 Page 23 Future Directions *Intense R&D by many groups – problem now understood *Key collaborators in experiments at other labs: –KEK: grooved chamber –CESR-TA: grooved chamber in dipole magnet and simulation support –FNAL: effect of SEY in Project-X proton ring –SPS/LHC: grooved chamber in dipoles, simulations and measurements. *Continue to investigate remaining issues: –TiN long term durability (measure PEP-II TiN chamber samples) –SEY measurement in magnetic field

SLAC DOE HEP Review July 7 - 9, 2008 Page 24 Plans for Cesr-TA *CesrTA Program at Cornell has been funded jointly by the US NSF and DOE *Dedicated damping ring R&D program starting in mid-2008 *Electron cloud studies is one of the core research areas: –Cloud build-up in wigglers, dipoles, quadrupoles, and drift regions –Mitigation studies –Beam-cloud dynamics at lowest achievable emittances: tune-shift measurements and comparison with simulation *SLAC participation: –Experimental effort: redeploy ECLOUD1,2,3 (plus grooved chamber in dipole). –Simulation: build-up, beam instability, and SEY in magnetic and field-free regions

SLAC DOE HEP Review July 7 - 9, 2008 Page 25 ECLOUD3 Grooved chamber for Cesr-TA *Grooved chamber for dipole: Chamber fabricated, but needs final assembly and TiN coating (originally built for ECLOUD3, but was not installed due to budget cuts.) Morrison, Pivi, Wang, SLAC

SLAC DOE HEP Review July 7 - 9, 2008 Page 26 Plans for CERN SPS and LHC *Grooved chamber in dipoles in SPS: provide grooved insertions. Installation to start summer (Pivi, Wang). *Simulation: benchmarking and large-scale computations for SPS and LHC. (Pivi, Wang) *Electron cloud density measurement in SPS via RF transmission. (Fox,Pivi, collaboration with LBNL)

SLAC DOE HEP Review July 7 - 9, 2008 Page 27 2mm Aluminum+coating triangular grooves (pictures above), manufactured by SLAC. 1mm depth stainlees steel grooved insertion under development: CERN/SLAC Lanfa Wang, SLAC Tip Valley Aluminum triangular groove, SLAC. Depth 1.9mm, Opening angle 20 o, radius top 95um, radius valley 144um Mauro Pivi - SLAC April 2008 Tip Grooved chamber for CERN SPS simulation

SLAC DOE HEP Review July 7 - 9, 2008 Page 28 Additional Plans *Plans for Project-X: –Re-deploy ECLOUD1 (SEY Station) to Fermilab (after CesrTA) –Conditioning and SEY at a high-intensity proton machine *KEK-B: –Provide test insertions for experiment at KEK-B –Compare grooved and flat TiN coated surfaces, and clearing electrodes.

SLAC DOE HEP Review July 7 - 9, 2008 Page 29 Summary *A successful R&D program on electron cloud has been carried out at SLAC *TiN coating has been demonstrated to have an SEY reliably below the instability threshold. Work continues to address a few remaining issues. *Requirements at future colliders (5 pico-meter emittance at the ILC, e.g.) are challenging. *SLAC is a key collaborator with other labs to develop complementary mitigation techniques.

SLAC DOE HEP Review July 7 - 9, 2008 Page 30 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 vacuum and fabrication facilities.