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

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
ILC Damping Rings Collaboration Mtg, 3/4/09

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

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

5. ILC Damping Rings Collaboration Mtg, 3/4/09
Recap: ECLOUD1 Results
Goal: monitor the reduction in-situ of the SEY due to conditioning
Results:
TiN coating: SEY reduced to < 1. Stable after long term (>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

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

7. ILC Damping Rings Collaboration Mtg, 3/4/09
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-13283
M. Pivi et al. accepted for publication in J. of Appl. Phys. 2008
ILC Damping Rings Collaboration Mtg, 3/4/09

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

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

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

11. ECLOUD3: New resonance effect in a dipole
ECLOUD signal vs. B-field, summed over all strips
Uncoated Al
TiN-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

12. ILC Damping Rings Collaboration Mtg, 3/4/09
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

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

14. ILC Damping Rings Collaboration Mtg, 3/4/09
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

15. ILC Damping Rings Collaboration Mtg, 3/4/09
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.
ILC Damping Rings Collaboration Mtg, 3/4/09