electron clouds at slac johnny ng ilc damping rings collaboration meeting march 4, 2009
TRANSCRIPT
Electron Clouds at SLAC
Johnny Ng
ILC Damping Rings Collaboration Meeting
March 4, 2009
ILC Damping Rings Collaboration Mtg, 3/4/09
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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. 2007 – Apr. 2008): Conditioning effect on SEY– ECLOUD2 (Jan. 2007 – Apr. 2008): Test grooved chambers– ECLOUD3 (Dec. 2007- 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
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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
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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
Flatchamber
Electron detectors
ILC Damping Rings Collaboration Mtg, 3/4/09
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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
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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
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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
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ECLOUD3: Magnetic field strength
periodcyclotron electron
in time spacingbunch n =
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 observedmodulation in electron flux atthe chamber wall.
ILC Damping Rings Collaboration Mtg, 3/4/09
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ECLOUD3: New resonance effect in a dipole
2 4 6 8 10 120
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
n
E-current
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
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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
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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 doneLeak check this week, then welding and coating, etc..
• Expect completion early May
Morrison, Pivi, Wang, SLAC
ILC Damping Rings Collaboration Mtg, 3/4/09
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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.
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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.