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

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. 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


Page 5

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


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

Flatchamber

Electron detectors


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-13283– M. Pivi et al. accepted for publication in J. of Appl. Phys. 2008


Page 8

ECLOUD3 – Electron Cloud in a Dipole

Retarding Field Analyzer (RFA): - electron flux at the wall- energy spectrum- lateral distribution

e+


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.


Page 10

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.


Page 11

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.


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


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 doneLeak check this week, then welding and coating, etc..

• Expect completion early May

Morrison, Pivi, Wang, SLAC


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.


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.

Documents

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