# Presentation: 064594

## US LARP Proposal

- for Electron Cloud Activities (FY04)
- Miguel A. Furman (LBNL)
- mafurman@lbl.gov
*US LARP Collaboration Mtg.*
*Danfords Inn (Port Jefferson), Sept. 16–18, 2003*

## Regular contacts/collaborators  for LHC-related work

- CERN:
- F. Zimmermann
- G. Arduini
- J. M. Jiménez
- N. Hilleret
- SLAC:
- M. Pivi
- R. Kirby

- In addition, related work (PSR, APS, PEP-II, ...) in collaboration and/or consultation with:
- R. Macek
- M. Blaskiewicz
- K. Harkay
- Y. H. Cai
- G. Rumolo
- R. Cimino
- I. Collins

## Electron clouds

- Main issue: power deposition *P/l* on the beam screen
- max. load from all sources =1.17 W/m per ring
- In LHC, the EC is seeded by photoelectrons:
- synchrotron radiation has:
- leading to:                                         photons per proton per dipole
- which leads, in turn, to ~6x10–4 electrons/proton/m (assuming QE=0.05)
- key parameters: QE and photon reflectivity *R* (specular and diffused components)
- ...and amplified by secondary electron emission:
- both the SEY **(*E*0) and the emitted-energy spectrum *d****/dE* are important
- In summary: key players are: QE, *R, ***(*E*0) and *d****/dE*
- plus, of course, bunch population, bunch spacing and bunch train length

## Effect of photon reflectivity R

- If *R*~0, electrons remain confined in outer edge (at least for a while)
- If *R*~1, electrons emitted ~uniformly  higher *P/l* than for *R*~0
- estimate: factor of ~a few times larger for a 72-bunch train

## St. St. spectrum (d/dE) at E0=300 eV (max=2.04):

- Depends on material and state of conditioning
- St. St. sample, E0=300 eV, normal incidence, (Kirby-King, NIMPR A469, 1 (2001))

- _st. steel sample_
**= 2.04
**e =   6%
**r = 37%
**ts =57%
**e+**r =43%

-  Hilleret’s group CERN: Baglin et al, CERN-LHC-PR 472.
-  Other measurements: Cimino and Collins, 2003 -- see later)

- _Cu sample_
**= 2.05
**e =   1%
**r =   9%
**ts =90%
**e+**r =10%

## Sensitivity to relative ratios of e, r and ts at fixed max=2.05

- Simulated power deposition vs. time (LHC arc dipole)

**e+**r = 10%

**e+**r = 0

**e+**r = 43%

- 2 W/m

- 10 W/m

- 150 W/m

## Activities at CERN (mostly SPS)

- 3+ years of EC studies with dedicated instrumentation at SPS
- in-situ measurements: measure **(*E*0) of Cu samples in the vacuum chamber
- calorimeters, RT and cold: measure *P/l*
- strip detectors: measure EC distribution at the wall, including *B*-dependence
- RFAs: measure intensity and energy spectrum of EC at the wall
- photon *R* and QE off Cu samples: measured at EPA, ELETTRA  and BINP
- simulations (code ECLOUD)

## Some observations (e.g., APC mtg. 8/1/03)

- Beam scrubbing works well; favorable effects seen in:
- vacuum pressure
- electron flux at wall (strip monitors)
- conditioning is faster by ~x3-5 at RT than at 30K
- electron distribution at wall not fully understood (dependence on *B* field and chamber height)
- heat load higher by ~x3 at RT than at 30K
- in-situ SEY measurements
- Cu sample: **max decreases from ~2.3 to ~1.6 in ~2 days’ run
- calorimeters COL_x0008_DEX and WAMPAC
- heat load ~same at RT and at 30K
- TiZrV coating suppresses ions and electrons after activation at 200C
- not appropriate solution for the arcs, unfortunately
- Various measurements of QE and *R* not perfectly consistent

## Other SEY measurements

- Bench measurements in mu-metal chamber
- R. Cimino and I. Collins (ASTEC2003, Daresbury Jan. 03)
- conditioning of **max but not of **(0) is consistent with PSR experience for stainless steel
- the result **(0)≈1 seems unconventional
- if validated, it could have a significant unfavorable effect on the EC power deposition in the LHC
- because electrons survive longer in between bunches

## Suggestions from F. Zimmermann

## Electron-cloud LARP goals: FY04 and beyond

- Simulations for the SPS
- reproduce measured electron energy spectrum and spatial distribution
- dependence on B field and chamber geometry
- reproduce calorimeter results
- POSINST vs. ECLOUD: understand and iron out differences
- Better data for **(*E*0) and *d****/dE* for actual Cu samples
- region *E*0 < 20 eV important (and hard to measure)
- possibly at SLAC
- Better data for QE and *R* for actual Cu samples, both RT and cold
- at ALS (J. Byrd)
- attempt to resolve existing discrepancies
- Electron-cloud interaction with microwaves (novel diagnostics)
- Assess effects of EC on beam (emittance growth, instabilities)

## Electron-cloud LARP goals: FY04 and beyond (contd.)

- Improve simulation codes
- parallelize for speed
- self-consistent calculation of single-bunch effects
- this work is leveraged by other efforts/labs/programs:
- SciDAC program (particularly beam-beam work at LBNL)
- NERSC (LBNL) (supercomputer support)
- PSR (LANL) (electron-cloud measurements)
- SNS (ORNL) (electron-cloud simulations)
- HIF-VNL (electron-cloud measurements and simulations)
- Ongoing benchmarking at other machines (PSR, PEP-II, ...)

## Additional information

- Important websites:
- http://lhc-beam-beam.web.cern.ch/lhc-beam-beam/
- http://wwwslap.cern.ch/collective/electron-cloud/electron-cloud.html
- http://www.aps.anl.gov/asd/physics/ecloud/ecloud.html
- http://ab-div.web.cern.ch/ab-div/Meetings/APC/Welcome.html

## SEY for a copper sample

## SEY for a St. St. sample

## NOTE: rediffused+elastics~50%

- (assuming low-energy cutoff=50 eV)

## Electron-cloud interaction with microwaves

- electron cyclotron motion in dipoles:
- 			eB/2mec=2.4x1011 Hz     (for B=8.4 T)
- would resonate with a THz-range signal
- from reflection and transmission, infer EC intensity
- experiments at CERN (F. Caspers)

## NOTE: rediffused+elastics~5%

- (assuming low-energy cutoff=50 eV)