# Presentation: 064585

## Electron Cloud Activities

- Miguel A. Furman (LBNL)
- _[mafurman@lbl.gov](mailto:mafurman@lbl.gov)_
*LARP Collaboration Mtg.*
*Napa Embassy Suites, Oct. 19-21, 2004*

***bnl - fnal- lbnl - slac***

_**US LHC Accelerator Research Program**_

## Developments since FNAL LARP mtg. (June 2004)

-  Participation in SPS EC runs (June 21-26, 2004)
-  CERN: Arduini, Jiménez, Baglin, Schulte; LARP: Iriso, Pivi, Furman
-  initial results: LHC-MAC mtg. #14 (Jul. 12-13, 2004)
-  ongoing analysis of results (US and CERN)
-  more RHIC results
-  Hseuh, Iriso, Zhang
-  initial results: Workshop on RHIC experiments (Sep. 16-17, 2004)
-  M. Jiménez visited BNL (late Sept. 2004)
-  formal proposal for e-detectors in RHIC
-  Iriso to leave BNL April 05
-  We’ll participate in the CARE HHH-2004 wkshp. (CERN, Nov. 8-11, 2004)
-  ECLOUD04 proceedings almost done!
- ...

## SPS EC runs (mostly June 2004)

- 1-4 batches
- 1 batch=a train of 72 bunches spaced by 25 ns (nominal)
- 		     or
-                   a train of 24 bunches spaced by 75 ns
- a few runs with interleaved batches (25-75-25-75)
- varied batch separation (225 ns [nom.]; 550 ns; 800 ns; and 1050 ns)
- E=27 GeV (mostly); N=1.4x1011 (mostly)
- our simulations are in progress (Pivi-Furman)
- more slowly than I’d wanted...

## SPS observations: weak dependence on batch spacing

- P. Strubin, LHC-MAC jul. 2004
- *** preliminary ***

- qualitatively similar results for:
- FF, dipole, and quad.
- e-det. or calorimeters
- 25 ns or 75 ns
- consistent with simulations *if* one assumes a large value for **(0) (ie., **(0)~0.5-1)
- However, COLDEX (FF calorimter) shows that 25-75-25-75 interleaved pattern has ~1/3 less EC “activity” than uniform pattern with same no. of bunches
- might be more a more favorable operation configuration (?)

## SPS observations: cold Cu “beam screen” conditions like RT surfaces

- desorbed gas composition:
- mostly H2O and CO
- H2O layer is bad (high SEY)
- extrapolation of these results to the LHC might need more work (IMHO)
- conditioning mechanism at cryogenic T might be different from RT conditioning

- P. Strubin, LHC-MAC jul. 2004
- *** preliminary ***

## Conditioning of (E0) for E0≈0

- Long survival time of low-energy electrons at SPS
- consistent with PSR experience
- consistent with bench results for Cu (Cimino-Collins)
- the upturn of **(*E*0) as *E*00 seems unconventional
- SPS experience needs better understanding

- R. Cimino and I. Collins

## SPS e-detectors

-  e-detectors identical to those at SPS
-  baseline (RT):
- 1 strip detector (SD) in an adjustable magnet
- 1 retarding field det. (RFD)
-  ultimate: 1 SD in a cold magnet
-  total est. cost:
- 6.3 m-months+89 kCHF
-  baseline delivery & installation:
- June-August ‘05
-  this is ~8 months later than we would have ideally liked
-  goal: study e-cloud as a function of bunch intensity, bunch spacing and bunch pattern in a **cold** environment

- at RHIC

- DRAFT

## Some RHIC observations

- U. Iriso, RHIC expts. wkshp. 9/04

- e-cloud directly observed in warm SS
- indirectly observed in cold arcs (P)
- measure tune shift to disentangle
- 				 =e-cloud density)
- observe Qh=2Qv ≈0.002 in arcs
- “” e-cloud in arc dipoles
- however, Q from warm SS is ~0.005, so conclusion not firm
- installed more TiZrV-coated chambers
- “works better than solenoids”

## EC schedule

## Comments & conclusions

- Continue and increase SPS analysis via simulations
- plan to hire an UG student 1/2 time for this (soon, I hope)
- code benchmarking as part of the process (LARP-CARE informal collaboration)
- Iriso-Peggs map technique: needs continuity after UI leaves
- who?
- Hopefully RHIC will not fully suppress the e-cloud with coated chambers!
- we need an e-cloud in the warm regions for better testing our simulations
- make sure we reach the point of installing the cold SD in RHIC
- I feel a lack of “critical mass” in the e-cloud effort
- leads to infrequent communication with CERN people
- it’s a nontrivial effort to keep up with CERN’s and other’s activities
- maybe it’s a temporary state...

## Additional material

## Some Issues

- EC survives for a long time at SPS (~few s)
- e– flux at wall for dipole magnet ~3x simulations both warm and cold detectors
- Measured e– spectrum “could agree better with simulations”
- Old vs. new ECLOUD simulations show some discrepancies
- some comparisons with other codes carried out (after ECLOUD02)
- qualitative agreement, but differences not explained (for lack of dedicated effort)
- e– flux dependence on vac. chamber height: peaks at 80 mm (=max. achievable)
- Main “knobs”: bunch length, batch spacing, vac. chamber height, N
- should be plenty to constrain the model significantly
- need to constrain SEY model; devise experiment (ie., build-up and dissipation of the EC)
- revisit satellite bunch scheme

## Partial List of Electron Cloud Tasks

- Main goal: specify optimal LHC conditioning scenario
- Conditioning of cold surface at LHC likely to be very different from warm at SPS
- What to do if beam screen SEY does not condition as hoped
- First attempt at defining scenario
- Tasks at RHIC (suggested by “all” CERN people)
- Install CERN EC detector in a RHIC cold magnet (J. M. Jiménez, A. Drees)
- Measure  along batch (U. Iriso)
- Simulate ECE at RHIC, calibrate code(s), understand warm vs. cold EC
- UI to learn POSINST; go to LBNL, and/or MF to BNL
- Understand conditioning process in cold sections vs. warm
- Understand global parameter space (eg., EC density vs. a few parameters)
- Understand physics of map simulation technique

## List (contd.)

- SPS
- Devise experiment to be compared against upcoming SPS measurements to constrain SEY model
- eg., build-up and decay time of EC vs. N, sB and batch gap length (FY04-05)
- Estimate EC build-up and decay in quads (SPS plans to install “sweeping” detector) (FY05+)
- US-LARP personnel to participate in scrubbing SPS MDs (next week)
- Reproduce measured spectrum and spatial distribution (FY05)
- Reproduce calorimeter results (FY05)
- Understand POSINST-ECLOUD differences (FY05) (suggested by FZ)
- Think about BTF measurements (requested by GA)
- Think about microwave transmission measurements of EC density (suggested by FZ)
- Measure ion desorption count and composition by ion bombardment (requested by JMJ: send one person to CERN for a year to do measurements)

## List (contd.)

- Better measurements for simulation input (requested by FZ)
- SEY at low energy (<20 eV); reproduce CERN data (Cimino-Collins)
- Photoelectric yield and photon reflectivity (cold vs. RT; B-field effect) for actual sawtooth beam screen samples; resolve existing discrepancies (at ALS?). *Further discussions with CERN needed before proceeding.*
- LHC
- CERN will install an ECE diagnostic bench in IR4 (J. M. Jiménez) similar to SPS.
- Simulate and predict! Good for LARP to play important role in this.

##      SPS schedule 2004

- Scrubbing runs (weeks 24 & 26):
-   N=(0.3-1.3)x1011, min. , fixed z, 1-4 batches, sB=25 or 75 ns
- Some expected results:
-  max. N and fill pattern at 25 and 75 ns for given cooling rate
-  improve precision in measurement of conditioning efficiency for cold dipoles
-  measure heat load and partial pressures in COLDEX
-  EC build-up in quads
-  EC build-up in TiZrV-coated chamber before activation (use artificial seed electrons)

## More SPS MD details (from G. Arduini and J. M. Jiménez)

- Weeks 24 and 26: scrubbing (MD people have full control of beam)
- Week 27: beam stability, optimize the machine settings to get rid of the last 10-20% in emittance blow-up in order to get the nominal parameters. Measurements with COLDEX and electron clould detectors and calorimeters.
- Weeks 29 and 31: coasts (with RF on) of 1-2 LHC batches at SPS injection energy (p=26 GeV/c). Study the issues of long term emittance blow-up for the nominal LHC beam. Benchmark HEADTAIL or similar codes (which are predicting important emittance blow-up).
- Week 40: coast with 1-2 LHC batches (nominal intensity) at p=270 GeV/c for similar purposes as above.
- Week 45: not yet defined.

## Our Plans

- SPS shifts during “scrubbing runs” (next week)
- Ubaldo Iriso, Mauro Pivi, Miguel Furman
- CERN contact: Gianluigi Arduini
- Deliverables for FY05:
- Participate in SPS EC experiments and studies (next week)
- Install cold EC detector in RHIC (10/04)
- Report on simulated reproduction of measured spectrum & spatial distribution of SPS e-cloud (4/05)
- Report first cut at defining optimal LHC conditioning scenario (6/05)
- Report on applicability of map simulation technique to LHC (9/05)
- Report on cold EC in RHIC (9/05)
- Report on simulated EC at IR4 diagnostic bench (10/05)
- FY05 budget: 0.3 FTE for LBNL plus 0.3 FTE for BNL