# Presentation: 802206

## Beam-beam wire compensation,status and plans

- W. Fischer
- N. Abreu, R. Calaga, Y. Luo, G. Robert-Demolaize, **BNL**; U. Dorda, J.-P. Koutchouk, F. Zimmermann, **CERN**; H.J. Kim, T. Sen, **FNAL**; J. Qiang, **LBNL**; A. Kabel, **SLAC**

- LARP Collaboration Meeting 9,** **Fermilab, 17 October 2007

## Content

- Measurement in 2007
- Simulation status
- Measurement plans for 2008

## RHIC BBLR wires in tunnel

## Wire operation	

- Two degrees of freedom:
- Current (0 – 50 A)
- Vertical position (0 – 65 mm)
- Local PIN diodes (middle of BBLR and downstream end of BBLR)
- Temperature sensors

## Experiments in RHIC Run-7 (2007)

- No actual long-range compensation
- Beam-beam effect too small with Au
- Test effect of wire (= strong long-range beam-beam effect) on Au beam, to benchmark simulation
- At injection	(  10 GeV/nucleon Au beam)
- At store 		(100 GeV/nucleon Au beam)
- Test effect of wire on collimation efficiency

## Experiments in RHIC Run-7 (2007)

- Parasitic time
- 03/13 0-4am during setup at injection (B)
- 03/27 2:30-3pm during store in collision (B),          for background observation
- Scheduled time
- 04/11 5:30-8am (permit dropped after BBLR movement)
- 04/25 5-8am (B+Y)
- 05/09 5-8am (B+Y)
- 06/20 5-8am (B+Y, lost after 1 h due to abort kicker problem)

## Distance scan at injection – 5A current, Au beam

## Distance scan at injection – 50 A current, Au beam

## Distance scan at store – 50 A, Au beam

- See increase in experimental background – no help for collimation.

## Check tune and orbit response

## Distance scans: 5, 50 A, Blue, Yellow

## Current scan: Blue, Yellow

## Chromaticity scan: Yellow

- Loss vs. vertical chromaticity

- Current scan at largest 

## Benchmark simulations

- RHIC detailed model includes:
- Magnetic field errors in DX,D0,Q1,Q2,Q3
- Randomized sextupole errors in arc dipoles
- Tune ripple
- Simulations by
- U. Dorda, CERN
- H.J. Kim, T. Sen, FNAL
- A. Kabel, SLAC
- J. Qiang, LBNL

## Benchmark simulations

- Blue beam at store (Exp. 1, 12.5 Am), U. Dorda

## Benchmark simulations

- Blue at injection, simulated by H.J. Kim, T. Sen

## Benchmark simulations

- 30 mm

- Blue at store, A. Kabel

## Open items in experiments

- Only Au beams tested with BBLR, proton beams have 2-3 larger beam-beam parameter, and different tunes
- No head-on collisions included in scan
- No attempt to compensate for single head-on interaction
- No pulsed wire tested (under study by U. Dorda)

## Planned test with RHIC BBLR wires in 2008

- Will ask for 33 hr dedicated time again
- Would like to test effect on background with protons too (parasitic)
- Parameter scans (distance, strength) with protons
- Including head-on
- Different working points
- Attempt to compensate one long-range interaction

## RHIC – possible location for compensation

**IP6**

**Small phase advance between long-range beam-beam interaction****and possible compensator can only be realized at store.**

## Summary – long-range beam-beam in RHIC

- Parasitic measurements done with Au beams in 2007:
- At injection
- At store with colliding beams
- Dedicated experiments with Au beams at store (100 GeV/n):
- Loss rate vs. distance
- Loss rate vs. wire strength
- Loss rate vs. chromaticity
- Simulations for 2007 experiments coming to conclusion
- Experimental plans for 2008:
- Parameter scans with p-beam (including head-on, new tunes)
- Attempt to compensate single long-range interaction