Study and Compensation of the LongRange Beambeam Effect

Study and Compensation of the Long-Range Beam-beam Effect Proponents: Tanaji Sen, Vladimir Shiltsev, FNAL Wolfram Fischer, BNL Miguel Furman, Ji Qiang, LBNL Jean-Pierre Koutchouk, Jorg Wenninger, Frank Zimmermann, CERN presentation by T. Sen with further details

Motivation • performance of nominal LHC is limited by long-range beam-beam interactions • even more drastic limit for LHC upgrade or for any new higher energy collider • compensation of the long-range beam-beam force by wires (‘BBLR’) is highly efficient as all multipoles are corrected at once • first experimental confirmation with two BBLR’s at SPS in 2004 • space for possible beam-beam compensators is reserved in LHC v. 6. 5 on either side of IP 1 and IP 5. • technology possible today at relatively low cost • compensation device is new type of non-linear lens which can lend itself to potentially other uses, such as electromagnetic beam scraping • challenging development is design of pulsed wire for selective processing of nominal and PACMAN bunches • successful demonstration that compensation works on a colliding beam in a real machine environment will build confidence that the compensation will be effective in the LHC • outcome of this study on long-range beam-beam compensation will greatly influence IR design for a luminosity upgrade: if the compensation is shown to be effective, then the quadrupole first design in the upgrade would be the simpler and more straightforward path therefore we propose to include this topic in the LARP Accelerator R&D program

Goals 1) experimental demonstration of the principle in the SPS with one wire simulating the beam and the second carrying out the compensation; issues: study of required compensation accuracy (betatron phase shift, wire current and position, possible tune dependence, effect of current ripple…) & comparison with tracking (well advanced, already with some US/LARP participation) 2) experimental demonstration in a hadron collider (RHIC or Tevatron) or lepton collider (e. g. PEP-II) where conditions closer to that of LHC or future colliders can be met with wires compensating a real beam; demonstrate the use of the wire for the benefit of this collider, e. g, as scraper, or future upgrades, e. g. , for compensation of long-range collisions in e. RHIC or after RHIC IR upgrades, or for improving performance of Tevatron Run-II; study robustness of 3) compensation against realistic errors 3) 4) R&D on pulsed wire compensation system; possible test of pulsed wire on 4) design of compensation device for LHC assuming success of former points. beam in existing machine

Possible Contributions of the US/LARP - 1 1) SPS experimental programme: in 2004, 4 machine study sessions were dedicated to BBLR studies, one of which attended by T. Sen and V. Shiltsev. 2) These experiments generated a vast amount of information which require a few man-month of analysis; a partial involvement of a scientist and of a fellow in the analysis would be extremely useful; the analysis efficiency would benefit from assistance by computer scientists; these experiments could indeed be used as a test bed for information sharing as a preparation to remote participation in machine studies; important issues are the most efficient and convenient methods (web? ) and formats (xml? ) for the sharing of data and analysis procedures and results which lend itself to a future on-line use 2) experimental full-size demonstration: the second line of study is to 3) 4) 5) investigate which of the existing colliders is most suitable for creating the nominal LHC long-range beam-beam conditions (with proper scaling) and evaluate the requirements for such an experiment; if such conditions can be 6) 7) 8) fulfilled, refit the SPS devices or build new ones and carry through an experimental study programme; from SPS experience, 50 to 100 machine hours spread over one to two years are suitable

Possible Contributions of the US/LARP - 2 3) pulsed wire: R&D in collaboration with CERN on a pulsed wire 4) (typically a few hundred Amperes pulsed at a few MHz or, alternatively, 5) at 40 MHz). 4) LHC implementation: design of a movable wire compensator suitable for LHC, solving all its specific challenges: limited space between the two beams to move in a wire, safe conduction cooling of the wire with a high current density, protection of the wire against incident beam and avoidance of scattering towards the IP’s, impedance issue

back-up slides scientific issues and SPS MD results

Long-Range Collisions in LHC and SPS Wires 4 primary collision points in the LHC around each primary IP there are 30 long-range collision points! these perturb the motion of the protons and reduce the dynamic aperture; this effect did not exist in previous hadron colliders (SPS, HERA, Te. V-I) # LR encounters SPS 9 Tevatron 70 LHC 120 the long-range collisions cause a large diffusion and proton losses the effect of the SPS wire resembles the LHC long-range collisions; the SPS wires allow us to verify the simulations and to study the compensation scheme proposed for the LHC 1 mm/s LHC beam 1 mm/s SPS wire

3 -wire prototype device (‘BBLR’) installed in the CERN SPS

tune scan with compensation of 2 BBLRs in the CERN SPS near the LHC working point lifetime versus vertical tune 30. 07. 04 no BBLR path in the tune diagram compensation 1 BBLR ? nearly perfect compensation