LongRange Beambeam Compensator Outline Motivation Principle Simulation Results

Long-Range Beam-beam Compensator: Outline • • Motivation Principle Simulation Results Parameters of the BBLR Compensator • Conclusions 9/9/2021 JPK/LCC 06/11/2002 1

Motivation At the nominal performance level, the long-range beam effect has been recognized to be the limiting mechanism. The `enlarged’ crossing angle (300 mrad, i. e. 9. 5 s average separation) and the alternate crossing (cancellation of the linear tune shift) do not appear to leave a sufficient aperture where the beam motion is well behaved (Beambeam workshops Cern 1999, Fermilab 2001). Proposal made of an active system to cancel the LRBB kicks (LHC Project Note 223 & PAC 01 & LHC MAC ). 9/9/2021 JPK/LCC 06/11/2002 2

Principle • A straight conductor at ~9. 5 s from the beam (transverse) simulates the other beam magnetic field to large accuracy (4% , 1% averaged over the betatron angle) in the useful aperture; it is used to cancel the LR beam-beam kicks (all orders). • The topology must be identical for the BB kicks and for the correction (separation, plane, aspect ratio, i. e. identical ratios of the functions) + no phase shift. • The integrated corrector current is simply -the integrated (other) beam current; nominal: 1 meter * 80 Amperes. • The corrector need not be pulsed for normal bunches. 9/9/2021 JPK/LCC 06/11/2002 3

Position of the Correctors 9/9/2021 JPK/LCC 06/11/2002 4

Position of the Correctors • To correct for all non-linear effects (detuning is insufficient), the correction must be local. • Layout: 41 m upstream of D 2, both sides of IP 1/IP 5 9/9/2021 JPK/LCC 06/11/2002 5

Simulation Results • . 16 s • . 005 s • . 016 s Beam separation at IP 9/9/2021 JPK/LCC 06/11/2002 6

Moving out the corrector at 12 s and scaling up its current 16/11/01, F. Zimmermann 9/9/2021 JPK/LCC 06/11/2002 7

Preliminary Result from SPS MD Question: is it really the onset of diffusion or an orbit effect or a tune effect? 9/9/2021 JPK/LCC 06/11/2002 8

Experimental Set-up at the SPS Miniteam: J. P. Koutchouk, G. de Rijk, J. Wenninger, F. Zimmermann. Tech. Coord. J. Camas/BI Help from many groups 9/9/2021 JPK/LCC 06/11/2002 9

Conclusion 1) In simulation, the LRBBC is efficient and robust and opens the way to higher LHC performance. 2) It may already be needed to reach nominal performance. 3) It makes the performance independent of the Xing scheme (but is easier to implement for V Xing). 4) A set-up is under test in the SPS (dc mode), with performance beyond LHC requirements (>100 A/mm 2). 5) The pulsed mode for PACMAN is a technical challenge requiring R&D and doable (G. Schroeder). 9/9/2021 JPK/LCC 06/11/2002 10