Beam-Beam Interaction

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Beam-beam interaction refers to the electromagnetic forces and effects that occur when two charged particle beams collide or pass through each other in accelerators. This interaction can lead to phenomena such as beam degradation, luminosity enhancement, and particle scattering, significantly influencing the performance and outcomes of high-energy physics experiments.

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Observations and Open Questions in Beam-beam Interactions

by Tanaji Sen

2010, ICFA Beam Dynamics Newsletter

A review article on the physics of beam-beam interactions in circular colliders.

This machine had two interleaved rings in which first unbunched beams of protons and later antiprotons and other particles were brought into collision. There were 8 crossing points of which 5-6 were used for experiments [16, 17]. Another feature of the ISR was that it had a working line, shown in Figure 2, rather than a working point. ins wh colli wil his large tune spread was requ tability. As a consequence, the bea ich led to particle loss. Synch: be discussed further below. duri ired ro- be isions beam-beam effects also led accelerator physics issues in the for stability against the transverse resistive wall ms crossed some low order betatron resonances tatron resonances were not an issue. During to particle loss, often from coherent effects. This Beam currents in the range of 30-40 Amps were stored ng high luminosity runs with lifeti mes in the tens of hours. Overviews of the SR can be found in [19, 20].

ss Se During 2008, its last year of operation, PEPII operated with and achieved a peak lumi the performance was limi low energy ring (LER) cu beam in the high energy ring (HER). Additionally increasing LER also increased its own beam size, which was not understood [24]. The m nosity of 1.21x10°4cm7s" [24]. Att 1732 bunches i he highest bunch n each ring currents, ted by the head-on beam-beam interactions. For example, the rrents were limited by the losses and backgrounds from the the beam curren t in the beam- beam parameter ac hieved was 0.113 in the horizontal p aximum ane of the HER. These alone raised the luminosity by 15% and led to a peak luminosity of 2.1x10°*cm’ 51 in 2009 [22, 23].

Figure 4: Dependence of proton loss rates in the Tevatron on horizontal chromaticity at injection

Figures 5: Proton intensity decay rate and proton background rate as a function of Ihe horizontal tune at two separations (taken from [29]).

Figure 6: Proton loss rates vs. Na( ) during stores in 2008 (taken from Ref [4], é, [his shows a nearly linear dependence of proton losses on this product. This suggests an empirical law

In this theoretical calculatio small because the vertical di t take into account coupli ich would shift all the chi measured bunch by bunch c taken from [27], demonst nches and (b) that couplin chromaticities. n, the contrib spersion is al romatici rates (a) g tends to eq ng between th ties by constant am hromaticity in simil utions to the vertical chro so small around the ring. e two planes. The machin ts, Was the Tevatron wn in the ri maticity are fairly However this does e chromatici ar variation in chromatici ualize the horizon tal and verti ty between t cal not included. ght plot of Figure ty, The Ne

Table 1: Basic parameters of past and present fully commissioned hadron colliders

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Beam-beam simulation code BBSIM for particle accelerators

by Tanaji Sen

2011, Nuclear Instruments & Methods A

A highly efficient, fully parallelized, six-dimensional tracking model for simulating interactions of colliding hadron beams in high energy ring colliders and simulating schemes for mitigating their effects is described. The model uses... more

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The beam-beam interaction of finite length bunches in hadron colliders

by Tanaji Sen

2000

The influence of finite bunch lengths on the dynamics of head-on beam-beam interactions is studied analytically and by simulation. Compared to infinitesimally short bunches, the resonance widths of bunches in the Tevatron are an order of... more

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Renormalization Group Approach to the Beam-Beam Interaction in Circular Colliders

by Stephan I Tzenov

2001, Arxiv preprint physics/0106101

Building on the Renormalization Group (RG) method the beam-beam interaction in circular colliders is studied. A regularized symplectic RG beam-beam map, that describes successfully the long-time asymptotic behavior of the original system... more

Thus, we finally arrive at the system of integral equations for the invariant phase space densities fO (av)

The one-turn beam-beam map, derived in the previous Section can be further simplified by eliminating the canonical momentum variable p from (2.17). Multiplying the first of Eqs. (2.17) by cos 271, multiplying the second one by — sin 271,, and summing the two equations up we find

Here the coefficients ce are functions of the amplitude |A;,| and are given by the expression

Proceeding in the same way as above, we can write the canonical conjugate momentum Dy in the form

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Beam-Beam Interaction

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