Beam-beam Kick Research Articles

Fast failures in the LHC and the future high luminosity LHC

An energy of $362\:\text{MJ}$ is stored in each of the two LHC proton beams for nominal beam parameters. This will be further increased to about $700\:\text{MJ}$ in the future High Luminosity LHC (HL-LHC) and uncontrolled beam losses represent a significant hazard for the integrity and safe operation of the machine. In this paper, a number of failure mechanisms that can lead to a fast increase of beam losses are analyzed. Most critical are failures in the magnet protection system, namely the quench heaters and a novel protection system called Coupling-Loss Induced Quench (CLIQ). An important outcome is that magnet protection has to be evaluated for its impact on the beam and designed accordingly. In particular, CLIQ, which is to protect the new HL-LHC triplet magnets, constitutes the fastest known failure in the LHC if triggered spuriously. A schematic change of CLIQ to mitigate the hazard is presented. A loss of the Beam-Beam Kick due to the extraction of one beam is another source of beam losses with a fast onset. A significantly stronger impact is expected in the upcoming LHC Run III and HL-LHC as compared to the current LHC, mainly due to the increased bunch intensity. Its criticality and mitigation methods are discussed. It is shown that symmetric quenches in the superconducting magnets for the final focusing triplet can have a significant impact on the beam on short timescales. The impact on the beam due to failures of the Beam-Beam Compensating Wires as well as coherent excitations by the transverse beam damper are also discussed.

Effect of beam-beam kick on electron beam quality in first bunched electron cooler

The low energy RHIC electron cooler (LEReC) currently under commissioning at BNL is going to be the first non-magnetized bunched electron cooler (EC). For successful cooling LEReC requires that the electrons in the cooling section (CS) have small angles with respect to co-propagating ions. Since there is no strong magnetic field in the CS, the effects of ions on both the trajectory and focusing of the e-bunches is critical. In this paper we consider the ion beam kick on the electron bunches and derive requirements to the respective alignment of electron and ion beams in non-magnetized coolers.

Beam-Beam Effect: Crab Dynamics Calculation in JLEIC

The electron and ion beams of a future Electron Ion Collider (EIC) must collide at an angle for detection, machine and engineering design reasons. To avoid associated luminosity reduction, a local crabbing scheme is used where each beam is crabbed before collision and de-crabbed after collision. The crab crossing scheme then provides a head-on collision for beams with a non-zero crossing angle. We develop a framework for accurate simulation of crabbing dynamics with beam-beam effects by combining symplectic particle tracking codes with a beam-beam model based on the Bassetti-Erskine analytic solution. We present simulation results using our implementation of such a framework where the beam dynamics around the ring is tracked using Elegant and the beam-beam kick is modeled in Python.

Measurement of dynamic beam-beam effects

A series of measurements were carried out to investigate the dynamic beam-beam effects at KEKB. The beam-beam kick and the coherent beam-beam tune shift were measured by comparing the beam parameters between a colliding bunch and a noncolliding one. We found that collisions occur with a horizontal orbit offset to obtain the maximum luminosity, and that this reproducible offset appears to be attributed to an electron cloud effect, which might play an important role in the beam-beam interaction. The horizontal beam size estimated from the beam-beam kick slightly decreased as the beam-beam parameter increased. The horizontal emittance estimated from the beam-beam tune shift was higher than an unperturbed emittance, and agreed with the calculated emittance using a higher-mode tune. The ratio of the square-root betatron function between two locations in the ring was measured as a function of the beam-beam parameter. These experimental results would provide useful information on dynamic beam-beam effects.

Coherent synchrobetatron beam-beam modes: experiment and simulation.

Analytic calculation and numerical simulations reveal a multiline structure in the spectrum of coherent dipole oscillations in the colliding beam system due to coupled synchrobetatron beam-beam modes. The model employed in the analysis involves linearization of the beam-beam kick and takes into account the fact that the length of the colliding bunches is finite. In the present paper, we discuss the behavior of the synchrobetatron beam-beam modes, obtained both analytically and numerically, and compare it with the experimental results for the VEPP-2M collider. A particular case of the betatron tune close to the half-integer resonance is considered on the basis of the presented models.

Six-dimensional beam-beam kick including coupled motion

The six-dimensional beam-beam interaction as developed in 1992 by Hirata, Moshammer, and Ruggiero has been extended to include linear coupled motion and an arbitrary crossing plane. The technique of symplectic mapping in the six-dimensional phase space, called synchrobeam mapping, is applied to investigate the beam-beam kick within a solenoid. A linear beam-beam model including coupling is discussed in detail, also in the framework of a six-dimensional symplectic dispersion formalism.

Noise instability in nonlinear beam-beam interaction

Diffusion instability of a beam induced by random fluctuations in the size of an opposite colliding beam has been studied. It is shown, that the considered beam-beam configuration is always unstable at any value of beam-beam tune shift, if two conditions are valid: (i) beam-beam kick is a nonlinear function of coordinate and (ii) beam-beam kick is subject to noise. Meanwhile, the value of beam emittance is conserved even in the noise regime if the beam-beam kick is a linear function of the coordinate. Simple formula has been derived, which demonstrates quadratic dependence of diffusion coefficient in emittance expansion on beam-beam parameter and noise amplitude of the opposing beam size in case of nonlinear beam-beam interaction.

Vertical synchrobetatron resonances due to beam-beam interaction with horizontal crossing

Due to a nonlinearity of the beam-beam kick, the crossing-angle collisions of bunches in the horizontal plane can cause the coupling between the synchrotron and vertical betatron oscillations of particles. These resonances can be of the same strength as the coupling beam-beam resonances between vertical and horizontal betatron oscillations. A common influence of the crossing in the horizontal plane and of the phase-averaging effect on the vertical synchrobetatron resonances is briefly discussed.