The beam-beam interaction of finite length bunches in hadron colliders (original) (raw)
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Possible upgrade scenarios for the Large Hadron Collider (LHC) comprise the operation with either uniform (hollow) bunches or long super-bunches. We discuss the respective merits of these approaches with regard to beam-beam effects, electron cloud, and luminosity. Next, we compare the usual scheme of alternating collisions in the horizontal and vertical plane at two interaction points with that of inclined hybrid collisions at 45 o and 135 o . We then study the longitudinal dynamics for a barrier bucket rf system, including the effect of synchrotron radiation, and, finally, discuss the intrabeam scattering for both Gaussian and uniform bunches (or super-bunches).
Luminosity optimization near the beam-beam limit by increasing bunch length or crossing angle
Physical Review Special Topics - Accelerators and Beams, 2002
We discuss the choice of bunch length and crossing angle near the beam-beam limit in a storage-ring collider. First, we derive expressions for the tune shifts of either bunched or continuous round beams which are induced by a single collision with arbitrary crossing angle and bunch length and for the associated luminosities. Then, considering two collision points with alternating planes of crossing, we demonstrate that, if the total beam-beam tune shift is held constant, the collider luminosity increases as a function of bunch length and crossing angle. This implies a corresponding increase in the bunch intensity. As an illustration, we present numerical examples for a Large Hadron Collider upgrade and for the Very Large Hadron Collider.
Studies of the beam-beam interaction for the LHC
Proceedings of the 1999 Particle Accelerator Conference (Cat. No.99CH36366)
We have used the beam-beam simulation code CBI to study the beam-beam interaction for the LHC. We find that for nominal LHC parameters, and assuming only one bunch per beam, there are no collective (coherent) beambeam instabilities. We have investigated the effect of sweeping one of the beams around the other (a procedure that could be used as a diagnostic for head-on beam-beam collisions). We find that this does not cause any problems at the nominal current, though at higher currents there can be beam blow-up and collective beam motion.
Current Dependence of Bunch Dimensions in VEPP-2000 Collider
2018
The paper describes bunch dimension measurements in VEPP-2000 collider at energy 350 MeV. The three bunch dimensions (transverse sizes along with bunch length) was measured against bunch current to detect the energy spread growth. Emittance growth due to multiple intrabeam scattering was observed at bunch current below turbulence bunch lengthening threshold. The thresholds of these processes was used to estimate values of longitudinal impedance. Obtained values in a good agreement with predictions.
Of Instabilities in the LHC Due Tomissing Head-On Beam-Beam Interactions
2013
We report the observation of coherent instabilities on individual bunches out of the LHC bunch train. These instabilities occurred spontaneously after several hours of stable beam while in the other cases they were related to the application of a small transverse beam separation during a luminosity optimization. Only few bunches were affected, depending on their collision schemes and following various tests we interpret these instabilities as a sudden loss of Landau damping when the tune spread from the beambeam interaction becomes insufficient.
New aspects of beam-beam phenomena in hadron colliders
Long-range beam-beam interactions in Run II at the Tevatron are the dominant sources of beam loss and lifetime limitations of anti-protons, especially at injection energy. The main focus of the talk will be observations of the long-range effects during Run II and theoretical understanding of these effects. 0-7803-7739-9
Compensation of beam-beam effects in the Tevatron collider with electron beams
1999
The beam-beam interaction in the Tevatron collider sets limits on bunch intensity and luminosity. These limits are caused by a tune spread in each bunch which is mostly due to head-on collisions, but there is also a bunch-to-bunch tune spread due to parasitic collisions in multibunch operation. We propose to compensate these effects with use of a countertraveling electron beam, and present general considerations and physics limitations of this technique
Modelling and measurements of bunch profiles at the LHC
Journal of Physics: Conference Series, 2017
The bunch profiles in the LHC are often observed to be non-Gaussian, both at Flat Bottom (FB) and Flat Top (FT) energies. Especially at FT, an evolution of the tail population in time is observed. In this respect, the Monte-Carlo Software for IBS and Radiation effects (SIRE) is used to track different types of beam distributions. The impact of the distribution shape on the evolution of bunch characteristics is studied. The results are compared with observations from the LHC Run 2 data.
Bunch merging and splitting techniques in the injectors for high energy hadron colliders
1998
One problem in the design of TeV hadron colliders arises from the choice of the radio frequency. To produce economically the short bunches needed during collision, a high frequency (400 MHz or more) is essential. On the other hand, in the injector chain at lower energies, lower frequencies are generally preferred to alleviate space charge and instability problems and, partially also, for historical reasons. The classical solution is to transform the bunch structure by passing via a debunched beam state, during which the whole machine circumference becomes filled with particles and the beam is subjected to induced parasitic fields and is often prone to microwave instabilities. Bunch merging and bunch splitting have therefore been developed as alternative methods that allow the number of bunches to be changed without passing via that state. Bunch merging has been used in the CERN-PS since 1989 for the anti-proton production beam. The reverse process of bunch splitting was first proposed in the frame of the CERN injector complex for LHC, as a means of quasi-adiabatically changing the time structure of the beam, increasing the number of bunches from four at low energy in the PS Booster to 16 at high energy in the PS. When the CERN accelerator complex re-started in March 1998, this technique became a routine operation. New plans are now being considered to replace the debunching-rebunching process that is still needed at 26 GeV/c in the PS to generate the train of 84 bunches required by the SPS and LHC. The experience gained in the application of bunch merging and splitting techniques is reviewed in this paper together with the extensions now envisaged and the analysis of the expected advantages with respect to the more classical process of debunching-rebunching.