The machine commissioning of KEKB started in December 1998 and its operation was terminated at the end of June 2010 to upgrade KEKB to SuperKEKB. In this paper, we summarize the history of KEKB and show the achievements made there.

Achievements of KEKB

Beam instabilities cover a wide range of effects in particle accelerators and they have been the subjects of intense research for several decades. As the machines performance was pushed new mechanisms were revealed and nowadays the challenge consists in studying the interplays between all these intricate phenomena, as it is very often not possible to treat the different effects separately. The aim of this paper is to review the main mechanisms, discussing in particular the recent developments of beam instability theories and simulations.

/pdf/beam-instabilities-in-hadron-synchrotrons-38kx5owy2o.pdf

Beam Instabilities in Hadron Synchrotrons

High-intensity synchrotrons such as the proposed Advanced Hadron Facility (AHF) [1] and the Los Alamos Proton Storage Ring (PSR) [2] must have a low beam-coupling impedance for stability. The conflicting requirement of low eddy-current effects in the rapid cycling AHF makes the AHF beam-pipe design a particularly difficult problem. A ceramic pipe deposited with conducting stripes has been proposed for AHF. It can have adequately small eddy currents, but it may have an unexpectedly large coupling impedance. Therefore, a facility for measuring transmission-line impedances has been established and is described in this paper. Measurements of transverse and longitudinal coupling impedances for ceramic/metal and other beam-pipe segments are reported; a ceramic/metal chamber can have adequately small impedance. Results of impedance measurements for other AHF and PSR devices, such as a PSR beam pickup and bumper magnet, are also reported.

Transmission-line impedance measurements for an advanced hadron facility

Beam Dynamics Newsletter

A particle beam is a collection of a large number of charges and represents an electromagnetic potential for other charges, therefore exerting forces on itself (space charge) and other beams (Beam-Beam Interactions, BBIs). The control of the BBIs in particle colliders is fundamental to preserve beam stability and achieve the optimum collider performance. In the case of the Large Hadron Collider (LHC) at CERN, these forces are experienced as localized periodic distortions when the two beams cross each other in the four experimental areas. The forces are most important for high density beams, i.e. high intensity and small beam sizes. Each LHC beam is composed of 2808 bunches, each containing 1011 protons and with a transverse size of 16 µm at the interaction points. These extreme parameters are the key to obtain high "luminosity", i.e. the number of collisions per second needed to study \rare" physics phenomena. The BBI is therefore often the limiting factor for the luminosity of colliders. Within all BB effects, this thesis covers coherent and incoherent beam-beam effects in hadron colliders with particular emphasis on those with a large number of bunches, like the LHC. Complementary numerical tools have been developed to study the effects of BBIs on the particle beams. The use of new parallel algorithms was fundamental to allow the scale of the calculations. The objectives are a better understanding of these effects and if necessary to propose changes to the LHC beam parameters to keep detrimental effects small. We have demonstrated the numerical predictibility of bunch to bunch differences and for the first time compared the results to analytical predictions and experimental data from the Relativistic Heavy Ion Collider (RHIC). Beam-beam transfer function measurements had been reproduced and understood in terms of coherent beam-beam modes. An implementation of the measurement devices had been suggested in order to avoid misinterpreted diagnostics. An emittance growth caused by the BBIs had been observed and characterized with numerical studies and explained with a simple physical picture. A study of the parametrical dependency of this effect defines qualitatively the expected limiting factors to avoid detrimental deterioration of the beams. The variation of the LHC tune spectra for different collision symmetries and in the presence of long range as well as head-on collisions had been presented and explained. This will be of fundamental importance to correctly interprete the observations of single bunch measurements during the operation of the collider and to improve the performances.

A study of beam-beam effects in hadron colliders with a large number of bunches

Experimental and theoretical investigations have shown that the luminosity of the storage ring DORIS is limited by betatron-synchrotron resonances which are produced by the beam-beam interaction. The resonance frequencies are given by Qsa=(p+rQs)/q, where p, q, r are integers and Qs and Qs are the betatron and synchrotron wave numbers, respectively. It is proved that these resonances are caused by the crossing angle. Analytical investigations as well as computer simultionsare in good agreement with measurements made at DORIS. The analytical investigation further shows that also a dispersion at the interaction point will produce these satellite resonances.

Satellite Resonances Due to Beam-Beam Interaction

The penetration of the electro-magnetic field of a bunched beam through a ceramic vacuum chamber with a metallic coating on the inside is investigated. It is shown that the field will only penetrate the chamber if the thickness of the metallic coating is small as compared to the square of the skin depth in the metal, divided by the thickness of the ceramics. If, in addition, the chamber is surrounded by ferrite, as used in beam monitors, the field penetration is further reduced. The field outside of the chamber and the power losses in the metallic layer are calculated. It turns out that these losses can be larger by orders of magnitude than the, losses in a pure metallic vacuum chamber.

/pdf/penetration-of-the-field-of-a-bunched-beam-through-a-ceramic-1xaph99qm8.pdf

Penetration of the Field of a Bunched Beam through a Ceramic Vacuum Chamber with Metallic Coating

The limitation of beam currents in PETRA by the beam-beam effect is investigated. The horizontal and vertical betatron frequency shifts ?Q are measured as a function of bunch currents for different operating conditions. The direct measurement of ?Q by coherent excitation of the eigenmodes of the coupled betatron oscillations of the bunches is described. This method allows to determine independently the horizontal and vertical beam dimensions at the interaction point.

/pdf/observation-of-beam-beam-effects-in-petra-48owrxy9nx.pdf

Observation of Beam-Beam Effects in PETRA

The beam-beam interaction is simulated on a digital computer taking into account all three oscillation modes with quantum fluctuation and damping. It is shown that small asymmetries in phase advance between the interaction points and spurious dispersions at the interaction points are the main causes of an increase of the beam height and a corresponding loss of luminosity. A good agreement between simulations and measurements is found and the operating conditions for PETRA are improved according to the predictions of the simulations.

/pdf/computer-simulations-of-the-beam-beam-interaction-and-lnv4yrrtk0.pdf

A. Piwinski

Papers

Satellite Resonances Due to Beam-Beam Interaction

Penetration of the Field of a Bunched Beam through a Ceramic Vacuum Chamber with Metallic Coating

Observation of Beam-Beam Effects in PETRA

Computer Simulations of the Beam-Beam Interaction and Measurements with PETRA