Abstract
Microwave instability in the low energy ring of KEKB was studied using a broadband impedance model. The model gave excellent descriptions of longitudinal dynamics for both positive and negative momentum compactions. Moreover, it predicted that the threshold of microwave instability was a factor of 2 lower than the machine nominal operating bunch current. The prediction was confirmed by a measurement using the Belle detector. Furthermore, we integrated the longitudinal wakefield into the beam-beam simulation and applied it to study the combined effects in KEKB. As a result, the beam-beam simulation became truly three dimensional with emittance growth in all three dimensions simultaneously as the beam currents increase. In addition, an observed mystery of asymmetry in the horizontal scan could also be explained by our simulations.
Highlights
Collisions with a horizontal crossing angle have become an important feature in the design of modern colliders [1,2,3,4], since the success of KEKB [5] in achieving the record luminosity of 1:7 Â 1034 cmÀ2 sÀ1 in eþeÀ storage rings
The crab crossing improves the specific luminosity at low beam currents, the luminosity so far remains below the record of peak luminosity achieved without the crab cavities
In the second part of this paper, we will introduce several new features in our beam-beam simulation including a different treatment of crossing angle and crab cavity
Summary
Collisions with a horizontal crossing angle have become an important feature in the design of modern colliders [1,2,3,4], since the success of KEKB [5] in achieving the record luminosity of 1:7 Â 1034 cmÀ2 sÀ1 in eþeÀ storage rings. In the second part of this paper, we will introduce several new features in our beam-beam simulation including a different treatment of crossing angle and crab cavity. We will show the results of our simulations and their comparisons to the measurements
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