Professor Adrian Oeftiger

Abstract:

The Faddeeva error function is frequently used when computing electric fields generated by two-dimensional Gaussian charge distributions. Numeric evaluation of the Faddeeva function is particularly challenging since there is no single expansion that converges rapidly over the whole complex domain. Various algorithms exist, even in the recent literature there have been new proposals. The many different implementations in computer codes offer different tradeoffs between speed and accuracy. We present an extensive benchmark of selected algorithms and implementations for accuracy, speed and memory footprint, both for CPU and GPU architectures.

Abstract:

In order to reach the target beam parameters of the LHC injectors upgrade (LIU) project the beam degradation due to losses and emittance growth on the long injection plateau of the SPS needs to be minimized. A detailed study of the dependence of losses, transverse emittance blow-up and transverse beam tail creation as function of the working point is presented here for a high brightness single bunch beam with a vertical space charge tune spread of about 0.2 on the 26 GeV injection plateau. The beam behavior close to important betatron resonances is characterized and a region in the tune diagram with minimal beam degradation is identified. Implications about the performance for LIU beams are discussed.

Abstract:

In view of the LHC Injectors Upgrade (LIU) program of the LHC pre-accelerators LEIR [1], PSB [2], PS [3] and SPS [4] we have started a new working group at CERN to deal with space charge issues of these machines. The goal is to operate with basically twice the number of particles per bunch which will further increase the space charge tune shifts which presently are already large. Besides obvious remedies like increasing the injection energy we are obliged to better understand the space charge force to optimize our machines. To this end it has become clear that we need computer models that faithfully represent the linear but also the non-linear features of our machines. We have started close collaborations with several laboratories around the world to upgrade existing self-consistent space charge Particle-In-Cell (PIC) codes for our CERN needs. In parallel we have created a frozen space charge facility in CERN's MAD-X code. Both types of codes are being used to study long-term stability and to compare it with machine experiments.

Abstract:

One of the luminosity limits in a ring-ring electron-ion collider is the beam-beameffect on the electrons. In the limit of short ion bunches, simulation studies have shownthat this limit can be significantly increased by head-on beam-beam compensation with anelectron lens. However, with an ion bunch length comparable to the beta-function at the IPin conjunction with a large beam-beam parameter, the electrons perform a sizeable fractionof a betatron oscillation period inside the long ion bunches. We present recent simulationresults on the compensation of this beambeam interaction with multiple electron lenses.Copyright © 2012 by IEEE.