Theory of Factors Limiting High-gradient Operation of Warm Accelerating Structures
This research is supported by the Office of Higher Energy Physics of the Department of Energy. For successful development of multi-TeV linear colliders it is vitally important to have accelerating structures capable of reliable operation at gradients above 150 MV/m. Difficulties and obstacles in realizing such operation are associated with a number of physical effects. These effects were in focus of numerous studies for a long time, and results of those studies had led to impressive achievements. In spite of this progress, the accelerator physics and technology is still far from being able to provide stable reliable operation at very high gradients in sufficiently long pulses. Therefore both the experimental and theoretical studies of factors limiting such operation are extremely important. Our group is doing various theoretical studies of these limiting effects. Our theoretical work continues along two main directions:
- the theory of the RF breakdown and effects, which may cause its triggering in high gradient accelerating structures;
- the theory of multipactor in dielectric-loaded accelerating structures which are actively studied experimentally at Argonne National Lab (ANL) with participation of NRL and SLAC.
The first direction of proposed studies contains a number of topics. Among them (to mention a few) are such as
- analysis of field and current distribution in micro-protrusions in the presence of both electric and magnetic RF fields;
- corresponding heating of these protrusions and mechanical stresses there;
- ion bombardment and effect of a shower of field emitted electrons returning to the structure surface.
For studying the multipactor in dielectric-loaded accelerating structures we had developed a self-consistent, non-stationary, two-dimensional code. It was shown that results of calculations done with the use of this code agree well with the ANL-NRL experiments. At present, we are trying to generalize this code for the 3D-case by taking into account electron axial motion and compare results of 2D and 3D simulations.