Performance limiting effects inX-band accelerators

Abstract

Acceleration gradient is a critical parameter for the design of future TeV-scale linear colliders. The major obstacle to higher gradient in room-temperature accelerators is rf breakdown, which is still a very mysterious phenomenon that depends on the geometry and material of the accelerator as well as the input power and operating frequency. Pulsed heating has been associated with breakdown for many years; however, there have been no experiments that clearly separate field and heating effects on the breakdown rate. Recently, such experiments have been performed at SLAC with both standing-wave and travelingwave structures. These experiments have demonstrated that pulsed heating is limiting the gradient. Nevertheless the X-band structures breakdown studies show damage to the iris surfaces in locations of high electric field rather than of high magnetic field after thousands of breakdowns. It is not yet clear how the relative roles of electric field, magnetic field, and heating factor into the damage caused by rf breakdown. Thus, a dual-moded cavity has been designed to better study the electric field, magnetic field, and pulsed heating effects on breakdown damage.

Analysis and Simulation of Beam Ion Instability in ILC Damping Ring with Multi-gas Species

“…The density of ion-cloud linearly increases along the bunch train and exponentially decays during the bunch train gap with a decay time order of the ion oscillation period [7]. Therefore, the above equation can be used to calculate the wake with arbitrary beam filling pattern where the space charge force of ion cloud is negligible.…”

“…First the nonlinear force of ions should be included. The strong nonlinear field causes a low Q of the wake, which is about 16 by analysis [10] and 9 by the simulation [7], respectively. Secondly, the optics effect should be included.…”

“…Multi-bunch train is very effective on reduction of the ion density near the beam, for instance [2]. The effects of the beam filling pattern depend on both beam density and the mass of ion [7], therefore, the ion species in the vacuum. Hence it is essential to accurately model both the beam filling pattern and the vacuum simultaneously.…”

“…The wake field model [7] makes it easy to include both the nonlinear effect of space charge and optics. As we will see in this paper, it also is straightforward with wake field to study the instability with multi-gas species vacuum.…”

“…The analysis of beam ion instability has been done for single bunch train case [2,4,8,9] and multi-bunch-train case [7].…”