Advances in Normal Conducting Accelerator Technology from the X-Band Linear Collider Program

Abstract

In the mid-1990's, groups at SLAC and KEK began dedicated development of X-band (11.4 GHz) rf technology for a next generation, TeV-scale linear collider. The choice of a relatively high frequency, four times that of the SLAC 50 GeV Linac, was motivated by the cost benefits of having lower rf energy per pulse (hence fewer rf sources) and reasonable efficiencies at high gradients (hence shorter linacs). To realize such savings, however, requires operation at gradients and peak powers much higher than that hitherto achieved. During the past twelve years, these challenges were met through innovations on several fronts. This paper reviews these achievements, which include developments in the generation and transport of high power rf, and new insights into high gradient limitations.Presented at the 2005 Particle Accelerator Conference, Knoxville, Tennessee, May 16-20, 2005 * Work supported by Department of Energy contract DE-AC02-76SF00515. ADVANCES IN NORMAL CONDUCTING ACCELERATOR TECHNOLOGY FROM THE X-BAND LINEAR COLLIDER PROGRAM*C. Adolphsen Stanford Linear Accelerator Center, Stanford University, Stanford CA 94309 USA AbstractIn the mid-1990's, groups at SLAC and KEK began dedicated development of X-band (11.4 GHz) rf technology for a next generation, TeV-scale linear collider. The choice of a relatively high frequency, four times that of the SLAC 50 GeV Linac, was motivated by the cost benefits of having lower rf energy per pulse (hence fewer rf sources) and reasonable efficiencies at high gradients (hence shorter linacs). To realize such savings, however, requires operation at gradients and peak powers much higher than that hitherto achieved. During the past twelve years, these challenges were met through innovations on several fronts. This paper reviews these achievements, which include developments in the generation and transport of high power rf, and new insights into high gradient limitations.

An SLC-Type e<sup>+</sup/> e<sup>−</sup/>/γγ Facility at a Future Circular Collider

“…The choice of this technology is motivated by the cost benefits of having relatively low rf energy per pulse and high accelerating gradients. A comprehensive review of the status of X-band accelerator technology is given in [28]. Since then, significant advances have been made in pulsed HV and rf power generation, high gradient acceleration and wakefield suppression.…”

Observations About RF Breakdown From the CLIC High-Gradient Testing Program

“…There is clear evidence however, in data from both CLIC and NLC [5,6] which covers structures with a wide range of rf parameters, that a simple constant surface field limit is insufficient to predict the performances of different structures. In general the data shows that larger aperture and higher group velocity structures tolerate lower surface electric fields.…”

“…Breakdowns in accelerating structures will randomly cause loss in acceleration and, potentially more seriously, transverse kicks to the beam. Such transverse kicks have been measured to be about 10 KeV in X-band accelerating structures in the NLCTA [6]. A simple order of magnitude estimate for an acceptable breakdown probability for CLIC, based on the assumptions that all luminosity is lost on a pulse with a breakdown and that not more than 10% of total luminosity should be lost, gives that the breakdown probability for a structure should be 10 -6 since there will be approximately 10 5 accelerating structures in CLIC.…”

Planned waveguide electric field breakdown studies

“…It was hypothesized that the upstream damage was related to the higher group velocity in this region, and after studying the breakdown dependence in experimental structures of different group velocities (so called T-structures), a lower group velocity design was eventually adopted for NLC/GLC to meet the 65 MV/m gradient requirement [2].…”