Normal-conducting rf structure test facilities and results

Abstract

The designs for a next-generation linear collider based on normal-conducting rf structures require operation at gradients much higher than those in existing linacs. For the NLC/GLC 11.4-GHz structures, the design unloaded gradient is 65 MV/m, which is about four times that of the 2.9-GHz SLAC Linac. For the CLIC 30-GHz structures, a substantially higher gradient, 170 MV/m, is required. Both the NLC/GLC and CLIC groups are aggressively pursuing programs to develop structures that operate reliably at these gradients and also have acceptable efficiencies and transverse wakefields. Much progress has been made in the past few years, and this paper reviews the programs, test facilities and results from this research. Conference, Portland, Oregon, May 12-16, 2003 * Work supported by Department of Energy contract DE-AC03-76SF00515. Expanded version of paper presented at the 2003 Particle Accelerator NORMAL-CONDUCTING RF STRUCTURE TEST FACILITIES AND RESULTS *C. Adolphsen Stanford Linear Accelerator Center, Stanford University, Stanford CA 94309 USA AbstractThe designs for a next-generation linear collider based on normal-conducting rf structures require operation at gradients much higher than those in existing linacs. For the NLC/GLC 11.4-GHz structures, the design unloaded gradient is 65 MV/m, which is about four times that of the 2.9-GHz SLAC Linac. For the CLIC 30-GHz structures, a substantially higher gradient, 170 MV/m, is required. Both the NLC/GLC and CLIC groups are aggressively pursuing programs to develop structures that operate reliably at these gradients and also have acceptable efficiencies and transverse wakefields. Much progress has been made in the past few years, and this paper reviews the programs, test facilities and results from this research.

Breakdown Characteristics Study on an 18 Cell X-band Structure

“…For other cells, the pulsed heating is just between the two cells. Based on the experience on the NLC/GLC structure H60VG3, which has a pulsed heating temperature of 43K at 65MV/m with 400ns pulse [5] , it will not damage the surface on the scale of pulsed heating of T18 structure. …”

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

“…One of the key issues for reliable high luminosity operation of a linear collider is the breakdown probability of the individual accelerating structures [18]. Breakdowns in accelerating structures will randomly cause loss in acceleration and, potentially more seriously, transverse kicks to the beam.…”

Progress on high-gradient structures

“…A large amount of work to understand and mitigate the effects of rf breakdown was conducted during the development of the normal-conducting 11.424 GHz Next Linear Collider (NLC)/Global Linear Collider (GLC) [2,3,4], which has been superseded by the 12 GHz CERN-based linear collider CLIC [5]. Advances in understanding the factors that limit the accelerating gradient go beyond linear colliders and are used in such applications as inverse Compton scattering gamma ray sources [6]; compact Free-Electron Lasers (FELs) [7,8]; and compact medical linacs for hadron therapy [9].…”