Abstract
Radio frequency breakdown rate is a crucial performance parameter that ensures that the design luminosity is achieved in the CLIC linear collider. The required low breakdown rate for CLIC, of the order of ${10}^{\ensuremath{-}7}\text{ }\text{ }\text{breakdown}\text{ }{\text{pulse}}^{\ensuremath{-}1}\text{ }{\mathrm{m}}^{\ensuremath{-}1}$, has been demonstrated in a number of 12 GHz CLIC prototype structures at gradients in excess of the design $100\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ accelerating gradient, however without the presence of the accelerated beam and associated beam loading. The beam loading induced by the approximately 1 A CLIC main beam significantly modifies the field distribution inside the structures, and the effect on breakdown rate is potentially significant so needs to be determined. A dedicated experiment has been carried out in the CLIC Test Facility CTF3 to measure this effect, and the results are presented.
Highlights
The CLIC [1] TeV-range linear collider aims to collide electrons and positrons accelerated in two opposing linacs using normal-conducting high-gradient accelerating structures
Radio frequency breakdown rate is a crucial performance parameter that ensures that the design luminosity is achieved in the CLIC linear collider
An intensive high-gradient testing program has been carried out, and results demonstrate that such low breakdown rates are achievable in excess of the 3 TeV CLIC design gradient of 100 MV=m [3,4]
Summary
The CLIC [1] TeV-range linear collider aims to collide electrons and positrons accelerated in two opposing linacs using normal-conducting high-gradient accelerating structures. An intensive high-gradient testing program has been carried out, and results demonstrate that such low breakdown rates are achievable in excess of the 3 TeV CLIC design gradient of 100 MV=m [3,4]. These tests have been carried out without beam inside the structure. CLIC is designed for a high rf-to-beam efficiency requiring a high level of beam loading This is accomplished with a high beam current of approximately 1.2 A, unavoidably modifying the longitudinal field profile. Initial measurements with the beam can be found in [11,12], and this work presents a significantly improved set of measurements with better statistics
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