Beam Loading Compensation in the Main Linac of CLIC

Compensation of multi-bunch beam loading is of great importance in the main linac of the Compact Linear Collider (CLIC). The bunch-to-bunch energy variation has to stay below 1 part in 1000. In CLIC, the RF power is obtained by decelerating a drive beam which is formed by merging a number of short bunch trains. A promising scheme for tackling beam loading in the main linac is based on varying the lengths of the bunch trains in the drive beam. The scheme and its expected performance are presented.Comment: LINAC 2000, paper ID MOA0

Status of 30 GHz High Power RF Pulse Compressor for CTF3

A 70 ns 30 GHz pulse compressor with resonant delay lines has been built and installed in the CTF3 test area to obtain the high peak power of 150 MW necessary to demonstrate the full performance of the new CLIC accelerating structure. This pulse compressor will be commissioned at high power in 2006. Different methods to provide fast RF phase switching are discussed. The current status of the CTF3 RF pulse compressor commissioning and first results are presente

Mode Launcher as an Alternative Approach to the Cavity-Based RF Coupler of Periodic Structures

Recent studies of the accelerating structures at a high gradient showed problems associated with high surface electric fields. In particular it was observed that the input RF coupler of the structure suffered more severely from the surface damage caused by local RF breakdowns than regular accelerating cells. A new design of the RF coupler with reduced surface electric and magnetic fields is presented

Variable High Power RF Splitter and RF Phase Shifter for CLIC

During the routine operation of CLIC a way has to be found to divert RF power from a single accelerating structure that is continuously breaking down. One way to do this is to use a device, which re-directs or splits the RF power between the structure and the RF load. An extensive development programme of such devices is under way at SLAC [1], however, there is no reliable device available to date which can handle a few hundred MW at the CLIC high frequency of 30 GHz. Ultra-fast switching times are not required for CLIC, it is sufficient that the power be diverted. The device however should be extremely reliable. A novel design of a mechanically  driven high-power RF splitter/divider and RF phase shifter that satisfies the CLIC requirements is presented

A study of Failure Modes in the CLIC Decelerator

The CLIC Drive Beam decelerator is responsible for producing the RF power for the main linacs, using Power Extraction and Transfer Structures (PETS). To provide uniform power production, the beam must be transported with very small losses. In this paper failure modes for the operation of the decelerator are investigated, and the impact on beam stability and loss levels is presented. Quadrupole failure, PETS inhibition and PETS RF break down scenarios are being considered

CLIC RF High Power Production Testing Program

The CLIC Power Extraction and Transfer Structure (PETS) is a passive microwave device in which bunches of the drive beam interact with the impedance of the periodically loaded waveguide and generate RF power for the main linac accelerating structure. The demands on the high power production (~ 150 MW) and the needs to transport the 100 A drive beam for about 1 km without losses, makes the PETS design rather unique and the operation very challenging. In the coming year, an intense PETS testing program will be implemented. The target is to demonstrate the full performance of the PETS operation. The testing program overview and test results available to date are presented

Time Domain Simulations of the CLIC PETS (Power Extraction and Transfer Structure) with GdfidL

The Compact Linear Collider (CLIC) PETS is required to produce about 0.5 GW RF power per metre in the 30 GHz CLIC decelerator when driven by the high current beam (~ 270 A). To avoid beam break-up in the decelerator it is necessary to provide strong damping of the transverse deflecting modes. A PETS geometry with a level of damping consistent with stable drive beam operation has been designed, using the frequency domain code HFSS. A verification of the overall performance of this structure has been made recently using the code GdfidL, which permits a very fine mesh analysis of a full-length structure in the time domain. This paper gives the results of this analysis

Design of a 3 GHz Accelerator Structure for the CLIC Test Facility (CTF 3) Drive Beam

For the CLIC two-beam scheme, a high-current, long-pulse drive beam is required for RF power generation. Taking advantage of the 3 GHz klystrons available at the LEP injector once LEP stops, a 180 MeV electron accelerator is being constructed for a nominal beam current of 3.5 A and 1.5 microsecond pulse length. The high current requires highly effective suppression of dipolar wakes. Two concepts are investigated for the accelerating structure design: the "Tapered Damped Structure" developed for the CLIC main beam, and the "Slotted Iris - Constant Aperture" structure. Both use 4 SiC loads per cell for effective higher-order mode damping. A full-size prototype of the TDS structure has been built and tested successfully at full power. A first prototype of the SICA structure is being built.Comment: Contribution to Linac 2000 Conference, TUA16 (Poster

Slotted Iris Structure Studies

Accelerating structures with strong transverse-mode damping are required in both the 30 GHz CLIC main linac and the 3 GHz CTF3 drive-beam accelerator. Damping via slotted irises has been investigated for both structures. The transverse wake, the effect of the slots on the fundamental-mode parameters such as Q, sensitivity to tolerances, and surface-field enhancements have been computed. Terminating loads have been designed and machining studies to obtain rounded slot edges have been made. A 32-cell prototype 3 GHz structure is being fabricated for the drive beam accelerator of CTF3