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

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

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

CLIC Main Linac Beam-Loading Compensation by Drive Beam Phase Modulation

The CLIC final focus momentum acceptance of ± 0.5 % limits the bunch-to-bunch energy variation in the main beam to less than ± 0.1 %, since the estimated single-bunch contribution is ± 0.4 %. On the other hand, a relatively high beam-loading of the main accelerating structures (about 16 %) is unavoidable in order to optimize the RF-to-beam efficiency. Therefore, a compensation method is needed to reduce the resulting bunch-to-bunch energy spread of the main beam. Up to now, it has been planned to obtain the RF pulse shape needed for compensation by means of a charge ramp in the drive beam pulse. On the other hand, the use of constant-current drive beam pulses would make the design and operation of the drive beam injector considerably simpler. In this paper we present a possible solution adapted to the CLIC two-beam scheme with constant-current pulses, based on phase modulation of the drive beam bunches

Coupler Studies for CLIC Accelerating Structures

Due to high input power required to feed the accelerating structures of the Compact Linear Collider, the RF input and output couplers are critical components. Four different types of double-feed cavity-based couplers as well as a mode launcher have been investigated. Three of them are based on magnetic coupling between the input waveguides and the cavity while the fourth is based on electric coupling. The different designs have been optimized to minimize surface electric field as well as field asymmetry and to reduce the pulse surface heating and the sensitivity to mechanical errors

Progress on the CTF3 Test Beam Line

In CLIC, the rf power to accelerate the main beam is produced by decelerating a drive beam. The Test Beam Line (TBL) of the CLIC Test Facility (CTF3) is designed to study and validate the drive beam stability during deceleration. This is one of the R&D items required from the International Linear Collider Technical Review Committee to demonstrate feasibility of CLIC. It will produce 30 GHz rf power in the GW range and allow to benchmark computer codes used for the CLIC decelerator design. Different options of this experimental beam line are discusse

A New Damped and Tapered Accelerating Structure for CLIC

The main performance limits when designing accelerating structures for the Compact Linear Collider (CLIC) for an average accelerating gradient above 100 MV/m are electrical breakdown and material fatigue caused by pulsed surface heating. In addition, for stable beam operation, the structures should have low short-range transverse wakefields and much-reduced transverse and longitudinal long-range wakefields. Two damped and tapered accelerating structures have been designed. The first has an accelerating gradient of 112 MV/m with the surface electrical field limited to 300 MV/m and the maximum temperature increase limited to 100°C. The second, with an accelerating gradient of 150 MV/m, has a peak surface electrical field of 392 MV/m and a maximum temperature increase of 167°C. Innovations to the cell and damping waveguide geometry and to the tapering of the structures are presented, and possible further improvements are proposed