Parameters of the CLIC Transfer Structure for the Multi-Drive Beam Generation Scheme

Three versions of the CLIC Transfer Structure (CTS) have been studied by means of simulations using the MAFIA set of codes. Of these the high impedance version has been built as a prototype and tested in the CTF (CLIC Test Facility). The other two versions were designed with the aim of suiting the requirements of the two Drive Beam Generation schemes presently being pursued for the CLIC scheme. Here we report the simulation results for th CTS to be used in the multi-drive beam generation scheme

Loss factor Dependence on Group Velocity in Disk-Loaded Travelling-Wave Structures

The loss factor, a quantity linked to the energy lost by a point-like charge when traversing an accelerating (or decelerating) structure, can be computed using programs which solve Maxwell's equations in time domain and provide the correct result within the limitations inherent to the numerical simulation process. An alternative method, commonly used, consists in the derivation of the loss factor from the parameter R/Q, which is computed using codes operating in frequency-domain. Recent calculations of the loss factors for disk-loaded structures performed with the two methods have produced diverging results. The discrepancy of the results is a function of the group velocity and can be eliminated by introducing a correction term in the formula linking the loss factor to the R/Q obtained from frequency-domain calculations

PETS Output Power and Drive Beam Deceleration for Finite Q-Values and Tune Errors

PETS performance degradations caused by finite Q-values and small tune errors are estimated. A simple explanation of the recently discovered group velocity enhancement of the loss factor is given

The 30 GHz transfer structure for the CLIC study

In the so-called "Two-Beam Acceleration Scheme" the energy of a drive beam is converted to rf power by means of a "Transfer Structure", which plays the role of power source. In the Transfer Structure the bunched drive beam is decelerated by the electromagnetic field which it induces and builds up by the coherent interaction of successive bunches with the chosen longitudinal mode. The CLIC Transfer Structure is original in that it operates at 30 GHz and uses teeth-like corrugations to slow down the hybrid TM mode to make it synchronous with the drive beam. The beam energy is transformed into rf power, which travels along the structure and is collected by the output couplers. The 30 GHz rf power is then transported by means of two waveguides to two main linac disk-loaded accelerating structures. This report describes the CLIC Transfer Structure design, 3-D computer simulations, model construction and measure-ments as well as the prototype construction and testing with the low energy beam in the CLIC Test Facility. The result of this development is a compact, fully passive, relatively simple and low cost device, which offers a readily scalable solution to the problem of rf power extraction from high frequency bunched beams

Beam Stability in the Drive-Beam Decelerator of CLIC Using Structures of High-Order Symmetry

The RF power necessary to accelerate the main beam of the Compact Linear Collider (CLIC) is produced by decelerating a high-current drive beam in Power Extraction and Transfer Structures (PETS). The reference structure is not cylindrically symmetric but has longitudinal waveguides carved into the inner surface. This gives rise to a transverse component of the main longitudinal mode which can not be damped, in contrast to the transverse dipole wake- field. The field is non-linear and couples the motion of the particles in the two planes. Limits of the stability of the decelerated beam are investigated for different structures

A Multi-Drive Beam Scheme for Two-Beam Acceleration in a TeV Linear Collider

The Compact Linear Collider (CLIC) study of an e+/e- linear collider in the TeV energy range is based on Two-Beam Acceleration (TBA) in which the overall RF power needed to accelerate the beam is extracted from high intensity relativistic electron beams, the so-called drive beams. Due to the high beam power, acceleration and transport of the drive beams in an efficient and reliable way is specially challenging. An overview of a potentially effective scheme is presented. It is based on the generation of trains of short bunches, accelerated in low frequency c.w. superconducting cavities, stored in an isochronous ring and combined at high energy by funneling before injection by sectors into the drive linac. The various systems of the complex are discussed as well as the beam dynamics all along the process. An original method has been specially developed to stabilize such an intense beam during deceleration and RF power production in the drive lina

Design of a chopper line for the CERN SPL

The SPL (Superconducting Proton Linac), a 2.2 GeV linac for high-intensity applications under study at CERN, requires a fast chopping at low energy of the H . beam. The most stringent demands on the chopper come from the operation of a Neutrino Factory, which requires 44 MHz bunch frequency in the accumulator ring and in the muon bunch rotation. This imposes a chopper structure with fast rise and fall times, below 2 ns, to remove 3 consecutive 352 MHz bunches out of every 8. An improved design of the standard travelling-wave chopper structure has been analysed and tested on a prototype. Additional effort has gone into the design of a pulse generator or power amplifier capable of providing the required rise and fall times. Since short rise times and high chopper voltages are conflicting requirements, the maximum voltage has been limited to 500 V per plate. A prototype driver has been built and tested. A very compact beam line design is proposed, which is still compatible with the low chopper voltage. The line houses the chopper structure and the dump, provides the separation between chopped and unchopped beam, and matches both from the RFQ and to a DTL. Effects of space charge and of varying beam parameters are analysed. In particular, the influence of the beam energy at the chopper on the line components is discussed in detail. A diagnostic line designed to perform the measurements necessary to validate this set-up is also described

A new method of RF power generation for two-beam linear colliders

In this paper we discuss a new approach to two-beam acceleration. The energy for RF production is initially stored in a long-pulse electron beam which is efficiently accelerated to about 1.2 GeV by a fully loaded, conventional, low frequency (~1 GHz) linac. The beam pulse length is twice the length of the high-gradient linac. Segments of this long pulse beam are compressed using combiner rings to create a sequence of higher peak power drive beams with gaps in between. This train of drive beams is distributed from the end of the linac against the main beam direction down a common transport line so that each drive beam can power a section of the main linac. After a 180-degree turn, each high-current, low-energy drive beam is decelerated in low-impedance decelerator structures, and the resulti ng power is used to accelerate the low-current, high-energy beam in the main linac. The method discussed here seems relatively inexpensive is very flexible and can be used to accelerate beams for lin ear colliders over the entire frequency and energy range