Walter Wuensch

A 3 TeV

A possible design of a multi-TeV e+e- linear collider is presented. The design is based on the CLIC (Compact Linear Collider) two-beam technology proposed and developed at CERN. Though the study has shown that this technology is applicable to a linear collider with centre-of-mass energies from 500 GeV or less up to 5 TeV, the present report focuses on the nominal energy of 3 Te V. First, a short overview is given of the physics that could possibly be done with such a collider. Then, the description of the main-beam complex covers the injection system, the 30 GHz main linac, and the beam delivery system. The presentation of the RF power source includes the beam-generation scheme, the drive-beam decelerator, which consists of several 625 m long units running parallel to the main linac, and the power-extraction system. Finally, brief outlines are given of all the CLIC test facilities. They cover in particular the new CLIC test facility CTF3 which will demonstrate the feasibility of the power production technique, albeit on a reduced scale, and a first full-scale single-drive-beam unit, CLICI, to establish the overall feasibility of the scheme.

e^+ e^-

A new local field quantity is presented which gives the high gradient performance limit of accelerating structures due to vacuum rf breakdown. The new field quantity, a modified Poynting vector Sc, is derived from a model of the breakdown trigger in which field emission currents from potential breakdown sites cause local pulsed heating. The field quantity Sc takes into account both active and reactive power flow on the structure surface. This new quantity has been evaluated for many X-band and 30 GHz rf tests, both traveling wave and standing wave, and the value of Sc achieved in the experiments agrees well with analytical estimates.

Linear Collider Based on CLIC Technology

One of the major objectives of CTF3 (CLIC Test Facility) is the production of 30 GHz power for the high-gradient testing of CLIC accelerating structures. To this end a dedicated beam line, power generating structure and power transfer line have been designed, installed and commissioned. 52 MW of 30 GHz power with a pulse length of 74 ns and a repetition rate of 16 Hz were delivered to the high-gradient test area. This will allow operation of test accelerating structures in the first CTF3 run of 2005 up to the nominal CLIC accelerating gradient of 150 MV/m and beyond the nominal pulse length. The system is described and the performances of the CTF3 linac, beam line and the rf components are reviewed.

New local field quantity describing the high gradient limit of accelerating structures

The CLIC study is high power testing accelerating structures in a number of different materials and accelerating structure designs to understand the physics of breakdown, determine the appropriate scaling of performance and in particular to find ways to increase achievable accelerating gradient. The most recent 30 GHz structures which have been tested include damped structures in copper, molybdenum, titanium and aluminum. The results from these new structures are presented in this paper.

30 GHz Power Production in CTF3

We discuss the RF system, the drive linac, drive beam generation, the isochronous ring drive beam scheme, the main linac injector system, machine parameters, beam dynamics and final focus studies and the alignment test facility and beam monitor test results.

30 GHz high-gradient accelerating structure test results

The CLIC study group at CERN has built two X-band HDS (hybrid damped structure) accelerating structures for high-power testing in NLCTA at SLAC. These accelerating structures are novel with respect to their rf- design and their fabrication technique. The eleven-cell constant impedance structures, one made out of copper and one out of molybdenum, are assembled from clamped high-speed milled quadrants. They feature the same heavy higher-order-mode damping as nominal CLIC structures achieved by slotted irises and radial damping waveguides for each cell. The X-band accelerators are exactly scaled versions of structures tested at 30 GHz in the CLIC test facility, CTF3. The results of the X-band tests are presented and compared to those at 30 GHz to determine frequency scaling, and are compared to the extensive copper data from the NLC structure development program to determine material dependence and make a basic validation of the HDS design.

CLIC-a compact and efficient high energy linear collider

One of the most important objectives of the CLIC (Compact Linear Collider) study is to demonstrate the design accelerating gradient, which in the current parameter set targets 150MV/m, under practical operating conditions. A testing program has been put into place to achieve this objective. Recent advances in understanding and quantifying the effects which both limit the ultimate accelerating gradient and fix the practical operating gradient are presented.

High power test of an X-band slotted-iris accelerator structure at NLCTA

Two of the main requirements for CLIC 30 GHz accelerating structures are an average accelerating gradient of 150 MV/m and features which suppress long-range transverse and longitudinal wakefields. The main effects that constrain the design of a copper structure are a surface electric field limit of about 300 MV/m, from evidence produced by the CLIC high-gradient testing program, and a pulsed surface heating temperature rise limit estimated to be of the order of 100 K. The interplay between maximum surface electric field, maximum surface magnetic field, transverse-wakefield suppression and RF-to-beam efficiency has been studied in detail. Several structures with a 110/spl deg/ phase advance and rather constant peak surface electric field distributions have been designed. Different damping-waveguide geometries and waveguide-to-cavity couplings are compared.

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

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.

Progress in the design of a damped and tapered accelerating structure for CLIC

Active alignment algorithms for linear colliders such as the Compact LInear Collider (CLIC), require measurements of beam positions inside accelerating structures in order to control short and long-range transverse wakefields. Highly-damped accelerating structures offer the possibility that damping waveguides can provide position signals so the accelerating structure itself can be used to make these position measurements. A demonstration of beam position measurement using a 3 GHz slotted iris structure with a dipole mode Q/spl ap/16 was made in CTF II (CLIC Test Facility) and results are compared to computations using HFSS and GdfidL.