Antonio Millich

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^-

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 resulting 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 linear colliders over ...

Linear Collider Based on CLIC Technology

After almost one year of operation two kinds of problems dominate the longitudinal behaviour of the SPS beam. At high energy longitudinal coupled bunch instabilities occur. They are driven by the RF cavity impedance both on its fundamental and high-order passbands. Present cures include damping the high-order modes of the cavities, Landau damping techniques and feedback systems. At the injection energy a debunching-rebunching procedure is performed in order to change from the 9.5 MHz RF frequency of the injector to the 200 MHz of the SPS. Debunched beam instabilities driven by the cavity and vacuum chamber impedances (up to the GHz region) at present limit the RF capture efficiency.

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

The function of the CTS is to extract 30 GHz power from the drive beam and to make it available for the acceleration of the main beam. The simulation of a six cells section of the CTS using the MAFIA set of codes has provided the designers of the structure with a set of RF parameters at 30 GHz. The frequency domain analysis has allowed the plotting of the dispersion curves for the first few pass bands, whereas the time domain analysis has provided results on the shape and magnitude of the longitudinal and transverse wake fields and of the loss factors.

Longitudinal Phenomena in the CERN SPS

In the two-beam accelerator scheme of CLIC the Transfer Structure serves the purpose of extracting 30 GHz power from the drive beam. The purpose of the 3D simulations of the 30 GHz CTS using the MAFIA set of codes has been to assist the designers in the choice of the final dimensions by appreciating the sensitivity of the RF characteristics to the mechanical parameters. The results of the frequency domain analysis have allowed plotting of the dispersion curves of the waveguides and appreciation the relative importance of higher modes. The time domain investigations have produced results on the shape and magnitude of the beam-induced longitudinal and transverse wake fields and of the loss factors.<<ETX>>

Simulation of the CLIC transfer structure by means of MAFIA

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 wakefield. 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.

CLIC transfer structure (CTS) simulations using "MAFIA"

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 linac.

Beam stability in the drive-beam decelerator of CLIC using structures of high-order symmetry

The transfer structure for generation of microwave power from the bunched drive beam presently consists of a smooth beam tube and a periodically loaded wave guide running in parallel and coupled to it by a slot. The bunches are in synchronous interaction with a forward 2/spl pi3-mode. Both the coupling from the beam to the output wave guide and the wave propagation down the tube have been measured on a scaled model at 8.6 GHz with the wire method, giving the longitudinal beam impedance and wake field. Transverse wake fields can be calculated from the longitudinal ones measured with the wire close to a shorting plate introduced in the centre of the structure. Quantitative estimates are then deduced for the real-scale transfer structure at 30 GHz and compared with results obtained from the three-dimensional MAFIA package, both being in good agreement. While the longitudinal wake fields from leading bunches are in phase with the following bunches, the transverse wake fields have a 90/spl deg/ phase offset. The wake field functions resulting from these studies have been inserted into the tracking program DTRACK and the transverse beam blow-up obtained seems to indicate that the effects of such wake fields remain tolerable.<<ETX>>