R. Assmann

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^-

New acceleration technology is mandatory for the future elucidation of fundamental particles and their interactions. A promising approach is to exploit the properties of plasmas. Past research has focused on creating large-amplitude plasma waves by injecting an intense laser pulse or an electron bunch into the plasma. However, the maximum energy gain of electrons accelerated in a single plasma stage is limited by the energy of the driver. Proton bunches are the most promising drivers of wakefields to accelerate electrons to the TeV energy scale in a single stage. An experimental program at CERN—the AWAKE experiment—has been launched to study in detail the important physical processes and to demonstrate the power of proton-driven plasma wakefield acceleration. Here we review the physical principles and some experimental considerations for a future proton-driven plasma wakefield accelerator.

Linear Collider Based on CLIC Technology

In the E-157 experiment now being conducted at the Stanford Linear Accelerator Center, a 30 GeV electron beam of 2×1010 electrons in a 0.65-mm-long bunch is propagated through a 1.4-m-long lithium plasma of density up to 2×1014 e−/cm3. The initial beam density is greater than the plasma density, and the head of the bunch expels the plasma electrons leaving behind a uniform ion channel with transverse focusing fields of up to several thousand tesla per meter. The initial transverse beam size with σ=50–100 μm is larger than the matched size of 5 μm resulting in up to three beam envelope oscillations within the plasma. Time integrated optical transition radiation is used to study the transverse beam profile immediately before and after the plasma and to characterize the transverse beam dynamics as a function of plasma density. The head of the bunch deposits energy into plasma wakes, resulting in longitudinal accelerating fields which are witnessed by the tail of the same bunch. A time-resolved Cherenkov imag...

Proton-driven plasma wakefield acceleration: a path to the future of high-energy particle physics

The Advanced Proton Driven Plasma Wakefield Acceleration Experiment (AWAKE) aims at studying plasma wakefield generation and electron acceleration driven by proton bunches. It is a proof-of-principle R&D experiment at CERN and the world׳s first proton driven plasma wakefield acceleration experiment. The AWAKE experiment will be installed in the former CNGS facility and uses the 400 GeV/c proton beam bunches from the SPS. The first experiments will focus on the self-modulation instability of the long (rms ~12 cm) proton bunch in the plasma. These experiments are planned for the end of 2016. Later, in 2017/2018, low energy (~15 MeV) electrons will be externally injected into the sample wakefields and be accelerated beyond 1 GeV. The main goals of the experiment will be summarized. A summary of the AWAKE design and construction status will be presented.

E-157: A 1.4-m-long plasma wake field acceleration experiment using a 30 GeV electron beam from the Stanford Linear Accelerator Center Linac

Abstract The transverse beam dynamics in plasma channels of possible future plasma-based linacs is discussed. We represent the transverse focusing of both a beam-driven and a laser-driven plasma wakefield accelerator by a uniform focusing channel. The transverse beam sizes and a basic offset tolerance are calculated, finding that sub-micron beams must be transported with even smaller offset tolerances. The results emphasize the need to pursue further ideas for plasma structures with high-acceleration gradients but reduced transverse wakefields.

AWAKE, The Advanced Proton Driven Plasma Wakefield Acceleration Experiment at CERN

The beam optics in a linear accelerator may be changed significantly by variations in the energy and energy spread profile along the linac. In particular, diurnal temperature swings in the SLC klystron gallery perturb the phase and amplitude of the accelerating RF fields. If such changes are not correctly characterized, the resulting errors will cause phase advance differences in the beam optics. In addition RF phase errors also affect the amplitude growth of betatron oscillations. We present an automated, simple procedure to monitor the beam optics in the SLC linac routinely and non-invasively. The measured phase advance and oscillation amplitude is shown as a function of time and is compared to the nominal optics.

Transverse beam dynamics in plasma-based linacs

The collimation system of the Compact Linear Collider (CLIC) must fulfil a number of conflicting requirements, namely it should (1) remove beam halo to reduce the detector background, (2) provide a minimum distance between collimators and collision point for muon suppression, (3) ensure collimator survival and machine protection against errand beam pulses, (4) not be excessively long, and (5) not amplify incoming trajectory fluctuations via the collimator wake fields. Two optical systems have been designed — the first linear, the second non‐linear —, which promise to meet all these requirements for the design beam energy of 1.5 TeV. We decribe the various design criteria, a preliminary performance assessment, and outstanding questions.

Beam-based monitoring of the SLC linac optics with a diagnostic pulse

Beam dynamics issues affect many different aspects of the SLC performance. This paper concentrates on the multi-particle beam dynamics in the linac and the associated limitations that are imposed on the overall SLC performance. The beam behavior in the presence of strong wakefields has been studied in order identify ways to optimize the performance and to predict the expected emittances in high performance linacs. Emittance measurements and simulations are presented for the SLAC linac and are compared in detail. As the overall SLC performance depends on the accelerator stability, the tuning stability is discussed. Results are shown and the consequences for the performance of the SLC are discussed.

Collimation for CLIC

Diurnal temperature variations in the linac gallery of the Stanford Linear Collider (SLC) can affect the amplitude and phase of the rf used to accelerate the beam. The SLC employs many techniques for stabilization and compensation of these effects, but residual uncorrected changes still affect the quality of the delivered beam. This paper presents methods developed to monitor and investigate these errors through the beam response. Variations resulting from errors in the rf amplitude or phase can be distinguished by studying six different beam observables: betatron phase advance, oscillation amplitude growth, rms jitter along the linac, measurements of the beam phase with respect to the rf, changes in the required injection phase, and the global energy correction factor. By quantifying the beam response, an uncorrected variation of 14/spl deg/ (S-band) during 28/spl deg/F temperature swings was found in the main rf drive line system between the front and end of the linac.

Beam dynamics in SLC

Pulse-to-pulse variation of the transverse beam orbit, frequently referred to as jitter, has long been a major problem in SLC operation. It impairs the SLC luminosity both by reducing the average beam overlap at the IP and by hampering precision tuning of the final focus. The origin of the fast orbit variation is not fully understood. Measurements during the 1994/95 SLC run showed that it is random from pulse to pulse, increases strongly with current and grows steadily along the SLAC linac, with a typical final rms amplitude of about half the beam size. In this paper, they investigate possible sources of the vertical orbit jitter.