F. Zhou

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^-

Thomson scattering of high-power laser and electron beams is a good test of electrodynamics in the high-field region. We demonstrated production of high-intensity X-rays in the head-on collision of a CO2 laser and 60-MeV electron beams at Brookhaven National Laboratory, Accelerator Test Facility. The energy of an X-ray photon was limited at 6.5 keV in the linear (lowest order) Thomson scattering, but the nonlinear (higher order) process produces higher energy X-rays. We measured the angular distribution of the high-energy X-rays and confirmed that it agrees with theoretical predictions.

Linear Collider Based on CLIC Technology

The Accelerator Test Facility at Brookhaven National Laboratory (BNL ATF) offers to its users a unique combination of research tools that include a high-brightness 70-MeV electron beam, a mid-infrared (λ = 10 μm) CO2 laser of terawatt power, and a capillary discharge as a plasma source. These cutting-edge technologies have enabled us to launch a new R&D program at the forefronts of advanced accelerators and radiation sources. The main subjects that we are researching are innovative methods of producing wakes in a linear regime using plasma resonance with the electron microbunch train periodic to the laser’s wavelength and so-called “seeded” laser wakefield acceleration (LWFA) that is driven and probed by a combination of electron and laser beams. We describe the present status of the ATF experimental program, including simulations and preliminary experiments; in addition, we review previous ATF experiments that were the precursors to the present program. They encompass our demonstration of longitudinal-and transverse-field phasing inside the plasma wave, plasma channeling of intense CO2 laser beams, and the generation of e-beam microbunch trains by the inverse FEL technique.

Observation of the nonlinear effect in relativistic thomson scattering of electron and laser beams

We investigate a plasma wakefield acceleration scheme where a train of electron microbunches feeds into a high density plasma. When the microbunch train enters such a plasma that has a corresponding plasma wavelength equal to the microbunch separation distance, a strong wakefield is expected to be resonantly driven to an amplitude that is at least one order of magnitude higher than that using an unbunched beam. PIC simulations have been performed using the beamline parameters of the Brookhaven National Laboratory Accelerator Test Facility operating in the configuration of the STELLA inverse free electron laser (IFEL) experiment. A 65 MeV electron beam is modulated by a 10.6 μm CO2laser beam via an IFEL interaction. This produces a train of ∼ 90 microbunches separated by the laser wavelength. In this paper, we present both a simple theoretical treatment and simulation results that demonstrate promising results for the multibunch technique as a plasma-based accelerator.

Plasma-based advanced accelerators at the Brookhaven Accelerator Test Facility

We design a single bunch transverse beam size monitor which will be tested to measure the 28.5 GeV electron/positron beam at the SLAC FFTB beam line. The beam size monitor uses the CCD images of the interference pattern of the optical diffraction radiation from two slit edges which are placed close to the beam path. In this method, destruction of the accelerated electron/positron beam bunches due to the beam size monitoring is negligible, which is vital to the operation of the Linear Collider project.

A Multibunch Plasma Wakefield Accelerator

The CLIC polarized electron source is based on a DC gun where the photocathode is illuminated by a laser beam. Each micro-bunch has a charge of 6x10 9 e

Design of an optical diffraction radiation beam size monitor at SLAC FFTB

The major difficulty in using laser fields in the vacuum to accelerate the electrons is that its phase velocity of the electric field for accelerated electrons is faster than the speed of light when the electrons travel over long distance larger than 3 times the laser Rayleigh length. Its acceleration length can be defined with simple optics. In order to get the higher energy gain at ATF/BNL, the laser parameters and related electron beam are analytically investigated. The experiment specifics require an extremely small electron beam size. Achieving and measuring such small beams present a real challenge. The vacuum laser acceleration experiment will be conducted at the Brookhaven Accelerator Test Facility (ATF), using its high-power CO/sub 2/ laser and tiny focused electron beam. An energy gain of the order of 0.5 MeV is expected.

The CLIC electron and positron polarized sources

Measurement of X-rays produced in nonlinear Thomson scattering of high power laser and electron beams is a good test of electrodynamics in the high field region. We performed an experiment of head-on collision between sub-terawatt CO2 laser and 60-MeV electron beams at Brookhaven National Laboratory, Accelerator Test Facility. Angular distributions of X-rays produced in Thomson scattering were measured and contribution of the second order nonlinear interaction was observed by comparing the distributions with Monte Carlo simulations based on the semi-classical theory of photon-electron interactions.

Parameter optimizations for vacuum laser acceleration at ATF/BNL

We present a progress report on the BNL’s experiment on Thomson scattering from 60 MeV electrons in a counter‐propagating terawatt CO2 laser beam. The measured x‐ray yield averages to one photon per electron within the laser/e‐beam overlap region. The observed changes in the spectral and polar distributions of the x‐ray beam with the increase of the laser intensity mark the onset of a strong nonlinearity. This indicates that electron’s oscillation in the laser field transforms to the figure‐eight trajectory.

OBSERVATION OF NONLINEAR THOMSON SCATTERING AT BNL-ATF

ODR(Optical Diffraction Radiation) transverse beam size measurement at the SLAC FFTB at 28.5 GeV is a challenge and it requires special target and optics system, which is much difficult than the conventional ODR beam size measurement. We propose to use a curved disphased conductive slit target to recover the sensitivity in the measurement of the single bunch transverse beam size by using ODR photons from a conductive slit. In order to cancel the effect of the beam divergence, the conductive slit target surface must be curved. Also, we can obtain the focused interference pattern of the ODR photons at the detector at the shorter distance from the target than the γ2λ, by using lens optics system.