K. Bane

Dielectric laser accelerators

We describe recent advances in the study of particle acceleration using dielectric near-field structures driven by infrared lasers, which we refer to as Dielectric Laser Accelerators. Implications for high energy physics and other applications are discussed.

Research and development toward a 4.5−1.5 Å linac coherent light source (LCLS) at SLAC

Abstract In recent years significant studies have been initiated on the feasibility of utilizing a portion of the 3 km S-band accelerator at SLAC to drive a short wavelength (4.5−1.5 A) Linac Coherent Light Source (LCLS), a Free-Electron Laser (FEL) operating in the Self-Amplified Spontaneous Emission (SASE) regime. Electron beam requirements for single-pass saturation in a minimal time include: 1) a peak current in the 7 kA range, 2) a relative energy spread of e = λ 4π , where λ[m] is the output wavelength. Requirements on the insertion device include field error levels of 0.02% for keeping the electron bunch centered on and in phase with the amplified photons, and a focusing beta of 8 m/rad for inhibiting the dilution of its transverse density. Although much progress has been made in developing individual components and beam-processing techniques necessary for LCLS operation down to ∼20 A, a substantial amount of research and development is still required in a number of theoretical and experimental areas leading to the construction and operation of a 4.5−1.5 A LCLS. In this paper we report on a research and development program underway and in planning at SLAC for addressing critical questions in these areas. These include the construction and operation of a linac test stand for developing laser-driven photocathode rf guns with normalized emittances approaching 1 mm-mrad; development of advanced beam compression, stability, and emittance control techniques at multi-GeV energies; the construction and operation of a FEL Amplifier Test Experiment (FATE) for theoretical and experimental studies of SASE at IR wavelengths; an undulator development program to investigate superconducting, hybrid/permanent magnet (hybrid/PM), and pulsed-Cu technologies; theoretical and computational studies of high-gain FEL physics and LCLS component designs; development of X-ray optics and instrumentation for extracting, modulating, and delivering photons to experimental users; and the study and development of scientific experiments made possible by the source properties of the LCLS.

On Collinear Wake Field Acceleration

In the Voss-Weiland scheme of wake field acceleration a high current, ring-shaped driving bunch is used to accelerate a low current beam following along on axis. In such a structure, the transformer ratio, i.e. the ratio of the maximum voltage that can be gained by the on-axis beam and the voltage lost by the driving beam, can be large. In contrast, it has been observed that for an arrangement in which driving and driven bunches follow the same path, and where the current distribution of both bunches is gaussian, the transformer ratio is not normally greater than two. This paper explores some of the possibilities and limitations of a collinear acceleration scheme. In addition to its application to wake field acceleration in structures, this study is also of interest for the understanding of the plasma wake field accelerator.

The Next Linear Collider Test Accelerator

During the past several years, there has been tremendous progress on the development of the RF system and accelerating structures for a Next Linear Collider (NLC). Developments include high-power klystrons, RF pulse compression systems and damped/detuned accelerator structures to reduce wakefields. In order to integrate these separate development efforts into an actual X-band accelerator capable of accelerating the electron beams necessary for an NLC, we are building an NLC Test Accelerator (NLCTA). The goal of the NLCTA is to bring together all elements of the entire accelerating system by constructing and reliably operating an engineered model of a high-gradient linac suitable for the NLC. The NLCTA will serve as a testbed as the design of the NLC evolves. In addition to testing the RF acceleration system, the NLCTA is designed to address many questions related to the dynamics of the beam during acceleration. In this paper, we will report on the status of the design, component development, and construction of the NLC Test Accelerator.<<ETX>>

A 2 to 4 nm high power FEL on the SLAC linac

Abstract We report the results of preliminary studies of a 2 to 4 nm SASE FEL, using a photoinjector to produce the electron beam, and the SLAC linac to accelerate it to an energy up to 10 GeV. Longitudinal bunch compression is used to increase ten fold the peak current to 2.5 kA, while reducing the bunch length to the subpicosecond range. The saturated output power is in the multi-gigawatt range, producing about 1014 coherent photons within a bandwidth of about 0.2% rms, in a pulse of several millijoules. At 120 Hz repetition rate the average power is about 1 W. The system is optimized for X-ray microscopy in the water window around 2 to 4 nm, and will permit imaging a biological sample in a single subpicosecond pulse.

The Short-Range Resistive Wall Wakefields

In an accelerator when the bunch length becomes comparable to a characteristic distance s0, one which depends on the radius and the conductivity of the beam tube and in typical structures is on the order of tens of microns, the usual formulas for the resistive wall wakefield do not apply. In this report we derive the short‐range resistive wall wakefields of an ultra‐relativistic point particle in a metallic, cylindrical tube, both for a model in which the wall conductivity is taken to be independent of frequency and for one in which a frequency dependence is included. On this scale the wakefield is found to be dominated by a damped, high frequency resonator component. For the case of constant conductivity the resonant frequency is given by ω=∛c/s0 and the Q‐factor equals ∛/2. We provide a physical model to explain these results. For the case of a frequency dependent conductivity the resonator parameters depend also on the relaxation time of the metal τ. For cτ/s0≳0.5 the frequency ω∼√2ωpc/b, with ωp the p...

Wake fields and wake field acceleration

The concepts of wake fields and wake potential are introduced, some basic properties of their functions examined and briefly a few applications are looked. (AIP)

The SLAC soft X-ray high power FEL

We discuss the design and performance of a 2 to 4 nm FEL operating in Self-Amplified Spontaneous Emission (SASE), using a photoinjector to produce the electron beam, and the SLAC linac to accelerate it to an energy of about 7 GeV. Longitudinal bunch compression is used to increase the peak current to 2.5 kA, while reducing the bunch length to about 40 μm. The FEL field gain length is about 6 m, and the saturation length is about 60 m. The saturated output power is about 10 GW, corresponding to about 1014 photons in a single pulse in a bandwidth of about 0.1%, with a pulse duration of 0.16 ps. Length compression, emittance control, phase stability, FEL design criteria, and parameter tolerances are discussed.

Short-range dipole wakefields in accelerating structures for the NLC

By fitting to numerical results we obtain a simple model for the short-range transverse wakefield of linear accelerator structures over a parameter range useful for the NLC.

WAKEFIELD EFFECTS IN A LINEAR COLLIDER

Wakefields in the SLAC accelerating structure are the subject of this lecture. The effects of the transverse wakefield on the beam will be the main concern of this discussion. Energy variations along beam bunches and Landau damping are discussed. The results of modeling and simulation studies of wakefields and their effects on electron beams are described. (AIP)