Evan Stuart Dodd

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

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...

Test of the electron hose instability in the E157 experiment

The E157 experiment is designed to demonstrate high gradient plasma wake field acceleration over a significant length. It has been suggested that the electron hose instability of the drive beam will degrade the performance of this experiment because the hosing tail electrons will not fully sample the highest acceleration field. In this paper a parasitic experiment designed to test the extent of the hosing instability is described. In particular, we discuss how the initial beam conditions are determined so that the extent to which any transverse perturbations grow due to hosing can be determined.

Status of the plasma wakefield acceleration experiment at the Stanford Linear Accelerator Center

A plasma wakefield acceleration experiment is conducted at the Stanford Linear Accelerator Center. This experiment addresses the issues relevant to a meter-long plasma accelerator module in the context of a high-energy accelerator.

QuickPIC: a parallelized quasi-static PIC code for modeling plasma wakefield acceleration

There has been much recent interest in plasma wakefield acceleration. This is partly due to the possibility of using it as an energy doubler, i.e., an afterburner, stage at the end of an existing linear collider such as SLC. The process in this scheme is highly nonlinear and therefore particle models are required to study it. Furthermore, the key physics involves fully three-dimensional effects. Unfortunately, even on the largest computers it is still not possible to model a full energy doubler stage using existing codes such as OSIRIS. Fortunately however, for these cases the drive beam evolves on a much longer time scale than the plasma frequency. In these cases the beam appears static or frozen for long periods of time. Under these conditions one can make the quasi-static or frozen field approximation. We have recently developed a skeleton version of a parallelized quasi-static PIC code for modeling particle beam drivers. This code combines all the best features from WAKE and the work of D.H. Whittum (1997); and it is fully parallelized. We describe the basic equations and the algorithm. We will also present preliminary results, which include benchmarking it against our fully explicit code OSIRIS.

Observation of spontaneous emitted X-ray betatron radiation in beam-plasma interactions

An experiment is being carried out at the Stanford Linear Accelerator Center (SLAC) to see if an ion channel can wiggle a beam of ultra-relativistic electrons to produce X-ray radiation. The goal is to create an intense source of undulator radiation using a plasma wiggler in the 1-10 keV range and also to determine the suitability of such an electrostatic wiggler to create a coherent beam of X-rays via the ion channel laser mechanisml. Here we give some of the scaling laws for the power and frequency distribution of the spontaneous emission from sending an electron beam through such an ion channel. Some initial experimental observations are also presented.

Plasma wakefield acceleration experiments with 28.5 GeV electron and positron beams

Summary form only given, as follows. Large gradient accelerators are necessary to reach the very high energies required at the collision point of future electron/positron colliders In the plasma wakefield accelerator (PWFA), a short electron or positron bunch drives a large amplitude plasma wave or wake. The transverse component of the wake leads to focusing of the particle bunch, while longitudinal components of the wake lead to energy loss and energy gain by particles. The PWFA is an energy transformer in which the energy is transferred from the particles in the core of the bunch in a single bunch scheme, or from a driver bunch in a two bunch scheme, to the particles in the back of the same bunch, or to a trailing witness bunch In the experiments described here, the 28.5 GeV electron or positron beam of the Stanford Linear Accelerator Center Final Focus Test Beam line is sent in a long lithium plasma. The bunch charge density is density is larger than the plasma density and the plasma wake is driven in the non-linear regime. In the case of an electron bunch, the bunch space charge field expels all the plasma electrons from the beam volume. The pure plasma ion column left behind the bunch head acts as an aberration-free plasma lens on the bunch core.

E179: A 1.4 meter-long plasma wakefield acceleration experiment

Summary form only given. In the E-157 plasma wakefield experiment conducted at SLAC, a 30 GeV, 2 ps (/spl sigma//sub z/=0.6 mm) electron bunch is sent in a 1.4 m long lithium plasma with a density n/sub c/ in the 1-4/spl times/10/sup 14/ cm/sup -3/ range. The electron bunch density is larger than the plasma density, and the bunch completely expels the plasma electrons (blow-out regime), creating a focusing ion channel. When the plasma electrons rush back into the ion channel, they give rise to a large longitudinal accelerating gradient of the order of 1 GeV/m (with n/sub c/=2.1/spl times/10/sup 14/ cm/sup -3/, and 4/spl times/10/sup 10/ e per bunch). The electrons in the tail of the bunch (/spl sigma//sub z//spl ap//spl lambda//sub p/ the plasma wavelength) experience the accelerating gradient and gain energy. The plasma source consists of a heat-pipe oven producing a 1.4 m long lithium neutral column with a density n/sub 0/ in the 2-5/spl times/10/sup 15/ cm/sup -3/ range. The vapor column length is estimated from temperature profile measurements, and the neutral column density length product (n/sub 0/L) is measured using white light absorption, hook method, and uv absorption.