Brent Edward Blue

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...

Developments in Microcoining Rippled Metal Foils

Abstract Rippled metal foils are currently sought for high-strain-rate material strength studies at laser facilities. Because these metals typically cannot be diamond turned, we employ a microcoining process to imprint the [approximately]5-μm-deep by [approximately]50-μm-long ripples into the metal surface. This work details recent process developments to fabricate these rippled metal targets, specifically for iron and tantalum. The process consists of nitriding a steel die, diamond turning the die, and then pressing the die into a polished metal foil of choice. We show: advantages of deeper-nitrided dies, improved foil thickness uniformity and characterization, variation in coining stress over different materials, pattern quality characterization, bowing reduction, and patterning of multimode ripples.

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.

Dynamics of a 28.5 GeV electron or positron beam in a meter-long plasma

Summary form only given, as follows. A plasma wakefield acceleration (PWFA) experiment is presently being conducted at the Stanford linear Accelerator Center (SLAC). In this experiment 28.5 GeV, 2 ps long electron (e/sup -/) or positron (e/sup +/) bunches with /spl ap/2/spl times/10/sup 10/ particles are sent in a 1.4 m long plasma with a density in the 0-2/spl times/10/sup 14/ cm/sup -3/ range. The plasma is obtained by single-photon ionization of a lithium vapor. The focusing of the bunches is observed by imaging on a CCD camera the optical transition radiation emitted by the bunches when traversing thin titanium foils placed /spl ap/1 m upstream and downstream from the plasma. The time resolved dynamics is studied by imaging onto a streak camera the light emitted by the beam when traversing a thin piece of aerogel located /spl ap/25 m downstream from the plasma, after a dispersive magnet. Quadrupoles located between the plasma and the aerogel image the particle beam at the plasma exit onto the aerogel. At the aerogel location, the beam image in the dispersive (vertical) plane is dominated by the beam energy, whereas in the perpendicular, non-dispersive plane it is dominated by the beam spot size. The incoming bunches have a correlated energy spread, and time integrated images of the beam after dispersion in energy also give an insight into the beam transverse dynamics. The beam density is larger than the plasma density, and the experiment can access the non-linear or blow-out regime of the PWFA. The plasma acts as a thick focusing element. Both e/sup -/ and e/sup +/ bunches are focused by the plasma. The focusing dynamics is observed with single bunches. The bunch particles work on the plasma electron to expel them from (e/sup -/), or attract them into (e/sup +/) the bunch volume, and energy loss of the particles in the bunch core is observed. Some of the energy is transferred back from the plasma electrons to the particles in the back of the bunch, and plasma acceleration is observed with e/sup -/ bunches. The experimental set up as well as experimental results will be presented.

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.