D.J. Weidman

Time‐resolving electron energy spectrometer

A compact, time‐resolving, electron energy spectrometer, which measures the temporal energy behavior of a pulsed relativistic electron beam, is described. It is shown that typical experimental results obtained with an ∼700‐keV, 100‐ns electron beam are qualitatively in excellent agreement with the diode voltage waveform.

Pulse shaping a high‐current relativistic electron beam in vacuum

A simple method for shaping the output current pulse of a relativistic electron beam in vacuum is presented. This method has been employed to sharpen the rise time of a high‐current relativistic electron beam produced by a 2‐MV, 7‐kA, 20‐ns pulser. The beam has a pulse shape that is approximately triangular both in voltage and current, with a negligible instantaneous energy spread. The desired pulse shape is nominally rectangular in current. The technique utilizes a magnetic lens with a magnitude of approximately 1.5 kG to focus the beam. Passing beam electrons through the magnetic lens causes them to focus at different axial locations downstream from the lens depending upon their energy. The focal point of the beam current peak (corresponding to maximum energy) is then located furthest downstream. An aperture is used near the focus to select a portion of the beam having the desired parameters.

Radius tailoring of an electron beam using a fast rise‐time focusing coil: Experiment and simulation

An experiment demonstrating the production of a ‘‘radius‐tailored beam,’’ which has a larger head and smaller tail for more stable propagation through gas, using a fast rise‐time focusing coil is described. The results and their analyses for the radius‐tailored case, the untailored case, and the ‘‘reverse‐tailored’’ case are presented. A two‐dimensional particle simulation of the experiment was performed for each case using the parameters of the experiment for the inputs and it produces results consistent with the experiment.

Radius tailoring of an intense relativistic electron beam using a fast rise‐time focusing coil

A ‘‘radius‐tailored’’ electron beam, which is tapered with a larger head and a smaller tail, has been generated. This has been accomplished by injecting the electron beam into a fast rise‐time magnetic focusing coil, so that the beam head expands while the beam body and tail are confined by the axial magnetic field. Time‐resolved beam radius measurements indicate that a beam radius tailoring on the order of 3 to 1 has been achieved. This result is also in agreement with computer simulations.

Observation of plasma wakefield effects during high-current relativistic electron beam transport

Modulation of the beam current has been observed during ion focused regime (IFR) transport of a high-power relativistic electron beam immersed in a low-density background plasma. In this experiment, a 1.6-MeV, 1-kA, risetime sharpened electron beam is propagated on a KrF excimer-laser-produced IFR channel in TMA gas which is immersed in a low-density plasma filled transport tube. Experimental measurements demonstrating modulation of this high-current relativistic electron beam near the background plasma frequency are presented. >

Intense electron-beam radius-tailoring experiment

The growth rate of the hose instability may be reduced by tapering the beam radius from head to tail. Generation of such a beam has been achieved by a fast-rising magnetic field with a rise time of 30 ns and a peak field of 1.2 kG. The electron beam has an energy of 1.7 MeV, a current of 1 to 2 kA, and a flattop of 12 ns. The beam radius tailoring is indicated by time- resolved beam-radius measurements, from a scintillator in the beam path viewed by a streak camera.

Plasma wakefield effects on high-current relativistic electron-beam propagation in the ion-focus regime

Modulation of the beam current has been observed during ion focused regime (IFR) transport of a high-power relativistic electron beam propagating through a low-density background plasma In this experiment, a 1.7-MeV, 1-kA, risetime-sharpened electron beam is transported in a KrF excimer laser produced IFR channel in TMA gas. The IFR channel is immersed in a low-density plasma filled transport tube. We present experimental measurements and computer simulations demonstrating modulation of this high-current relativistic electron beam near the low-density background plasma frequency.

Plasma Wakefield Effects On High-current Relativistic Electron Beam Transport In The Ion Focus Regime

Abstract : Modulation of the beam current has been observed during ion focused regime (IFR) transport of a high power relativistic electron beam propagating through a low-density background plasma. Injecting a high current, high energy electron beam into an IFR channel immersed in a background plasma induces plasma oscillations. These background plasma oscillations, induced by the risetime portion of the beam ejecting plasma electrons from the vicinity of the beam into the background plasma, give rise to a modulated axial electric field. This field travels with the beam leading to beam energy and current oscillations. In the experiment, a 1.7-MeV, 1-kA, risetime-sharpened electron beam is propagated on a KrF excimer laser produced IFR channel in TMA gas, which is immersed in a low density plasma filled transport tube. We present experimental measurements and computer simulations demonstrating modulation of this high current relativistic electron beam near the low density background plasma frequency.

Fast risetime magnetic field coil for electron beam propagation studies

A new method for detuning the betatron frequency of an intense relativistic electron beam is investigated. The method employs a fast rising magnetic field to decrease the beam radius from the head to the tail of the beam. The magnetic field risetime is on the order of 30 ns with a peak value of about 2 kG. This method may be useful for detuning intense beam instabilities associated with betatron oscillations.<<ETX>>

Time-resolving electron energy analyzer measurements of intense relativistic beam transport

Summary form only given. A time-resolving electron energy (TREE) analyzer has been used to measure a 2-MeV, 20-ns intense relativistic electron beam. Time-resolved energy measurements have been taken immediately downstream of the diode and after a transport region. This provides direct experimental measurement of the effect of the transport region on beam energy and pulse shape. The TREE analyzer consists of a compact magnetic electron energy analyzer, a fast detector, and a streak camera. The characteristics of the analyzer are discussed