R.F. Schneider

Wave dispersion theory in a plasma column bounded by a cylindrical waveguide

A unified theory of the electromagnetic wave propagation in a plasma column immersed in an axial magnetic field is developed, including the important influence of finite geometrical effects on wave dispersion properties. The analysis is carried out within the framework of a macroscopic cold fluid model. Coupled eigenvalue equations for the electromagnetic perturbations are obtained for an arbitrary density profile. For a flat‐top density, a closed algebraic dispersion relation of the electromagnetic wave is obtained without any prior approximation. This transcendental dispersion relation is analytically solved in special cases of (a) uniform plasma, (b) infinite magnetic field, (c) zero magnetic field, (d) electrostatic perturbations, and (e) the low‐frequency whistlerlike mode. In order to demonstrate the important influence of finite geometrical effects, the low‐frequency whistlerlike mode is rigorously investigated for axisymmetric waves in a completely filled waveguide. From the analysis, it is shown ...

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.

Fast‐rise, large‐volume, 1.7‐kG magnetic‐field coil

A one‐turn coil of 20 cm diameter and 30 cm length produces a field up to 1.7 kG with a rise time of 30 ns. The rate of rise of field, nearly 6 T/μs, is faster than for any other coil of this size. Powering the coil is a transformer‐charged pulse‐forming line machine operating at up to 28 kA, 280 kV without deleterious arcing. The field is uniform to 5% over the coil length, focusing an electron beam passing along its axis.

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. >

Modulation of a High-Current Relativistic Electron Beam in a Low-Density Background Plasma

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.

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.