Recent developments in e-beam excited laser systems have led to a requirement for very fast rise and fall time, short pulse, low impedance e-beam generators. Advances in low impedance e-beam generator technology to meet this requirement are discussed. Two advanced design machines have been built — a 2 MeV, 200 kA generator with 10–90% rise and fall times of 10 ns, and a 1 MeV, 100 kA generator with rise and fall times of less than 5 ns. The design of these machines and their measured output characteristics are presented in this paper.

Design of Very Fast Rise and Fall Time, Low Impedance Megavolt Pulse Generators for Laser Excitation

Pulsed electron beam guns have been used extensively in high energy, pulsed laser systems. The two applications include direct electron beam pumping of the gain volume and the stabilization of electrical discharge lasers. Electron beam dimensions range from hundreds to thousands of square centimeters. Voltages range from a few hundred kilovolts to a megavolt or more and current densities can range from less than A/cm2 to a few hundred A/cm2. Pulse lengths range from tens of nanoseconds to greater than a microsecond. The electron gun diode and pulsed power driver have to be designed for the specific application.

Short Pulse Electron Beam Guns for Pulsed Laser Applications

Kinetics of electron beam pumped and electron beam controlled discharge pumped lasers are discussed. Device scaling criteria are given for window foil survival, electron beam pinching, electron beam pulse length, discharge pulselength, and discharge-electron beam interaction.© (1976) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

An Assessment Of The Electron Beam And Discharge Technologies For High Pressure Gas Laser Pumping In Terms Of Kinetics And Electrical Design

This dissertation presents theoretical and experimental
results from a research program that was aimed at finding
practical ways of transferring energy to various loads,
mainly from an inductive energy store fluxed by a primary
store such as a capacitor bank.
The main obj ecti ves of the work were to investigate and
develop high power opening and closing switches, together
with the transfer circuits needed to generate the fast (less
than lOOns duration) high energy, pulses required in many
applications. The study was to include a feasibility study of
the use of the Plasma Erosion Opening Switch (PEOS) in such a
system.
To produce the large fast pulses required, an opening switch
is required that:
* Carry a current of the order of several kA during the
inductor storage time. It should also be able to interrupt
this current and to withstand the high voltage it will
experience as the current is subsequently transferred to a
load.
* Conduct for as long as possible (up to one quarter period
of the current waveform), to maximise the inductively stored
energy which can be transferred to xhe load when the switch
opens.
* Open to an impedance that is large compared to the load
impedance . This ensures that most of the inductively stored
energy is transferred to the load.
Open sufficiently rapidly to produce the required sharp
pulse of voltage.
In pulsed-power applications, energy is usually supplied from
slow and relatively inexpensive power sources such as a
capacitor bank, or an explosive flux-compression generator,
which deliver large quantities of energy in the lO-lOO time
range. Although no single switch is currently available which
has such a long conduction time, together with a nanosecond
opening time, the PEOS is a potential candidate. To overcome
its short conduction time, while still obtaining an opening
time of less than lOOns, the PEOS is used together with an
additional slower stage or stages of switching.
The key to this method is that each successive switching
stage produces a considerably increased voltage. Various
different types of switch were investigated and these are
described in the thesis. Particular consideration is paid to
the performance of the PEOS, as the final conditioning stage.
Exploding foils are also investigated, together with a novel
Automatic Exploding Foil Change-Over Switch, since an
exploding foil opening switch is needed to condition the
output of the capacitor bank before the PEOS. The initial
resistance of the PEOS is very low, and the change-over
switch is required to ensure that the current transfer takes
place when the voltage across the fuse approaches its peak
value. An important part of the investigation was to develop
a mathematical model of the PEOS, as a part of the power
condi tioning circuit, in order to simulate the system for
different load conditions.
The thesis explains the design, operation and performance
characteristics of the various pulsed-power components, such
as capacitor banks, closing and opening switches, pulse
transformer, the vacuum system required for a PEOS, and high
voltage and current measurement techniques.

R. Miller

Papers

Design of Very Fast Rise and Fall Time, Low Impedance Megavolt Pulse Generators for Laser Excitation

Compact electron beam generators for laser and fusion research