Pulsed Power Systems:
Diode nanosecond
pulse generator - The generator produces 3
ns wide, 600 V amplitude pulses into 50 ohm load at the maximum
repetition rate of 100 kHz. Pulses shorter than 10 ns are
essential for the studies of biological cell response to high
electric fields while avoiding ordinary electroporation effects
dominant at long pulses. The use of a mass-produced fast recovery
surface-mount rectifier diode in this circuit substantially
simplifies the generator and results in low cost and very
small footprint. Similar diode switched pulse generators have
been described in the literature using mostly custom fabricated
snap-recovery diodes. Here we give an example of an ordinary
low cost diode performing similarly to the custom fabricated
counterpart. The diode switched circuit relaxes the requirement
on the speed of the main closing switch, in our case a low
cost power MOSFET – saturable core transformer combination.
The completed diode pulser
Output pulse of two diodes in series
Bipolar nanosecond
pulse generator - The generator produces 3.5
ns wide, ±350 V amplitude bipolar pulses into 50-ohm load
at the maximum repetition rate of 100 kHz. Short bipolar pulses
are used for the studies of biological cell response to high
electric fields when the net transfer of charge is undesirable.
The bipolar pulse is produced from a unipolar pulse by the
parallel connection of a shorted transmission line. This transmission
line delays and inverts the initial pulse, so the output is
the sum of the initial and the inverted and delayed pulses.
Proper terminations both at the entrance and the exit of the
transmission line system are essential if one is to avoid
spurious pulses. If preserving the exact shape of the pulse
is not necessary, a parallel L-C circuit can replace the shorted
transmission line. This L-C circuit provides near Gaussian
bipolar pulse shapes.
The unipolar diode pulser
Output of the bipolar diode pulser
Fast rise MARX
generator - Design and operation of a compact
floating housekeeping system for pseudospark switches in high-voltage
multi-switch applications is presented. The system provides
isolated power to the pseudospark reservoir heater, the keep-alive
gas discharge and the high-voltage trigger pulse generator.
The floating HV trigger pulse generator receives its external
trigger command signal via an optical fiber. The keep-alive
discharge current, representing the gas pressure in the pseudospark
switch, is monitored via an optical fiber as well. Pseudospark
switch operation in Marx generator applications depends on
the precise adjustability of the trigger to main discharge
delay. This delay, in turn, is a strong function of the gas
pressure inside the switch. A feedback circuit, adjusting
the heater current in response to change in the keep-alive
current, stabilizes the pressure.
The Marx assembly and its control system
Pulsed
Power Devices:
Mini-Pseudospark
Switch – Toward Ultracompact Pseudospark Switches -
Compact pulsed power technologies require small switches
with high hold-off voltages (20 ~ 30 kV) and reasonable discharge
current (several kA) for applications that include plasma
ignition and compact repetitive pulsed power sources. The
pseudospark has intrinsic advantages in geometry and housekeeping
that make it a candidate for compact applications. An initial
design for a compact pseudospark switch with a total effective
switch volume of 25 cm3 had been realized, and the size was
reduced by more than one order of magnitude relative to previously
published versions of the switch. The switch was operated
as a Back-Lighted Thyratron for more than one million shots.
A total charge of 455 C was transferred with no observed deterioration
in switch performance. Optical gating has the potential for
triggering one or more switches, in a Marx configuration,
for example.
Experimental Setup for mini-BLT (compact Back-lighted
Thyratron)
Among the present limitations on the peak voltage
of traditional Si-MOSFET switches are fundamental materials
properties that are related both to intrinsic properties (such
as bandgap), and to defects. Switches fabricated from semiconductors
such as GaAs, SiC and GaN hold promise if hold-off voltages
of several kilovolts and fast rise rates are needed. High
power and short pulse (< 1 ms) applications require both
fast switching speed and great current handling capability.
The question arises whether any single material has all of
these desired properties or whether there are intrinsic limitations.
Simulation of
High Power 4H-SiC VJFETs - we design and simulate
a novel 4H-SiC normally-off VJFET. This structure is designed
and optimized to achieve a high breakdown voltage, low on-state
resistance and fast switching speed. The 2-D simulator ATLAS
from Silvaco International was utilized to do the simulation
of VJFETs based on Possion’s, continuity and drift-diffusion
equations.
Simulation of
Defects Effects - In 4H-SiC, N and Al implantation
are commonly used because these atoms have fairly high solubility
and the lowest ionization energies of all impurities. Al implantation
caused deep level defects are called i-centers. i-centers
along the p-n junction cause the depletion region to shrink
and lower the hold-off voltage.
Novel Extreme Ultraviolet
Radiation Source – Pseudospark in Nano Photonics -
Gas discharge-based extreme ultraviolet (EUV) sources have
potential as compact, robust, and less expensive alternatives,
as compared with synchrotron sources and laser-produced plasmas.
EUV emission within the 11-17 nm wavelength range is produced
by a xenon pseudospark discharge plasma. The plasma was generated
in a cylindrical-hollow-electrode geometry with a 3 mm diameter
central through hole. The EUV emission was observed by a Si/Zr
filter-coated photodiode, and the plasma image was recorded
by a CCD camera.
Cathode Side
Anode Side
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