muri consortium on compact, portable pulsed power consortium team members: university of southern...
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MURI CONSORTIUM on
COMPACT, PORTABLE PULSED POWER
Consortium Team Members:
University of Southern California, Martin Gundersen, P.I.
University of Missouri-Columbia, William Nunnally
Texas Tech University, James C. Dickens, Andreas A. Neuber, and
Hermann Krompholz
Research Concentration Areas:
- III-V photoconductive and junction switching devices
- Super-emissive cathode switches
- Liquid breakdown for high voltage switching and energy storage
Purpose and Goals of the USC-Texas-Missouri MURI Consortium
To explore new methodologies for III-V and other device switching leading
to true optical hybrid architectures w/ vastly reduced size/weight.
To study super-emissive gas phase switching, and liquid switching
to advance understanding of underlying physics (such as the plasma-cathode interaction that enable super-emissive switches)
To apply the recent advances in optoelectronics and in electronic device design, growth, & performance to key components necessary for future compact, repetitive, portable pulsed power.
The USC-TTU-UM MURI team offers:
- Advanced university test capabilities TTU
- Liquid breakdown & switching experience TTU
- Photoconductive, bulk III-V switching UM, TTU
- Super-emissive cathode switching USC
- III-V junction pulsed power switching UM, USC
- Advanced III-V materials infrastructure USC
Size Comparison
BLT175
High Power Thyratron
42
95B L T1 7 5
Compact Pulse Power Photo-SwitchesUniv. of Missouri (Columbia)
Payoff: Improved lifetime Higher current capability Optimum High voltage, high
current switch Switching capability
1 GW/cm3 of material
Approach: Linear Photo-switch Increase optical absorption depth
by using long wavelength & interband doping
Reduce current density in GaAs & increase max current
Increase holdoff voltage by using multiple, stacked wafers &
conducting layers
Reduce optical closure energy Opportunity:
Picosecond closure, jitter
High Voltage, high current potential
Limited lifetime due to large current density in bulk, contacts
Current density limited by optical depth
Optical Waveguide
Optical ClosureEnergy
Electrode
Electrode
Semiconductor Material
Bulk Cu:Si:GaAs Photo-Switches
Semiconductor Switch SimulationsTexas Tech University
• Research Goals– Understand the behavior of
photoconductive switches (eg- GaAs) at 4
to 30 kV/cm – Computational studies of
breakdown and “lock-on”
• Approach – Collective impact ionization theory – Ensemble Monte Carlo simulations
• Personnel– Prof. Charles W. Myles, Physics– Ken Kambour, PhD Student
• Payoff– High-power solid state
switches
Photoconductive Semiconductor
Switch
GaAs phonon cooling rate vs. carrier temperature.
Energy balance must occur in steady state. Thus, the Joule heating rate (dashed) must equal the phonon cooling rate (solid). However, the carrier temperature corresponds to a density which is too low to sustain a filament. Thus, the quasi-equilibrium assumption is not valid.
Breakdown in Liquid NitrogenTexas Tech University
• New lab apparatus will examine breakdown voltages of 200 kV.
• Focus: phenomenological picture of surface flashover and volume breakdown
• Evaluate LN2 as isolating material in cryogenic compact PP devices.
• Possible use of LN2 as switching medium
Dielectric sample submerged in LN2.
Early flashovers are across center (middle).
After conditioning, discharge occurs at outer edge (bottom).
Photodiode
InstaSpec Camera
Level Monitor
Liquid N2
0.1 V/A
0.2 V/A
0.1 V/A
Voltage
Torr
Over PressureSafety
VacuumPump
OptoElectronic III-V Switches: The “SIT”University of Southern California
• The USC-SIT is a vertical GaAs FET• Advantageous mobility & band gap
make it a candidate for high speed & high hold-off voltage switching
• Can be fabricated in optically gated stacks to simplify triggering
• Will also examine II-VI, and other III-V’s.
Optical trigger for SIT stack
R G
RG
RG
VGSN
VGS2
VGS1
GROUND
VA
R L
LASER/LED
SIT1
SIT2
SITN
Gate Gate
Drain
Source
+ _
V GS
R G-V
GS
Optical stackof SITs withsimple LEDtrigger p
νn
V
V
DS
GS
Photons
R
RG
D
+
+
SI T
ν -GaAs
n -GaAs+
Pitch
xj
Lgs
L ss
Source
Gate
Drain
Source Source
Gate Gate
Source
Lsd
n -GaAs+
p - GaAs+
Silicon NitrideLT-MBE GaAs
AlAs
GaAs SIT (Static Induction Thyristor).Recessed gate configuration.
Integrated OptoElectronic SIT
Super-Emissive Cathode Switches“BLT” & “Pseudospark”
• Lower required power & parts-count make BLT attractive for “portable’ app’s
• Super-emissive cathode– 10,000 A/cm2, over 1cm2
• Stand-off voltage higher than thyratron’s • Very high rate of current rise (>1011 A/sec)• 100-kV forward voltage, 25 to >100kA peak
current, 1250-MW peak output power
Comparison of Thyratrons to BLT
Size Comparison
BLT175
High Power Thyratron
42
95B L T1 7 5
Model P (W) Wgt (gr) I (kA) Dia. (“)
1802 110 20 2 4
HY 5 190 50 5-104.5
HY 7 1660 400 40 7
BLT175 2 2 40�1.75
Standby Reservoir HOLLOW ANODE
HOLLOW CATHODE
FLASHLAMPfor triggering
3 mm electrodeseparation
University of Southern California
USC Pseudospark and BLT Switches:Comparison with Thyratron
Low pressure ( 0.1-0.5 torr)10's of kV, ~2-100 kA
Paschen Curve
X
BLT, thyratron
(pressure x d)
spark gap
High Voltage Hold-off Mechanism
Anode
Grid,grounded
Cathode
Insulator
Cathode
shield
Cathode Reservoir
Hydrogen Thyratron
Anode-grid separation3 mm for
high hold-off
Mo Anode
Mo Grid
Cathode (heatedthermionic)
Back-lighted thyratron,PseudosparkAnode-cathode separation3 mm for high hold-off
insulatorplasma
Mo Anode
Mo Cathode
Transition from “non-explosive” to “explosive” occurs nearly instantaneously, when
ne satisfies -->
Delay changes from seconds to nanoseconds when ne changes by ~ 2 For Tungsten --> -313 cm 105×≈cr
en
ne≥necr=
2ε0eUc
Eccr
β ⎛ ⎝ ⎜ ⎞
⎠
2Delay time of explosion
of cathodic micro-protrusions versus
plasma density (tungsten, 10 kV).
"Model for explosive electron emission in a pseudospark
superdense glow” A. Anders, S. Anders and M. A. Gundersen, Phys. Rev. Lett. 71 (3), 364 (1993). "On electron emission from pseudospark cathodes", A. Anders, S. Anders and M. A. Gundersen, J. Appl. Phys. (1984)
Hollow-CathodeEmission
BLT Switch
HollowCathoderegion
Anode
3 mm
plasma
cathode
Super-EmissionTransition
Transition from BLT Hollow Cathode mode (center) to Super-emissive mode.Hollow cathode plasma results in a virtual anode in close proximity to cathode.
Extremely Fast Transition from Hollow Cathode Emission to Super-Emission
Pseudospark Pulse Generator
• Used for corona assisted ignition• 70 kV peak amplitude• 1 Hz repetition rate• 50 ns pulse width• Long life
Primary pulse
30 kV 60 ns FWHM
Secondary pulse into load
200 A53 kV
Work in progress