technical issues: approach: construct a system that will allow high frequency, high voltage...
TRANSCRIPT
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Technical Issues:
Approach:
Construct a system that will allow high
frequency, high voltage switching to
monitor the recovery rate and jitter of
different gases and gas mixtures from
atmospheric to high pressures (1000 psi)
Construct a parallel test system for material
lifetime and geometry evaluation
Payoff:
High rep-rate low loss switch for pulsed ring-
down applications.
End Goals:
Allow accurate switching for a pulsed ring
down phased array antenna that has both
good recovery rate and low jitter
Accomplishments:
- Completed project design and construction- Integration and improvement of project
subsystems - Basic diagnostics setup and initial testing- Triggered repetitive operation (100Hz, 65 kV,
400 psi nitrogen)- Performed initial lifetime testing
JITTER AND RECOVERY RATE OF A TRIGGERED SPARK GAP WITH HIGH PRESSURE GAS MIXTURES
James Dickens, [email protected], 806-742-1254
-Use hermetically sealed high pressure spark gap design-Introduce a simple effective gas mixing subsystem -Fast diagnostics and data acquisition techniques-Modular design for both simple system integration and minimal corona and breakdown possibilities-System integrity at high voltages and high pressures
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PROJECT DESIGN IMAGES
Diagnostics
Trigger
High pressure
gases
Charge Line
Switch
Vacuum
Cha
rge
resi
stor6, 300 Ω HV
resistors
Load
Conta
inm
ent
Chamber
HV Charger
Hermetically sealed
>300 psi
RG 220 (10m)50 Ohm, 100 ns pulse, ~1 nF
>50kV, 25mA
Safet
y co
ntain
men
t
Gas
bac
kfill a
cces
sible
SOS pulser100 kV, 10 ns rise-time 1kHz in burst mode
>400V, 1.5 A power supply>10V trigger
dry air, N2, H2, SF6
various gas mixtures
1” Lexan Cover
Gas mix output
Exhaust
Gas Mix ChamberHold >1500 psi
Provide simple
gas mixing
Pressure monitor
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Gas flow
Copper tungsten electrode
Kel-F lining
G-10 housing
Gas input
RG220 fitting
Set screw
Switch Design
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Spark GapG-10 Housing
Al Connecting Pieces
CuW Electrodes
KEL-F Liner
Al Baffle
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Polished CuW Electrodes
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Eroded CuW Electrodes• Electrode wear after ~104
shots• Example of minimal erosion• Ablation measurements
indicate negligible material loss
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PROJECT IMAGES
HV Charge Line
125 KΩ Charging Resistor
Feed-through for seal and corona reduction
50 Ω Load
XHR 600 1.7 DC Power Supply
BNC 565 Pulse/Delay Generator
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Project wave forms
BNC trigger to capture 10th pulse
Rep-rated Self Break(30 kV, 30psi Nitrogen)
Externally triggered 35 kV, 10Hz operation
Signal from Capacitive V-probe
Integral of Capacitive V-probe signal
Triggered 35kV, 10Hz pulses
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Lifetime Test Setup
• Main and peaking gaps pressurized to ~500psig• Charging voltage = 90kVDC• Trigger pulse is created by peaking gap self-break• Voltage probes on the load side of peaking and main
gap record pulse
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FY07-FY08 SCHEDULE
Improve system connections for enhanced power transfer and corona reduction
Test with higher voltage and pressure to improve rise-time and jitter
Compare rise-time and jitter of different gasses
Introduce gas mixtures and record effects on jitter and rise-time
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Technical Issues: • Initial condition integration into model.
• Accurately accounting for material properties and effects.
• Proper modeling of a closing switch and the effects of jitter.
Approach: Construct an accurate model of a single element pulsed ring-down antenna using the Comsol Multi-physics software package allowing exotic antenna structures to be evaluated before they are physically constructed.
Payoff: Far field energy deposition for neutralization of Improvised Explosive Devices (IEDs) at long range distances.
End Goals: Be able to accurately model and simulate various multi-element antenna structures and the effects upon the performance of a pulsed ring-down phased array.
Accomplishments:• Achieved accurate results of multiple
antenna structures in a 2-D and 3-D regime using transient analysis.
• Constructed a two element array to demonstrate beam steer and the effect of high switch jitter.
• Achieved numerical results for energy density and magnitude at various far field points.
Pulsed Ring-downMulti-Element Antenna
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2-D and 3-D ModelingM
onoc
onic
al A
nten
na 2
-DD
ual D
ipol
e A
rray
3-D
Ele
ctric
Fie
ld 2
-DE
lect
ric F
ield
3-D
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Beam Steering
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Far Field Results
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PRDS arrayExample: radiated electric field for four dipole sources (spaced ½ wavelength apart), with no switch jitter
0
1
2
3
4
0
30
60
90
120
150
1800
1
2
3
4
Simulated single source radiated electric field waveform:
Peak electric field vs. direction, measured relative to that received from a single source:
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PRDS arrayExample: radiated electric field for four dipole sources (spaced ½ wavelength apart), with uniformly distributed switch jitter from 0 to ½ period (1 single shot)
Simulated single source radiated electric field waveform:
Peak electric field vs. direction, measured relative to that received from a single source:
0
1
2
3
4
0
30
60
90
120
150
1800
1
2
3
4
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PRDS array – Monte Carlo simulation
• Difficult to solve analytically for output variable statistical distributions given switch jitter distributions
• Use Monte Carlo method: simulate many firings of an array to build up output statistics
• Inputs: array parameters, simulated or experimentally measured switch jitter distributions
• Status: basic simulation is functional
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PRDS array – advanced concept
• Sources mounted on multiple vehicles
• Firing controlled using GPS timing, coordinated to place “hot spot” on desired location
• High rep-rate sources could be controlled to rapidly scan an area
• Modeling to include GPS timing and position errors in addition to individual switch jitter
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FY07-FY08 SCHEDULE
• Complete the Comsol model that accounts for material properties, initial charging conditions, and closing switch characteristics.
• Compare model to experimental results and adjust accordingly to match.
• Design and model various antenna structures along with the performance results when in an array.
• Examine the affect of jitter on a compact array (2 ft- 5ft antenna distance) and a large mobile array (2 m – 15 m antenna distance)
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Technical Issues: • Scaling laws and physics of ultra-fast
switching are unknown
Approach:• Empirical analysis of fast switching gas
• Pulses: <150 ps rise, <300 ps FWHM
• V(t), I(t) with 50 ps sampling rate
• X-ray analysis through fast PMT
• Streak-camera luminosity analysis
• FEM analysis of geometric gap transition
• Distributed Monte-Carlo electron motion /
amplification simulations
Payoff: Scaling laws and design criteria for ultra-
fast switching.
End Goals: Improve transmission line switching
for antenna coupling.
Accomplishments: • Empirical results
– Gap currents determined through lumped parameter modeling
– Formative delay times quantified– Runaway electron analysis– Ultra-fast luminosity imaging
• Monte-Carlo Analysis– Determination of electron multiplication rates– Direct calculation of space charge formation– Results support empirical analysis
Ultra-Fast Gas Switching
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PROJECT IMAGES1) Experimental Setup 2) Essential Experimental Results
Formative delay times as a function of pressure for different voltage amplitudes from 40-150 kV.
Streak-Camera results show breakdown structure as a function of time. The images show a region of high ionization near the cathode. The slope in the luminosity shows the transit time for the gap.
• Background gases are Argon and Dry Air with pressures from high vacuum to atmosphere.
• Rexolite lens between coaxial to biconical geometric transition limits wave distortion.
FEM simulation of open gap for line characterization (time not to scale).
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PROJECT IMAGES3) Monte Carlo Simulation 4) Simulation Results
Cathode Anode
• Electron amplification rates for varying pressures and field amplitudes can be combined with models to predict delay times.
• Space charges in the vicinity of the cathode lead to local fields on the order of the applied field.
• Ionization mapping shows a high ionization region near the cathode similar to the empirical results. Past this region electrons tend to accelerate to runaway velocities limiting further ionization.
• Simulations run on 32 node Beowulf cluster.
• Capable of > 5 Gflop/s
• Efficient internode communication using the standard message passing interface (MPI)
• Simulation based off null-collision method for determining collision type.