technical issues: approach: construct a system that will allow high frequency, high voltage...
TRANSCRIPT
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
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
Gas flow
Copper tungsten electrode
Kel-F lining
G-10 housing
Gas input
RG220 fitting
Set screw
Switch Design
Spark GapG-10 Housing
Al Connecting Pieces
CuW Electrodes
KEL-F Liner
Al Baffle
Polished CuW Electrodes
Eroded CuW Electrodes• Electrode wear after ~104
shots• Example of minimal erosion• Ablation measurements
indicate negligible material loss
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
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
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
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
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
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
Beam Steering
Far Field Results
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:
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
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
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
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)
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
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).
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.