High Voltage Pulsed Discharge
Levon Atoyan and Prof. John H.S. Lee
Shockwave Physics Group, Department of Mechanical Engineering, McGill University
Experimental Setup
Background
Charge Pumps: Uses Capacitors to create a higher or lower voltage power
source
Figure 1: Marx generator
(Vout roughly equals nVin)
1.90
3.90
5.90
Gap Switch open
7.90
Current (A)
Current (A)
Gap Switch closed
200
100
0
-1000.00
0.50
1.50
2.00
2.50
3.00
3.50
4.00
-300
-300
-400
Time (μs)
Time (μs)
Figure 7: Typical Response
Figure 6: Limiting Cases
Measuring Instruments:
-Current Transformer: 1:0.025
-Oscilloscope: up to 100 MHz
1.00
-200
-200
• Gap switch open: RLC with 1 capacitor Oscillation at 2 frequencies:
• Gap switch closed : RLC with 2 parallel • Period of 1.12 µs - case of RLC
circuit with 2 parallel capacitors
capacitors
• Period of 240 ns
Figure 3: Experimental Setup
Safety considerations:
-Ensure capacitors are fully discharged (discharge more than once) and
power supply/trigger module turned off before touching the circuit
-Proper grounding
-Corona effect
-Avoid sections with high charge concentrations as much as possible
10 kV - 4 mm
10 kV - 4 mm
500
500
400
400
300
300
200
100
0
-1000.00
0.20
0.40
0.60
0.80
1.20
1.40
100
0
-0.10
-100
0.10
0.30
0.50
0.70
0.90
1.10
1.30
1.50
-300
-300
-400
1.00
200
-200
-200
-400
Time (μs)
Time (μs)
Figure 8: Initial Discharge
Limitations: -Speed of oscilloscope
-For stronger discharge measurements, will need higher ratio for
current transformer and/or oscilloscope with bigger voltage range
Difficulty to reproduce results sensitive to air inside gap switch:
-Ensure air is not ionized due to
previous shot
-Possible presence of dust
particles/variable air humidity
-Clean surface of electrodes regularly
to remove build up of oxidized layer
Conclusion
• Fast discharge possible, but factors that influence initial discharge need to
be better understood
Future Steps:
• Optimize circuit for best possible discharge
• Build conical discharge gap
• Integrate ignition system with shock tube
Figure 2: Circuit
Figure 4: Discharge Setup
15 kV - 4 mm
15 kV - 4 mm
Current (A)
400
200
0
-2000.00
1.00
2.00
3.00
-600
-800
Time (μs)
4.00
5.00
6.00
Current (A)
600
800.00
600.00
400.00
200.00
0.00
-200.000.00
-400.00
-600.00
-800.00
References
15 kV - 4 mm
800
600
1.00
2.00
3.00
4.00
Current (A)
800
-400
Note: Rc will limit current from power supply, stopping the latter from
influencing the rest of the circuit in the time scale of interest
300
0
-0.10
-100
<1
Charge Capacitors
Trigger pulse to break down first gap and close the circuit
Second gap will break down on it’s own when the air’s
dielectric strength between the electrodes is exceeded
400
100
-High Rc & Rd
-Low R
1.
2.
3.
500
200
Circuit
𝑅 2 C2
4𝐿
10 kV - 3 mm
300
Current (A)
-decrease discharge time: discharge capacitors in
series (frequency inversely proportional to C)
Limiting Cases
Circuit Elements
-Gap switches – variable
distance, ambient conditions
-Trigger Module- 30 kV pulse
-30 kV Power Supply
-Capacitors (0.005-0.02μF)
-Air core inductor
-Build a high powered discharge circuit which will be used as the ignition
system of an electrically excited shock wave
-Introduction to high voltage circuits
For electric pinches, want strong discharge:
-increase energy stored: charge capacitors in
parallel (E proportional to C)
Results
Current (A)
Objectives
400
200
0
-200
0.00
1.00
2.00
-400
Time (μs)
-600
Figure 5: Difficulty in reproducing results
Time (μs)
3.00
4.00
[1] A.Young et al., “Power Unit for High Intensity Light Source”, NACA, 1951,
RM E50K27
[2] P.J. Hart, “Effect of Gas Pressure and Cone Angle on the Velocities of
Electrically Excited Shock Waves”, J. Appl. Phys., 1960, 31, p. 436