1. Fast Grid Pulse Modulation
Charles Turner
Undergraduate Researcher

2. Purpose of Pulse Modulator
Electron Gun Grid
Electron gun operates in same manner as a vacuum tube triode
Pulse modulator will control the duration and amount of electron beam current by applying voltage to the grid
HeatWave gun will be operated near -2KV with 600V square pulses.
Grid
Blow-up of grid.

3. Transformer Core Properties
Pulse
Form
BH Curve
Volts
~600
Volts
Volts
Active
Core
Reset
Rise/Fall Time: ~5ns
Frequency Range: 1-10MHz
Burst Mode: ~100 repetitions at Hz
There are two ways to avoid core saturation. The core can be biased to the negative saturation region with a DC source. Alternatively, each square pulse may be followed by an equal and opposite negative pulse to reset the core.

4. Resetting the Core Input Output + V1 + VOUT - V2 1:1 600V 0V 600V time_
600V 0V +
VOUT _
600V
time
BH curve image. - V2 +
-600V 0V
-600V
1:1
With active reset of the core, two switching circuits are attached to the primary side of the transformer. The core is pulsed with a positive voltage, then an equal and opposite voltage.

5. Inductive Adder Concept
Input
Output + V1 _
600V 0V +
VOUT _
1.2KV
time
BH curve image. + V2 _ 0V
600V 0V
1:1
The purpose of an inductive adder is to sum voltages while maintaining a rapid rise and fall time.

6. Overall Pulse Form 1:1 - V1 + + V2 - + V4 - - V3 + IOUT IRESET
Option 1:
Active Core Reset
- V1 +
+ V2 -
+ V4 -
- V3 +
1:1
Option 2:
Passive Core Reset
BH curve image.
IOUT
IRESET
V12 = V1 – V2
V34 = V3 – V4
VOUT = V12 + V34
Overall pulse combines signal to reset core and inductive adder concept

7. Inductive Adder Circuit-
2VHV +
Clean up schematic
Capacitors will be utilized with a 100-pulse burst to reduce power consumption to levels appropriate for the HeatWave gun.

8. CAD Visual of Inductive Adder
Transformer Primary Case
Secondary Rod
PCB
Replace
Electron Gun Socket
MOSFET Board
CM5005 NiZn Material

9. Initial Results Test: 50V input 1 MHz Pulse 100ns Width 10 Hz Burst
Without Snubber
Notes: The two issues here are the voltage overshoot and oscillations during and after the pulse.
(+)Primary
(-) Primary
Label lines, blow up picture,
Secondary

10. Modified Circuit Results
Test: 50V input
1 MHz Pulse
200ns Width
100 Hz Burst
With Voltage Clamp
Notes: Adding voltage clamp and snubber capacitor provides a smoother output. Additional circuit design modification should further smooth out oscillations.
(+)Primary
(-) Primary
Secondary

11. Conclusion Slide
Inductive Adder concept is well established through testing at LLNL and University of Rochester
This project is unique in that it utilizes the inductive adder concept for a gridded accelerator
Main challenge removing ripples in the pulse waveform
Next step is to develop a DC reset circuit