Fast Grid Pulse Modulation Charles Turner Undergraduate Researcher

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.

Transformer Core Properties Pulse Form BH Curve -19700 Volts ~600 Volts -20300 Volts Active Core Reset Rise/Fall Time: ~5ns Frequency Range: 1-10MHz Burst Mode: ~100 repetitions at 10-100Hz 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.

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.

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.

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

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.

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

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

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

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