The APELC MG15-3C-940PF (MG15) is a compact 15-stage Marx generator designed for high-power RF applications. The generator delivers 300 kV into a matched load, or as much as 600 kV into an open circuit. The MG15 is designed to deliver 33 J per pulse and has an impedance of 52 Ohms. Additionally, the MG15 is capable of achieving sub-ns rise times through the use of a modular peaking circuit and can also attain GW peak power levels. Operation of the MG15 without a peaking circuit results in output pulse rise times on the order of 4-5 ns with a field-ready coaxial cable output section. The range of lengths provided are due to the wide range of output configurations that can be specified. With a fast rise time, the MG15 measures 51 inches from input flange to output flange. The laboratory-ready MG15 with input and output cabling (normal configuration) measures 37 inches from flange to flange. A deployable device with permanently attached input and output cables could measure as little as 33 inches flange to flange. A laboratory-ready MG15 is shown in the figure below.
- Maximum open circuit voltage: 600 kV
- Peak voltage into matched load: 300 kV
- Maximum repetition rate: 200 Hz
- Energy per pulse: 33 J
- Pulse risetime: 500 ps – 7 ns
|Number of Generator Stages||15||N/A|
|Maximum Marx Energy per pulse||33.0||J|
|Maximum vessel pressure||150||PSI|
|Marx Peak Charge Voltage||40||kV|
|Peak Erected Voltage||600||kV|
|Capacitance Per Marx Stage||2.8||nF|
|Length||33 – 51||inches|
|Max Burst-Mode Repetition Rate||200||Hz|
- APELC high voltage trigger generator
- Inline, coaxial Current Viewing Resistor (CVR)
- APELC integrated pressurized load module
- 0 – 40 kV dc charge voltage
- 175 psi dry air source
- Suitable high-voltage trigger source
A CAD rendering of the MG15 is shown below. The nominally configured footprint measures 37.3″ in length by 6.5″ flange diameter. The field use cradle has a maximum height of 9″ and footprint of 13″ x 8″. The entire system weighs approximately 45 lbs. but can be made lighter for use in deployment scenarios.
High rep rate use of the MG15 requires the use of a demand charge system. During rep rate operation, charge is withheld from the MG15 as long as possible, until just prior to the desired event time (Marx event). The subsequent figure illustrates demand charge operation of the MG15 high voltage power supply (HVPS) and trigger unit for an 18 shot burst at a repetition rate of 200 Hz with maximum charge voltage (40 kV) applied to the MG15. An 8 kW (9 kW peak) HVPS (Lambda 802L) is capable of charging the MG15 within approximately 3.75 ms, leaving 1.25 ms of null time between Marx events (see waveform in blue). The APELC trigger generator operates on a similar principle; however, null time between shots and withholding charge prior to the Marx event are less important for proper operation of the APELC trigger generator (see waveform in red).
The waveforms shown below are a superposition of 18 unique Marx events that correspond to the charge waveforms from above. The superposition of the measured waveforms demonstrates the MG15s reliability and reproducibility.
The resulting MG15 output waveform specifications are as follows:
|Rise Time (10-90)||Rise Time (20-80)||FWHM|
|4.69 ns +/- 0.15 ns||3.41 ns +/- 0.08 ns||23.46 ns +/- 0.26 ns|
The standard, laboratory ready, output section can be replaced with a modular output peaking section that increases the overall length of the Marx by 14 inches. The resulting output waveform rise time is reduced from approximately 4-5 ns to < 1 ns when driving a cable load. Rise time is a great concern when using any system for direct radiation as the rise time (and fall time) dictates the available frequency content for radiation. The following waveforms were acquired for a range of charge voltages and demonstrate the capability of the peaking circuit. The peaking circuit requires up to 1000 psig of dry air to ensure proper operation. NOTE: The rise time realized at the load is dependent on the load parameters (capacitance, inductance, resistance) and should be conveyed to APELC for proper peaking circuit design.
The rise time for each waveform from above is summarized below:
|Rise Time (10-90)
|Rise Time (20-80)