Charger–1: A Pulsed Fusion Propulsion Testbed

Summary

This presentation introduces Charger-1, an academic high-power pulsed facility capable of delivering 572 kJ (1 TW at 100 ns) for thermonuclear fusion propulsion research, astrophysics modeling, and radiation physics. It details the pulsed power architecture—including the Marx bank, transfer capacitor, output lines, and vacuum test stand—as well as planned experiments such as Pulsed Fission-Fusion (PuFF), magnetic nozzle physics, coronal mass ejection simulations, and lunar regolith plasma interactions.

Title and Facility Introduction

Charger–1: A Pulsed Fusion Propulsion Testbed Dr. Robert B. Adams, NASA-MSFC Dr. Jason Cassibry, UAHuntsville Ross Cortez, UAHuntsville

What We’re Building • A test facility for high power and thermonuclear fusion propulsion concepts, astrophysics modeling, radiation physics • Located in the UAH Aerophysics Lab at Redstone (Decade Module 2)

Facility Specifications & Z-Pinch Concept

What We’re Building • The highest instantaneous pulsed power facility in academia – 572 kJ (1 TW at 100 ns) • Main equipment donated by DTRA to UAHuntsville • MSFC loaning experiment side equipment, expertise, other equipment

Operation of a Z Pinch • Components: Cathode, Anode, Hypersonic Nozzle, Gas Cylinder, Evacuated Chamber, Current (I)

Operation of a Z Pinch

Operation of a Z Pinch • Current (I) generates azimuthal magnetic flux (B) • Lorentz force drives Ion Motion inward (pinch compression), producing intense X-rays and plasma conditions.

Pulsed Power System Architecture & Marx Bank

How It Works • Successive systems compress and intensify pulse: 1.2 MV @ 1 MA over 100 ns • Pulse Compression Stages: Marx Bank (Oil Insulated) -> Transfer Capacitor (Water Insulated) -> Triggered Output Switches -> Output Line (Water Insulated) -> Opening Switch -> Vacuum Insulator / Inductive Energy Storage -> Bremsstrahlung Diode / Plasma Opening Switch.

Marx Bank • Full power: charged to ±85 kV • Aerovox capacitors, C = 2.2 μF, rated at 100 kV • Once triggered, erected Marx looks more or less like a single capacitor with value 1.1 μF, charged to 1.02 MV • Total stored energy: 572 kJ

Transfer Capacitor & Output Line Switches

Transfer Capacitor • Collection of 32 coaxial lines bussed together on either end • Water filled • Urethane diaphragm that separates oil in Marx tank from water in the TC • Total capacitance C = 0.43 μF • Divertor switches located on both upstream and downstream ends of TC • Designed to remove 320 kJ immediately after forward pulse has passed

Output Line: Switches • 6 switches control output from TC: these switches are fired simultaneously and are in parallel to share the output current equally

• Pressurized with SF6 to ~90 psig (variable depending on test)
• Last triggered stage in pulsed power system
• Peak voltage on switches: 1.2-1.4 MV
• Total current carried: 1.6-1.8 MA • Jitter in the firing of output switches is ~2-3 ns leading to an overall jitter in the arrival time of the current at the front end of 4-5 ns

Output Line & Test Stand

Output Line • Single line has impedance Z ~ 0.5 Ω and is 100 ns long • Total insulator stack height is 35 cm

• This design requires cleaning of the insulator surface after 20-30 full power discharges • At the end of the water OL is an oil section isolated on the upstream side from water by a 1 inch thick polyurethane diaphragm and isolated on the downstream side from the vacuum components by a 16 gradient ring, polyurethane and Dendresist, high voltage insulator

Test Stand • Formerly GDM experiment in PRC – loaned to Aerojet • 48” dia x 5 ft long vacuum chamber

• 15 ports, large sight glass
• Hinged end door • Alcatel Pascal Series roughing pumps • Alcatel turbopumps • Miscellaneous valves, controllers, isolation gate, cables, etc. • Larger roughing pumps acquired

Planned Experiments: PuFF, Magnetic Nozzle, Wire Arrays & CME

Planned Experiments (Slide 13) • Pulsed Fission-Fusion (PuFF) (Subscale Thermonuclear Test)

• Leverages legacy nuclear experience
• Potential for nearer term thermonuclear fusion
• Addresses plasma instability issues • Magnetic Nozzle Experiment (Pulsed Plasma Propulsion)
• Seed field propagation
• Field line freezing
• Scaling laws relating solar and laboratory scales
• Test bed for space weather codes

Planned Experiments (Slide 14) • LiD Wire Array Diode (Subscale Thermonuclear Test)

• Measure x-ray and neutron output
• Estimate fusion energy output
• Code validation
• Optimization of diode design
• Scaling for break even design
• Diode options: Basic (Al, Cu Wire Arrays), Option 1 (Li Wire Array / D-Li Axial Core), Option 2 (Liquid Injection) • Simulation of Coronal Mass Ejection (Space Weather Experiment)
• Measure jet velocity
• Magnetic reconnection physics
• Scaling laws relating solar and laboratory scales
• Test bed for space weather codes
• Stages: 1. Two wire loops in series, 2. Wires ablate and magnetic reconnection begins at center, 3. Plasma jet formed and accelerated

Planned Experiments: Lunar Regolith & Propulsion Landscape

Planned Experiments (Slide 15) • Solar Wind Interaction with Lunar Regolith (Space Weather)

• Tests possible depth of H2O on Moon
• Measures shielding capabilities of regolith
• Improves understanding of plasma impingement physics • Other Experiments
• Ablative Z-pinch
• Radiation shielding

Propulsion Technologies Trade Space • Specific Power α (W/kg) vs. Specific Impulse Isp (sec) map:

• Primary Research Area (TRL 1-3 unproven technology): Inertial Confinement Fusion, Magnetic Inertial Fusion, Antimatter Initiated Fusion, Magnetic Confinement Fusion.
• Secondary Research Area / Other Systems: Nuclear Pulse, Advanced NEP, Nuclear Thermal, Solar Thermal, Chemical, Plasma Sails, Solar Sails, Solar Electric, Nuclear Electric.

Propulsion System Concept & Facility Status

Propulsion Technologies Vehicle Architecture • Vehicle configuration including Stacked Capacitor Modules (2) (10 m long x 3.6 m x 7.2 m, 8 plcs), Z-Pinch Nozzle, Lithium Hydride Radiation Shield, SMES Envelope, Deuterium-Tritium Tank, SP-100 Reactor, Lithium-6 Tanks, Radiators, RCS Thrusters, Lander, Surface Habitat, ISRU, and Transhab.

Status - Facility • Layout detailing MDAS, EDAS, Screen Room, Water (H2O), Oil, and SF6 storage subsystems and current operational / processing status.

Radiation Fluence & Shielding Concepts

Fluence • Decade Quad designed to:

• Produce 20 krad over 2,500 cm2 in a 45 sec pulse
• Generate hot x-rays (30 keV to 2 MeV) using Bremsstrahlung Radiation Source (BRS) • Charger – 1:
• Only stores 572 kJ
• Does not include BRS
• Could create multiple fluences by z-pinch of various fuels • Target:
• 100-140 mrad outside wall per year

Shielding Concepts • Currently two major design concepts:

• Polycarbonate/Acrylic shell with sand filler
• Concrete

Conclusions

Conclusions • Target Date for low power testing is Spring 2013 • Other experimenters are welcome! • Charger – 1 will enable research into multiple propulsion concepts, astrophysics and radiation protection.