ARPA-E Pulsed Power Workshop, IMGs, and The California Sun

Fusion, Lasers, and the Beach

It was a great week to escape Colorado and Cleveland with Dr. Mike Poniting and head to the ARPA-E Pulsed Power Workshop at UCSD. The picture above was taken as I sat in traffic along the Pacific Coast Highway across from the Del Mar Race track. It was as close as we got to the beach, but it was fitting to get a great shot of the sunset as we spent the day discussing how to recreate the sun's power.

The University of California San Diego's Center for Energy Research recently hosted a significant Fusion Energy and Pulsed Power workshop, supported by the Department of Energy's Fusion Energy Sciences and ARPA-E. Scheduled for November 19-20, 2024, this event brought together experts and researchers in fusion energy and pulsed power technology. The workshop covered a range of fusion energy and pulsed power topics, including:

• New drivers utilizing pulsed power technology

• Target designs and driver-target coupling

• Impedance-matched Marx generator

• Chamber concepts, including tritium breeding and waste stream management

• Diagnostics and simulations

The speakers included pulsed power and energy leaders from UC San Diego, the University of Rochester, General Atomics, Fuse Energy, CalTech, UC Berkley, Lawrence Livermore National Laboratory, Pacific Northwest National Laboratory, Sandia National Laboratories, ZAP Energy, MIFTI, Xcimer Energy, Altruism, Pacific Fusion, and many others.

What is an Impedance-Matched Marx Generator?

An impedance-matched Marx generator (IMG) is a new approach for pulsed-power accelerators. The fundamental building block of an IMG is called a "brick," which consists of two capacitors connected in series with a single switch. These bricks are then arranged into stages, which can be distributed axially and connected in series. The key feature of an IMG is its ability to drive an impedance-matched coaxial transmission line with a conical center conductor. When the stages are triggered sequentially, they launch a coherent traveling wave along the coaxial line. This process achieves electromagnetic-power amplification through the triggered emission of radiation, making a multistage IMG analogous to a laser in the pulsed-power domain.

ICF Fusion Moves from Big Burst to Pulse Power Drive (IMGs) 

Fuse Energy announced a Cooperative Research and Development Agreement (CRADA) with Sandia National Laboratories (Sandia). This strategic collaboration will accelerate the development of next-generation pulsed power technologies critical for ensuring the safety and reliability of U.S. nuclear and advancing fusion energy, a clean and limitless future energy source. Additionally, they added James Owen, who spent over 28 years at Los Alamos National Laboratory as the chief engineer for nuclear weapons, to the Fuse team to help the company continue to develop Impedance-matched Marx generators (IMGs).

IMGs are considered next-generation pulsed-power drivers because of their long lifetime (> 10,000 shots), repetition rate (> 0.1-Hz), fast rise time (~ 100-ns), and high-energy-delivery efficiency (~ 90%). “TITAN” is a 14-stage IMG that delivers 1-TW to a 2-Ω matched load. The IMG Paper from Fuse Energy describes the design, simulation, and experimental results for six stages of TITAN, including its triggering system, air delivery system, and pulse shaping. To achieve efficiency over 85% and maximize the capability of an IMG, synchronized triggering, reduced pre-fire rate, and pulse shaping ability are crucial. The 6-stage TITAN test, powered by 102 identical bricks and 102 field-distortion-triggered gas switches, could generate ~ 600-kA and ~ 700-kV across a ~ 0.9-Ω matched load when fully charged to ± 100-kV. In these experiments, 6-stage TITAN is tested up to ± 70-kV charge voltage, delivering a peak power of 330-GW to a 1.2-Ω resistive load.

Image of the TITAN pulse power driver, from Fuse Energy Technology.

What Makes IMG Right for ICF Fusion Energy?

The IMG concept represents a significant advancement in pulsed power technology for several reasons:

1. Efficiency: IMGs can achieve a maximum energy efficiency of up to 90%, surpassing traditional Marx generators and linear transformer drivers.

2. Power Output: Depending on the design, IMGs can deliver peak electrical power ranging from tens of gigawatts to a terawatt to matched-impedance loads.

3. Flexibility: IMGs' modular nature allows for scalable designs, with the ability to adjust the number of stages and bricks per stage to meet specific power requirements.

4. Fast Rise Times: IMGs can generate pulses with speedier rise times in nanoseconds, which is crucial for creating efficient non-thermal plasmas.

5. Repetition Rate: Advanced IMG designs can operate at repetition rates exceeding 0.1 Hz, making them suitable for high-frequency applications.

6. Longevity: IMGs have demonstrated the potential for long operational lifetimes, with some designs capable of laser shot rates up to 10,000+ shots.

7. Cost-Effectiveness: For a given electrical power output, IMGs are generally less expensive than comparable linear transformer drivers, as they do not require ferromagnetic cores.

The Pulsed Power ICF Fusion Supply Chain

The development of fusion energy technology, particularly in pulsed power systems, presents significant supply chain challenges that limit technological progress and national security. One critical component in these systems is high-performance capacitor film, which is essential for energy storage and power delivery in pulsed power applications.

Today, China is out investing the US in new fusion and supply chain development. The People’s Republic of China (PRC) State Council has declared that “controlled nuclear fusion is the only direction for future energy.” A list of ‘future industries’ released this January by the Ministry of Science and Technology and six other ministries prominently includes nuclear fusion. And China’s fusion efforts go beyond statements – the PRC is out-investing, out-organizing, and out-building the United States across the fusion ecosystem.

One critical example of China's dominance in producing capacitor films(70+% of world production) and other components for pulsed power systems presents a significant national security risk for the United States and its allies. This dependency leaves fusion energy research and development vulnerable to geopolitical tensions and potential supply disruptions. Moreover, it could compromise the integrity and security of critical energy infrastructure and research facilities.

The strategic importance of developing a domestic supply chain for these components cannot be overstated. As fusion energy research progresses, with projects like the impedance-matched Marx generators (IMGs) showing promise for high-power, efficient pulsed power delivery, the need for a secure and reliable supply of advanced capacitor films becomes increasingly critical.

More Shots on Goal with IMG For ICF Fusion

IMGs utilize a series of capacitors arranged in stages to generate high-voltage, high-current pulses necessary for powering fusion laser processes. At the conference, many talks touched on the need to grow from thousands to billions of shots to achieve commercial-grade solutions for the power grid. One of the critical supply chain components for IMG is high-energy capacitor film, which is required for these parts of the IMG process:

• Charging: Each stage of the IMG contains one or more bricks with capacitors that are charged to a relatively low voltage.

• Sequential Triggering: When activated, the switches in each stage are triggered precisely, causing the capacitors to discharge.

• Voltage Multiplication: As the stages discharge in series, the voltages add up, creating a much higher output voltage than the initial charging voltage of individual capacitors.

• Impedance Matching: The IMG's design ensures that the output impedance matches that of the transmission line and, ultimately, the load (e.g., the fusion laser system), maximizing power transfer efficiency.

• Pulse Shaping: Advanced IMG designs allow pulse shaping by varying parameters, such as gas-switch fill pressures between stages, enabling customization of the output waveform for specific fusion applications.

• Energy Delivery: The resulting high-voltage, high-current pulsed power fusion laser process provides the intense energy required to heat and compress the fusion fuel.

• Repetition: In some designs, IMGs can operate at relatively high repetition rates, allowing for multiple fusion attempts in rapid succession.

NanoPlex HDC Enhances Impedance-Matched Marx Generators

NanoPlex HDC (High-Dielectric Constant) capacitor films represent a significant advancement in capacitor technology that can significantly improve the performance of impedance-matched Marx generators (IMGs) compared to traditional capacitor films. Here's how NanoPlex HDC capacitors can enhance IMG performance:

• Increased Energy Density: NanoPlex HDC-based films offer up to 4x more energy storage capacity than traditional capacitor films. This increased energy density allows IMGs to store more energy in a smaller footprint, potentially increasing each stage's power output without increasing the generator's overall size.

• Reduced Footprint: NanoPlex HDC can create up to 2x smaller capacitors than traditional designs, enabling the construction of more compact IMGs. This size reduction can lead to more efficient designs and potentially lower large-scale pulsed power systems costs.

• Improved Thermal Stability: NanoPlex HDC films offer significantly improved thermal stability compared to traditional capacitor films. This enhanced thermal performance allows IMGs to operate at higher temperatures without degradation, potentially increasing the repetition rate and overall system efficiency.

• Extended Device Lifetime: NanoPlex HDC-based capacitors' improved thermal stability and robustness can extend the operational lifetime for IMGs. This increased longevity can reduce maintenance requirements and improve pulsed power systems' overall reliability in fusion energy research and other high-power applications.

• Higher Breakdown Strength: NanoPlex HDC films boast a breakdown strength of up to 840 kV/mm, significantly higher than traditional capacitor films. This increased breakdown strength allows for higher voltage operation in IMG stages, potentially leading to higher power outputs and improved efficiency.

• Enhanced Power Delivery: NanoPlex HDC-based capacitors' ability to store more energy and deliver it more efficiently can result in stronger power bursts for IMGs. This improved power delivery is crucial for applications such as fusion reactors, where massive bursts of power are required to drive lasers or magnets.

• Improved Efficiency for Laser Fusion Applications: In the context of fusion energy research, NanoPlex HDC-based capacitors can help enhance fusion machines' power generation efficiency ratio. By enabling more efficient energy storage and delivery in IMGs, these advanced capacitors can contribute to lowering the cost per kilojoule of fusion energy production.

Peak’s NanoPlex HDC high-energy capacitors can be integrated into impedance-matched Marx generators so researchers and engineers can create more powerful, efficient, and compact pulsed power systems. These improvements are precious in pursuing practical fusion energy, where the demands on pulsed power technology are extreme. Every efficiency gain can bring us closer to the goal of clean, abundant energy. Peak is the only US-based manufacturer of high-energy capacitor films to help ICF fusion machine developers optimize and secure their supply chains and accelerate IMG outputs.

Closing thought on Pulsed Power and IMG

The sun has set on the ARPA-E Pulsed Power Workshop at UCSD. The impedance-matched Marx generators show a roadmap to scale and create efficiency for ICF fusion. We have more work to do and new engineering challenges to overcome, and we need a secure supply chain to ensure our future fusion energy.