R.A. Cooper

High energy density pulsed power capacitors

Pulsed power in mobile systems requires high energy density capacitors as energy storage and power compression devices. Applications range from medical defibrillators to naval artillery, with a wide envelope of operating conditions requiring several technology approaches. The ongoing, multifaceted development effort on high energy density pulsed power capacitors at General Atomics Energy Products has yielded capacitors with significantly higher energy densities (> 5 J/cc) than were available a few years ago. Substantially higher energy densities are also being achieved in capacitors designed for microsecond discharge applications. This paper describes this progress and the state of the art in pulsed power capacitors.

Progress in the reduction of inductance in the standard 100 kV energy storage capacitor

The basic metal case low profile bushing energy storage capacitor design has changed little from the 1.85 /spl mu/F, 60 kV capacitor developed for the LANL SCYLLAC program in the late 1960s. Their enduring use testifies to a robust design. Today energy storage capacitors having a lower equivalent series inductance (ESL) will contribute to increasing the power capability of new or revised pulsed power machines. Lower ESL coupled with an improved terminal configuration for better integration with the system design, will produce faster discharge times and lower driver impedance, making higher power systems more sensible and energy efficient. A lower ESL capacitor that is compatible with existing proven hardware will also make upgrading more cost effective. This paper discusses the establishment of standardized test methods for determining the inductance of different SCYLLAC style energy storage capacitors; for example Maxwell Type C capacitors, which are now manufactured by General Atomics Energy Products, a part of Sorrento Electronics, and units from Aerovox. The effects leading to imprecision in inductance measurements will be noted. The inductance of existing designs will be compared with new hardware compatible prototype configurations with a goal of reducing the inductance up to 50%.

High-Specific-Power Capacitors

Energy density is not the only metric for capacitors. In high pulse repetition rate modulators and other types of power conditioning systems, the reactive power (kVAR) is often the factor driving the physical size of capacitors. The specific power (kVAR/cm3) capability of a capacitor depends on many factors, including frequency, voltage, waveform, duty cycle, ambient temperature, and available cooling. The design of capacitors for high specific power requirements will be described. Designs using high-temperature polymer films as dielectrics and metallized electrodes will be compared to designs using common dielectrics such as polypropylene and both metallized and discrete foil electrodes.

Pulsed power capacitor development and outlook

Pulsed power capacitors are one of the key components the pulsed power systems for applications in mobile platforms including vehicles, ships and airplanes. The advances of capacitor technology have evolved slowly but steadily in the past 25 years. The energy density of large format millisecond discharge capacitors in >50 kJ sizes has been increased from 0.7 J/cc in the early 1990s to >2.4 J/cc in the 2010s with lifetimes over 10,000 shots. The energy density of microsecond discharge capacitors has been increased from 0.7 J/cc with a DC life less than 100 hours in early 1990s to 1.3 J/cc with a DC life of 2000 hours. The self-healing electrode has been the key to achieving higher energy density capacitors. The fault tolerance provided by these electrodes enables reliable operation near intrinsic breakdown strengths. In addition, the availability of higher quality and thinner biaxially oriented polypropylene (BOPP) film starting 2000s has contributed significantly by increasing the intrinsic breakdown strength of the films themselves. Coupled with design improvements, capacitors based on BOPP film have had significant, order-of-magnitude scale improvements in peak energy densities and peak power densities. The unfortunate consequence of this development is that these technologies have reached a point of diminishing returns, leading to significant efforts to develop new films to replace BOPP. We take this opportunity to review the advances and reflect what works so far to think about the future path.

Performance comparison of high energy capacitor technologies part 2: Metalized electrodes

Summary form only given. High energy (>5kJ) capacitors based on a number of different dielectric and electrode technologies are available for use in pulse power systems. Metalized electrode technologies allow higher energy densities to be achieved (up to 3 J/cc) at lower voltages, higher capacitances, and longer discharge timescales. Self-healing is a key feature of metalized film capacitors, allowing polymer film or paper dielectrics either to be used close to their intrinsic breakdown strengths, or providing greatly enhanced reliability and lifetime. Both metallic and insulating plastic cases can be combined with different dielectric/electrode winding types to provide optimized capacitors. While oil-filled capacitors still provide enhanced performance in high voltage applications, dry type capacitors are becoming popular. This work will compare the capabilities of different capacitor technologies for a wide range of operating conditions and provide guidance in selection of high energy capacitors for future applications.

High energy density capacitors for EML applications

Power systems in mobile EML applications require high energy density capacitors as power conversion, energy storage, and power compression devices. Applications include the electromagnetic launch of aircraft, ETC guns and naval launchers for shore bombardment. There is a wide envelope of operating conditions requiring several technology approaches. The ongoing, multifaceted development effort on high energy density pulsed power capacitors at General Atomics Energy Products has yielded capacitors with significantly higher energy densities (>5 J/cc) than were available a few years ago. This paper will describe the performance of this latest generation of capacitors and includes near term projections for products presently under development.

Conceptual designs of 300-TW and 800-TW pulsed-power accelerators

We have developed conceptual designs of two next-generation petawatt-class pulsed-power accelerators. The designs are based on the architecture described in Ref. [1]. The prime power source of both designs is a system of lineartransformer drivers (LTDs) [2,3]. Both designs use six water-insulated radial-transmission-line impedance transformers [1,4,5] to transport the power generated by the LTDs to a six-level vacuum-insulator stack. The stack is connected to six radial magnetically insulated transmission lines (MITLs); the MITLs are joined in parallel at small radius by a triple-post-hole vacuum convolute [6-9]. The convolute delivers the combined power of the six MITLs to a single short MITL that transmits the power to the load. The first accelerator will generate a peak electrical power of 300 TW, and deliver an effective peak current of 50 MA to a z pinch that implodes in 130 ns. This accelerator is 35 m in diameter, and will fit within the existing Z-accelerator building. The second, which is 52 m in diameter, will generate 800 TW, and deliver an effective peak current of 66 MA to a pinch that implodes in 120 ns. Both accelerators will allow high-energy-density physics experiments to be conducted over heretofore inaccessible parameter regimes.

PPPS-2013: Performance comparison of high energy capacitor technologies part 1: Discrete foil electrodes

High energy (>5kJ) capacitors based on a number of different dielectric and electrode technologies are available for use in pulse power systems. Discrete foil electrode capacitors are appropriate for higher voltage, lower capacitance, and faster discharge. Discrete foil capacitors offer the highest peak power and average power capabilities and elements can be connected in series to achieve extremely high voltages, up to a few megavolts. Both metallic and insulating plastic cases can be combined with different dielectric/electrode winding types to provide optimized capacitors. This work will compare the capabilities of different capacitor technologies for a wide range of operating conditions and provide guidance in selection of high energy capacitors for future applications.

Development of low inductance high power plastic case capacitors for the SNS polyphase resonant converter-modulator

Los Alamoss development of the polyphase resonant converter-modulator is the critical high-voltage klystron power conditioning system for the Oak Ridge National Laboratorys Spallation Neutron Source Linear Accelerator. Sixteen systems each can operate up to 11 MW peak, 1.1 MW average, with pulse voltages to 140 kV. This converter-modulator system requires seven unique, low inductance plastic case capacitors with applications ranging from 2 to 120 kV, with voltage and current reversals up to 100%. The high-power switching waveforms require capacitors capable of running at high frequencies with high RMS currents coupled with high reliability. Following a competitive technical performance and cost evaluation of these critical components, Los Alamos determined capacitors from General Atomics Energy Products, Division of Sorrento Electronics met or exceeded all design requirements. This paper covers the different applications, the resulting capacitor designs, their characteristics, and operating history to date.