Publications

This report documents the key safety and operational aspects of a Z-pinch Externally Driven Nuclear Assembly (ZEDNA) reactor concept which is envisioned to be built and operated at the Z-machine facility in Technical Area IV. Operating parameters and reactor neutronic conditions are established that would meet the design requirements of the system. Accident and off-normal conditions are analyzed using a point-kinetics, one-dimensional thermo-mechanical code developed specifically for ZEDNA applications. Downwind dose calculations are presented to determine the potential dose to the collocated worker and public in the event of a hypothetical catastrophic accident. Current and magnetic impulse modeling and the debris shield design are examined for the interface between the Z machine and the ZEDNA. This work was performed as part of the Advanced Fusion Grand Challenge Laboratory Directed Research and Development Program. The conclusion of this work is that the ZEDNA concept is feasible and could be operated at the Z-machine facility without undue risk to collocated workers and the public.

A 70-MA, 7-MV, ∼100-ns driver for a Z-pinch Inertial Fusion Energy (Z-IFE) power plant has been proposed. In this summary we address the transition region between the 70 Linear Transformer Driver (LTD) modules and the center Recyclable Transmission Line (RTL) load section, which convolves from the coaxial vacuum Magnetically Insulated Transmission Lines (MITL) to a parallel tri-plate and then a bi-plate disk feed. An inductive annular chamber terminates one side of the tri-plate in a manner that preserves vacuum and electrical circuit integrity without significant energy losses. The simplicity is offset by the disadvantage of the chamber size, which is proportional to the driver impedance and decreases with the addition of more parallel modules. Inductive isolation chamber sizes are estimated in this paper, based on an optimized LTD equivalent circuit simulation source driving a matched load using transmission line models. We consider the trade-offs between acceptable energy loss and the size of the inductive isolation chamber; accepting a 6% energy loss would only require a 60-nH chamber.

Abstract not provided.

Abstract not provided.

Designing and developing the 1.7 to 2.1-MJ Power Conditioning System (PCS), that will power the flashlamps of the main and power amplifiers for the National Ignition Facility (NIF) lasers, is one of several responsibilities assumed by Sandia National Labs (SNL) in support of the NIF Project. Maxwell Physics International has been a partner in this process. The NIF is currently being constructed at Lawrence Livermore National Labs (LLNL). The test facility that has evolved over the last three years to satisfy the project requirements is called FANTM, for the First Article NIF Test Module. It was built at SNL and operated for about 17,000 shots to demonstrate component performance expectations over the lifetime of NIF. A few modules similar to the one shown in Fig. 1 will be used initially in the amplifier test phase of the project. The final full NIF system will require at least 192 of them in four capacitor bays. This paper briefly summarizes the final design of the FANTM facility and compares its performance with the predictions of circuit simulations for both normal operation and fault-mode response. Applying both the measured and modeled power pulse waveforms as input to a physics-based, semi-empirical amplifier gain code indicates that the 20-capacitor PCS can satisfy the NIF requirement for an average gain coefficient of 5.00 %/cm and can exceed 5.20 %/cm with 24 capacitors.

The laser glass for the National Ignition Facility (NIF) Main Amplifier system is pumped by a system of 192 pulsed power/flash lamp assemblies. Each of these 192 assemblies consists of a 1.6 MJ (nominal) capacitor bank working with a Pre-Ionization/Lamp Check (PILC) pulser to drive an array of 40 flash lamps. This paper describes the predicted performance of these Power Conditioning System (PCS) modules in concert with flashlamp assemblies in NIF. Each flashlamp assembly consists of 20 parallel sets of lamps in series pairs. The sensitivity of system performance to various design parameters of the PILC pulser and the main capacitor bank is described. Results of circuit models are compared to sub-scale flashlamp tests and to measurements taken in tests of a PCS module driving a flashlamp assembly in the First Article NIF Test Module facility at Sandia National Laboratories. Also included are predictions from a physics-based, semi-empirical amplifier gain code.

Upon achieving ignition and gain, the Laboratory Microfusion Facility (LMF) will be a major tool for Inertial Confinement Fusion (ICF) research and defense applications. Our concept for delivering [approximately]10 MJ with a peak on-target light ion power of [approximately]700 TW involves a multi-modular approach using an extension of the compact inductively isolated cavity and Magnetically Insulated Transmission Line (MITL) Voltage Adder technology that is presently being used in several large accelerators at Sandia/New Mexico. The LMF driver design consists of twelve 8-TW and twelve 38-TW accelerating modules, each with a triaxial MITL/Adder that delivers power to a two stage ion extraction diode. The desired energy, power pulse shape, and deposition uniformity on an ICF target can be achieved by controlling the energy and firing sequence of the A'' and B'' accelerator modules, plus optimizing the beam transport and focusing. The multi-modular configuration reduces risk by not scaling significantly beyond existing machines and offers the flexibility of staged construction. It permits modular driver testing at the full operating level required by the LMF.

The Recirculating Linear Accelerator (RLA) is returning to operation with a new relativistic electron beam (REB) injector and a modified accelerating cavity. Upon completion of our pulsed-power test program, we will capture the injected beam on an Ion Focussed Regime (IFR) guiding channel in either a spiral or a closed racetrack drift tube. The relativistic beam will recirculate for four passes through two accelerating cavities, in phase with the ringing cavity voltage, and increase to 8--12 MeV before being extracted. We designed the METGLAS ribbon-wound core, inductively isolated, four-stage injector to produce beam parameters of 4 MeV. 10--20 kA, and 40--55 ns FWHM. The three-line radial cavity is being modified to improve the 1-MV accelerating pulse shape while an advanced cavity design study is in progress. This is a continuation of the Sandia National Laboratory program to develop compact, high-voltage gradient, linear induction accelerators. The RLA concept is based on guiding an injected REB with an IFR channel. This channel is formed from a plasma created with a low energy electron beam inside a beam line containing about 2 {times} 10{sup {minus}4} Torr of argon. The REB is injected onto the IFR channel and is transported down the beamline through a water dielectric accelerating cavity based on the ET-2 design. If the round-tip path of the beam matches the period of the cavity, the REB can be further accelerated by the ringing waveform on every subsequent pass. We have installed the new REB injector because we need a higher amplitude, longer duration., flat-topped pulse shape with a colder beam than that produced by the previous injector. We made extensive use of computer simulations in the form of network solver and electrostatic field stress analysis codes to aid in the design and modifications for the new RLA. The pulsed-power performance of the RLA injector and cavity and the associated driving hardware are discussed.

The Recirculating Linear Accelerator (RLA) is returning to operation with a new electron beam injector and a modified accelerating cavity. Upon completion of our experimental program the RLA will capture the injected beam on an IFR guiding plasma channel in either a spiral or a closed racetrack drift tube. The relativistic beam will be efficiently recirculated for up to four passes through two or more accelerating cavities, in phase with the ringing cavity voltage waveforms, and thereby increased in energy to 10 MeV before being extracted. The inductively isolated four-stage injector was designed to produce beam parameters of 4 MeV, 10--20 kA, and 40--55 ns FWHM. The three-line radial cavity is being modified to improve the 1-MV accelerating voltage pulse shape while an advanced cavity design study is in progress. The actual versus predicted pulsed-power performance of the RLA injector and cavity and the associated driving hardware will be discussed in this paper.

Concerns about energy spreads due to degradation of 1.1-MV, 34-ns duration accelerating cavity repeating pulse shapes have resulted in improving the 24-switch trigger system for the ET-2 cavity, and identifying critical factors in the cavity design that affect the pulse shape. The authors summarize the improvements (completed and proposed) for the existing ET-2 cavity and the status of the design analysis and modeling of accelerating cavities. A relativistic electron beam (REB) injector for the RLA is being installed which will provide a higher amplitude

In the Recirculating Linear Accelerator, we will inject a 10-kA to 20-kA electron beam, and then focus and guide it with an IFR plasma channel, which is created with a low energy electron beam. The REB will be transported through a closed racetrack or a spiral beam line to be re-accelerated by the ringing waveform of dielectric cavities. By adding more accelerating cavities along the beam line, high energies can be achieved. Experiments are in progress to study IFR beam transport issues. A new injector is needed for beam re- acceleration experiments. We are presently installing this new REB injector which will-provide a higher amplitude ({approximately}4 MV), longer duration ({approximately}40-ns FWHM), more rectangularly shaped({approximately}25-ns full width at 90% peak) waveform and a colder beam than were achievable with the previous 1.5-MV injector. The resultant constant beam energy can be more efficiently matched the guiding IFR plasma channel in the beam line and to the turning section magnetic fields. We are now developing new cavities that produce accelerating voltage pulses with improved waveform flatness, width, and amplitudes that do not suffer unacceptable degradation over the first four ringing periods. This effort requires network solver and electrostatic field stress analysis computer codes, and a scaled test model to compare actual waveforms to those predicted by the simulations. 10 refs., 9 figs.

Concerns about low-{gamma} relativistic electron beams (REB) being initially injected into the RLA and about energy spreads due to degradation of the accelerating cavity repeating pulse shapes have resulted in our designing a new 4-MV, 20-kA injector, improving the 24-switch trigger system for the ET-2 cavity, and identifying critical factors in the cavity design that affect the pulse shape. We summarize the Metglas inductively isolated, stacked cavity injector design and report on the improvements (completed and proposed) for the ET-2 cavity pulsed power. 7 refs., 6 figs.