D.W. Bowman

Series fault limiting resistors for Atlas Marx modules

The proposed Atlas pulsed power supply design provides a current pulse to the experiment chamber from a set of 20, 3-Marx-unit-wide modules radially positioned around a rectangular disk transmission-line system (total of 60 Marxes in parallel). The Atlas circuit is designed to be a near-critically-damped network with a total erected capacitance of 200 /spl mu/F at 600 kV. The justification for the necessary circuit resistance in this approach is based on reliability, fault tolerance and operational maintenance. Also the use of high energy-density capacitors that have lower tolerance to voltage reversal is a primary reason for the damping provided by significant series resistance. To obtain the damping there are two system resistors in the Atlas design. One resistor is a shunt element designed to damp the resonance caused by the relatively high-Q disk transmission-line capacitance and the Marx bank inductance. The second, more significant resistor is a series, fault-current limiting element that also performs the necessary damping for voltage reversal at the bank capacitors. The series resistor is the subject of this paper.

Atlas-a facility for high energy density physics research at Los Alamos National Laboratory

Atlas is a facility designed to perform high energy-density experiments in support of weapon-physics and basic-research programs at Los Alamos. The capacitor bank design consists of a 36-MJ array of 600-kV Marx modules. The system is designed to deliver a peak current of 20-25 MA with a 2-3 /spl mu/s rise time. The capacitor bank is resistively damped to limit fault currents and capacitor voltage reversal. Both oil- and air-insulated Marx module designs are being evaluated. An experimental program for testing both prototype components and the air-insulated concept is currently underway. The capacitor bank design contains 300 closing switches. The primary candidate is a modified version of a Maxwell railgap switch originally designed for the DNA-ACE machines. An alternative candidate is a low-inductance surface-discharge switch. Because of the large number of switches in the system, individual switch prefire rates are required to be less than 10/sup -4/ to protect the high-value loads and targets. Experiments are underway to determine if switch-prefire probability can be reduced by increased capacitor charging rates. A pulse-charging system is described which is capable of charging the 36-MJ capacitor bank to full voltage in 40 milliseconds. This system would use the LANL 1430-MVA generator and a 50-MJ set of intermediate energy-storage inductors. Charging the capacitor bank with a large rectifier connected directly to the generator is another option, and would produce charging times in the 1-6 s range. Conventional rectifiers and grid power would be used for charging times >6 seconds.

Design of the Atlas 240 kV Marx modules

A prototype 240 kV, oil-insulated Marx module has been designed and constructed at the Los Alamos National Laboratory (LANL). The prototype will be used for testing and certifying the design of the Marx module and certain components, including the closing switches, series resistor, and the capacitors themselves. The prototype will also be used to evaluate proposed mechanical systems designs. Information gained from the construction and testing of the 4-capacitor prototype will be folded into the design of the 16-capacitor maintenance unit. The prototype module consists of four 60 kV capacitors, two closing switches, one shunt resistor, and one series resistor. Cables are used to deliver the current to a dummy load scaled to match Atlas system parameters. The Marx unit is contained in a structure made from G-1O, suspended from a steel frame that also serves to support components of the trigger, charging, and control system. Appropriate safety and charging systems are an integral part of the prototype design.

The Atlas pulsed power facility for high energy density physics experiments

The Atlas facility, now under construction at Los Alamos National Laboratory (LANL), will provide a unique capability for performing high-energy-density experiments in support of weapon-physics and basic-research programs. Here, the authors describe how the primary element of Atlas is a 23-MJ capacitor bank, comprised of 96 separate Marx generators housed in 12 separate oil-filled tanks, surrounding a central target chamber. Each tank will house two, independently-removable maintenance units, with each maintenance unit consisting of four Marx modules. Each Marx module has four capacitors that can each be charged to a maximum of 60 kilovolts. When railgap switches are triggered, the Marx modules erect to a maximum of 240 kV. The parallel discharge of these 96 Marx modules will deliver a 30-MA current pulse with a 4-5-ys risetime to a cylindrical, imploding liner via 24 vertical, tri-plate, oil-insulated transmission lines. An experimental program for testing and certifying all Marx and transmission line components has been completed. A complete maintenance module and its associated transmission line are now under construction and testing.

Atlas chamber, power flow channel, and diagnostic interface design

The Atlas pulsed-power machine, being designed at Los Alamos, will deliver a pulse of /spl sim/45 MA, in 4-5 /spl mu/sec, with energies of up to 6 MJ (from a bank of 36 MJ maximum) to a load assembly, located in vacuum. Design considerations for the vacuum vessel, power flow channel from the vessel inward, are presented. In contrast to Sandias PBFA II-Z, where 20 MA currents and 2-2.5 MJ of energy are delivered to (/spl sim/15 mg) loads in /spl sim/100 nsec, the Atlas structures will have to be designed for longer timescales and higher energies to drive heavy liners (/spl sim/70 g). Design issues for the chamber include materials stresses, formation of (and protection from) debris and molten jets, impulse loading, and survivability and ease of replacement of internal structures. For the power flow channel designs, issues are minimizing inductance, preventing movement of conductors during and after firing, damage mitigation, reducing the cost of materials and installation, and electrical insulation. A key issue for damage mitigation is the radius within which total destruction of material objects occurs. Choices of vessel size, insulator materials, cost and ease of manufacturing, and mechanical stability issues are presently in the conceptual design phase. Typical access requirements for diagnostics (including radial and axial X-ray backlighting, flux loops, spectroscopy, interferometry, bolometry, etc.) are provided for in the design.

An overview of the Atlas pulsed-power systems

Atlas is a facility being designed at Los Alamos National Laboratory (LANL) to perform high energy-density experiments in support of weapon-physics and basic-research programs. It is designed to be an international user facility, providing experimental opportunities to researchers from national laboratories and academic institutions. For hydrodynamic experiments, it will be capable of achieving pressures exceeding 20-Mbar in a several cm/sup 3/ volume. With the development of a suitable opening switch, it will also be capable of producing soft X-rays. The 36 MJ capacitor bank will consist of 240 kV Marx modules arranged around a central target chamber. The Marx modules will be discharged through vertical triplate transmission lines to a parallel plate collector inside the target chamber. The capacitor bank is designed to deliver a peak current of 45 to 50 MA with a 4- to 5-/spl mu/s risetime. The Marx modules are designed to be reconfigured to a 480 kV configuration for opening switch development. Predicted performance with a typical load is presented. Descriptions of the major subsystems are also presented.

An overview of the mechanical design of the Atlas pulsed power machine

Atlas is a pulsed-power facility being designed at Los Alamos National Laboratory to perform high-energy density experiments in support of Science-Based Stockpile Stewardship and basic research programs. Atlas will consist of 24 individual maintenance units, each consisting of 4 240-kV Marx units. Maintenance units are contained in large oil tanks arrayed in a circle about a central target chamber. Total stored energy of the capacitor bank will be 23 MJ. Maintenance units will discharge through an output shorting switch into a vertical tri-plate transmission line, and from there into a transition area/collector inside a large vacuum chamber. An overview of mechanical design aspects of the Atlas machine is presented. These include maintenance unit design and design of the tri-plate transmission line and transition region. Findings from fabrication and testing of prototype systems are discussed.