W.M. Parsons

The Atlas project-a new pulsed power facility for high energy density physics experiments

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 a pressure exceeding 30 Mbar in a several cubic centimeter volume. With the development of a suitable opening switch, it will be capable of producing more than 3 MJ of soft X-rays. The capacitor bank design consists of a 36 MJ array of 240 kV Marx modules. The system is designed to deliver a peak current of 45-50 MA with a 4-5-/spl mu/s rise time. The Marx modules are designed to be reconfigured to a 480-kV configuration for opening switch development. The capacitor bank is resistively damped to limit fault currents and capacitor voltage reversal. An experimental program for testing and certifying prototype components is currently under way. The capacitor bank design contains 300 closing switches. These switches are a modified version of a railgap switch originally designed for the DNA-ACE machines. Because of the large number of switches in the system, individual switch prefire rates must be less than 10/sup -4/ to protect the expensive target assemblies. Experiments are under way to determine if the switch-prefire probability can be reduced with rapid capacitor charging.

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.

The atlas power-flow system - A status report

The design requirements, design features, test results and status of the Atlas high-energy pulsed-power facility power flow system are described

Atlas transmission line breakdown analysis

The Atlas facility will use 24 radially converging, vertically oriented and tapered, oil insulated, triplate transmission lines between the Marx generators and the central load region. Among the requirements of the transmission lines are low inductance and high reliability. The inter-conductor gap is nominally 2 cm and the lines taper from a height of 1.75 m at the Marx end to 0.32 m at the output end. The aluminum conductors, held together by 20 insulating spacers, are assembled and inserted as a unit into radial oil-filled steel tanks. The negative, high-voltage, center conductor is 2.54-cm thick and the outer ground conductors are 1.59-cm thick. All 24 triplate transmission lines connect to a transition section at near 1 m radius that couples the transmission lines to a disk/conical solid-dielectric-insulated power flow channel transmission line terminating at the load. Peak operating voltage on the lines can be as high as 240 kV with an effective stress time of 0.8 /spl mu/s. Testing of small sections of the total area have been completed and the test results are analyzed to show that the probability of failure at these voltage levels is less than 1 in 1000 system shots.

Pegasus II experiments and plans for the Atlas pulsed power facility

Atlas will be a high-energy (36 MJ stored), high-power (/spl sim/10 TW) pulsed power driver for high energy-density experiments, with an emphasis on hydrodynamics. Scheduled for completion in late 1999, Atlas is designed to produce currents in the 40-50 MA range with a quarter-cycle time of 4-5 /spl mu/s. It will drive implosions of heavy liners (typically 50 g) with implosion velocities exceeding 20 mm//spl mu/s. Under these conditions, very high pressures and magnetic fields are produced. Shock pressures in the 50 Mbar range and pressures exceeding 10 Mbar in an adiabatic compression will be possible. By performing flux compression of a seed field, axial magnetic fields in the 2000 T range may be achieved. A variety of concepts have been identified for the first experimental campaigns on Atlas. Experimental configurations, associated physics issues, and diagnostic strategies are all under investigation as the design of the Atlas facility proceeds. Near-term proof-of-principle experiments employing the smaller Pegasus II capacitor bank have been identified, and several of these experiments have now been performed. This paper discusses a number of recent Pegasus II experiments and identifies several areas of research presently planned on Atlas.

Rail-gap switch modifications and test data for the Atlas capacitor bank

Atlas is a facility being designed at the Los Alamos National Laboratory (LANL) to perform high energy-density experiments in support of weapons-physics and basic-research programs. The capacitor bank design consists of a 36 MJ array of 240 kV Marx modules. The system is designed to deliver a peak current of 40-50 MA with a 4-5 /spl mu/s risetime. Evaluation, testing and qualification of key components of the Marx module are being conducted. One key element of the Marx module is the low inductance, high-voltage, high-current, high-coulomb transfer spark-gap switch needed for this application, 304 of which will be used in the Atlas capacitor bank. Because of the Marx module configuration, overall system inductance requirements and the need for a triggered switch, the design team initially selected the Maxwell Technologies rail-gap switch. The switch has been used in other high-voltage, high-current, high-coulomb transfer applications and would meet the Atlas facility requirements with some modifications. Testing of the Maxwell rail-gap switch under expected Atlas conditions is in progress. For the Atlas application, the rail-gap switch required some mechanical design modifications, which are discussed. Maxwell provided two modified switches for testing and evaluation. Results of this testing, before and after modifications, and inherent maintenance improvements to meet overall system reliability are discussed.

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.

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.

Atlas - a new pulsed power tool at Los Alamos

The Atlas pulsed power driver has recently been commissioned at Los Alamos National Laboratory. This paper provides an overview of the ATLAS facility, its initial experimental program and plans for the future. The reader desiring more detailed information is referred to papers in this conference by Keinigs et al. on materials studies, Cochrane et al. on machine performance and Ballard et al. on fabrication and assembly. Atlas is a high current generator capable of driving 30 megamps through a low-inductance load. It has been designed to require minimal maintenance, provide excellent diagnostic access, and rapid turnaround. Its capacitor bank stores 23.5 megajoules in a four-stage Marx configuration which erects to 240 kV at maximum charge. It has a quarter-cycle time of 4.5 microseconds. It will typically drive cylindrical aluminum liners in a Z-pinch configuration to velocities up to 10 mm/usec while maintaining the inner surface in the solid state. Diagnostic access includes 360/spl deg/ of radial view as well as axial views from above and below. The photograph shows the circle of tanks containing capacitor banks, the diagnostic platform and load area. Atlas construction began in 1996 and high-current acceptance tests were completed in December of 2000. Initial shots include liner characterization shots using a target design similar to NTLX experiments (see several papers by Turchi et al., this meeting). These will be followed by experiments studying hydro features, useful for validating hydrodynamic algorithms used in weapons computer codes. DOE plans to relocate the Atlas generator to the Nevada Test Site as early as 2002, where it will continue its experimental program supporting the Stockpile Stewardship program and other users.