E.L. Neau

The Repetitive High Energy Pulsed Power module

In the Repetitive High Energy Pulsed Power (RHEPP) module, pulse compression is done exclusively with magnetic switches (saturable reactors). Such switches have the potential of performing efficiently and reliably for >10/sup 10/ shots. The objective of the RHEPP project is to explore the feasibility of using magnetic pulse compression technology in continuous high average power applications. The RHEPP system consists of a compressor driving a linear induction voltage added with a diode load. Construction and initial testing in a bipolar mode of the first two stages of the compressor have been completed. This system has operated for a total of 332 min (4.8*10/sup 6/ pulses) at full power (600 kW) with an efficiency of 94+/-3%. The first stage magnetic switch has a pulse compression factor of 8.4 (4.2 ms to 500 mu s time to peak). It has two parallel-connected, 67 n turns copper coils and a 760 kg core of 2 mil silicon steel with a magnetic cross sectional area of 0.065 m/sup 2/. The second stage magnetic switch has a pulse compression factor of three (500 mu s to 170 mu s). It has two parallel-connected, 36 turn copper coils and a 361 kg core of field annealed 2605 CO Metglas with a magnetic area of 0.019 m/sup 2/.<<ETX>>

A pulse power modulator system for commercial high power ion beam surface treatment applications

The ion beam surface treatment (IBEST/sup TM/) process utilizes high energy pulsed ion beams to deposit energy onto the surface of a material allowing near instantaneous melting of the surface layer. The melted layer typically re-solidifies at a very rapid rate which forms homogenous, fine-grained structure on the surface of the material resulting in significantly improved surface characteristics. In order to commercialize the IBEST/sup TM/ process, a reliable and easy-to-operate modulator system has been developed. The QM-1 modulator is a thyratron-switched five-stage magnetic pulse compression network which drives a two-stage linear induction adder. The adder provides 400 kV, 150 ns FWHM pulses at a maximum repetition rate of 10 pps for the acceleration of the ion beam. Special emphasis has been placed upon developing the modulator system to be consistent with long-life commercial service.

Channel cooling techniques for repetitively pulsed magnetic switches

Design data on cooling channel fabrication techniques, size, and geometries tailored to magnetic switches are presented. Free and forced convection channel structures suitable for magnetic switches are proposed and experimentally characterized. Magnetic core temperature data from earlier experiments are formulated into design graphs relating maximum allowable build between cooling channels to maximum core temperature and thermal generation rate. The resultant design curves are applicable to both magnetic cores and electrical windings. Practical limits on interchannel build and thermal generation for free convection are established. Effects of forced convection on the cooling capacity of a channel are discussed. Design curves are applied to a full-scale magnetic switch design. Measured temperatures in two full-scale switches are compared to model predictions. Thermal measurements from full-scale prototypes of the first two RHEPP (Repetitive High Energy Pulsed Power) magnetic switches are compared to predictions from both a simple, one-dimensional model and a more sophisticated simulation. The thermal effects due to the nonuniform current distribution in the flat winding of an actual pulsed switch are observed and discussed.<<ETX>>

High average power, high current pulsed accelerator technology

High current pulsed accelerator technology was developed during the late 60s through the late 80s to satisfy the needs of various military related applications such as effects simulators, particle beam devices, free electron lasers, and as drivers for inertial confinement fusion devices. The emphasis in these devices is to achieve very high peak power levels, with pulse lengths on the order of a few 10s of nanoseconds, peak currents of up to 10s of MA, and accelerating potentials of up to 10s of MV. New high average power systems, incorporating thermal management techniques, are enabling the potential use of high peak power technology in a number of diverse industrial application areas such as materials processing, food processing, stack gas cleanup, and the destruction of organic contaminants. These systems employ semiconductor and saturable magnetic switches to achieve short pulse durations that can then be added to efficiently give MV accelerating potentials while delivering average power levels of a few 100s of kilowatts to perhaps many megawatts. The Repetitive High Energy Pulsed Power project is developing short-pulse, high current accelerator technology capable of generating beams with kJs of energy per pulse delivered to areas of 1000 cm/sup 2/ or more using ions, electrons, or X-rays. Modular technology is employed to meet the needs of a variety of applications requiring from 100s of kV to MVs and from 10s to 100s of kA. Modest repetition rates, up to a few 100s of pulses per second (PPS), allow these machines to deliver average currents on the order of a few 100s of mA. The design and operation of the second generation 300 kW RHEPP-II machine, now being brought on-line to operate at 2.5 MV, 25 kA, and 100 PPS will be described in detail as one example of the new high average power, high current pulsed accelerator technology.

Ion beam surface treatment: a new technique for thermally modifying surfaces using intense, pulsed ion beams

The emerging capability to produce high average power (10-300 kW) pulsed ion beams at 0.2-2 MeV energies is enabling us to develop a new, commercial-scale thermal surface treatment technology called Ion Beam Surface Treatment (IBEST). This new technique uses high energy, pulsed (/spl les/500 ns) ion beams to directly deposit energy in the top 1-20 micrometers of the surface of any material. The depth of treatment is controllable by varying the ion energy and species. Deposition of the energy in a thin surface layer allows melting of the layer with relatively small energies (1-10 J/cm/sup 2/) and allows rapid cooling of the melted layer by thermal conduction into the underlying substrate. Typical cooling rates of this process (109 K/sec) are sufficient to cause amorphous layer formation and the production of non-equilibrium microstructures (nanocrystalline and metastable phases). Results from initial experiments confirm surface hardening, amorphous layer and nanocrystalline grain size formation, corrosion resistance in stainless steel and aluminum, metal surface polishing, controlled melt of ceramic surfaces, and surface cleaning and oxide layer removal as well as surface ablation and redeposition. These results follow other encouraging results obtained previously in Russia using single pulse ion beam systems. Potential commercialization of this surface treatment capability is made possible by the combination of two new technologies, a new repetitive high energy pulsed power capability (0.22 MV, 25-50 kA, 60 ns, 120 Hz) developed at SNL, and a new repetitive ion beam system developed at Cornell University.

Commercial applications and equipment for ion beam surface treatment

The capability to reliably produce rapidly pulsed, intense ion beams with beam geometry suitable for commercial surface treatment applications has remained elusive, in spite of the effort of many researchers. Work at Quantum Manufacturing Technologies, Inc. (QMT) since 1996 has resulted in commercial equipment that can produce rapidly pulsed, intense ion beams, and in commercial applications for these beams. QMTs QM1 facility uses magnetic switching to achieve pulse compression from a 60 Hz wall plug power to 150 ns pulses with over 60% electrical efficiency. A magnetically-confined anode plasma (MAP) ion beam system is used to convert this electrical energy into a 3 billion watt beam of ions. This system has now produced a half million ion beam pulses with typical beam parameters of 0.5 kJ/pulse of ions, ion energy of 400 keV, pulse length of 150 ns, and pulse repetition rates of up to 5 pulses per second. Beams of either hydrogen or nitrogen ions are typically produced. This system functions reliably in automated commercial operation, incorporating, real time fault detection and synchronization with automated part handling. Confirmed applications for this capability include smoothing of metal surfaces by rapid melt and resolidification, production of harder, more wear resistant surfaces for tools and dies, hardening of polymer surfaces by crosslinking, and stripping coatings from carbide tools. The new capabilities offered by ion beam surface treatment have clear applications in many markets, including treatment of medical parts, tools, and dies.

Ion beam surface treatment: A new capability for surface enhancement

The emerging capability to produce high average power (5--350 kW) pulsed ion beams at 0.2--2 MeV energies is enabling the authors to develop a new, commercial-scale thermal surface treatment technology called Ion Beam Surface Treatment (IBEST). This new technique uses high energy, pulsed ({<=}250 ns) ion beams to directly deposit energy in the top 2--20 micrometers of the surface of any material. The depth of treatment is controllable by varying the ion energy and species. Deposition of the energy with short pulses in a thin surface layer allows melting of the layer with relatively small energies and allows rapid cooling of the melted layer by thermal diffusion into the underlying substrate. Typical cooling rates of this process (10{sup 9}--10{sup 10} K/sec) cause rapid resolidification, resulting in the production of non-equilibrium microstructures (nano-crystalline and metastable phases) that have significantly improved corrosion, wear, and hardness properties. The authors conducted IBEST feasibility experiments with results confirming surface hardening, noncrystalline grain formation, metal surface polishing, controlled melt of ceramic surfaces, and surface cleaning using pulsed ion beams.

Status of the PBFA-II light ion beam fusion program

A summary of recent progress and the present status of the PBFA-II (Particle Beam Fusion Accelerator II) light-ion beam fusion program is given. An analytic theory of applied-B ion diodes has been developed that correctly predicts the diode operating points at peak power, and there is agreement between simulations and experiment for the ion beam transport to the diode axis. The anode plasma has been identified as an area for study to improve the ion beam focusing and diode impedance behavior further. An extensive array of ion beam diagnostics has been developed and proven to operate well in the harsh X-ray environment of PBFA II. Work on interpreting data from these diagnostics has provided insights into the physics of beam generation and transport and has stimulated advances in both analytic and calculational modeling of the processes. Three plasma opening switch configurations have been identified and tested. Efficient ion beam generation has been demonstrated, and a focal spot diameter of <5.5 mm at 3/4 energy has been achieved. The peak proton power density achieved on PBFA II has risen from approximately 0.3 TW/cm/sup 2/ to approximately 3.8 (+0.7, -0.8) TW/cm/sup 2/, and the total proton energy on a 1.0-cm radius target has increased from 30 kJ to 140 kJ.<<ETX>>