Regan W. Stinnett

Thermal Surface Treatment Using Intense, Pulsed Ion Beams

Surface treatment experiments using intense pulsed ion beams have demonstrated new capabilities for materials surface treatment. These experiments have confirmed corrosion resistance, surface hardening, amorphous layer and nanocrystalline grain size formation, metal surface polishing, controlled melt of ceramic surfaces, surface cleaning and oxide layer removal by rapid melting and resolidification. Deposition of beam energy in a thin surface layer allows melting of the layer with relatively small energies (1-10 J/cm 2 ) and allows rapid cooling (10 9 -10 10 K/sec) and resolidification of the melted layer by thermal diffusion into the underlying substrate. At higher intensities (≥20 J/cm 2 ), this technology can provide rapid ablation of material from targets followed by rapid, congruent deposition of polycrystalline thin films on substrates. This technology uses high energy pulsed (40–400 ns) ion beams to directly deposit energy in the top 2–20 micrometers of the surface of materials.

Negative ion formation in magnetically insulated transmission lines

Negative ion intensities of over 3×105 A/m2 at energies of 2 MeV have been measured in a magnetically insulated transmission line. This negative ion production can affect the power flow in multiterawatt pulsed power devices, and may also have applications in the generation of high‐intensity neutral or negative ion beams.

The use of pulsed, intense ion beams for thermal surface treatment

Summary form only given. New developments in repetitive pulsed power and ion beam technology at Sandia National Laboratories and Cornell University may enable the use of repetitively pulsed, intense ion beams for commercial surface treatment applications. This capability is being developed in the joint Sandia-Cornell Ion BEam Surface Treatment (IBEST) program. This program uses the Repetitive High Energy Pulsed Power (RHEPP) facility together with magnetically confined anode plasma (MAP) ion diode technology to produce a system capable of operation at 0.5-1 MV and 2.5 kJ/pulse at repetition rates up to 120 Hz. This system should make it possible to treat metal and ceramic surfaces with ion beams which deposit 2-20 Joule/cm/sup 2/ uniformly in the top 2-10 /spl mu/m of the surface. Initial results of thermal surface treatment of 0-1 tool steel with a 10 J/cm/sup 2/, 1 MeV mixed proton and carbon ion beam on the LION accelerator at Cornell University demonstrated an increase in surface hardness by a factor of three and the formation of a finer-grain structure in the treated region.

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.

Energy losses in magnetically insulated transmission lines due to microparticles

We discuss the effects of high‐velocity and hypervelocity microparticles in the magnetically insulated transmission lines of multiterawatt accelerators used for particle beam fusion and radiation effects simulation. These microparticles may be a possible source for plasma production near the anode and cathode in early stages of the voltage pulse, and current carriers during and after the power pulse, resulting in power flow losses. Losses in the current pulse, due to microparticles, are estimated to be approximately 12 mA/cm2 (0.3 kA) as a lower limit, and ∼0.3 A/cm2 (7.2 kA) for microparticle initiated, anode plasma positive ion transport. We have calculated the velocities reached by these microparticles and the effects on them of Van der Waals forces. Field emission from the particles and their effects on cathode and anode plasma formation have been examined. Particle collision with the electrodes is also examined in terms of plasma production, as in the electron deposition in the particles in transit a...

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.

Pulsed ion beam surface treatment for preparing rapidly solidified corrosion resistant steel and aluminum surfaces

Intense, pulsed ion beams were used to melt and rapidly resolidify Types 316F, 316L and sensitized 304 stainless steel surfaces to eliminate the negative effects of microstructural heterogeneity on localized corrosion resistance. Anodic polarization curves determined for 316F and 316L showed that passive current densities were reduced and pitting potentials were increased due to ion beam treatment. Type 304 samples sensitized at 600 C for 100 h showed no evidence of grain boundary attack when surfaces were ion beam treated. Equivalent ion beam treatments were conducted with a 6061-T6 aluminum alloy. Electrochemical impedance experiments conducted with this alloy exposed to an aerated chloride solution showed that the onset of pitting was delayed compared to untreated control samples.

Active plasma source formation in the MAP diode

The ion beam surface treatment (IBEST) program is exploring using ion beams to treat the surface of a wide variety of materials. These experiments have shown that improved corrosion resistance. Surface hardening, grain size modification, polishing and surface cleaning can all be achieved using a pulsed 0.4-0.8 MeV ion beam delivering 1-10 J/cm/sup 2/. The magnetically-confined anode plasma (MAP) diode, developed at Cornell University, produces an active plasma which can be used to treat the surfaces of materials. The diode consists of a fast puff valve as the source of gas to produce the desired ions and two capacitively driven B-fields. A slow magnetic field is used for electron insulation and a fast field is used to both ionize the puffed gas and to position the plasma in the proper spatial location in the anode prior to the accelerator pulse. The relative timing between subsystems is an important factor in the effective production of the active plasma source for the MAP diode system. The MAP diode has been characterized using a Langmuir probe to measure plasma arrival times at the anode annulus for hydrogen gas. This data was then used to determine the optimum operating point for the MAP diode on RHEPP-1 accelerator shots. Operation of the MAP diode system to produce an ion beam of 500 kV, 12 kA with 40% efficiency (measured at the diode) has been demonstrated.

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.

Initiation of Quasi Spherical Direct Drive capsules for inertial fusion

Summary form only given. Magnetically driven, Quasi Spherical Direct Drive (QSDD) fusion capsules potentially offer much higher efficiency implosions for inertial fusion energy than x-ray driven implosions with the comparable pulsed power generator. However, these solid liners must initiate uniformly to produce a quality implosion. Previous experiments by Stinnett, et al, showed that 20 to 200 nm thick aluminum liners on thick insulating substrates require a local action integral of ~6×108 (A/cm2)2-s or ~8×1016 A/cm2 rising in 7 ns to initiate uniformly. The underlying physical processes are complicated by the presence of ~3 monolayers of adsorbed gas and 7.5 nm of AlO2O3. Since QSDD liners are typically 100 micron thick beryllium, we have used a rad-hydro MHD code to analyze the initiation of both thin aluminum liners, to understand the underlying physics, and thick beryllium liners, to predict the drive requirements for uniform initiation of QSDD implosions. Both simulations had 3 monolayers of adsorbed hydrogen on the metal. The simulations provided the local electric field, density, and temperature profile of the metal and gas. The results were analyzed with J. C. Martins multi-channel switching relationships. We infer that the metal must reach approximately 1 eV temperature before the gas, which is heated by thermal conduction, can expand to provide an alternative path for current channel formation through the gas. The results also suggest that an ignition-class QSDD capsule will need ~40 ns implosion times with a 40 MA drive pulse. A 2 micron polyimide coating may significantly improve the initiation of solid liners, as it has improved the initiation of wire arrays in work by D. B. Sinars, et. al., and by G. S. Sarkisov, et. al.