C.P. Munson

Adherent diamond-like carbon coatings on metals via plasma source ion implantation

Various techniques are currently used to produce diamond-like carbon (DLC) coatings on various materials. Many of these techniques use metallic interlayers, such as Ti or Si, to improve the adhesion of a DLC coating to a ferrous substrate. An alternative processing route would be to use plasma source ion implantation (PSII) to create a carbon composition gradient in the surface of the ferrous material to serve as the interface for a DLC coating. The need for interlayer deposition is eliminated by using a such a graded interface. A PSII approach has been used to form adherent DLC coatings on magnesium, aluminum, silicon, titanium, chromium, brass, nickel and tungsten. A PSII process tailored to create a graded interface allows deposition of adherent DLC coatings even on metals that exhibit a positive heat of formation with carbon, such as magnesium, iron, brass and nickel.

Energetic electron measurements in the edge of a reversed-field pinch

The edge plasma of the ZT‐40M [Fusion Technol. 8, 1571 (1985)] reversed‐field pinch has been studied using a combination of three different plasma probes: a double‐swept Langmuir probe, an electrostatic energy analyzer, and a calorimeter–Langmuir probe. The edge plasma has been measured both with and without a movable graphite tile limiter present nearby in the plasma. Without a limiter a fast nonthermal tail of electrons (T≂350 eV) is detected in the edge plasma with nearly unidirectional flow along B and having a density between 2% and 10% of the cold edge plasma (T≂20 eV). The toroidal sense of this fast electron flow is against the force of the applied electric field. A large power flux along B is measured flowing in the same direction as the fast electrons and is apparently carried by the fast electrons. With the limiter present the fast electrons are still detected in the plasma, but are strongly attenuated in the shadow of the limiter. The measured scrape‐off lengths for both the fast electrons and...

Advances in PSII techniques for surface modification

Abstract Recent activities in plasma source ion implantation (PSII) technology include scale-up demonstrations for industry and development of variations on the original PSII concept for surface modification. This paper presents an overview of the continued growth of PSII research facilities world-wide and the industrial demonstrations within the USA. In order to expand the applicability of PSII, Los Alamos is actively researching a PSII-related technique called plasma immersion ion processing (PIIP). In one case, a pulsed-biased target can be combined with cathodic arc sources to perform ion implantation and coating deposition with metal plasmas. Erbium plasmas have been combined with oxygen to deposit erbia (Er 2 O 3 ) coatings that are useful for containment of molten metals. In a second case, hydrocarbon, inorganic and organometallic gases are utilized to create a graded interface between the substrate and the coating that is subsequently deposited by using pulsed-bias techniques. PIIP represents a significant advance since it allows coating deposition with all the strengths of the original PSII approach. Diamond-like carbon (DLC) and boron carbide are two such coatings that will be highlighted here for tribological applications.

Recent advances in plasma source ion implantation at Los Alamos National Laboratory

Abstract Plasma source ion implantation (PSII) is an environmentally benign, potentially cost-effective alternative to conventional lineof-sight, accelerator-based implantation and wet-chemical plating processes. PSII offers the potential of producing a high dose of ions in a relatively simple, fast and cost-effective manner, allowing the simultaneous implantation of large surface areas (many square meters), complex shapes and multiple components. The dynamics of the transient plasma sheath present during PSII have been modeled in both 1 1/2-D and 2 1/2-D (one or two spatial dimensions, plus time), and recent results from these efforts are compared with measurements of the uniformity of the implanted ion dose in complex configurations. Ammonia gas (NH 3 ) has been used as a nitrogen source for PSII processing of electroplated hard chromium. A retained dose of 2.2 × 10 17 N atoms cm −2 has been demonstrated to increase the surface hardness of the electroplated Cr by 24%, and decrease the wear rate by a factor of four, without any evidence of increased hydrogen concentration in the bulk material. By adjusting the repetition rate of the applied voltage pulses, and therefore the power input to the target, controlled, elevated temperature implantations have been performed, resulting in enhanced diffusion of the implanted species with a thicker modified surface layer. Experimental work has been performed utilizing cathodic arcs as sources of metallic ions for implantation, and preliminary results of this work are given. The area of ion-beam-assisted deposition (IBAD) has been explored utilizing PSII, with large surface area diamond-like carbon (DLC) layers being generated which can exhibit hardnesses in excess of 20 GPa.

Oscillating field current drive experiments in a reversed field pinch

Steady‐state current sustainment by oscillating field current drive (OFCD) utilizes a technique in which the toroidal and poloidal magnetic fields at the plasma surface are modulated at audio frequencies in quadrature. Experiments on the ZT‐40M reversed field pinch [Fusion Technol. 8, 1571 (1985)] have examined OFCD over a range of modulation amplitude, frequency, and phase. For all cases examined, the magnitude of the plasma current is dependent on the phase of the modulations as predicted by theory. However, evidence of current drive has only been observed at relatively low levels of injected power. For larger modulation amplitudes, the data suggest that substantial current drive is offset by increased plasma resistance as a result of modulation enhanced plasma–wall interactions. The initial experimental results and supporting theoretical interpretations of OFCD are discussed.

Fluctuations and transport in a reversed field pinch edge plasma

Edge fluctuations are characterized and their associated transport is determined from Langmuir probe measurements in the ZT-40M reversed field pinch. It is found that the fluctuations have high normalized amplitudes and |n|/n = 0.4). There are significant contributions from magnetic perturbations acting on the equilibrium gradients. Compared to the global estimates, the fluctuation driven particle flux is large, whereas the corresponding electron energy flux is not. In the limiter shadow, the equilibrium density and electron temperature scale lengths are shorter and the fluctuation levels are higher. The fluctuation driven particle flux in the limiter shadow is 60% less than that in the plasma edge; most of the reduction is in the low frequency spectral region, which is where global MHD magnetic fluctuations are strongest.

Materials Science Issues of Plasma Source Ion Implantation

Ion beam processing, including ion implantation and ion beam assisted deposition (IBAD), are established surface modification techniques which have been used successfully to synthesize materials for a wide variety of tribological applications. In spite of the flexibility and promise of the technique, ion beam processing has been considered too expensive for mass production applications. However, an emerging technology, Plasma Source Ion Implantation (PSII), has the potential of overcoming these limitations to become an economically viable tool for mass industrial applications. In PSII, targets are placed directly in a plasma and then pulsed-biased to produce a non-line-of-sight process for intricate target geometries without complicated fixturing. If the bias is a relatively high negative potential (20-100kV) ion implantation will result. At lower voltages (50-1200V), deposition occurs. Potential applications for PSII are in low-value-added products such as tools used in manufacturing, orthopedic devices, and the production of wear coatings for hard disk media. This paper will focus on the technology and materials science associated with PSII.

Etching of UO2 in NF3 RF Plasma Glow Discharge

Abstract A series of single effect, RF plasma, glow discharge experiments were conducted using NF3 gas to decontaminate depleted uranium dioxide from stainless-steel substrates. In the experiments, the plasma absorbed power was varied from 25 to 210 W and the pressure from ∼10 to 40 Pa. The results demonstrated that UO2 can be completely removed from stainless-steel substrates after several minutes processing at under 100 W with initial etch rates ranging from 0.2 to 7.4 μm/min. A primary etch mechanism is proposed in which F atoms created in the plasma diffuse to the UO2 surface and react to form successive intermediates of uranium fluorides and/or oxyfluorides with reactions continuing to form volatile UF6 which desorbs into the gas phase to be pumped away. Ions created in the plasma are too low in concentration to be the primary etch mechanism, yet they can deliver enough energy to enhance the reaction process. UO2 etching is a self-limiting process due to the formation of non-volatile uranium oxyfluorides and fluorides which form over the UO2 surface, slowing or completely blocking the reaction to UF6.

A Penning-assisted subkilovolt coaxial plasma source

A Penning-assisted 20MW coaxial plasma source (plasma gun), which can achieve breakdown at sub-kV voltages, is described. The minimum breakdown voltage is about 400V, significantly lower than previously reported values of 1–5kV. The Penning region for electrons is created using a permanent magnet assembly, which is mounted to the inside of the cathode of the coaxial plasma source. A theoretical model for the breakdown is given. A 900V 0.5F capacitor bank supplies energy for gas breakdown and plasma sustainment from 4to6ms duration. Typical peak gun current is about 100kA and gun voltage between anode and cathode after breakdown is about 200V. A circuit model is used to understand the current-voltage characteristics of the coaxial gun plasma. Energy deposited into the plasma accounts for about 60% of the total capacitor bank energy. This plasma source is uniquely suitable for studying multi-MW multi-ms plasmas with sub-MJ capacitor bank energy.

Time of flight measurement of ion temperatures in spheromaks

The energy distribution of neutral particles is detected from spheromak plasmas by a time of flight neutral atom spectrometer. These particles originate in charge exchange interactions within the bulk plasma and carry the temperature of the majority ion component. This is the first direct measurement of temperatures of the main ion species in spheromaks. The data are found to be in the range of 500 eV during the sustainment and late decay phases and are in agreement with impurity Doppler temperatures for species expected to be localized to the plasma centre.