David M. Sanders

Review of cathodic arc deposition technology at the start of the new millennium

Abstract The vacuum cathodic arc has been known as a means of producing coatings since the second half of the 19th century. This makes it one of the oldest known vacuum coating techniques. In the last century it has been recognized that the copious quantities of ions produced by the process provides certain coating property advantages. Specifically, ions can be steered and/or accelerated toward the parts to be coated. This, in turn, can provide enhanced adhesion, film density, and composition stoichiometry in the case of compound coatings. The ions generated by the cathodic arc have high ‘natural’ kinetic energy values in the range 20–200 eV, leading to enhanced surface mobility during the deposition process and even ion subplantation. In many cases, dense coatings are achieved even when the ions arrive at non-normal angles. The ion energy can be further manipulated by the plasma immersion biasing technique. Macroparticle contamination has been alleviated by a variety of novel plasma filters. The purpose of this review is to describe recent developments in macroparticle filtering and arc control. These developments promise to broaden the range of applications to the semiconductor, data storage, and optical coatings industry.

A compact linac for intensity modulated proton therapy based on a dielectric wall accelerator

A novel compact CT-guided intensity modulated proton radiotherapy (IMPT) system is described. The system is being designed to deliver fast IMPT so that larger target volumes and motion management can be accomplished. The system will be ideal for large and complex target volumes in young patients. The basis of the design is the dielectric wall accelerator (DWA) system being developed at the Lawrence Livermore National Laboratory (LLNL). The DWA uses fast switched high voltage transmission lines to generate pulsed electric fields on the inside of a high gradient insulating (HGI) acceleration tube. High electric field gradients are achieved by the use of alternating insulators and conductors and short pulse times. The system will produce individual pulses that can be varied in intensity, energy and spot width. The IMPT planning system will optimize delivery characteristics. The system will be capable of being sited in a conventional linac vault and provide intensity modulated rotational therapy. Feasibility tests of an optimization system for selecting the position, energy, intensity and spot size for a collection of spots comprising the treatment are underway. A prototype is being designed and concept designs of the envelope and environmental needs of the unit are beginning. The status of the developmental new technologies that make the compact system possible will be reviewed. These include, high gradient vacuum insulators, solid dielectric materials, SiC photoconductive switches and compact proton sources.

Design of vacuum arc-based sources

Vacuum arc sources can produce copious quantities of ions which can be used to engineer surfaces for tribological applications. The energetic and ionic character of arc-produced coating species can lead to unusually hard, dense, slippery and/or adherent coatings which can be applied successfully to both flat surfaces and complex shapes. Arc coating technology can take many forms with each having their own advantages and limitations. The purpose of the current review is to give the reader an overview of the wide range of options which are possible with vacuum arc technology while providing specific detailed examples to show how several of these option sets translate into actual source designs. Emphasis is given to more recent findings.

Modeling plasma flow in straight and curved solenoids

The ‘‘flux‐tube’’ model originated by Morozov is a very simple and numerically efficient method for simulating ion motion in plasma filters. In order to test its utility as a design tool, we compare the predictions of the model to recent experimental measurements of plasma flow in both straight and curved solenoids.

Plasma transport in a new cathodic arc ion source, theory and experiment

Abstract We have developed a plasma transport code based upon the “flux tube” model and applied it to the ion transport in a recently developed metal-ion source based on the cathodic vacuum arc. This model is compared with ion current measurements made at various locations within the source. The agreement is sufficient to justify use of this model for future arc source design.

Deposition of durable wide-band silver mirror coatings using long-throw, low-pressure, DC-pulsed magnetron sputtering

Sputter deposition at long-throw distances (15-30 in.) and low pressures (<1 mTorr) were developed mainly for the semiconductor industry to deposit metals and dielectrics into trenches or vias on silicon and gallium arsenide wafers. Scientists found that sputter depositions performed at pressures below 1 mTorr (0.13 Pa) results in a virtually collision-free trajectory of the sputtered atoms from the target to the substrate. If the throw distance (source to substrate) is increased at these low pressures, the activated (ionized) gas and target atoms maintain their energy. We used this methodology along with dc-pulsed sputtering to deliver additional energy at the substrate. This allowed us to coat large optics (>21-in. diameter) in a standard box coater using smaller-diameter sputter cathodes. This paper will discuss the process used to successfully coat a 22-in.-diameter optic for the Keck Telescope in Hawaii with a new Wide-Band Durable Silver Mirror. The process uses smaller-diameter sputter cathodes in a 4-ft.-x-4-ft.-x-5-ft. box coater. We will also discuss how the process can be scaled to 36-in. or larger optics for use on terrestrial or space-based platforms.

High gradient multilaver insulator technology

We are investigating a novel insulator concept that involves the use of alternating layers of conductors and insulators with periods less than 1 mm. These structures perform 1.5 to 4 times better than conventional insulators in long pulse, short pulse, and alternating polarity applications. We have surveyed our ongoing studies by investigating the performance under long pulse electron beam, short pulse, and full reversing conditions

Rigid-rotor models of plasma flow

Publisher Summary This chapter discusses the theoretical underpinnings of rigid-rotor type models of plasma flow. The chapter discusses the theoretical basis for the flux-tube model and compare its predictions to three sets of experimental data. The chapter includes rigid-rotor equilibria, Aksenovs filter and the dome source. Plasma equilibria of the rigid-rotor type were first investigated in detail by Davidson. Rigid-rotor equilibria have been experimentally produced and extensively studied in vacuum arc centrifuges. In these systems, plasma about one meter long and 5 cm in diameter is produced in a long solenoid. The electron densities are about 1014 cm-3 and the ion temperatures are about 3 eV. The measured potentials are found to be quadratic, except near the solenoid walls, and the density profiles are well described by Gaussians centered on the axis. The rigid-rotor frequencies are measured to be about 105 rad/s, and correspond to the slow mode. The fast mode has never been observed in these devices, but the existence and nature of rigid-rotor equilibria in vacuum arc plasmas appear to be well established both experimentally and theoretically. A rigid-rotor model has also been used to describe collective focusing of ion beams in thin magnetic lenses and in solenoidal fields.

Spacecraft Fabrication and Test Manufacturing Operations and Development Integration Laboratory (MODIL): Establishing a spacecraft fabrication culture

MODILs (Manufacturing Operations and Development Integration Laboratory) were established to mitigate risk and cost escalation of producing SDI systems. The Spacecraft Fabrication and Test MODIL has been established to impact spacecraft producibility and create a spacecraft industry quantity production culture. We describe the background of MODILs, objectives and scope, current organization (including cooperating government agencies), and the current thrusts of Materials and Structures. Test and Assembly, Spacecraft Integration Technology, and Precision Technologies. The current plan is to initiate selected productivity demonstration projects with industry to show benefits of the MODIL approach and prepare comprehensive plans for follow-up activities.