Orson Sutherland

High brightness inductively coupled plasma source for high current focused ion beam applications

A high brightness plasma ion source has been developed to address focused ion beam (FIB) applications not satisfied by the liquid metal ion source (LMIS) based FIB. The plasma FIB described here is capable of satisfying applications requiring high mill rates (>100μm3∕s) with non-gallium ions and has demonstrated imaging capabilities with sub- 100-nm resolution. The virtual source size, angular intensity, mass spectra, and energy spread of the source have been determined with argon and xenon. This magnetically enhanced, inductively coupled plasma source has exhibited a reduced brightness (βr) of 5.4×103Am−2sr−1V−1, with a full width half maximum axial energy spread (ΔE) of 10eV when operated with argon. With xenon, βr=9.1×103Am−2sr−1V−1 and ΔE=7eV. With these source parameters, an optical column with sufficient demagnification is capable of forming a sub-25-nm spot size at 30keV and 1pA. The angular intensity of this source is nominally three orders of magnitude greater than a LMIS making the source more a...

Helicon Double Layer Thrusters

The Helicon Double Layer Thruster is a new type of magneto-plasma thruster which combines the helicon technology for an efficient coupling of the electrical power to the plasma and a current-free double layer (formed spontaneously in the physical and magnetic nozzle of the thruster) for an optimized acceleration of the plasma ions. A large area, low divergence supersonic ion beam (the source of thrust) is measured in the nozzle for various propellants (xenon, argon and hydrogen). In addition to the scalability in geometry and electrical power, the simplicity, the absence of any moving parts, electrodes, or neutralizer give the HDLT an infinite lifetime.

Advancing Active Vision Systems by Improved Design and Control

This paper presents the mechanical hardware and control software of a novel high-performance active vision system. It is the latest in an ongoing research effort to develop real-world vision systems based on cable-drive transmissions. The head presented in this paper is the laboratory’s first fully cable-driven binocular rig, and builds on several successful aspects of previous monocular prototypes. Namely, an increased payload capacity, a more compact transmission, and a design optimised for rigidity. In addition, we have developed a simple and compact controller for real-time tracking applications. It consists of two behavioural subgroups, saccade and smooth pursuit. By using a single trapezoidal profile motion (TPM) algorithm, we show that saccade time and motion smoothness can be optimised.

Experimental evidence of parametric decay processes in the variable specific impulse magnetoplasma rocket (VASIMR) helicon plasma source

This project was proudly supported by the International Science Linkages programme established under the Australian Government’s innovation statement Backing Australia’s Ability.

Initial Experiments on a Dual-Stage 4-Grid Ion Thruster for Very High Specific Impulse and Power

A new and innovative type of gridded ion thruster, the “Dual-Stage 4-Grid” or DS4G concept, has been proven under laboratory conditions under a preliminary research, development and test programme. The DS4G concept is able to operate at very high specific impulse, power and thrust density values well in excess of conventional 3-grid ion thrusters at the expense of a higher power-to-thrust ratio. A small low-power experimental laboratory model was designed and built, and its performance was measured during an extensive test campaign. The principal goals of the initial laboratory experiment were to prove the practical feasibility of the overall concept, demonstrate the performance predicted by analytical and simulation models, and investigate critical design parameters and technological challenges. In the present paper, the basic concept of the DS4G ion thruster is presented, along with the design, operating parameters and measured performance obtained from the first and second phases of the experimental campaign. Finally, the implications of these findings for future gridded ion thruster developments and future mission applications are addressed.

Ion heating in the presheath

A one-dimensional model of a small plasma ion source (10cm long) is studied. A hybrid simulation where ions are treated as particles and electrons as a fluid obeying the Boltzmann relation is used to investigate ion heating in the plasma presheath. At low pressure (below a few mTorr), the ion velocity distribution is Maxwellian in the bulk and becomes a drifting Maxwellian distribution while transiting the presheath. The distribution remains essentially isotropic as the ions are accelerated through the presheath to satisfy the Bohm criterion. At intermediate pressures (around 10mTorr), ion-neutral collisions scatter a significant part of the ion kinetic energy from the parallel direction to the perpendicular direction, leading to a net heating of the ions. In addition, the ion velocity distribution becomes distinctly anisotropic. At higher pressure (above a few tens of mTorr), ion heating is still observed, but yields isotropic ion velocity distributions.

Operating the Helicon Double Layer Thruster in a Space Simulation Chamber

A prototype of the helicon double layer thruster (HDLT) is designed and manufactured. Initial tests with the thruster mounted on a small vacuum chamber (pumping speed of 700 l ldr s-1) show successful operation in xenon with the formation of the double layer which generates a low divergence ion beam, which is the source of thrust. The prototype is subsequently inserted inside a much larger space simulation chamber (pumping speed of 7000 l ldr s-1). A high-density blue mode is found when increasing the RF power above 380 W, and measurements with a Langmuir probe give an estimated density of 1012 cm-3 in the thruster. An image of the HDLT operating in the high-density blue mode is presented.

Generalization of the Langmuir–Blodgett laws for a nonzero potential gradient

The Langmuir–Blodgett laws for cylindrical and spherical diodes and the Child–Langmuir law for planar diodes repose on the assumption that the electric field at the emission surface is zero. In the case of ion beam extraction from a plasma, the Langmuir–Blodgett relations are the typical tools of study, however, their use under the above assumption can lead to significant error in the beam distribution functions. This is because the potential gradient at the sheath/beam interface is nonzero and attains, in most practical ion beam extractors, some hundreds of kilovolts per meter. In this paper generalizations to the standard analysis of the spherical and cylindrical diodes to incorporate this difference in boundary condition are presented and the results are compared to the familiar Langmuir–Blodgett relation.

Spatially limited ion acoustic wave activity in low-pressure helicon discharges

Ion acoustic wave phenomena are studied and compared in two low-pressure argon discharges created by helicon sources. The wave amplitudes are spatially localized near the edge of a plasma column as the amplitudes of the “mirror waves” that are separated from the helicon source frequency by the ion wave frequency. Dependencies of the ion wave on radial position, pressure, input power, and magnetic field are investigated. Measurements of the wavelength show that the wave is traveling azimuthally at approximately the ion sound speed in the direction of electron gyration. Although the wave spectra are indicative of a parametric decay phenomenon, it seems more likely that the radial plasma pressure gradient drives an ion acoustic instability which then modulates the helicon source.

Comparison between experiment and two simulation strategies for the extraction of focused ion beams

(.10 12 cm 23 ) with a three electrode extraction system and compare the extracted current and the angular divergence with the results of two computer simulation programs. The first is called PBgun and is a commercially available ray tracing code; the second, called simulation d’extraction de faisceaux d’ions ~SEFI! uses a particle-in-cell code to simulate the plasma and ion beam. It is the purpose of this article to ascertain whether these codes can adequately model the plasma/beam interface and hence successfully predict the extracted current and beam form across a broad range of extraction parameters. We found that SEFI could accurately predict the function of extracted current versus extraction voltage and that PBgun gave accurate simulations when the current or current density could be specified near the meniscus. Also for a thin plasma aperture and a fixed current at the meniscus, PBgun gave roughly 60% of the functional dependence of the extracted current on the extraction voltage and the other 40% on variations in the plasma pre-sheath. Both codes had some error from beam crossing near the axis which changed the amount of meniscus curvature predicted.