A Planar Hall Thruster for Investigating Electron Mobility in ExB Devices

Stable operation of a Hall thruster that emits and collects the Hall current across a planar discharge channel is describe d. The planar Hall thruster (PHT) is being investigated for use as a test bed to study electron mobility in ExB devices. The planar geometry attempts to de-couple the complex electron motion found in annular thrusters by using simplified geometry. During this initial test, the PHT was operated at discharge voltages between 50-150 V to verify operability y and stability of the device. Hall current was emitted by hollow cathode electron sources and collected by electrodes on the opposing wall of the thruster. Internal channel wall probes along with a downstream Faraday probe and retarding potential analyzer measured change s in thruster plasma as the Hall current, discharge voltage, magnetic field, and mass flow rates were changed. Results show that most of the plume ions are created in the acceleration zone. Further, increasing the magnetic field confines electrons to the Hall-drift region. This causes the Hall current to increase and the discharge current to decrease. Future experiments with this thruster are being planned to shed light on electron mobility in both planar and annular ExB geometry

Experimental Results for an Addressable Xenon Microdischarge EUV Source Array for HVM Lithography

The joint specification projected in-band EUV power requirements at the intermediate focus will rise beyond 185W 2%- bw to maintain the necessary 80-100WPH throughput for economic viability. New improvements in photon efficiency and mask illumination are needed to reduce reflections and power demand, as well as improving source spatial uniformity. In 2006, Starfire presented a novel approach to the EUV source-optic architecture using a high-brightness light source array for direct integration within the illumination optical system. Spatial uniformity and Kohler illumination across the entrance pupil is achieved by dividing the incident light into discrete bundles on a fly\u27s eye mirror. These light bundles form a secondary source image plane that is projected onto the pupil of the projection optics. This configuration allows electronic adjustment of partial coherence and depth of focus for improved lithographic contrast and resolving capability. By distributing total EUV power across discrete units, thermal and particle loadings become manageable without the need for exotic materials or cooling schemes and sources of contaminating debris are reduced. Experimental data from a 5×5 xenon-fed microdischarge source array is presented, demonstrating repetition rate and source addressability for illumination patterning and grayscaling capability. In addition, experimental data from xenon-based sources will be presented with a suite of plasma and optical diagnostic instruments, including conversion efficiency, spectral purity and debris generation. Projections for scaling to HVM conditions will also be presented

Retention/Diffusivity Studies in Free-Surface Flowing Liquid Lithium

FLIRE was designed to measure the hydrogen and helium retention and diffusivity in a flowing stream of liquid lithium, and it has accomplished these goals. Retention coefficients for helium in the flowing liquid stream were 0.1-2% for flow speeds of 44 cm/s and implantation energies between 500 and 2000 eV. The energy dependence of retention is linear for the energy range considered, as expected, and the dependence of retention on flow velocity fits the expected square-root of flow speed dependence. Estimates of the helium diffusion coefficient in the flowing lithium stream were {approx} 4 x 10{sup -7} cm{sup 2}/s, and are independent of implantation energy. This value is much lower than expected, which could be due to several factors, such as mixing, bubble formation or surface film formation. In the case of hydrogen, long term retention and release mechanisms are of greatest importance, since this relates to tritium inventory in flowing lithium PFCs for fusion applications. The amount of hydride formation was measured for flowing lithium exposed to neutral deuterium gas. Thermal desorption spectroscopy (TDS) measurements indicate that the hydride concentration was between 0.1 and 0.2% over a wide range of pressures (6.5 x 10{sup -5} to 1 Torr). This result implies that the deuterium absorption rate is limited by the surface dissociation rate, since deuterium (hydrogen/tritium) is absorbed in its atomic form, not its molecular form

Progress in Modeling of Pre-Ionization and Geometric Effects on a Field-Reversed Configuration Plasma Thruster

In recent years, compact toroid (CT) plasma (e.g., field-reversed configurations, plasmoids, or spheromaks) has been considered for propulsion applications. A limited number of studies have been conducted thus far with each investigating different aspects of CT plasma. The current investigation into CT plasma documented here focuses on developing a thruster concept to assess the efficiencies of CT plasma formation and acceleration. The assessment consists of developing MHD simulations that model a typical CT test article. The pre-ionization geometry and device geometry parameters are varied in these simulations to determine the efficiencies

Compact Toroid Formation Using an Annular Helicon Preionization Source

Formation and ejection of compact plasma toroids for high-thrust and high-specific impulse applications are modeled in conjunction with experimental efforts for concept development. in particular, use of field-reversed configuration plasma with an annular helicon pre-ionization source is being investigated. This type of thruster would have high thrust and no need for electrodes or grids that limit lifetime and reliability. Results from modeling the pulsed power system, the FRC formation process, and acceleration indicate that the annular helicon pre-ionization source is ideal for FRC processes to maximize coupling between the pulsed field and the plasma

Plasma Properties in the Magnetic Nozzle of an Electron Cyclotron Resonance Plasma Source

State-of-the-art electric propulsion systems use plasma discharges that require an electrode in contact with plasma. Therefore, these devices suffer from lifetime-limiting erosion processes due to the harsh plasma environment. A potential solution to this problem is the use of an electrodeless propulsion scheme, such as microwave electron cyclotron resonance (ECR). In the ECR process, electrons resonantly gain energy from the microwave field and acquire enough energy to ionize neutral gas atoms. Acceleration of ions to generate thrust can also be an electrodeless process if a magnetic nozzle is employed. We present plasma property measurements in the downstream diverging magnetic nozzle of an ECR plasma source. Results show plasma number densities as high as 1.0x10¹²cmˉ³, electron temperatures of 2-4 eV, and plasma potentials of 15-30 V. Ion energy-per-charge distributions show two peaks during low pressure operation (2.0x10ˉ⁴ Torr). The first peak corresponds with the plasma potential and represents ions falling through the plasma sheath. The second peak is attributed to an ion beam component within the plasma and has values of 30-50 V, increasing with decreasing pressure

Flowing liquid lithium plasma-facing components – Physics, technology and system analysis of the LiMIT system

The use of low atomic number liquid metals has been shown to have the potential to solve many of the prevalent problems like erosion and radiation losses associated with the interaction of fusion plasma with the plasma facing component (PFC) structures in tokamaks. Since the first evidence of lithium increasing plasma performance in TFTR [1], the benefits of using lithium in fusion environments have been seen in many devices, including CDX-U [2], NSTX [3], LTX [4], and DIII-D [5]. While both fast flow and slow flow concepts have been studied with regards to liquid lithium first wall alternatives, this report will focus on efforts placed on fast flow research and will mainly focus on advancements in the LiMIT device that help to eliminate concerns over the broad use of liquid lithium. Due to the promising TFTR results along with results obtained at the University of Illinois at Urbana-Champaign [6], suitably designed trench structures holding liquid lithium could be an appropriate fast flow candidate for PFC modules in future fusion devices. There are four potential shortcomings of this approach: (1) Droplet ejection, (2) Wetting control, (3) Tritium retention, and (4) Limited heat flux handling. Droplet ejection is discussed in a companion publication [7], while this paper addresses the topics of wetting control and heat flux handling. Limitations in wetting and prevention of lithium creep (i.e. getting and keeping the lithium only where it should be) have been solved by laser-texturing the base material with extreme short laser pulses (pico – femto second) of high power (several 10s of W). Micro- and nano-structuring results indicate that the textured substrates displayed significant change in their wetting properties, increasing the temperature needed to wet from 310 °C to 390 °C. Lastly, initial designs for the Lithium Metal Infused Trenches (LiMIT) [6] showed dryout above 3 MW/m2, but new designs of the trench shaping show potential to be able to handle up to 10MW/m2. Dryout is accompanied by lithium evaporation which is shown to mitigate the incident heat flux, which may be viewed as beneficial [8]. The advances shown here will increase the viability of the LiMIT system in large-scale testing, and allow for extensive design iteration to begin tackling the large powers and heat fluxes present in reactor-relevant systems. Keywords: Liquid lithium, Plasma-facing components, Thermoelectric magnetohydrodynamic