Formation of TiN by femtosecond laser processing in controlled gas atmosphere is reported. A dual-stage process was designed and aimed to first remove and restructure the native oxide layer of titanium surface through laser irradiation under an argon-controlled atmosphere, and then to maximize titanium nitride formation through an irradiation under a nitrogen reactive environment. An extensive XPS study was performed to identify and quantify laser-induced titanium surface chemistry modifications after a single-stage laser process (Ar and N2 individually), and a dual-stage laser process. The importance of each step that composes the dual-stage laser process was demonstrated and leads to the dual-stage laser process for the formation of TiO, Ti2O3 and TiN. In this study, the largest nitride formation occurs for the dual stage process with laser conditions at 4 W/1.3 J cm−2 under argon and 5 W/1.6 J cm−2 under nitrogen, yielding a total TiN composition of 8.9%. Characterization of both single-stage and dual-stage laser process-induced surface morphologies has been performed as well, leading to the observation of a wide range of hierarchical surface structures such as high-frequency ripples, grooves, protuberances and pillow-like patterns. Finally, water wettability was assessed by means of contact angle measurements on untreated titanium surface, and titanium surfaces resulting from either single-stage laser process or dual-stage laser process. Dual-stage laser process allows a transition of titanium surface, from phobic (93°) to philic (35°), making accessible both hydrophilic and chemically functionalized hierarchical surfaces.

As the use of liquid metals in plasma facing components becomes more widespread, it is important to investigate how these liquid metals interact with the surfaces onto which they are deposited. An important example of these interactions is the ability to control liquid metal wettability on fusion relevant substrates. In this work, we explore the influence of femtosecond laser induced nanostructured surfaces on the wetting degree of liquid lithium versus temperature. Three material candidates as a lithium wall in magnetic fusion devices have been investigated: molybdenum, tungsten and 304 L stainless steel. Laser parameters were tuned to induce periodical self-organized nanostructures (ripples or LIPSS) formation on each material. Wettability of laser treated materials was changed from lithiumphilic to lithium-phobic for temperatures beyond 320 degrees C - 360 degrees C compared to untreated material. The effect of both laser induced topography and chemistry are quantified to explain the observed liquid lithium contact angles on each material. Finally, it was shown that topography in the form of selforganized periodical nanostructures as well as the surface chemistry in the form of oxides enrichment, both induced by a single step laser process, strongly influence the wetting degree of liquid lithium and enhance lithium-phobicity at high temperatures. (C) 2018 Elsevier B.V. All rights reserved.

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 10 s 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 degrees C to 390 degrees C. Lastly, initial designs for the Lithium Metal Infused Trenches (LiMIT) [6] showed dryout above 3 MW/m(2), but new designs of the trench shaping show potential to be able to handle up to 10 MW/m(2). 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. (C) 2017 The Authors. Published by Elsevier Ltd.

Liquid metals are garnering increased attention as an alternative divertor solution to tungsten divertors. While tungsten suffers from a myriad of potentially critical issues, such as bulk erosion, melting under significant transient heat loads, and nanostructuring colloquially referred to as "fuzz", liquid metals avoid many of these entirely. In order to implement liquid metal concepts, the interactions between the liquid metal and the substrate it is deposited upon must be characterized. One such critical interaction is the wetting of a liquid metal on the surface of the PFC structure. The wetting ability of a substance determines many significant properties, including the thickness of the liquid film and the propensity of a flowing liquid to break into rivulets. A previous study conducted at the University of Illinois [1] characterized wetting as a measurement of the contact angle of lithium when deposited as liquid droplets onto a surface. The dependence of the contact angle on temperature was measured, finding a transition between non-wetting and wetting at a critical temperature. For example, at 215 °C, stainless steel registers a contact angle of 137°, whereas above its wetting temperature of 315 °C, the contact angle is less than 80°. The impact of nanostructuring of the surface is detailed herein. A novel method of rapid laser nanostructuring was developed to create the samples. To further the knowledge of liquid metal PFC surface interactions, results of experiments on the relationships between material and temperature and the contact angle of lithium are presented for a variety of nanostructured surfaces.

Recent advances in pulsed power supply technology has allowed the star mode inertial-electrostatic confinement (IEC) to pulse to high currents, 17 A, at a peak voltage of 50 kV, and a pulse width of 100 /spl mu/s at a frequency of 10 Hz. These results represent an increase in cathode currents of three orders of magnitude over steady state sources. Neutron production at the peak of the pulse was found to be /spl sim/10/sup 9/ n/s of D-D neutrons. This increase in pulsed current operation, and corresponding linear scaling of fusion reaction rates, represents a significant step forward in the development of IEC controlled fusion. An "effective-Q" of this operation was calculated to be 6/spl times/10/sup -5/. Analysis of IEC operation at higher current indicates that breakeven, with an effective-Q of 1.0, might be reached with additional increase in cathode current of only /spl sim/2 orders of magnitude.

Summary form only given, as follows. One approach to fullerene production is the a use of a hydrocarbon such as methane in a plasma discharge. The efficiency of this approach is hampered, however, because hydrogen atoms in the discharge can quench the recombination of carbon atoms prior to full C/sub 60/ formation. Inertial electrostatic confinement (IEC) offers a possible solution, however. A potential well structure develops in the center of a spherical IEC discharge such that carbon and hydrogen ions tend to concentrate in different regions of the well, giving a higher conversion to C/sub 60/. Experiments with He-methane mixtures have confirmed the basic principle, but further research is under way to determine optimum conversion efficiencies achievable. In this case the IEC is operated in a pulsed mode so that carbon recombination occurs rapidly as the plasma cools between pulses. Removal of product C/sub 60/ is done through a double valve arrangement at the bottom of the chamber, so that vacuum need not be broken. An alternate approach, also under study, is to operate the IEC in the "jet" mode. Then, the plasma entering the jet is predominately from the outer region of the potential well structure, again providing separation. Preliminary results and calculations for both configurations will be presented.

Inertial Electrostatic Confinement (IEC) is a unique approach to fusion and plasma energy systems that was conceptualized in the 1960s (Hirsch 1967) and has been the focus of recent development in the 1990s (Miley et al. 1995a). In the interests of space power and propulsion systems, conceptual rocket design studies (Bussard and Jameson 1994, Miley et al. 1995b) using the IEC have predicted excellent performance for a variety of space missions, since the power unit avoids the use of magnets and heavy drives resulting in a very high, specific impulse compared to other fusion systems. In their recent survey of prior conceptual design studies of fusion rockets, Williams and Borowski (1997) found that the Bussard IEC conceptual study (the “QED” engine) offered a thrust-to-weight ratio of 10 milli-g’s, a factor of five higher than conventional magnetic confinement concepts and even slightly above anti-proton micro fission/fusion designs. Thus there is considerable motivation to study IEC concepts for eventual ...