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The advanced beam-driven FRC is a Field Reversed Configuration (FRC) with the addition of neutral beam (NB) injection, electrode biasing, and magnetic expander divertors. The resulting configuration has novel features that make it necessary to revisit many key results in FRC theory. Three of these features include (i) a large energetic ion population, (ii) in-principle capability to adjust the electric field and rotation profiles, and (iii) a combination of magnetic and electrostatic confinement of electrons in the SOL. In some fueling scenarios the electron density profile may exhibit a significant peak outside of the separatrix. To explore these features a hybrid fluid/kinetic equilibrium model has been used to reconstruct typical experimental profiles of the C-2W experiment. Results indicate that the energetic ions provide at least 50% of the total plasma pressure. These equilibrium profiles have been used as initial conditions for global, cross-separatrix, turbulent transport simulations using the 3D electrostatic particle-in-cell code ANC. Electrostatic fluctuations were found to nonlinearly saturate at an amplitude which is an order magnitude lower than that observed previously. The tokamak turbulence code GTC code has also been extended to handle FRC physics in the new GTC-X version, which has been used to perform simulations of turbulent transport in the SOL relevant to electrode biasing. It is found that equilibrium × flow shear significantly decreases ion temperature gradient saturation amplitude and ion heat transport. Also in the SOL, a 1D2V continuum code has been developed and applied to parallel electron heat transport. Results show the formation of pre-sheath potential and reduction of parallel electron heat loss close to the ideal ambipolar limit, a result which has been validated by experimental diagnostics. These transport modifications caused by the three novel configuration features help to explain the remarkable plasma performance of the C-2W experiment.

TAE Technologies' research is devoted to producing high temperature, stable, long-lived field-reversed configuration (FRC) plasmas by neutral-beam injection (NBI) and edge biasing/control. The newly constructed C-2W experimental device (also called "Norman") is the world's largest compact-toroid (CT) device, which has several key upgrades from the preceding C-2U device such as higher input power and longer pulse duration of the NBI system as well as installation of inner divertors with upgraded electrode biasing systems. Initial C-2W experiments have successfully demonstrated a robust FRC formation and its translation into the confinement vessel through the newly installed inner divertor with adequate guide magnetic field. They also produced dramatically improved initial FRC states with higher plasma temperatures (Te ~250+ eV; total electron and ion temperature g1.5 keV, based on pressure balance) and more trapped flux (up to ~15 mWb, based on rigid-rotor model) inside the FRC immediately after the merger of collided two CTs in the confinement section. As for effective edge control on FRC stabilization, a number of edge biasing schemes have been tried via open field-lines, in which concentric electrodes located in both inner and outer divertors as well as end-on plasma guns are electrically biased independently. As a result of effective outer-divertor electrode biasing alone, FRC plasma diamagnetism duration has reached up to ~9 ms which is equivalent to C-2U plasma duration. Magnetic field flaring/expansion in both inner and outer divertors plays an important role in creating a thermal insulation on open field-lines to reduce a loss rate of electrons, which leads to improvement of the edge and core FRC confinement properties. Experimental campaign with inner-divertor magnetic-field flaring has just commenced and early result indicates that electron temperature of the merged FRC stays relatively high and increases for a short period of time, presumably by NBI and ExB heating.

Fusion reactivity for the pB11 fuel has been reassessed for magnetic confinement devices. This study is based on two factors: new measurements of the fusion reaction cross-sections and an accounting of the kinetic effects that lead to the increase of the number of protons at higher energies (with respect to a pure Maxwellian). The net effect leads to an approximately 30% increase of the fusion yield for the same global plasma parameters compared to the previous assessments.

Linear fusion devices can use large magnetic flux flaring in the end tanks to reduce the heat load on the end structures. In order to reduce parallel electron heat loss, one has to create conditions where the neutral gas density in the end tanks is low, as otherwise cold electrons produced by the ionization of the neutrals would cool down the core plasma electrons. The processes determining the neutral gas formation and spatial distribution are analysed for the case where neutrals are formed by the surface recombination of the outflowing plasma. The conditions under which the cooling of the core plasma is negligible are formulated.

Conventional field-reversed configurations (FRC) face notable stability and confinement concerns, which can be ameliorated by introducing and maintaining a significant fast ion population in the system. This is the conjecture first introduced by Norman Rostoker multiple decades ago and adopted as the central design tenet in Tri Alpha Energy’s advanced beam driven FRC concept. In fact, studying the physics of such neutral beam (NB) driven FRCs over the past decade, considerable improvements were made in confinement and stability. Next to NB injection, the addition of axially streaming plasma guns, magnetic end plugs, as well as advanced surface conditioning lead to dramatic reductions in turbulence driven losses and greatly improved stability. In turn, fast ion confinement improved significantly and allowed for the build-up of a dominant fast particle population. This recently led to the breakthrough of sustaining an advanced beam driven FRC, thereby demonstrating successful maintenance of trapped magnetic flux, plasma dimensions and total pressure inventory for times much longer than all characteristic system time scales and only limited by hardware and electric supply constraints.

The transport phenomenon of a Field Reversed Configuration (FRC) is studied using the newly developed two-dimensional code Q2D, which couples a magnetohydrodynamic code with a Monte Carlo code for the beam component. The simulation by Q2D of the transport parallel to the simple open θ-pinch fields and its associated outflow phenomenon shows an excellent agreement with one of the leading theories, elevating the Q2D validity and simultaneously deepening the theoretical understanding of this fundamental process. We find a sharp distinction between the evolved radial density profiles of the FRC and mirror plasmas as a result of the transport processes, underpinning the crucial role of the closed flux surfaces of the FRC to enhance the confinement over that of the mirror. We characterize the scrap-off layer (SOL) transport by including the mirror trapping effects, and we find a relationship between the confinement time in the SOL and the ion collisional time. The Q2D code further illuminates the basic transpor...

Critical dimension measurement is the most essential metrology needed in nanofabrication processes and the practice is most commonly executed using SEMs for its flexibility in sampling, imaging, and data processing. In bit patterned media process development, nanoimprint lithography (NIL) is used for template replication and media fabrication. SEM imaging on templates provide not only individual dot size, but also information for dot size distribution, the location of dots, pitch and array alignment quality, etc. It is very important to know the SEM measurement limit since the feature nominal size is less than 20 nm and the dot feature size and other metrics will relate to the final media performance. In our work an analytical SEM was used. We performed and compared two imaging analysis approaches for metrology information. The SEM beam was characterized using BEAMETR test sample and software for proper beam condition setup. A series of images obtained on a 27 nm nominal pitch dot array patterns were analyzed by conventional brightness intensity threshold method and physical model based analysis using myCD software. Through comparison we identified the issues with threshold method and the strength of using model based analysis for its improvement in feature size and pitch measurement uncertainty and accuracy. TEM cross sections were performed as accuracy reference for better understanding the source of measurement accuracy deviation.

The uncertainty associated with scanning electron microscopy (SEM) metrology is significant because SEM image brightness is complexly related to the size and shape of the feature, its material, the geometry of the pattern, as well as SEM setup. While regularly used methods of extracting critical dimensions (CD) rely on image brightness analysis, the myCD software uses a physical model of the SEM in order to improve the accuracy of measurements. Metrology below 10 nm was studied in this paper. Patterns were fabricated using electron beam lithography and nanoimprint; they were imaged by SEM and examined using myCD. Factors that are important for metrology at the sub-10 nm size range were studied using advanced Monte Carlo software; the beam size, voltage, detector and linewidth were varied. SEM images were processed using myCD, which utilizes an analytic model of the SEM and so does not require any libraries. The top and bottom sizes, as well as wall angles and line width roughness were analyzed. The CD and profile results from top down SEM images were compared to the vertical crossections. The challenges of sub-10 nm metrology are discussed, mainly regarding the quality of SEM images and the physics of image formation.

Conventional field-reversed configurations (FRCs), high-beta, prolate compact toroids embedded in poloidal magnetic fields, face notable stability and confinement concerns. These can be ameliorated by various control techniques, such as introducing a significant fast ion population. Indeed, adding neutral beam injection into the FRC over the past half-decade has contributed to striking improvements in confinement and stability. Further, the addition of electrically biased plasma guns at the ends, magnetic end plugs, and advanced surface conditioning led to dramatic reductions in turbulence-driven losses and greatly improved stability. Together, these enabled the build-up of a well-confined and dominant fast-ion population. Under such conditions, highly reproducible, macroscopically stable hot FRCs (with total plasma temperature of ∼1 keV) with record lifetimes were achieved. These accomplishments point to the prospect of advanced, beam-driven FRCs as an intriguing path toward fusion reactors. This paper reviews key results and presents context for further interpretation.