An electron-beam ion trap (EBIT) is used to measure extreme ultraviolet spectra between 10 and 25 nm from highly charged ions of tungsten with an open 3d shell (W XLVIII through W LVI ). We found that almost all strong lines are due to the forbidden magnetic-dipole (M1) transitions within 3d n ground configurations. A total of 37 previously unknown spectral lines are identified using detailed collisional-radiative (CR) modeling of the EBIT spectra. A level-merging scheme for compactification of rate equations is described. The CR simulations for Maxwellian plasmas show that several line ratios involving these M1 lines can be used to reliably diagnose temperature and density in hot fusion devices.

Overview of C-2 field-reversed configuration experiment plasma diagnosticsa) Rev. Sci. Instrum. 85, 11D836 (2014); 10.1063/1.4884616 Density fluctuation measurements by far-forward collective scattering in the MST reversed-field pincha) Rev. Sci. Instrum. 83, 10E302 (2012);A new high performance field reversed configuration operating regime in the C-2 devicea)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. V C 2015 AIP Publishing LLC. [http://dx.

The time history of the local ion kinetic energy in a stagnating plasma was determined from Doppler-dominated line shapes. Using independent determination of the plasma properties for the same plasma region, the data allowed for inferring the time-dependent ion temperature, and for discriminating the temperature from the total ion kinetic energy. It is found that throughout most of the stagnation period the ion thermal energy constitutes a small fraction of the total ion kinetic energy; the latter is dominated by hydrodynamic motion. Both the ion hydrodynamic and thermal energies are observed to decrease to the electron thermal energy by the end of the stagnation period. It is confirmed that the total ion kinetic energy available at the stagnating plasma and the total radiation emitted are in balance, as obtained in our previous experiment. The dissipation time of the hydrodynamic energy thus appears to determine the duration (and power) of the K emission.

Abstract. The electron beam ion trap (EBIT) at the National Institute of Standards and Technology was used to produce highly-charged ions of hafnium, tantalum and gold with an open 3d shell. The extremeultraviolet (EUV) spectra from these ions were recorded with a flat-field grazing-incidence spectrometer in the wavelength range of 4.5 nm to 25 nm. A total of 133 new spectral lines, primarily due to magneticdipole transitions within the ground-state 3d n configurations of the Co-like to K-like ions, were identified by comparing energy-dependent experimental spectra with a detailed collisional-radiative modeling of the EBIT plasma.

Tri Alpha Energy's experimental program has demonstrated reliable field-reversed configuration (FRC) formation and sustainment, driven by fast ions via high-power neutral-beam (NB) injection. The world's largest compact-toroid device, C-2U, was upgraded from C-2 with the following key system upgrades: increased total NB input power from ~4 MW (20 keV hydrogen) to 10+ MW (15 keV hydrogen) with tilted injection angle; enhanced edge-biasing capability inside of each end divertor for boundary/stability control. C-2U experiments with those upgraded systems have successfully demonstrated dramatic improvements in FRC performance and achieved sustainment of advanced beam-driven FRCs with a macroscopically stable and hot plasma state for up to 5+ ms. Plasma diamagnetism in the best discharges has reached record lifetimes of over 11 ms, timescales twice as long as C-2. The C-2U plasma performance, including the sustainment feature, has a strong correlation with NB pulse duration, with the diamagnetism persisting even several milliseconds after NB termination due to the accumulated fast-ion population by NB injection. Power balance analysis shows substantial improvements in equilibrium and transport parameters, whereby electron energy confinement time strongly correlates with electron temperature; i.e. the confinement time in C-2U scales strongly with a positive power of T e .