Various DD and DT plasmas are analysed for effects of fast ion transport with a time dependent, 1 1/2 -D transport simulation code (TRANSP). The sensitivity of the simulations to fast ion diffusion modelling is tested against numerous parameters. Strong correlations are found with beam power and plasma stored energy. The neutron emission sensitivity is mostly affected by the fraction of beam-beam neutrons. Wall recycling is essential in interpreting the results for DT plasmas heated with pure deuterium or pure tritium beams. The decay of the 14 MeV neutron emission following a short DT beam pulse implies a small fast ion diffusion coefficient (Df<0.05 m2/s). The agreement of the measured neutron emission and diamagnetic flux with the simulations in DT plasmas heated with various numbers of tritium and deuterium beams, and power, implies that Df

We present evidence that the fast-ion diffusion coefficient changes across the TFTR plasma column. Two MHD quiescent discharges are analyzed: a high power D-T plasma heated with 21 MW of deuterium and tritium beams, and an ohmic plasma into which a 10 MW, 20 ms deuterium beam pulse was injected. The localized charge-exchange measurements in the ohmic plasma, and the neutron flux measurements in the D-T plasma are compared with predictions from the 1 1/2 D transport simulation code TRANSP. We have modified the code to allow modelling with arbitrary fast-ion diffusion profiles Df(r). Significant improvement in the agreement between measurement and simulation is obtained with a Df(r) profile that has low values in the inner half of the plasma column (Df<0.05 m2 s-1) and then rises rapidly towards the plasma periphery. This suggests a common underlying mechanism of enhanced beam ion transport in the two discharges, such as stochastic ripple diffusion.

The Dα light emitted by neutralized deuterium fast ions is measured in magnetohydrodynamics (MHD)-quiescent, magnetically confined plasmas during neutral beam injection. A weighted Monte Carlo simulation code models the fast-ion Dα spectra based on the fast-ion distribution function calculated classically by TRANSP [R. V. Budny, Nucl. Fusion 34, 1247 (1994)]. The spectral shape is in excellent agreement and the magnitude also has reasonable agreement. The fast-ion Dα signal has the expected dependencies on various parameters including injection energy, injection angle, viewing angle, beam power, electron temperature, and electron density. The neutral particle diagnostic and measured neutron rate corroborate the fast-ion Dα measurements. The relative spatial profile agrees with TRANSP and is corroborated by the fast-ion pressure profile inferred from the equilibrium. © 2007 American Institute of Physics.

A detector system based on partially depleted silicon surface barrier detectors and fast front-end electronics has been built and cross calibrated to a set of absolutely calibrated 4He recoil detectors. The cross-calibration factor for the channel with the widest dynamic range is 2.5×10-13 counts per 14 MeV source neutron. These data agree well with the independent neutron activation data. The new detector system covers a large dynamic range (corresponding to 1013-1018 neutrons/s). The response is linear, except at the highest count rates where the detector dead time (∼200 ns) causes departure from linearity. The noise discrimination against 2.5 MeV neutrons and γ pileup is excellent. Measurements of D-T neutrons from a tritium gas puff experiment as well as from a high-power D-T discharge in the TFTR tokamak are presented. © 1995 American Institute of Physics.

Hydrogenic fast-ion populations are common in toroidal magnetic fusion devices, especially in devices with neutral beam injection. As the fast ions orbit around the device and pass through a neutral beam, some fast ions neutralize and emit Balmer-alpha light. The intensity of this emission is weak compared with the signals from the injected neutrals, the warm (halo) neutrals and the cold edge neutrals, but, for a favourable viewing geometry, the emission is Doppler shifted away from these bright interfering signals. Signals from fast ions are detected in the DIII-D tokamak. When the electron density exceeds ̃7 × 1019 m-3, visible bremsstrahlung obscures the fast-ion signal. The intrinsic spatial resolution of the diagnostic is ̃5cm for 40keV amu-1 fast ions. The technique is well suited for diagnosis of fast-ion populations in devices with fast-ion energies (̃30 keV amu-1), minor radii (̃0.6 m) and plasma densities (≲ 1020 m-3) that are similar to those of DIII-D.

A search is made for signs of enhanced beam ion transport in a set of TFTR plasmas heated with various numbers of tritium and deuterium beams. Our investigation is based on the time dependent, 11/2-D simulation code TRANSP, and an ad hoc diffusion model of enhanced fast ion transport. Spatially constant and spatially variable diffusion models are used (the code was upgraded to allow for Df(r) modelling). Simulations with spatially constant diffusion coefficients resulted in an upper bound of Df 0.2 m2/s for a set of high power DT supershots. One discharge is analysed in particular detail, in terms of both various diffusion models and the effects of systematic errors. Best agreement between the measured neutron flux in this discharge and the corresponding TRANSP predictions is obtained by assuming that Df has low values in the inner half of the plasma column (Df 0.1 m 2/s) and then rises rapidly in the outer half, suggesting that stochastic ripple diffusion is the likely mechanism for the enhanced beam ion transport. This hypothesis is supported by the modelling results from two other plasmas with large major radii.

A code thatmodels signals produced by charge-exchange reactions between fast ions and injected neutral beams in tokamak plasmas is described. With the fastion distribution function as input, the code predicts the efflux to a neutral particle analyzer (NPA) diagnostic and the photon radiance of Balmer-alpha light to a fastion Dá (FIDA) diagnostic. Reactions with both the primary injected neutrals and with the cloud of secondary "halo" neutrals that surround the beam are treated. Accurate calculation of the fraction of neutrals that occupy excited atomic states (the collisionalradiative transition equations) is an important element of the code. Comparison with TRANSP output and other tests verify the solutions. Judicious selection of grid size and other parameters facilitate efficient solutions. The output of the code has been validated by FIDA measurements on DIII-D but further tests are warranted. © 2011 Global-Science Press.

An instability with a lower frequency than the toroidicity-induced Alfvén eigenmode was initially identified as a beta-induced Alfvén eigenmode (BAE). Instabilities with the characteristic spectral features of this "BAE" are observed in a wide variety of tokamak plasmas, including plasmas with negative magnetic shear. These modes are destabilized by circulating beam ions and they transport circulating beam ions from the plasma core. The frequency scalings of these "BAEs" are compared to theoretical predictions for Alfvén modes, kinetic ballooning modes, ion thermal velocity modes, and energetic particle modes. None of these simple theories match the data. © 1999 American Institute of Physics.

The fast-ion distribution function in the National Spherical Torus Experiment is modified from shot to shot while keeping the total injected power at ∼2 MW. Deuterium beams of different energy and tangency radius are injected into helium L-mode plasmas, producing a rich set of instabilities, including compressional Alfvén eigenmodes, toroidicity-induced Alfvén eigenmodes (TAE), 50-100 kHz instabilities with rapid frequency sweeps or chirps, and strong, low frequency (10-20 kHz) fishbones. The experiment was motivated by a theory that attributes frequency chirping to the formation of holes and clumps in phase-space. In the theory, increasing the effective collision frequency of the fast ions that drive the instability can suppress frequency chirping. In the experiment, high-power (≲3 MW) high harmonic fast wave (HHFW) heating accelerates the fast ions in an attempt to alter the nonlinear dynamics. Steady-frequency TAE modes diminish during the HHFW heating but there is little evidence that frequency chirping is suppressed. © 2006 IOP Publishing Ltd.