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Waves and Energetic Particles

NSTX is contributing to wave heating and current drive techniques applicable to high-beta, over-dense plasma conditions. NSTX also has a unique combination of fast-ion instability drive flexibility and complete diagnostic coverage that can lead to new discoveries.

Research Priorities:

• Utilize HHFW heating and current drive to assist non-inductive plasma current ramp-up and sustainment (R12-2)
• Characterize and optimize high-harmonic fast wave coupling in deuterium H-mode plasmas
• Assess predictive capability of mode-induced fast-ion transport (IR12-2)
• Extend TAE/EPM studies to H-mode plasmas

High Harmonic Fast Wave Research

The highest priority will be to study the coupling of HHFW into low-current flattop, inductive current ramp-up, and co-axial helicity injection (CHI) startup plasmas. The second priority will be to prepare for NSTX-U by studying HHFW+NBI high current H-mode plasmas at NBI powers up to 6 MW. These experiments will study the interaction of fast-ions with the antenna and antenna heating, surface waves at maximum HHFW and NBI powers, and the dependence of HHFW heating and current drive efficiency on launch wavelength, antenna plasma gap and plasma scrape off layer (SOL) density. We will attempt to use a larger plasma-antenna gap than in the past in order to permit greater stability at higher power (more voltage standoff and greater power for the same voltage). Results from these experiments will be important for benchmarking the 3-D AORSA and TORIC codes. Experiments will also continue to study HHFW interactions with edge localized modes, the SOL, and NBI fast-ions, as well as HHFW-induced rotation effects. New and upgraded diagnostics will aid HHFW research in FY11-12, including the MSE-LiF diagnostic that will provide q(r) without NBI heating, additional MPTS channels that will improve RF modeling, and tangential FIDA that will improve the study of RF fast-ion interaction.

Energetic Particle Research

The highest priority will be to complete validation of numerical models (NOVA-K, ORBIT, M3D-K, SPIRAL) for predicting fast ion transport caused by TAE modes and TAE avalanches. The comparison will initially focus on reproducing the dynamics of mode frequency and amplitude measured in the experiments, with particular emphasis on the weakly bursting/chirping TAE regime observed in L-mode discharges. As a second step, the comparison will be extended to TAE avalanches. Experiments will be extended to H-mode scenarios to complement the dataset collected in the past years for L-mode plasmas. The internal structure of the modes will be documented with the upgraded multi-channel reflectometer system and the newly installed BES diagnostic. The TAE dynamics and associated fast ion transport will be characterized as a function of q-profile, fast ion distribution (pitch angle, energy) and Vfast/VAlfvén through NB power, toroidal field and density scans. In parallel with the studies of TAEs, the characterization of high-frequency GAE/CAE modes will also be completed. The experimental results will be used to validate the numerical code HYM, which will then be exploited to investigate the effects of GAE/CAE modes on fast ion transport and redistribution and on electron thermal transport.

The study and modeling of the impact of EPMs on beam driven currents will continue. Improved measurements of the fast ion population will be available from a second FIDA system, sensitive to co-going fast ions. In addition, mode structure measurements from reflectometer and BES will be used to validate the NOVA and PEST linear ideal codes as well as the M3D-K non-linear code. Predictions of fast ion transport with ORBIT and M3D-K will be compared with experimental data and used to estimate the effects of fast ion losses on NB current drive on NSTX-U.

Milestones:

IR(12-2): Assess predictive capability of mode-induced fast-ion transport (incremental)

Responsible TSGs: Wave-Particle Interactions

"Good confinement of fast-ions from neutral beam injection and thermonuclear fusion reactions is essential for the successful operation of ST-CTF, ITER, and future reactors. Significant progress has been made in identifying the Alfvénic modes (AEs) driven unstable by fast ions, and in measuring the impact of these modes on the transport of fast ions. However, theories and numerical codes that can quantitatively predict fast ion transport have not yet been validated against a sufficiently broad range of experiments. To assess the capability of existing theories and codes for predicting AE-induced fast ion transport, NSTX experiments will aim at improved measurements of the mode eigenfunction structure utilizing a new Beam Emission Spectroscopy (BES) diagnostic and enhanced spatial resolution of the Multi-Channel Reflectometer. Improved measurements of the fast-ion distribution function will be available utilizing a tangentially viewing Fast-Ion D-alpha (FIDA) diagnostic. In order to broaden the range of discharge conditions studied to those relevant to future devices, experiments will be conducted for both L-mode and H-mode scenarios. Specific targets for the experiment-theory comparison are those between the measured and calculated frequency spectra, spatial structure and induced fast ion transport. Both linear (e.g., NOVA-K, ORBIT) and non-linear (e.g., M3D-K, HYM) codes will be used in the analysis. In addition, the newly developed full-orbit particle-following code SPIRAL will be adapted to the NSTX geometry and used to model fast ion losses by Alfvénic modes."

ITPA and BPO Participation:

• TC-9 Scaling of intrinsic plasma rotation with no external momentum input
• TC-14 RF rotation drive
• IOS-5.2 Maintaining ICRH coupling in expected ITER regime
• EP-2 Fast-ion Loss and Redistribution from Localized Alfven eigenmodes
• EP-4 Effect of dynamical friction (drag) at resonance on nonlinear Alfven eigenmode evolution
• EP-6 Fast ion losses and associated heat load from edge perturbations (ELMs and RMPs)