A fully-neoclassical finite-orbit-width version of the CQL3D Fokker–Planck code

Petrov, Yu. V.; Harvey, R. W.

doi:10.1088/0741-3335/58/11/115001

Cited by 48 publications

(60 citation statements)

References 33 publications

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“…Additional losses of fast electrons associated with the radial diffusion will likely lead to smaller driven current and may bring the predicted value closer to the experimental observation. Either Monte-Carlo approach [22] or Fokker-Planck solver valid for finite orbit width [23] is necessary to account for these effects and also to evaluate bootstrap current in the presence of fast electrons.…”

Section: Outboard-launch Experimental Resultsmentioning

confidence: 99%

Fully non-inductive plasma start-up with lower-hybrid waves using the outboard-launch and top-launch antennas on the TST-2 spherical tokamak

et al. 2017

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Abstract. Removal of the central solenoid is essential to realize an economical spherical tokamak fusion reactor, but non-inductive plasma start-up is a challenge. On the TST-2 spherical tokamak, non-inductive plasma start-up using lower-hybrid (LH) waves has been investigated. Using the capacitively-coupled combline (CCC) antenna installed at the outboard midplane, fully non-inductive plasma current ramp-up up to a quarter of that of the typical Ohmic discharges has been achieved. Although it was desirable to keep the density low during the plasma current ramp-up to avoid the LH density limit, it was recognized that there was a maximum current density that could be carried by a given electron density. Since the density needed to increase as the plasma current was ramped-up, the achievable plasma current was limited by the maximum operational toroidal field of TST-2. The top-launch CCC antenna was installed to access higher density with up-shift of the parallel index of refraction. Numerical analysis of LH current drive with the outboard-launch and top-launch antennas was performed and the results were qualitatively consistent with the experimental observations.

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Section: Outboard-launch Experimental Resultsmentioning

confidence: 99%

Fully non-inductive plasma start-up with lower-hybrid waves using the outboard-launch and top-launch antennas on the TST-2 spherical tokamak

et al. 2017

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“…Instead, we use a modified version of the coordinates first promoted by Rome 13 and others. 14 Here, we define the action coordinates, hereby called orbit-space variables, to be…”

Section: B Orbit Weight Functionsmentioning

confidence: 99%

Action-angle formulation of generalized, orbit-based, fast-ion diagnostic weight functions

Stagner

Heidbrink

2017

Physics of Plasmas

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Due to the usually complicated and anisotropic nature of the fast-ion distribution function, diagnostic velocity-space weight functions, which indicate the sensitivity of a diagnostic to different fast-ion velocities, are used to facilitate the analysis of experimental data. Additionally, when velocity-space weight functions are discretized, a linear equation relating the fast-ion density and the expected diagnostic signal is formed. In a technique known as velocity-space tomography, many measurements can be combined to create an ill-conditioned system of linear equations that can be solved using various computational methods. However, when velocity-space weight functions (which by definition ignore spatial dependencies) are used, velocity-space tomography is restricted, both by the accuracy of its forward model and also by the availability of spatially overlapping diagnostic measurements. In this work, we extend velocity-space weight functions to a full 6D generalized coordinate system and then show how to reduce them to a 3D orbit-space without loss of generality using an action-angle formulation. Furthermore, we show how diagnostic orbit-weight functions can be used to infer the full fast-ion distribution function, i.e., orbit tomography. In depth derivations of orbit weight functions for the neutron, neutral particle analyzer, and fast-ion D-α diagnostics are also shown.

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“…In some case of the top launch conditions, a computing error in implicit solver in CQL3D code occurred. We found this error is removed using the recent fully-neoclassical finite-orbit-width version of CQL3D [4]. In the ray tracing simulation, the toray module in the genray code is used with the finite beam divergence at the launch position.…”

Section: Simulation Codementioning

confidence: 99%

Ray Tracing Study on Top ECCD Launch in KSTAR

2017

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Abstract. The current drive efficiency of electron cyclotron (EC) wave is typically low compared with other RF and neutral beam heating system in tokamak. It is known that EC current drive by outboard launch suffers from low current drive efficiency due to electron trapping. However, the heating and current drive by EC wave is being regarded as a strong candidate for DEMO reactor due to the simplicity of the launcher, none of its interaction with plasma, and no coupling issue at the plasma edge. Also, off-axis heating and current drive by EC wave plays an important role of steady state operation optimization. To enhance the current drive efficiency in DEMO-relevant operation condition having high density and high temperature, the top launch of EC wave is recently proposed in FNSF design [2]. In FNSF, a top launch makes use of a large toroidal component to the launch direction adjusting the vertical launch angle so that the rays propagate nearly parallel to the resonance layer increasing of Doppler shift with higher n||. The results shows a high dimensional efficiency for a broad ECCD profile peaked off axis. In KSTAR, the possibility of efficient off-axis ECCD using top launch is investigated using the ray tracing code, GENRAY [3] for the operating EC frequencies (105 GHz or 140 GHz, and 170 GHz). The high current drive efficiency is found by adjusting the toroidal magnetic field and the radial pivot position of the final launcher mirror for fundamental O-mode and second harmonic X-mode. A large Doppler shift is not quite sure in the typical plasma profile in KSTAR, but the simulation results show high current drive efficiency. This paper presents ray tracing results for many cases with the wave trajectories and damping of EC by scanning the launching angle for specific launcher pivot positions and toroidal magnetic field, and two equilibriums of the KSTAR.

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A fully-neoclassical finite-orbit-width version of the CQL3D Fokker–Planck code

Cited by 48 publications

References 33 publications

Fully non-inductive plasma start-up with lower-hybrid waves using the outboard-launch and top-launch antennas on the TST-2 spherical tokamak

Fully non-inductive plasma start-up with lower-hybrid waves using the outboard-launch and top-launch antennas on the TST-2 spherical tokamak

Action-angle formulation of generalized, orbit-based, fast-ion diagnostic weight functions

Ray Tracing Study on Top ECCD Launch in KSTAR

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