Simulations of density profiles, pellet fuelling and density control in ITER

Abstract

Abstract. The paper presents the results of 1.5-dimensional simulations of density profiles and pellet fuelling for the ITER baseline scenario performed with the ASTRA and JETTO transport codes by the ITER Scenario Modelling working group within the European Task Force on Integrated Tokamak Modelling. The first part of the paper describes the physics of the problem and how it is implemented in the different codes available to the working group. The second part presents the results of the simulations. Results obtained with the GLF23 physics based transport model and a simplified description of the pellet particle source are described alongside results obtained with the simpler Bohm/gyro-Bohm semi-empirical transport model and a more sophisticate pellet ablation/deposition code providing a completely self-consistent description of the pellet source. A parametric study has been performed to assess the effect of varying independently parameters, the values of which in ITER are either uncertain or not easily controllable (such as particle diffusivity, edge stability, wall recycling and boundary conditions), on the target plasma density, temperature, Q and pellet frequency required to achieve a certain degree of density control. To this end the edge particle diffusivity was increased by a factor of three, the pedestal normalized critical pressure gradient for ballooning stability was decreased by 20%, the boundary conditions on density and temperature were modified by 30-40% and the wall recycling particle source was increased from zero to 20% of the particle outflux. The results show that variations in the order of 15% for density and temperature, 40% for Q and 100% for the pellet frequency can be expected. Open problems and modelling needs are also discussed in the paper.

Direct gyrokinetic comparison of pedestal transport in JET with carbon and ITER-like walls

“…Particle fueling and transport in the pedestal remain large open questions, with some estimates predicting that an edge particle pinch or pellet fueling may be required to fuel ITER [67,68]. Here we discuss the potential role of ITG in pedestal particle transport.…”

Particle transport in low-collisionality H-mode plasmas on DIII-D

“…So the focus is shifting from collisionality to the role of turbulence and toroidal rotation in determining particle transport [5]. In this paper we will study the effects of the underlying turbulence structure on particle transport in low torque, low collisionality H-modes on DIII-D. 2 In order to study the effect of turbulence on particle transport in the DIII-D tokamak we performed a set of experiments in which the heating power is altered from predominantly ion heating (using the neutral beam injection (NBI) system) to electron heating (using electron cyclotron heating (ECH)). In DIII-D the ion-electron collisional coupling is weak enough that in low collisionality (ν ∼ * 0.2) discharges switching from ion to electron heating alters both the temperature gradients and thus the turbulence drive in the core plasma.…”

A new method for determining the plasma electron density using optical frequency comb interferometer

“…The result also represents that the method can measure absolute density without temporal evolution of the phases even when the each phase shift caused by plasma density change is over 1 fringe; Most of interferometers (such as two-color and dispersion interferometers) requires temporal evolution of the phases in such case. Therefore, rapid density change in ITER experiments, e.g., ∼10 23 m −2 during disruption by killer pellet 15 and ∼10 20 m −2 during pellet injection 16 do not cause fringe jump error except 100 GHz comb interval of over ∼5 μm wavelength case in Fig. 1.…”

“…12 These characteristics enable high density plasma measurements without the fringe jump errors. The basic concepts is a) Present address: Teikyo University, [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] Misaki-machi, Omuta-shi, Fukuoka 836-8505, Japan. Electronic mail: arakawa@fmt.teikyo-u.ac.jp.…”