Modelling of pellet ablation in additionally heated plasmas

Abstract

A neutral gas and plasma shielding model is presented that describes the interaction of a pellet with the high energy ions and electrons generated during heating or current drive experiments. The main improvements are the selfconsistent calculations of the electrostatic sheath at the cloud-plasma interface and of the extra ablation due to the fast tail of the electron and ion distributions, including heating in the volume of the pellet. With regard to the comparison between the code predictions and the experimental results, realistic threedimensional (space, energy, pitch angle) distributions have been used for both the ions and electrons. For ohmic discharges, the code has been tested on more than 40 well-documented pellets selected in the International Pellet Ablation DataBASE. For additionally heated plasmas (ion cyclotron resonance heatingminority regime-and lower hybrid current drive, 2-4 MW of injected power), Tore Supra data have been used. In these different cases, the calculations are in good agreement with the experimental penetrations and ablation profiles. A parametric study is also presented, which enlightens the control parameter that governs the pellet penetration. In what concerns the capability of pellet injection to fuel reactor grade plasmas, it is shown that no strong extra ablation due to the α-particles is expected.

Experimental studies and simulations of hydrogen pellet ablation in the stellarator TJ-II

“…At present, experimental penetration depths and ablation rates are well reproduced by ablation models [6][7][8][9][10][11][12], some of which consider the anisotropic effects associated with the confining magnetic field [10][11][12], e.g., the latter references [11,12] are 2-D. Moreover, regarding plasma density evolution, i.e., particle deposition, a number of models include an ExB drift of the ablated material to explain the discrepancy between ablation and deposition profiles, where the electric field, E, is produced by the acceleration of plasmoid charged particles in the background inhomogeneous magnetic field [13].…”

“…The HIP2 code was developed to simulate the ablation of a cryogenic pellet (hydrogen, deuterium or a mixture of deuterium and tritium) injected into a magnetic confined plasma created in a tokamak device [10,19] as well as the evolution of the pellet plasmoid, using a 0-D, two-cell, four-fluid Lagrangian system [13,19,39]. The code takes into account specific machine geometrical data, plasma energy and density profiles as well as the magnetic field configuration of the device.…”

Core Fueling of DEMO by Direct Line Injection of High-Speed Pellets From the HFS

“…INJECTED THROUGH "DIRECT LINE" GUIDE TUBES The capability of fuelling DEMO with high speed pellets injected by "direct line" guide tubes has been investigated through simulations with the pellet ablation-deposition code HPI2. This latterwhich is valid for any magnetic and plasma configuration -computes the pellet ablation taking into account thermal ions and electrons, as well as supra-thermal ions generated by the plasma heating systems [4]. The drift model is based on the compensation of the cloud polarization by parallel currents [6].…”

“…This proposal is presently undergoing preliminary investigation. The fuel deposition profiles that can be achieved by this approach are being explored using the HPI2 pellet ablation-deposition code [4], [5], [6]. Some preliminary simulations have been carried out, showing that, within the speed limits attainable by present technologies, there are possible geometrical schemes for direct line injection providing good fueling performance, comparable to those achievable with curved guide tubes.…”

Observation of the Effect of Energetic Ions on Pellet Ablation in the Large Helical Device

“…This is due to the lack of availability of an experimental condition which contains a large amount of energetic ions. Recently, a sophisticated ablation model that describes the interaction of a pellet with energetic ions and electrons in ICRH and LHCD experiments has been reported [11]. However, the current experimental documentation of the effect of fast ions is insufficient.…”