Physics and design interplay phenomena in an actively cooled tokamak: Tore Supra

Abstract

In order to achieve long pulse high performance plasma discharges, actively cooled plasma facing components (PFCs) have been installed since the beginning of Tore Supra in 1988. So far, up to 280 MJ of energy could be removed within a single discharge of 2 mn duration. Active cooling creates a specific environment, like, e.g., constant low wall temperature (<200 °C) or the presence of water pipes close to the plasma boundary, as compared to inertially cooled devices. Physical processes, specific of the actively cooled environment occur, which may sometimes induce irreversible damage that would not even have been observed on conventional PFCs. After a short description of the development status of the actively cooled PFCs program at Tore Supra, the paper concentrates on those aspects where physics and design aspects are mixed, which deserve thorough analysis for the conception of a next step fusion device environment.

Modeling of dust-particle behavior for different materials in plasmas

“…Table I lists the materials used for plasma facing components ͑PFC͒ in different fusion devices around the world and in ITER. [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] As seen, the commonly used materials are Be, C, Fe, Mo, and W. The choice of material in current devices is typically governed by specific thermochemical characteristics in hydrogen plasma environment, cost, and suitable construction properties as well as by plasma performance considerations. Note that boron was widely used in recent fusion plasma experiments as the restorable coating of PFCs.…”

Analysis of PWI footprint traces and material damage on the first walls of the spherical tokamak QUEST

“…The energetic electrons (e.g. run away electrons) are known to cause severe damages on the remote regions of the PFCs [2,3,22]. Hence the electron trajectories, whose toroidal launching positions are corresponding to those of the four limiters (˚ = 10 • , 103 • , 167 • and 268 • respectively) have been calculated for a typical limiter configurations (I P = 10 kA).…”

Analysis of the footprint traces on the first walls of the compact plasma wall interaction device (CPD) using surface analysis and electron orbit calculations

“…Fusion plasma devices are generally susceptible to a large heat load on plasma facing components (PFCs) due to the plasma wall interaction (PWI). PWI is responsible for various adverse effects such as erosion and degradation, re-distribution of impurity materials and damaging of PFCs [1][2][3][4][5][6][7][8][9][10][11]. PWI can cause the re-deposition of insulating materials, which may lead to a very high surface temperature and even makes it impossible to diagnose the actual surface temperature [1,2].…”

“…Although these loss mechanisms are understood due to their poor confinement caused by the insufficient poloidal magnetic field (B P ), the prompt and stochastic 'ripple' effects or waveparticle interactions of various instabilities [6][7][8], locations of the damages must be inferred by the help of complicated drift trajectories intersecting the PFCs. The abrupt generation or steady-state interaction with these energetic particles is also taken into account for off-normal events such as disruptions [8,9] or in steady-state operations [10]. Furthermore, in addition to severe damages hindering steady-state operation of the fusion devices, enhanced recycling of fuelled particles due to symmetric [5] or localized [11] heat load on PWI regions must be clarified from a viewpoint of steady-state density control.…”