Operating a full tungsten actively cooled tokamak: overview of WEST first phase of operation

WEST is an MA class superconducting, actively cooled, full tungsten (W) tokamak, designed to operate in long pulses up to 1000 s. In support of ITER operation and DEMO conceptual activities, key missions of WEST are: (i) qualification of high heat flux plasma-facing components in integrating both technological and physics aspects in relevant heat and particle exhaust conditions, particularly for the tungsten monoblocks foreseen in ITER divertor; (ii) integrated steady-state operation at high confinement, with a focus on power exhaust issues. During the phase 1 of operation (2017–2020), a set of actively cooled ITER-grade plasma facing unit prototypes was integrated into the inertially cooled W coated startup lower divertor. Up to 8.8 MW of RF power has been coupled to the plasma and divertor heat flux of up to 6 MW m−2 were reached. Long pulse operation was started, using the upper actively cooled divertor, with a discharge of about 1 min achieved. This paper gives an overview of the results achieved in phase 1. Perspectives for phase 2, operating with the full capability of the device with the complete ITER-grade actively cooled lower divertor, are also described

Analysis of the dosimetry campaign performed during the CABRI commissioning tests

International audienceCABRI is an experimental pulse reactor operated by CEA at the Cadarache research center and funded by the French Nuclear Safety and Radioprotection Institute (IRSN).For the purpose of the CABRI International Program (CIP), operated and managed by IRSN under an OECD/NEA framework it has been refurbished since 2003 to be able to provide experiments in prototypical PWR conditions (155 bar, 300 DC) in order to study the fuel behavior under Reactivity Initiated Accident (RIA) conditions.This paper first reminds the design and the goals of the dosimetry program that was built in support of the commissioning tests performed for the reactor restart and requalification. Then it focuses on the irradiation conditions for each dosimeter and presents the measurement results. Finally, an analysis of the dosimetry campaign including measurement-calculation comparisons is presented

On plasma rotation with toroidal magnetic field ripple and no external momentum input

International audienceRipple-induced thermal loss effect on plasma rotation is investigated in a set of Ohmic L-mode plasmas performed in Tore Supra, and comparisons with neoclassical predictions including ripple are performed. Adjusting the size of the plasma, the ripple amplitude has been varied from 0.5% to 5.5% at the plasma boundary, keeping the edge safety factor constant. The toroidal flow dynamics is understood as being likely dominated by turbulence transport driven processes at low ripple amplitude, while the ripple-induced toroidal friction becomes dominant at high ripple. In the latter case, the velocity tends remarkably towards the neoclassical prediction (counter-current rotation). The radial electric field is not affected by the ripple variation and remains well described by its neoclassical prediction. Finally, the poloidal velocity is of the order of the neoclassical prediction at high ripple amplitude, but significantly departs from it at low ripple

Collisionality scaling in Tore Supra: detailed energy confinement analysis, turbulence measurements and gyrokinetic modelling

A collisionality scaling experiment associating a confinement analysis, turbulence measurements across the whole plasma and gyrokinetic modelling is reported. In Tore Supra L-mode plasmas, mid-radius dimensionless collisionality nu* has been varied performing a four-points scan from similar or equal to 0.1 to similar or equal to 0.7. The normalized confinement time exhibits a dependence with respect to collisionality: B tau(E) proportional to nu*(-0.3 +/- 0.3) which is strongly modified when accounting for the confinement dependence on the normalized Larmor radius, rho*, and normalized pressure, beta, since one obtains B tau(E) proportional to nu*(0.0 +/- 0.7). This weak dependence is consistent with ITER L mode scaling laws and dedicated experiments elsewhere (Luce 2008 Plasma Phys. Control. Fusion 50 043001). The global analysis is confirmed by normalized effective heat transport coefficients which do not vary outside their error bars in a limited radial range of reliability. The analysis is completed by density fluctuation delta n(e)/n(e) measurements across the whole plasmas. For normalized radius r/a < 0.7, delta n(e)/n(e) does not depart from its error bars and the radial wave-vector spectra are not modified. These observations are well reproduced by non-linear gyrokinetic simulations, where, despite high nu* values, no zonal flow damping mechanism is at play. At the plasma edge (r/a > 0.7), the lowest poloidal wave-vector measured by the Doppler reflectometer exhibits a decrease in delta n(e)/n(e) with increasing nu*, while the other turbulence measurements remain unaffected

Collisionality scaling in Tore Supra: detailed energy confinement analysis, turbulence measurements and gyrokinetic modelling

International audienceThis paper presents the first observation of geodesic acoustic modes (GAMs) on Tore Supra plasmas. Using the Doppler backscattering system, the oscillations of the plasma flow velocity, localized between r/a = 0.85 and r/a = 0.95, and with a frequency, typically around 10 kHz, have been observed at the plasma edge in numerous discharges. When the additional heating power is varied, the frequency is found to scale with Cs/R. The MUltiple SIgnal Classification (MUSIC) algorithm is employed to access the temporal evolution of the perpendicular velocity of density fluctuations. The method is presented in some detail, and is validated and compared against standard methods, such as the conventional fast Fourier transform method, using a synthetic signal. It stands out as a powerful data analysis method to follow the Doppler frequency with a high temporal resolution, which is important in order to extract the dynamics of GAMs

Operating near the L-H power threshold in WEST full tungsten environment

International audienc