Overview of JET results

Abstract

Scientific and technical activities on JET focus on the issues likely to affect the ITER design and operation. Our understanding of the ITER reference mode of operation, the ELMy H-mode, has progressed significantly. The extrapolation of ELM size to ITER has been re-evaluated. Neoclassical tearing modes have been shown to be meta-stable in JET, and their beta limits can be raised by destabilization (modification) of sawteeth by ion cyclotron radio frequency heating (ICRH). Alpha simulation experiments with ICRH accelerated injected 4He beam ions provide a new tool for fast particle and magnetohydrodynamic studies, with up to 80–90% of plasma heating by fast 4He ions. With or without impurity seeding, a quasi-steady-state high confinement (H98 = 1), high density (ne/nGW = 0.9–1) and high β (βN = 2) ELMy H-mode has been achieved by operating near the ITER triangularity (δ∼ 0.40–0.5) and safety factor (q95∼ 3), at Zeff∼ 1.5–2. In advanced tokamak (AT) scenarios, internal transport barriers (ITBs) are now characterized in real time with a new criterion, . Tailoring of the current profile with lower hybrid current drive provides reliable access to a variety of q profiles, lowering access power for barrier formation. Rational q surfaces appear to be associated with ITB formation. Alfvén cascades were observed in reversed shear plasmas, providing identification of q profile evolution. Plasmas with ‘current holes’ were observed and modelled. Transient high confinement AT regimes with H89 = 3.3, βN = 2.4 and ITER-relevant q < 5 were achieved with reversed magnetic shear. Quasi-stationary ITBs are developed with full non-inductive current drive, including ∼50% bootstrap current. A record duration of ITBs was achieved, up to 11 s, approaching the resistive time. For the first time, pressure and current profiles of AT regimes are controlled by a real-time feedback system, in separate experiments. Erosion and co-deposition studies with a quartz micro-balance show reduced co-deposition. Measured divertor thermal loads during disruptions in JET could modify ITER assumptions.

ELM control strategies and tools: status and potential for ITER

“…As the plasma energy is expelled by the ELMs in very short timescales (~100s s), the local power fluxes caused by the ELMs are expected to be significant and cause local overheating of the plasma facing components, a problem whose seriousness is expected to increase with the size of the tokamak.. Whereas for mid-size tokamaks (minor radius a 0 about 0.5 m) ELMs are not found to cause any damage to plasma facing components, the larger sized JET (a 0 about 1.0 m) observed already melting of the Be divertor surfaces and large impurity influxes caused by loosely attached hydrocarbon layers affecting the plasma performance for the largest ELMs [4]. In ITER, uncontrolled type-I ELMs are thus expected to cause significant impurity influxes into the main plasma and shorten the lifetime of plasma facing component including by evaporation and melting during these events.…”

Investigation of lower hybrid wave coupling and current drive experiments at different configurations in experimental advanced superconducting tokamak

“…Nuclear fusion experiments have made a rapid progress since 1980s in many tokamaks by using LHCD. [1][2][3][4][5][6][7][8] A 2 MW 2.45 GHz LHW system has been installed and run in the experimental advanced superconducting tokamak (EAST), in which LHW-plasma coupling and LHCD experiments have been performed systematically recently.…”

Computational Center for Studies of Plasma Microturbulence

“…CCSM supported detailed analyses of data from the National Spherical Torus Experiment (NSTX) at the Princeton Plasma Physics Laboratory, [1,2] from the Joint European Torus (JET) in the United Kingdom, [3,4] from the Doublet III-D (DIII-D) tokamak at General Atomics (San Diego, CA), [5,6,7] from the Frascati Tokamak Upgrade (FTU) in Italy, [8] from the Mega-Ampere Spherical Tokamak (MAST) in the United Kingdom, [9,10] and from the Alcator C-Modified (Alcator C-Mod) tokamak at the Massachusetts Institute of Technology. [11,12] Clear identification of key confinement trends and correlation with fluctuation measurements was made in this work, which focused on confinement in the "core" plasma as well as in "internal transport barriers" (ITB's).…”