Overview of recent experimental results from the DIII-D advanced tokamak program

Abstract

The DIII-D research program is developing the scientific basis for advanced tokamak (AT) modes of operation in order to enhance the attractiveness of the tokamak as an energy producing system. Since the last international atomic energy agency (IAEA) meeting, we have made significant progress in developing the building blocks needed for AT operation: (1) we have doubled the magnetohydrodynamic (MHD) stable tokamak operating space through rotational stabilization of the resistive wall mode; (2) using this rotational stabilization, we have achieved β N H 89 10 for 4τ E limited by the neoclassical tearing mode (NTM); (3) using real-time feedback of the electron cyclotron current drive (ECCD) location, we have stabilized the (m, n) = (3, 2) NTM and then increased β T by 60%; (4) we have produced ECCD stabilization of the (2, 1) NTM in initial experiments; (5) we have made the first integrated AT demonstration discharges with current profile control using ECCD; (6) ECCD and electron cyclotron heating (ECH) have been used to control the pressure profile in high performance plasmas; and (7) we have demonstrated stationary tokamak operation for 6.5 s (36τ E ) at the same fusion gain parameter of β N H 89 /q 2 95 ∼ = 0.4 as ITER but at much higher q 95 = 4.2. We have developed general improvements applicable to conventional and AT operating modes: (1) we have an existence proof of a mode of tokamak operation, quiescent H-mode, which has no pulsed, edge localized modes (ELM) heat load to the divertor and which can run for long periods of time (3.8 s or 25τ E ) with constant density and constant radiated power; (2) we have demonstrated real-time disruption detection and mitigation for vertical disruption events using high pressure gas jet injection of noble gases; (3) we have found that the heat and particle fluxes to the inner strike points of balanced, double-null divertors are much smaller than to the outer strike points. We have made detailed investigations of the edge pedestal and scrape-off layer (SOL): (1) atomic physics and plasma physics both play significant roles in setting the width of the edge density barrier in H-mode; (2) ELM heat flux conducted to the divertor decreases as density increases; (3) intermittent, bursty transport contributes to cross field particle transport in the SOL of H-mode and, especially, L-mode plasmas.

Conference Summary: Experiments in confinement and wave–plasma interaction

“…Figure 4. A record value of β N H 89P > 10 has been obtained in an ATS pulse of DIII-D during four confinement times[7]. The high β N of 4 is close to the ideal wall-limit and made possible by error-field compensation.…”

“…In DIII-D [7] impressive results were obtained in 'advanced tokamak scenarios (ATS)' with slightly negative shear. The record value of β N H 89P exceeding 10 for four times τ E has been made possible by removing error magnetic fields.…”

Role of pinch in Argon impurity transport in Ohmic discharges of Aditya-U Tokamak

“…Aditya-U 34 is a medium-sized air-core tokamak having stainless steel vacuum vessel with major (R) and minor (a) radii of 0.75 m and 0.25 m, respectively. The maximum toroidal magnetic field, BT = 1.5 T. The parameters of circular Ohmic plasmas obtained in limiter configuration with a high-field side toroidal belt limiter in the Aditya-U tokamak are: plasma current ~ 100 -250 kA, plasma duration of ~ 100 -350 ms with electron density and temperature in the range of 1 -3.5 x 10 19 m -3 and 220 -500 eV respectively 35 .…”