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 βNH89 ⩾ 10 for 4τE 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 βT 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 (36τE) at the same fusion gain parameter of as ITER but at much higher q95 = 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 25τE) 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.
Highlights
The DIII-D research program is developing the scientific basis for advanced modes of operation in order to enhance the attractiveness of the tokamak as an energy producing system
Experiments on DIII-D have demonstrated that the impact of disruptions on first wall or in-vessel components can be greatly reduced by the injection of noble gas using a high pressure gas jet [21,22,23]
We have made significant progress in developing the building blocks needed for advanced tokamak (AT) operation: (1) We have substantially increased the MHD stable tokamak operating space through rotational stabilization of the resistive wall mode (RWM)
Summary
The DIII-D research program is developing the scientific basis for advanced modes of operation in order to enhance the attractiveness of the tokamak as an energy producing system. Previous studies [1,2,3,4,5,6] have shown that an attractive tokamak requires high power density (which demands high toroidal beta βT = 2μo p /BT2), high ignition margin (high energy confinement time τE), and steady-state operation with low recirculating power (high bootstrap fraction fBS), as well as adequate divertor heat removal, particle and impurity control. These requirements demand an integrated approach, optimizing the plasma from the core, through the edge pedestal and into the divertor. SOL studies have shown that intermittent convective transport is an important particle transport mechanism in the region outside the separatrix [31,32,33]
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