Progress Toward Commissioning and Plasma Operation in NSTX-U
Authors: M. Ono, J. Chrzanowski, L. Dudek, S. Gerhardt, P. Heitzenroeder, R. Kaita, J.E.Menard, E. Perry, T. Stevenson, R. Strykowsky, P. Titus, A. von Halle, M. Williams
Abstract: The National Spherical Torus Experiment – Upgrade (NSTX–U) is the most powerful spherical torus facility at PPPL, Princeton USA. The major mission of NSTX–U is to develop the physics basis for an ST–based Fusion Nuclear Science Facility (FNSF). The ST–based FNSF has the promise of achieving the high neutron fluence needed for reactor component testing with relatively modest tritium consumption. At the same time, the unique operating regimes of NSTX–U can contribute to several important issues in the physics of burning plasmas to optimize the performance of ITER. NSTX–U further aims to determine the attractiveness of the compact ST for addressing key research needs on the path toward a fusion demonstration power plant (DEMO). The upgrade will nearly double the toroidal magnetic field BT of 1 Tesla (T) at a major radius of R0 = 0.93 m, plasma current Ip of 2 mega-Amperes (MA) and NBI heating power of 14 MW. The anticipated plasma performance enhancement is a quadrupling of the plasma stored energy and near doubling of the plasma confinement time, which would result in 5 – 10 fold increase in the fusion performance parameter nτ T. With βT ~ 25% at BT = 1T, the absolute average plasma pressure in NSTX–U could become comparable to that of present-day tokamaks. A much more tangential 2nd NBI system, with 2–3 times higher current drive efficiency compared to the 1st NBI system, is installed to attain the 100% non-inductive operation needed for a compact FNSF design. With higher fields and heating powers, the NSTX–U plasma collisionality will be reduced by a factor of 3–6 to help explore the favorable trend in transport towards the low collisionality FNSF regime. NSTX–U first plasma is planned for March 2015, at which time the transition to plasma operations will occur.
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Submitted to: Nuclear Fusion
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Download PPPL-5116 (pdf 2.75 MB 19pp)
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