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Title: High-beta, steady-state hybrid scenario on DIII-D

The potential of the hybrid scenario (first developed as an advanced inductive scenario for high fluence) as a regime for high-beta, steady-state plasmas is demonstrated on the DIII-D tokamak. Our experiments show that the beneficial characteristics of hybrids, namely safety factor ≥ 1 with low central magnetic shear, high stability limits and excellent confinement, are maintained when strong central current drive (electron cyclotron and neutral beam) is applied to increase the calculated non-inductive fraction to ≈ 100% (≈ 50% bootstrap current). Moreover, the best discharges achieve normalized beta of 3.4, IPB98(y,2) confinement factor of 1.4, surface loop voltage of 0.01 V, and nearly equal electron and ion temperatures at low collisionality. A 0D physics model shows that steady-state hybrid operation with Qfus ~ 5 is feasible in FDF and ITER. One advantage of the hybrid scenario as an advanced tokamak regime is that the external current drive can be deposited near the plasma axis where the efficiency is high; additionally, good alignment between the current drive and plasma current profiles is not necessary as the poloidal magnetic flux pumping self-organizes the current density profile in hybrids with an m/n = 3/2 tearing mode.
Authors:
 [1] ;  [2] ;  [3] ;  [1] ;  [4] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [5] ;  [1] ;  [6]
  1. General Atomics, San Diego, CA (United States)
  2. CompX, Del Mar, CA (United States)
  3. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  4. Univ. of California, Los Angeles, CA (United States)
  5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  6. Ecole Polytechnique Federale Lausanne (Switzlerland). Centre de Recherches en Physique des Plasmas.
Publication Date:
OSTI Identifier:
1295134
Grant/Contract Number:
AC05-00OR22725; FC02-04ER54698; AC52-07NA27344; FG02-08ER54984; FG02-04ER54761
Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 56; Journal Issue: 1; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY steady state tokamak; hybrid; advanced tokamak; CYCLOTRON CURRENT DRIVE; HIGH-PERFORMANCE DISCHARGES; INTERNAL TRANSPORT BARRIER; NEOCLASSICAL TEARING MODE; FUSION POWER-PLANT; ASDEX UPGRADE; D TOKAMAK; BOOTSTRAP CURRENT; COMPLETE SUPPRESSION; IGNITION TOK