Observation of plasma toroidal-momentum dissipation by neoclassical toroidal viscosity.

Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027, USA.
Physical Review Letters (Impact Factor: 7.73). 07/2006; 96(22):225002. DOI: 10.1103/PhysRevLett.96.225002
Source: PubMed

ABSTRACT Dissipation of plasma toroidal angular momentum is observed in the National Spherical Torus Experiment due to applied nonaxisymmetric magnetic fields and their plasma-induced increase by resonant field amplification and resistive wall mode destabilization. The measured decrease of the plasma toroidal angular momentum profile is compared to calculations of nonresonant drag torque based on the theory of neoclassical toroidal viscosity. Quantitative agreement between experiment and theory is found when the effect of toroidally trapped particles is included.

  • [Show abstract] [Hide abstract]
    ABSTRACT: The spherical tokamak (ST) is a leading candidate for a fusion nuclear science facility (FNSF) due to its compact size and modular configuration. The National Spherical Torus eXperiment (NSTX) is a MA-class ST facility in the U.S. actively developing the physics basis for an ST-based FNSF. In plasma transport research, ST experiments exhibit a strong (nearly inverse) scaling of normalized confinement with collisionality, and if this trend holds at low collisionality, high fusion neutron fluences could be achievable in very compact ST devices. A major motivation for the NSTX Upgrade (NSTX-U) is to span the next factor of 3-6 reduction in collisionality. To achieve this collisionality reduction with equilibrated profiles, NSTX-U will double the toroidal field, plasma current, and NBI heating power and increase the pulse length from 1-1.5s to 5s. In the area of stability and advanced scenarios, plasmas with higher aspect ratio and elongation, high β<sub>N</sub>, and broad current profiles approaching those of an ST-based FNSF have been produced in NSTX using active control of the plasma β and advanced resistive wall mode control. High non-inductive current fractions of 70% have been sustained for many current diffusion times, and the more tangential injection of the 2nd NBI of the Upgrade is projected to increase the NBI current drive by up to a factor of 2 and support 100% non-inductive operation. More tangential NBI injection is also projected to provide non-solenoidal current ramp-up (from I<sub>P</sub> = 0.4MA up to 0.8-1MA) as needed for an ST-based FNSF. In boundary physics, NSTX and higher-A tokamaks measure an inverse relationship between the scrape-off layer heat-flux width and plasma current that could unfavorably impact next-step devices. Recently, NSTX has successfully demonstrated very high flux expansion and substantial heat-flux reduction using a snowflake divertor configuration, and this type of divertor is incorporated in the NSTX-U des- - ign. The physics and engineering design supporting NSTX Upgrade are described.
    Fusion Engineering (SOFE), 2011 IEEE/NPSS 24th Symposium on; 07/2011
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The non-resonant magnetic braking effect induced by a non-axisymmetric magnetic perturbation is investigated on JET and TEXTOR. The collisionality dependence of the torque induced by the n = 1, where n is the toroidal mode number, magnetic perturbation generated by the error field correction coils on JET is observed. The observed torque is located mainly in the plasma core (normalized radius ρ < 0.4) and increases with decreasing collisionality. The neoclassical toroidal plasma viscosity (NTV) torque in the collisionless regime is modelled using the numerical solution of the bounce-averaged drift kinetic equation. The calculated collisionality dependence of the NTV torque is in good agreement with the experimental observation on JET. The reason for this collisionality dependence is that the torque in the plasma core on JET mainly comes from the flux of the trapped electrons, which are still mainly in the 1/ν regime. The strongest NTV torque on JET is also located near the plasma core. The magnitude of the NTV torque strongly depends on the plasma response, which is also discussed in this paper. There is no obvious braking effect with n = 2 magnetic perturbation generated by the dynamic ergodic divertor on TEXTOR, which is consistent with the NTV modelling.
    Nuclear Fusion 01/2012; 52:083007. · 2.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A new system for fast measurements of the plasma toroidal velocity has been installed on the National Spherical Torus Experiment, NSTX [M. Ono et al., Nucl. Fusion 40, 557 (2000)]. The diagnostic, based on active charge-exchange recombination spectroscopy, can measure at up to six radial locations with maximum sampling rate of 5 kHz. The system is interfaced in real time with the NSTX plasma control system, in order to feed back on plasma velocity by means of actuators such as neutral beams and external coils. The paper describes the design criteria and implementation of the diagnostic. Examples from the initial tests of the system during neon glows are also discussed.
    The Review of scientific instruments 03/2012; 83(3):033503. · 1.52 Impact Factor


Available from