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Transport and Turbulence

The ultimate goal of NSTX is to develop a first-principles understanding of the transport of thermal energy, particles and angular momentum by taking advantage of the novel plasma regimes in which it operates including: high-beta, strong E_r shear, dominant electron heating, and localized measurements of electron-scale turbulence.

Research Priorities:

• Measure fluctuations responsible for turbulence particle and impurity transport.
• Investigate mechanisms for turbulence electron thermal transport
• Confinement scaling to very low aspect ratio
• L-H transition physics
• Role of turbulence in driving intrinsic rotation and the ρ* scaling of intrinsic torque.

Milestones:

R(11-1): Measure fluctuations responsible for turbulent electron, ion and impurity transport

Responsible TSGs: Transport & Turbulence

"The thermal transport scalings of electrons and ions with magnetic field and plasma current in NSTX H-mode plasmas have been found to be different from those of high-aspect-ratio tokamaks. Furthermore, recent experiments show that lithiated wall conditions can affect global confinement of NSTX H-mode plasmas and lead to different scalings with magnetic field and plasma current from un-lithiated plasmas. High-k scattering measurements have identified ETG turbulence as one candidate for the anomalous electron energy transport for both H and L-mode plasmas. However, low-k fluctuations and fast-ion-driven modes, e.g. GAE, may also contribute to electron transport. Furthermore, low-k fluctuations may also contribute significantly to momentum, ion thermal, and particle/impurity transport. In addition to measuring high-k fluctuations, the low-k turbulence and fast-ion-driven modes will be measured with a Beam Emission Spectroscopy (BES) diagnostic. Additional low-k fluctuation measurements will be made using the upgraded reflectometer, interferometer, and gas puff imaging systems. The turbulence k spectrum will be measured as function of plasma parameters and coupled with power balance analysis. Experiments on particle transport will be carried out by using gas puffs coupled with density measurements and low-k to high-k turbulence measurements. Impurity transport will be studied by coupling impurity puff and edge SXR measurements."

FY2012 OFES 3 Facility Joint Research Milestone (FY2012 JRT):

Responsible TSGs: Transport & Turbulence

"Conduct experiments on major fusion facilities leading toward improved understanding of core transport and enhanced capability to predict core temperature and density profiles. In FY 2012, FES will assess the level of agreement between predictions from theoretical and computational transport models and the available experimental measurements of core profiles, fluxes and fluctuations. The research is expected to exploit the diagnostic capabilities of the facilities (Alcator C-Mod, DIII-D, NSTX) along with their abilities to run in both unique and overlapping regimes. The work will emphasize simultaneous comparison of model predictions with experimental energy, particle and impurity transport levels and fluctuations in various regimes, including those regimes with significant excitation of electron modes. The results achieved will be used to improve confidence in transport models used for extrapolations to planned ITER operation."

 ITPA and BPO Participation:

• TC-9 Scaling of intrinsic rotation with no external momentum input
• TC-10 Experimental identification of ITG, TEM and ETG turbulence and comparison with codes
• TC-12 H-mode transport and confinement at low aspect ratio
• TC-14 RF rotation drive
• TC-17 rho-star scaling of intrinsic torque
• TC-19 Characteristics of I-mode plasmas