TJ-II:Comparison of transport of on-axis and off-axis ECH-heated plasmas

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Experimental campaign

2017 Spring

Proposal title

Comparison of transport of on-axis and off-axis ECH-heated plasmas

Name and affiliation of proponent

José Luis Velasco, Edi Sánchez, Teresa Estrada, Álvaro Cappa, the HIBP team et al.

Details of contact person at LNF (if applicable)

Description of the activity, including motivation/objectives and experience of the proponent (typically one-two pages)

Motivation.

Particle transport of ECH plasmas[1] is not well understood, as neoclassical simulations seem to overestimate the radial particle flux of on-axis heated ECH-plasmas; on the other hand, preliminary analyses show that this problem does not exist for off-axis ECH-heated plasmas. A comparison between these two situations (including neoclassical and gyrokinetic simulations and corresponding measurements) may shed some light on this problem, probably relevant for assessing the fuelling requirements of reactor plasmas[2]. Even if the results along this line are finally not conclusive, the experimental and theoretical characterization of turbulence with different profiles (peaked/hollow $ T_e $ with hollow/peaked $ n_e $) is itself relevant. We will also have a look at impurity transport, as off-axis heated plasmas have been predicted to have negative radial electric field in the core and positive radial electric field closer to the edge, contrary to typical ECH plasmas.

Objectives.

In this experiment we plan to scan (shot-to-shot) the radial position of ECH absortion and measure:

  • Electron density and temperature profile.
  • Radial electric field profile.
  • ....

We will compare the measurements with neoclassical and gyrokinetic simulations.

If applicable, International or National funding project or entity

EUROfusion WP17.S1.A2, WP17.S1.A3, WP17.S2.1.8,ENE2015-70142-P

Description of required resources

Required resources:

  • Number of plasma discharges or days of operation: 1 day.
  • Essential diagnostic systems:

We will measure:

- The time evolution of the line-averaged density $ <n_e(t)> $ with interferometry.

- The radial profiles of electron density $ n_e(r,t_0) $ and temperature $ T_e(r,t_0) $ at one time instant $ t_0 $ with Thomson Scattering (TS) and the He beam.

- The time evolution of the electron temperature profile $ T_e(r,t) $ with Electron Cyclotron Emission (ECE), when available, calibrated with TS.

- The time evolution of the ion temperature in the core and in an outer radial position, $ T_i(r/a=0.2,t) $ and $ T_i(r/a~=0.6,t) $, with the Neutral Particle Analyzer (NPA).

- The time evolution of the radial electric field in the gradient region $ E_r(r/a~=0.65,t) $, with reflectometry.

- The profiles of the electrostatic potential.

- ...


  • Type of plasmas (heating configuration): ECH plasmas with constant line-averaged density. From previous experiments, we have on-axis heated plasmas, and plasmas with one gyrotron on-axis and the other off-axis, so we will focus in totally off-axis heating.
  • Specific requirements on wall conditioning if any: recent lithium-coating for good density control.
  • External users: need a local computer account for data access: yes/no
  • Any external equipment to be integrated? Provide description and integration needs:

Preferred dates and degree of flexibility

Preferred dates: (format dd-mm-yyyy):

References

  1. Yokoyama 2005 NF
  2. Maassberg 1999 NF

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