TJ-II: Validation of neutral beam current drive

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Experimental campaign

Spring 2022

Proposal title

Validation of neutral beam current drive

Name and affiliation of proponent

A. Cappa, S. Mulas, M. Liniers, T. Estrada, E. Ascasibar, J. Velasco, K. McCarthy et al.

Details of contact person at LNF


Description of the activity

The goal of the experiment associated to this proposal is to measure the toroidal current driven by each of the two neutral beams (NBCD). To this end, it is important to achieve long NBI plasmas with stable density. Long pulses are needed to approach the current stabilization phase and stable density ensures that the time dependence of the toroidal current is mainly due to its electrodynamic evolution and is not caused by a different coupling of the beam power issued from variations in the thermal plasma parameters. Additional ECRH power can be used for density control purposes. Plasmas with co-NBI (NBI1) and counter-NBI (NBI2), as well as plasmas with balanced injection (NBI1+NBI2), will be explored. The level of optimum ECRH power will be determined depending on the operation conditions considering that moderate electron temperature (below 800 keV) are desirable to favour shorter stabilization times. Using off-axis ECRH injection may also help to reduce L/R time. The measured toroidal current will be compared to the computational/numerical estimates of the toroidal current generated by both neutrals beams.

However, since both bootstrap and NBCD are contributing to the toroidal plasma current, the validation of NBCD needs first a numerical computation of the bootstrap contribution, ideally with a validated tool. Validating bootstrap current is a long standing issue in TJ-II ECRH plasmas. Experimental proposals devoted to this task have been unsuccessful because of the difficulties encountered to achieve pulses long enough to observe current stabilization. Two days are requested to carry out this proposal. In its first part, and following the procedure described in (Velasco et al.), we will carry out an attempt to achieve long ECRH pulses, looking for a current stabilization phase, in order to fulfill as best as possible the goals detailed in the proposal by Velasco et al. If proved unfeasible, we will switch to NBI plasmas and carry out the rest of the experiments.

International or National funding project or entity

Include funding here (grants, national plans)

Description of required resources

Required resources:

  • Number of plasma discharges or days of operation: 2 days.
  • Essential diagnostic systems: Rogowski (Ip), Microwave Interferometer, Scattering Thomson (ne & Te), Doppler Reflectometry (Er), ECE (Te), NPA (Ti), MSE (rotational transform)
  • Type of plasmas (heating configuration): NBI plasmas with background ECRH power for density control purposes
  • Specific requirements on wall conditioning if any: Density control and long pulses are critical for this proposal.
  • External users: need a local computer account for data access: no
  • Any external equipment to be integrated? Provide description and integration needs: N/A

Preferred dates and degree of flexibility

Preferred dates: (format dd-mm-yyyy)


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