# TJ-II:Radial electric field of low-magnetic-field low-collisionality NBI plasmas

2017 Spring

## Proposal title

Radial electric field of low-magnetic-field low-collisionality NBI plasmas

## Name and affiliation of proponent

José Luis Velasco et al.

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

Motivation. Impurity hole plasmas are characterized by having negative radial electric field that is smaller in absolute value than the ion tempererature gradient[1]. In this work, we also showed data from NBI-only plasmas of TJ-II: as the density was reduced, the core electrostatic potential got closer to zero. In this experiment, we plan to make the radial electric field even smaller by creating the plasmas with NBI in configurations of reduced magnetic field strength, since $E_r$ should be proportional to $B$ for impurity-hole-relevant plasmas.

Objectives. In this experiment we plan to measure the ion temperature and radial electric field, and the plasma profiles of comparable NBI-only plasmas with different magnetic field strength. Additionally, over the NBI-created plasmas, we will check whether additional ECH power can be absorbed and this has an effect on impurities.

## If applicable, International or National funding project or entity

EUROfusion WP17.S1.A2, ENE2015-70142-P

## Description of required resources

Required resources:

• Number of plasma discharges or days of operation: 1 successful day (which may require more than 1 day, as HIBP and Doppler will have to be calibrated).
• 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). The time instant should be that of minimum $<n_e>$.

- 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 with reflectometry.

- The time evolution of the electrostatic potential and its radial profile: one HIBP should be fixed in the core region and the other one scanning radially.

• Type of plasmas (heating configuration): plasmas created with NBI without ECH; the two NBIs should inject sequentially. $B=0.6T$.
• Specific requirements on wall conditioning if any: inmediately after 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): better before 01-04-2017

## References

1. Velasco 2017 NF