# TJ-II: Filter spectroscopy for pellet ablation cloud in TJ-II NBI plasmas

2020 Spring

## Proposal title

Filter spectroscopy for pellet ablation cloud in TJ-II NBI plasmas

## Name and affiliation of proponent

G. Motojima, National Institute for Fusion Science, Toki, Japan

## Description of the activity

Here we propose filter spectroscopy measurements to measure the emission from the pellet ablation cloud in TJ-II. The electron density and temperature of the pellet ablation cloud are important to understand the ablation physics and to compare the simulation of the pellet ablation. The filter spectroscopy measurements contribute to the estimation of the cloud density and temperature assuming that ablation cloud is in local thermodynamic equilibrium (LTE).

In LHD, the filter spectroscopy shows that the cloud electron density is estimated to be from $1 × 10^{22}$ to $3 × 10^{23} m^{−3}$. Also, the observed plasma cloud temperature, being about 1 eV, indicates the presence of a weakly ionized plasma cloud [1]. Recently, the similar measurements have been conducted in Heliotron J. Preliminary results suggest the similar density range of plasma cloud density. If the measurements will be conducted also in TJ-II, the pellet ablation cloud parameters could be compared with various stellarator/heliotron devices. This could contribute to the physics understanding of pellet ablation. Moreover, the results are probably important for the development of stellarator/heliotron concept.

NIFS budget

## Description of required resources

Required resources:

• Number of plasma discharges or days of operation:
• Essential diagnostic systems: TS, microwave interferometer, Fast-frame camera with fibre-optic bundle.
• Type of plasmas (heating configuration): NBI heating (NBI1 + NBI2 if possible).
• Specific requirements on wall conditioning if any:
• External users: need a local computer account for data access: no
• Any external equipment to be integrated? Provide description and integration needs: Filters and a converter from photon emission to voltage are prepared by G. Motojima.

## Preferred dates and degree of flexibility

Preferred dates: 16-03-2020 to 27-03-2020

## References

1. G. Motojima, Review Scientific Instruments (2012)