TJ-II:Title of my proposal

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Experimental campaign

2016 Fall

Proposal title

Impurity transport with TESPEL on TJ-II

Name and affiliation of proponent

Dr. Naoki Tamura (NIFS, Japan)

Details of contact person at LNF (if applicable)

K. J. McCarthy, J. L. Velasco, J. Hernández, N. Panadero

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

In the TJ-II heliac, in-surface electrostatic potential asymmetries have been found in the edge region with Langmuir probes [1], and very recently in the core region with heavy ion beam probes [2]. These differences of electrostatic potential could have possibilities of giving rise to substantial changes of radial impurity flux, and then this variation may be a key component of understanding a HDH mode in the W7-AS stellarator and an impurity hole in the LHD heliotron. Therefore, the effect of such in-surface electrostatic potential variations on the impurity transport must be investigated experimentally. To this end, it is intended to continue the tracer-encapsulated solid pellet (TESPEL) injections performed in TJ-II during 2015 when 300 μm TESPELs were successfully injected into ECRH & NBI plasmas. As we already know, the TESPEL can deposit locally the tracer impurity particles, with a known amount, inside the plasma [3]. Owing to these advantages, we could investigate more clearly its effect on the in-surface impurity density variations. In the proposed experiment, a plasma density scan will be a basic action. In this line, we can also investigate a parametric window of tracer (i.e. core-sulphur) impurity accumulation in TJ-II. This investigation could shed light on the nature of the impurity accumulation in helical plasmas. If time permitted, we would like to check the ECRH effect of the tracer impurity accumulation in TJ-II. The scheme of the experiment proposed here is as follows: • Tracer impurity will be injected by a tracer-encapsulated solid pellet (TESPEL). As a tracer impurity, sulphur (S) is the candidate for 2016. In the previous year (2015), aluminum was the tracer impurity. A mass dependence is highly expected in the NC-predicted impurity density variations and the effect of the electrostatic potential variations. As a secondary study, VUV emission lines of sulphur are of high interest for plasma impurity studies, e.g. sulphur ions were seen in the core of W7-X plasmas created during OP1 - however emission line data is scarce in the VUV wavelength range. • Plasma density will be scanned from low to high. The experiment, with the same condition as which the HIBP and/or Langmuir probes have confirmed the electrostatic potential asymmetries previously, will be repeated. • If time permits, ECRH effect will be investigated by ECRH power scan

[1]

If applicable, International or National funding project or entity

Enter funding here or N/A

Description of required resources

Required resources:

  • Number of plasma discharges or days of operation: 6 days
  • Essential diagnostic systems:

- spectrometer, bolometers and SXR for the impurity measurement -ECE for the fast Te measurement -HIBP, Doppler reflectomety and Langmuir probes for potential (radial electric field) measurements – Thomson scattering diagnostics will be utilized for measuring the ne and Te profiles before and after impurity injection.

  • Type of plasmas (heating configuration): ECRH power scan
  • Specific requirements on wall conditioning if any:
  • 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

N. Tamura will make two visits to Ciemat. – Visit 1 will be from 23rd Nov to 2nd Dec. During the 2nd week (29th, 30th Nov and 1st Dec) we will require 3 experimental days (the first day will be for checking system alignment, etc, and can be done as a piggyback experiment, the other 2 days will be dedicated to TESPEL). – Visit 2 will be from 19th Dec to 23rd Dec when will require 3 experimental days (the first day will be for checking system alignment, etc, and can be done as a piggyback experiment, the other 2 days will be dedicated to TESPEL). Preferred dates: (format dd-mm-yyyy)

References

<M.A. Pedrosa et al., Nucl. Fusion 55 (2015) 052001. /> < references/> <N. Tamura et al., Plasma Fusion Res. 10 (2015) 1402056. />


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