TJ-II:Routine and systematic use of the LIBS

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Experimental campaign

2019 Spring

Proposal title

Routine and systematic use of the Laser Induced Blow-off Spectroscopy technique to follow the evolution of the hydrogen composition in the wall of the TJ-II stellarator and monitoring its contribution to the total impurities of the plasma using optical emission spectroscopy

Name and affiliation of proponent

B. López-Miranda1, A. Baciero1, K. J. McCarthy1, M. Ochando1, F. Medina1, I. Pastor1 and TS and TJ-II team.

(1 Laboratorio Nacional de Fusión, CIEMAT, Madrid, Spain)


Details of contact person at LNF

B. López-Miranda: belen.lopez@ciemat.es

Description of the activity

Motivation.

Laser induced breakdown spectroscopy (LIBS) is a promising method for remote in-situ monitoring of erosion/deposition processes and retention of plasma fuel (D, T) on the first walls of fusion devices [1, 2]. Previously, several LIBS systems [3-6] have been developed for use outside the main chamber of magnetic fusion devices, where complementary and sophisticated surface analysis technique can be used. However, LIBS has rarely been performed in-situ; partially due to the difficulty of access and partially due to difficulties of analysis, i.e. how to obtain quantitative information on the deposited layers on the wall of the device. In [2] we developed a in-situ system to investigate the behavior of the hydrogenic composition of the TJ-II wall chamber.


Proposal.

Within the present proposal, we plan to perform LIBS daily in-situ in the TJ-II device, with the purpose of probing the wall composition each time significant changes are performed in experimental conditions, e.g. boronization, lithiumization, Electron Cyclotron Resonance Heating (ECRH), versus Neutral Beam Injection heating (NBI), changes in gas fueling, or changes in wall structures (insertion of probes and limiters, etc.). We study the simultaneous evolution of impurities with a dual spectrometer in order to determine the contribution of the wall composition to the whole impurity content of the TJ-II plasmas.


International or National funding project or entity

This work was funded by the Spanish “MINECO” under Grant No. ENE2014-56517-R. B.L.M. would like to acknowledge her scholarship, Grant No. BES-2015-075704.

Description of required resources

Required resources:

• Number of plasma discharges or days of operation: We do not need specific operational days, rather every day we need some time previous to the beginning of machine operation in order to perform the experiment with the proper security requirements. We do not need triggers or plasma, we only need to manually operate the laser safely.

• Essential diagnostic systems: Nd-YAG laser and a dual visible spectrometer.

• Type of plasmas (heating configuration): We need changes in experimental conditions in order to determine its influence on the wall composition and its contribution to the impurity rate. It would be of interest to perform LIBS experiments with deuterium plasmas.

• Specific requirements on wall conditioning if any: No, but we will try to compare the wall composition with and without lithium and boron treatments.

• External users: need a local computer account for data access: No.


Preferred dates and degree of flexibility

Preferred dates: () We would like to perform the experiment in the early morning.


References

1. V. Philipps et al., Development of laser-based techniques for in situ characterization of the first wall in ITER and future fusion devices Nucl. Fusion 53, 093002 (2013).

2. B. López-Miranda, B. Zurro, A. Baciero, Rev. Sci. Instrum., 87, 11 D811 (2016); https://doi.org/10.1063/1.4959569

3. L. Mercadier et al., In situ tritium measurements and control by laser techniques, Fusion Sci. Tech. 60, 1049-1052 (2011).

4. P. Paris et al., Development of laser induced breakdown spectroscopy for studying erosion, deposition, and fuel retention in ASDEX Upgrade, Fusion Eng. Des. 98-99, 1349-1352 (2015).

5. G.S. Maurya et al., Proof-of-concept experiment for on-line laser induced breakdown spectroscopy analysis of impurity layer deposited on optical window and other plasma facing components of Aditya tokamak, Rev. Sci. Instrum. 86, 123112 (2015).

6. G.S. Maurya et al., Analysis of deposited impurity material on the surface of the optical window of the Tokamak using LIBS, Phys. Scr. 89 (2014) 075601 (2014).



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