TJ-II:Investigation of the ECRH power level and deposition radius on impurity confinement after injection by laser blow-off in TJ-II

Experimental campaign

2018 Spring

Proposal title

Investigation of the ECRH power level and deposition radius on impurity confinement after injection by laser blow-off in TJ-II

Name and affiliation of proponent

B. López-Miranda (LNF, CIEMAT, Spain), B. Zurro (LNF, CIEMAT, Spain), A. Baciero (LNF, CIEMAT, Spain), E.M. Hollmann (University of California, San Diego, La Jolla, CA, USA), M. Ochando, (LNF, CIEMAT, Spain), F. Medina (LNF, CIEMAT, Spain), K. McCarthy (LNF, CIEMAT, Spain), I. Pastor (LNF, CIEMAT, Spain), G. Rattá (LNF, CIEMAT, Spain) and TJ-II team (LNF, CIEMAT, Spain).

Details of contact person at LNF (if applicable)

A. Baciero (alfonso.baciero@ciemat.es)

B. López-Miranda (belen.lopez@ciemat.es)

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

In stellarators and tokamaks, achieving impurity control that is compatible with long energy confinement times is of paramount importance for relevant magnetically confined nuclear fusion plasmas. The confinement and transport properties of light and heavy impurity particles have been studied with spatial resolution in the stellarator TJ-II as a function of electron density, working gas (H/D) as well as charge and mass of the injected ions . At present, there are indications that the ECRH power level influences significantly impurity confinement as a consequence of confinement degradation with injected power. Moreover, the influence of ECRH power level and deposition radius is critical to understand its role on impurity mitigation effect . The goal of the present study is to investigate the behaviour of transport mechanisms operating at different plasma radii and distinct levels of heating power for light and heavy impurities. For these purposes, relaxation decay times will be determined for different power deposition levels and for different radius of power deposition. Within the present proposal, we plan to inject impurities into TJ-II ECRH plasmas by means of laser blow-off. We intend to study the influence of ECRH power level and its deposition at different radii. In order to obtain stable target plasmas, we will need low-electron density plasmas that are in turn sufficiently high to ensure good Thomson scattering profiles.

If applicable, International or National funding project or entity

This work is partially funded by Grant No. ENE2014-56517-R from the “Ministerio de Economía y Competitividad” and by the US Department of Energy under DE-FG02-07ER54917. B.L.M. receives a scholarship, BES-2015-075704.

Description of required resources

Days: We request three or more operational days: one (compatible with other experiments) to adjust all the variables of the laser blow-off system plus two to perform the power heating level scan and the power deposition radius scan and to complete the experiment with various kinds of impurities.

Diagnostics: Standard TJ-II diagnostics: Main radiation diagnostics (X-ray diagnostics, bolometers, VUV-spectrometer, Thomson scattering, etc.) plus the laser blow-off system . A PMT detector, compatible with the experiment, will be located at the focal plane of a visible spectrometer. Finally, a low spectral resolution PMA spectrometer will be used to acquire the spectra between 200 to 700 nm.

Magnetic configurations and experimental set-up: The 100_40_44 magnetic configuration offers a good plasma view. ECRH power focus at different radius (on/off axis). ECRH scan at 3 different power levels (500, 250, 100 kW).

Preferred dates and degree of flexibility

We would like to perform the experiments during the last weeks of June 2018, since the experiments will be made in collaboration with Dr. Eric M. Hollmann of UCSD.

References

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