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TJ-II:Observation of suprathermal ions with Neutral Particle Analyzers during electron cyclotron heating in the TJ-II stellarator: Difference between revisions
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TJ-II:Observation of suprathermal ions with Neutral Particle Analyzers during electron cyclotron heating in the TJ-II stellarator (view source)
Revision as of 17:16, 12 February 2018
, 12 February 2018→Description of the activity, including motivation/objectives and experience of the proponent (typically one-two pages)
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== Description of the activity, including motivation/objectives and experience of the proponent (typically one-two pages)== | == Description of the activity, including motivation/objectives and experience of the proponent (typically one-two pages)== | ||
Suprathermal ions have been detected using optical spectroscopy techniques in TJ-II <ref> Rapisarda et al. Plasma Phys. Control. Fusion 49 309 (2007). </ref> but without conclusive results when using NPA diagnostics <ref> Fontdecaba et al. Review of Scientific Instruments 85 | Suprathermal ions have been detected using optical spectroscopy techniques in TJ-II <ref> Rapisarda et al. Plasma Phys. Control. Fusion '''49''' 309 (2007). </ref> but without conclusive results when using NPA diagnostics <ref> Fontdecaba et al. Review of Scientific Instruments '''85''' 11E803 (2014). </ref>. One experiment of the 2016 campaign, designed to investigate this population, consisted in operating one gyrotron along all the discharge while modulating the second gyrotron at 100% of its power <ref> Zurro et al. 44thEPS Conference on Plasma Physics P1.145 (2017).</ref> and changing the power deposition position in a shot-to-shot basis. No neutral beam power was injected. When both gyrotrons were on an indication of suprathermal ions was observed by the NPA diagnostic, see figure 1. | ||
In the shot plotted in figure 1 the NPA was tuned to 200 eV in the lowest energy channel. As can be seen, the count rate in the lower energy channels (NPA 01 – NPA 06, 200 eV to 446 eV) dropped, as did the Halpha signal. In contrast, in the higher energy channels (NPA 07 – NPA 09, 540 eV to 826 eV) the count rate fell when the gyrotron was turned off. This can be a indication of the existence of suprathermal ions. The amount of suprathermal ions depends on the position of the plasma heating, so not all discharges presented the same behaviour. | In the shot plotted in figure 1 the NPA was tuned to 200 eV in the lowest energy channel. As can be seen, the count rate in the lower energy channels (NPA 01 – NPA 06, 200 eV to 446 eV) dropped, as did the Halpha signal. In contrast, in the higher energy channels (NPA 07 – NPA 09, 540 eV to 826 eV) the count rate fell when the gyrotron was turned off. This can be a indication of the existence of suprathermal ions. The amount of suprathermal ions depends on the position of the plasma heating, so not all discharges presented the same behaviour. | ||
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[[File:NPA42626.png |1000px]] | [[File:NPA42626.png |1000px]] | ||
A possible explanation for the suprathermal ions is a parametric decay of the injected waves <ref> E.Z Gusakov and A. Yu. Popov Plasma Phys. Comtrol. Fusion 60 | A possible explanation for the suprathermal ions is a parametric decay of the injected waves <ref> E.Z Gusakov and A. Yu. Popov Plasma Phys. Comtrol. Fusion '''60''' 025001 (2018)</ref>. In order for this to occur, a hollow profile of the density is necessary, as in TJ-II ECR heated plasmas. | ||
In this proposal we want to reproduce the results of the 2016 campaign and in addition, change the position of the NPA in order to check the radial extension of the suprathermal ion population. Also it is intended to inject hydrogen pellets at suitable moments along the discharge in order to change the density profile, i.e. to test the validity of the assumption in [4] of the necessity of a local maximum of a non-monotonous density profile to produce the parametric decay. | In this proposal we want to reproduce the results of the 2016 campaign and in addition, change the position of the NPA in order to check the radial extension of the suprathermal ion population. Also it is intended to inject hydrogen pellets at suitable moments along the discharge in order to change the density profile, i.e. to test the validity of the assumption in [4] of the necessity of a local maximum of a non-monotonous density profile to produce the parametric decay. | ||