TJ-II:NBI contribution to plasma fuelling

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Experimental campaign

2017 Spring

Proposal title

NBI contribution to plasma fuelling

Name and affiliation of proponent

Macarena Liniers Ciemat

Details of contact person at LNF (if applicable)

Enter contact person here or N/A

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

The contribution of heating Neutral Beams to plasma fuelling is a critical piece of data in the analysis of plasma confinement and transport properties as well as in the search for strategies to control the plasma density. Neutral beams contribute to plasma fuelling through three different sources: 1. A fraction of the gas injected in the Ion Source and neutralizer is transported through the Beam Box and duct alongside the beam. 2. The gas adsorbed in the wall is re-emitted upon interaction of the beam particles and the vacuum chamber wall. These two gas sources can be treated as a kind of gas puffing. 3. The fast ions trapped in the plasma and subjected to slowing down through collisions with the plasma ions and electrons. In TJ-II as in many stellarators, the contribution of the puffing-like mechanisms is important due to the relatively high fraction of beam power directly intercepted by the wall . Due to the relatively low gas conductance between TJ-II periods the gas re-emitted from the wall has a strongly “local” characterii. Fast pressure gauges (FIG’s) symmetrically located at the four machine periods will allow us to estimate the equivalent flows from the main interaction areas. The beam-related gas affects the plasma fuelling in multiple ways: 1.-As a contribution to gas puffing 2.-Reionization of the fast neutrals that are lost to the plasma 3.-Neutralization of the fast ions inside the plasma: “Charge exchange” losses

In order to have an estimate of the fast ion contribution to plasma fuelling, it is desirable to have information on the “shine through” and reionization losses, which must be subtracted from the neutral beam power into the torus. Infrared imaging of the main targets hit by the beam can supply this information. A new infrared camera has been purchased with enhanced spatial and temporal resolution, which will constitute a powerful tool in the study of the neutral beam-plasma interaction. The new camera will be installed and commissioned during this experimental campaign, and first results will be obtained on the correlation of -beam losses and local pressure (IR & FIG’s) -beam losses and plasma density (IR) -local pressure and plasma fuelling (Halpha &FIG’s) -local pressure and cx fast ion losses (NPA’s & FIG’s & IR)

TJ-II experimental campaign needs: -The first week of the campaign presents an interesting opportunity to study the correlation between local pressure and beam losses, due to the non-conditioned wall (previous to B-Li wall treatment). Several beam pulses with B/wo B/with plasma are required. -When the new IR system is fully operative, two days should be devoted to obtain shots with several plasma densities, and reference B/noB (no plasma) shots. A different set of camera lenses (25 mm & 50 mm) will be used each of the days to obtain images of the different targets inside TJ-II vacuum vessel.


If applicable, International or National funding project or entity

Proyecto Plan Nacional ENE2013-48679-R

Description of required resources

Required resources:

  • Number of plasma discharges or days of operation:2 days of operation + 2 beam pulses to be used for reference in several experiments
  • Essential diagnostic systems:plasma density, NPA (tangential), IR Thermography, Fast Ion gauges, Halpha
  • Type of plasmas (heating configuration):several different densities
  • Specific requirements on wall conditioning if any:one day previous to Li, one day end of campaign
  • 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 ==one day previous to Li, one day end of campaign

Preferred dates: (format dd-mm-yyyy)

References



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