TJ-II:Infrared thermography of the NBI Beam Stop: NBI contribution to plasma fuelling (2)

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Experimental campaign

2019 Autumn

Proposal title

Infrared thermography of the NBI Beam Stop: NBI contribution to plasma fuelling (2)

Name and affiliation of proponent

Macarena Liniers Vázquez (Laboratorio Nacional de Fusión)

Details of contact person at LNF

Macarena Liniers

Description of the activity

To study the power balance of the injected beams, and their contribution to plasma fuelling, Infrared thermography of the NBI Beam Stop (BS) will be used. The IR camera FLIR X6580sc, commissioned during the previous campaign, gave preliminary results on the “shine-trough” and reionization losses through the IR images of the “Beam Stop”. A correlation between reionization losses and local pressure at the beam duct was established. The obtained IR images did not fully correspond to the expected behaviour of the BS material, a textured graphite with easy conductivity in the plate plane. The temperatures were higher than expected, and their time traces showed a “saturation” effect. A number of tests were performed to ascertain the thermal character of this behaviour. It was confirmed that the saturation is not a camera detector effect, but a “real” evolution of the IR radiance on the camera. In order to perform a correct analysis of the thermal images, it is necessary to study the relative importance of the different effects that contribute to the plate temperature evolution, and to the IR radiance of the plate surface in the camera wave-length range (3.5-5 μm). Aside from the heat conduction in the graphite plate bulk upon beam interception: -thermal behaviour (conduction) of the layers of Li, B, and their compounds, that are deposited on the BS graphite during Li and B evaporation, and subsequent plasma operation -Emissivity changes of the graphite surface with temperature due to the deposited layers -Line emission of H0, Li, B, C and their compounds, in the 3.5-5.0 μm range.

In order to obtain the beam fraction deposited in the plasma, a well-defined correlation between the beam power intercepted by the BS, and the measured surface temperature must be found. The high frame rate of the new camera will allow us to discriminate between fast processes (such as line-emission) and slow processes (thermal conduction), and thereby interpret the observed IR radiation behaviour. TJ-II experimental campaign needs: -As soon as the beams are ready (mid-May) beam pulses without B are required. 1. Spectrograms of the IR light (between 0.8-1.5 μm ) coming from the BS area are necessary, to study relevant emission lines and determine their correlative lines in the 3.5-5 μm range, and their intensity relative to the “background” grey body emission 2. Visible and UV spectra of light coming from the BS area, to study the species present and their contribution to radiance in the 3.5-5 μm range 3. Capture IR images of the BS with increased frequency to study the Temperature rise and fall and compare with the time scales of the IR emission effects (grey body, line emission) 4. Perform beam power scans to study the correlation between BS temperature and Beam power 5. Perform a number of pulses with B to estimate the re-ionization losses -Towards the end of the campaign: 6. Beam pulses on the Beam Calorimeter with the new 12 mm lens. [1]

International or National funding project or entity

Proyecto Plan Nacional FIS2017-89326-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:: IR spectroscopy, VUV spectroscopy 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:reference pulses one day previous to Li, one day next to Li
  • External users: need a local computer account for data access: no
  • Any external equipment to be integrated? Provide description and integration needs:

Preferred dates and degree of flexibility

One day in Mid-November (one day previous to Li, one day next to Li) and one day at end of campaign

References

  1. M. Liniers et al., New infrared imaging diagnostic for the Neutral Beam Heating System at the TJ-II stellarator Journal of Instrumentation, Volume 14, September 2019 3rd European Conference on Plasma Diagnostics (ECPD2019)

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