TJ-II:The influence of a core fast electron population on pellet fuelling efficiency in TJ-II

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Experimental campaign

2018 Spring

Proposal title

The influence of a core fast electron population on pellet fuelling efficiency in TJ-II

Name and affiliation of proponent

N. Panadero, K. J. McCarthy, B. Pégourie (CEA, Saint-Paul-lez-Durance, France ), M. Calvo (Universidad Politécnica de Madrid, Spain) , J. Hernández, E. de la Cal (Laboratorio Nacional de Fusión, CIEMAT, Spain)


Details of contact person at LNF (if applicable)

Kieran J. McCarthy

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

The influence of fast electrons, that reside in the plasma core, on pellet ablation and fuelling efficiency is a topic that was recently highlighted in a work made on TJ-II.[1] The work reported therein was part of the current effort to benchmark the pellet simulation code HPI2 for W7-X.[2] It was found that simulations made using a stellarator-adapted version of the HPI2 code did not fully agree with experimental observations for plasmas with a significant population of fast electrons in the core. While the presence of such a population gives rise to local enhanced pellet ablation it also appears to modify the fast outwards drifting of pellet particles and thereafter particle deposition and fuelling efficiency.[3] Assuming that the fast electron population does not modify strongly the magnetic configuration it is hypothesized that this observation could be due to subtle modifications in the ablation phase, the deposition phase and/or the post-deposition transport phase of the pellet injection process. It is considered that the contribution of the first of these phases, i.e., ablation, may be minor, therefore it remains to closely evaluate the other two phases. In order to help understand this, it is intended to perform injections into #41777-like (with fast electrons) and #44614-like (no fast electrons) discharges to determine if the outward plasmoid drift significantly changes between these two scenarios. For this the fast-frame camera will be critical. The outcome of these experiments will be used to include a routine in the HPI2 code to account for such situations. For this, it will be attempted to simulate the fast-electron observations with the HPI2 code by modifying the contribution of the drift effect until agreement is reached. The stellarator-adapted version of HPI2 code for the W7-X was previously benchmarked on TJ-II.[4] New routines will need similar benchmarking on the TJ-II.

If applicable, International or National funding project or entity

FIS2017-89326-R and WP18.S1.A4

Description of required resources

Required resources:

  • Number of plasma discharges or days of operation: 2 days
  • Essential diagnostic systems: Fast-frame camera with fibre-optic bundle. Thomson Scattering, microwave interferometer, ECE, soft x-rays, and plasma current measurements.
  • Type of plasmas (heating configuration): ECRH plasmas (#41777-like (with fast electrons) and #44614-like)
  • Specific requirements on wall conditioning if any:
  • 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

Preferred dates: Not possible between 12-04-2018, 24-04-2018 to 26-04-2018.

References

  1. N. Panadero, et al, Nucl. Fusion 58 (2018) 026025.
  2. F. Koechl F. et al, "Integrated modelling of pellet experiments at JET", Proc. 37th EPS Conf. on Plasma Physics (Dublin, 2010) 34A, O4.123
  3. B. Pégourié, Plasma Phys. Control. Fusion 49 (2007) R87.
  4. N. Panadero, et al, Nucl. Fusion 58 (2018) 026025.

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