TJ-II:Pellet Injections into TJ-II plasmas with core fast electron population

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Experimental campaign

2018 Autumn

Proposal title

Pellet Injections into TJ-II plasmas with core fast electron population

Name and affiliation of proponent

Kieran J. McCarthy, LNF Ciemat and R. Bussiahn, IPP Greifswald

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 influence of fast electrons, that reside in the plasma core of TJ-II, on pellet ablation and fuelling efficiency is a topic that was recently highlighted.[1] The work reported therein was part of the current effort to benchmark the stellarator versions of the pellet simulation codes HPI2 for TJ-II and W7-X.[2] It was found that simulations made using the 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] In particular, increased electron deposition was observed when an injected pellet undergoes increased ablation in the core due to such electrons. 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 plasmoid drift phase. the pellet particle 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 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.

If applicable, International or National funding project or entity

PN FIS2017-89326-R

Description of required resources

Required resources:

  • Number of plasma discharges or days of operation: 4
  • Essential diagnostic systems: Pellet Injector, HIBP, Fast Camera, Thomson Scattering, UWave interferometer, ECE
  • Type of plasmas (heating configuration): ECRH
  • Specific requirements on wall conditioning if any: None
  • External users: need a local computer account for data access: yes
  • Any external equipment to be integrated? Provide description and integration needs:

Preferred dates and degree of flexibility

Preferred dates: (19-10-2018 to 05-12-2018) and (18-12-2018 to 20-12-2018). Not possible: (05-11-2018 to 15-11-2018)

References

  1. K. J. McCarthy et al., Nucl. Fusion 57 056039 (2018)
  2. N. Panadero et al, Nucl. Fusion 58 026025 (2017)
  3. K. J. McCarthy et al., accepted in Plasma Phys. Control. Fusion (2018)

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