TJ-II: Studies of the dynamics of injected hydrogen pellets in the stellarator TJ-II

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Experimental campaign

2021

Proposal title

Studies of the dynamics of injected hydrogen pellets in the stellarator TJ-II

Name and affiliation of proponent

D. Medina, (Universidad Carlos III de Madrid, Spain) N. Panadero, K. J. McCarthy, J. Hernánde (Laboratorio Nacional de Fusión, CIEMAT, Spain)

Details of contact person at LNF

N. Panadero

Description of the activity

Pellet injection is a widely used tool in magnetically confined plasma devices for core fueling. Although the main physics of pellet ablation and of the subsequent particle deposition processes is fairly well understood, significant research is still needed to achieve a more complete knowledge. For instance, pellets are found to be accelerated, in the absence of suprathermal particles, in, at least, the vertical and radial directions in tokamaks and in some stellarators, such as W7-X [1]. This acceleration is usually attributed to an asymmetry of its shielding cloud, however, the particular mechanism responsible for such an asymmetry remains outstanding [2]. In TJ-II ECRH plasmas, fast camera measurements show that pellet acceleration is negligible along most of the pellet trajectory [3]. However, at the end of the pellet lifetime, a small variation of the pellet trajectory is sometimes observed. It should be possible to measure such deflection and to relate it to a non-negligible acceleration. For that, pellet injections, recorded with a double-bundle fast camera system, in TJ-II ECRH plasmas are proposed here. The aim of these experiments is, on the one hand, to quantify pellet acceleration and its relationship with quantities, such as plasma density and temperature or magnetic configuration. On the other hand, it is intended to compare experimental results with a recent extension of the acceleration model include in HPI2, that allows handling poloidal accelerations as well as radial ones. These studies are part of D. Medina Fusion-EP master thesis, as well as of current effort to benchmark the stellarator version of HPI2 for TJ-II, W7-X and Heliotron-J devices [4].

International or National funding project or entity

N/A

Description of required resources

Required resources:

  • Number of plasma discharges or days of operation: 2 days
  • Essential diagnostic systems:: pellet injector, Thomson Scattering, fast-frame camera with fiber-optic bundle.
  • Type of plasmas (heating configuration):ECRH
  • Specific requirements on wall conditioning if any: Sufficient density control for good reproducibility
  • External users: need a local computer account for data access: no

Preferred dates and degree of flexibility

Not available from 14-02-2021 to 01/03/2021

References

  1. J. Baldzuhn, Plasma Physics and Controlled Fusion (2019)
  2. T. Szepesi, Journal of Nuclear Materials (2009)
  3. N. Panadero, Nuclear Fusion (2018)
  4. N. Panadero, 22nd ISHW (2019)

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