TJ-II: Magnetic fluctuations induced by pellet injections in TJ-II

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Experimental campaign

2021

Proposal title

TJ-II: Magnetic fluctuations induced by pellet injections in TJ-II

Name and affiliation of proponent

Kieran J McCarthy, Isabel García-Cortes, Ciemat

Details of contact person at LNF

As above

Description of the activity

In recent years, cryogenic hydrogen pellets and Tracer Encapsulated Solid PELlets (TESPELs) have been injected regularly into ECRH and NBI-heated plasmas in the TJ-II [1] [2]. Whilst cryogenic pellets and TESPELs are intended for studying plasma fuelling and impurity transport, respectively, in this device, several transitory effects have been observed during, and immediately after, the pellet ablation and homogenization phases. For instance, it is known to modify plasma turbulence for several milliseconds after pellet ablation [3]. In addition, numerous transitory effects have been observed as a pellet travels through the plasma. These include cloud detachment from the pellet producing striations in ablation light profiles or fast-electrons incident on a pellet causing increased ablation or pellet rupture [4]. More recently, short-lived magnetic activity has been observed to accompany cryogenic pellet ablation. One effect is the excitation of clear, short-lived, magnetic instabilities that are triggered only by cryogenic pellets (not by TESPEL) as they approach the magnetic axis. A second effect is a significant short-lived reduction in broadband magnetic fluctuations immediately after either a cryogenic pellet or TESPEL is injected into microwave-heated plasmas. THis is not seen for NBI-heated plasmas. In this work, it is intended to study magnetic fluctuations induced by both pellet types in plasmas created with a broad range of magnetic configurations in both ECRH and NBI-heated plasmas, in particular configurations with low order rational surfaces. This will be done in order to determine if interactions between outward drifting pellet particles and rational surfaces lead to the observed magnetic instabilities and if changes in plasma pressure profiles lead to the observed reduced broadband magnetic fluctuations.

International or National funding project or entity

Ministerio de Economía, Industria y Competitividad (FIS2017-89326-R)

Description of required resources

Required resources:

  • Number of plasma discharges or days of operation: 2 days
  • Essential diagnostic systems: Pellet Injector, magnetic arrays, Thomson Scattering
  • Type of plasmas (heating configuration): ECRH and NBI
  • Specific requirements on wall conditioning if any: none
  • External users: need a local computer account for data access: no
  • Any external equipment to be integrated? no

Preferred dates and degree of flexibility

Flexible

References

  1. K. J. McCarthy et al, Nucl. Fusion 57 (2017) 056039
  2. K. J. McCarthy et al, Europhys. Lett. 120 (2017) 25001
  3. A. Zhezhera et al, 21st International Stellarator-Heliotron Workshop (ISHW2017)
  4. K. J. McCarthy et al, Plasma Phys. Control. Fusion 61 (2019) 014013

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