TJ-II: Plasma turbulence and cryogenic pellet injection

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Experimental campaign

2019 Autumn

Proposal title

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Name and affiliation of proponent

Nerea Panadero, Kieran J McCarthy, Ciemat

Details of contact person at LNF

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Description of the activity

Cryogenic pellet injection (PI) is widely used to fuel the core of magnetic confinement plasmas. PI can also serve as a plasma diagnostic, for example to locate fast-electron populations or to shed new light on plasma turbulence [1]. For instance, preliminary studies on the effects of hydrogen pellets on radial electric fields, Er, and turbulence in Electron Cyclotron Resonance Heated (ECRH) discharges in TJ-II revealed that the level of core turbulence is reduced strongly for a short time scale (1 ms) after PI, this being followed by an increase in the evolution of plasma density and the recovery of the electron temperature.[2]

Goal: To study the effects of cryogenic pellets on Er and on plasma turbulence across the TJ-II.

Experiment scenario: Injection of cryogenic pellets into low and medium-density ECRH plasmas (Ñe = 4x1018 m-3 to 6x1018 m3).

Characteristics to be measured: Pellet ablation and penetration into the plasma using light diodes. Post injection radial deposition using Thomson Scattering. Plasma potential before, during and after PI with the dual Heavy Ion Beam Probe systems. Measurement of core plasma density fluctuations with the same system. Measurement of edge plasma turbulence during PI with Langmuir probes.

Plasma scenarios: Injection into low-density and medium-density ECRH plasmas with line-averaged electron density of ≤4x1018 m-3 and of 4 to 5.5x1018 m-3.

Expected outcome: The evolution and characterization of plasma turbulence before, during and after pellet injection.

International or National funding project or entity

IAEA Joint Experiment, IAEA Agreement No. 22766/R0 concerning Research Project: “Fusion Physics and Technology Studies at the TJ-II Stellarator”, part of the IAEA Coordinated Research Project 'F13019' entitled ‘Network of Small and Medium Size Magnetic Confinement Fusion Devices for Fusion Research’

Description of required resources

Required resources:

  • Number of plasma discharges or days of operation: 1 -2 days
  • Essential diagnostic systems: HIBP, pellet injector, Thomson scattering
  • Type of plasmas (heating configuration): ECRH
  • 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: 31-03-2020 to 02-04-2020

References

  1. K. J. McCarthy, et al, Plasma Phys. Control Fusion 61 (2019) 014013
  2. A. Zhezhera, et al., "Search for physical mechanisms that lead to increased turbulence following pellet injection in the stellarator TJ-II, 44th EPS Conf. Plasma Physics (2017) Belfast, Ireland, P2.171"

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