TJ-II: Studies of pellet plasmoid drift in different magnetic configurations

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Experimental campaign

Spring 2022

Proposal title

Studies of pellet plasmoid drift in different magnetic configurations

Name and affiliation of proponent

Nerea Panadero, Kieran McCarthy, Julio Hernández, Isabel García-Cortés, Daniel Medina

Laboratorio Nacional de Fusión, CIEMAT

Details of contact person at LNF


Description of the activity

Pellet injection is not only a widely used tool in magnetically confined plasma devices for core fuelling, but it is also expected to be a key part of the operation of future fusion reactors. Although the main physics of pellet ablation and of the subsequent particle deposition processes are fairly well understood, significant research is still needed to achieve a more complete knowledge of these processes. In particular, the drift of the ionized part of the pellet material, or plasmoid, is not fully comprehended. For instance, experimental observations deviate significantly from theoretical expectations in several stellarators [1] [2]. Understanding the mechanisms responsible for these differences is highly important, since plasmoid drift determines the deposition of the pellet material and the efficiency of the fuelling. Plasmoids and their drifts have been observed in TJ-II plasmas using a fast camera. However, the experimental conditions under which plasmoid drifting has been recorded to date are very limited. In order to increase our knowledge of plasmoid drift and its dependence of different parameters, a scan in magnetic configuration is proposed for both ECRH and NBI plasmas. The aim of these experiments is, on the one hand, to quantify plasmoid drift in the early stages of the homogenization process, and its relationship with quantities, such as plasma density and temperature or magnetic configuration (rational surfaces). On the other hand, it is intended to compare experimental results with HPI2 predictions, which will be part of the current effort to benchmark the stellarator version of HPI2 for TJ-II, W7-X, LHD and Heliotron-J devices.

UPDATE: after the first part of the campaign, goals are:

- Complete configuration scan in ECRH: 100_50_65 
- Complete configuration scan in balance NBI: 100_50_65, 100_52_66 and 100_64_67
- New scan configuration in ECRH to study plasmoid drift for different magnetic well (for instance: 100_44_ 77, 099_44_99 and 100_43_104)

International or National funding project or entity

Studies of fuelling and impurity control in the stellarators TJ-II and W7-X through the use of cryogenic and TESPEl pellets (Estudios de abastacimiento y control de impurezas en los stellarators mediante el uso de perdigones criogenicos y TESPEL", Ref: PID2020-116599RB-I00

Description of required resources

Required resources:

  • Number of plasma discharges or days of operation: 1 or 2 days of ECRH operation and 1 or 2 days of ECRH + NBI operation
  • Essential diagnostic systems: Pellet injector (pellet 1 for ECRH and pellet 3 for NBI), fast camera, TS
  • Type of plasmas (heating configuration): ECRH and NBI 1 + NBI2
  • Specific requirements on wall conditioning if any: Good control of NBI heated plasmas
  • External users: need a local computer account for data access: no
  • Any external equipment to be integrated? No

Preferred dates and degree of flexibility


  1. J. Baldzuhn et al., Plasma Phys. Control. Fusion 61 (2019) 095012
  2. A. Matsuyama et al., Nucl. Fusion 52 (2012) 123017

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