View source for LNF:Fuelling and Impurity Control Studies in the stellarators TJ-II and W7-X using Cryogenic Pellets and Tracer-Encapsulated Solid Pellets (TESPEL)

== LNF - Nationally funded project ==

'''Title''': '''Fuelling and Impurity Control Studies in the stellarators TJ-II and W7-X using Cryogenic Pellets and Tracer-Encapsulated Solid Pellets (TESPEL)e'''

'''Reference''': PID2020-116599RB-I00

'''Funding Umbrella''': Plan Estatal de Investigación Científica y Técnica y de Innovación 2021-2023

'''Funding Programme''': Proyecto de investigación subvencionado por el Ministerio de Ciencia e Innovación
	
'''Subprogramme''': Proyectos de I+D+i Retos Investigación

'''Programme and date''': Proyectos I+D+i 2020

'''Programme type/ Modalidad''': 

'''Area/subarea''': Physical Sciences / Physics and its applications

'''Principal Investigator(s)''': [https://orcid.org/0000-0002-5881-1442 Kieran Joseph McCarthy] [https://orcid.org/0000-0002-5223-391X María Isabel García Cortés]

'''Project type''': Investigación Orientada Tipo B

'''Start-end dates''': 01/09/2021 - 31/08/2024

'''Financing granted (direct costs)''': 130000 €

== Description of the project ==

The main aim of this project, which falls within the realm of magnetic confinement nuclear fusion, is to continue research initiated in projects ENE2013-48679-R and FIS2017-89326-R on fuelling and impurity control of plasmas in the stellarators TJ-II (Ciemat, Madrid) and W7-X (Greifswald, Germany). Further research on fuelling and impurity control is essential, as resolving these issues is critical to demonstrate steady-state operation of helical-type fusion reactors. Thus it will contribute to the development and scientific exploitation of stellarators, a priority highlighted in the document "Fusion Electricity: a roadmap to the realization of fusion energy" (EFDA 2012).

The first goal is to investigate some aspects of plasma fuelling that are still not fully understood (influence of fast electrons, magnetic configuration, and heating method on pellet ablation and deposition) as well as the effects of fuel pellets on plasma turbulence and magnetic activity. For this, the medium-sized heliac TJ-II will be used. It is equipped with a cryogenic pellet injector (PI) for fuelling with solid hydrogen. During previous projects it was found that fuelling efficiency is less that 30% for pellets reaching the centre but increases when fast electrons are present. In this project, it is intended to evaluate fuelling efficiency across a broad range of magnetic configurations and to explore some unexpected ablation phenomena observed in TJ-II, e.g. transitory increases in plasma core electron and ion temperatures and cold wave propogation ahead of injected pellets. While TJ-II is equipped with a large number of modern diagnostics, it is proposed to develop a new filterscope-based system to measure pellet cloud density and temperature to extend knowledge of pellet physics.

The second aim is to continue to support impurity transport and accumulation studies in TJ-II and W7-X. In a trilateral collaboration with National Institute for Fusion Science (Japan) and IPP-Max-Planck (Greifswald, Germany), Tracer-Encapsulated Solid Pellet (TESPEL) injections systems have been installed on both TJ-II and W7-X. TESPEL are polystyrene speheres (diameter <1 mm) loaded with impurity tracers (elements other than fuel). This allows delivering a precise quantify of tracer to a preselected location in the plasma core. An important aspect of the collaboration was the establishment of a laboratory to fabricate TESPELs at Ciemat for both devices (FIS2017- 89326-R). Key parts of this proposal are to continue TESPEL fabrication at this laboratory, therby allowing Ciemat to maintain this fruitful collaboration, and to upgrade a vacuum ultraviolet spectrometer on TJ-II to provide important spectral line data for impurity identification in W7-X as well as in other fusion devices.

The PI and TESPEL systems on TJ-II share a common injection system and guide lines. This unique set-up allows direct compartive studies of ablation, deposition and plasma perturbation to be made thereby facilitating the understanding of common physics. Given that fuelling and impurity control are critical issues for stellarator steady-state operation, the project will allow LNF researchers to continue to contribute to, and participate in, research programmes on W7-X, the stellarator of reference. Finally, team members have significant experience in the formation of young researchers at Master and PhD levels and in disseminating research to second level students and to the general public.

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== References ==
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