View source for TJ-II: On the search of Zonal Flows and the influence of Alfvén Eigenmodes in the TJ-II stellarator

== Experimental campaign ==
Spring 2022

== Proposal title ==
'''TJ-II: On the search of core Zonal Flows and the influence of Alfvén Eigenmodes in the TJ-II stellarator'''

== Name and affiliation of proponent ==
A. Melnikov, G. Sarancha, M. Drabinskiy and the HIBP Kurchatov Institute team, Russia;

A. Kozachek and the HIBP Kharkov Institute team, Ukrania;

D. Zarzoso, Marseille University, France;

J. Varela, Carlos III University, Spain 

Ciemat team

== Details of contact person at LNF ==
Arturo Alonso, Carlos Hidalgo

== Description of the activity ==

While most previous research efforts have been focussed on the excitation and impact of fast ions modes in plasma performance, because of the drain of energy related to fast particle losses with concomitant potential damages in the plasma facing components, there is a growing interest on the impact of fast particles on plasma turbulence and self-organization phenomena. Nonlinear electromagnetic stabilization by suprathermal pressure gradients has been found in gyrokinetic (GK) simulations providing an interpretation of the experimentally observed ion heat flux and stiffness reduction in the JET tokamak <ref> CITRIN, J. et al., Nonlinear Stabilization of Tokamak Microturbulence by Fast Ions, Phys. Rev. Lett 111, 155001(2013)</ref>. Understanding the underlying physics of this non-linear electromagnetic stabilization mechanism is an essential task for future fusion reactors where plasmas will be dominated by fast particle dynamics. The coexistence and interplay of fast ions with main instabilities such as ITG and TEM is an active area of research []. In particular, non-linear excitations of zonal structures by fast particle driven modes have been predicted but validation is still missing <ref> HIDALGO, C. et al., Overview of the TJ-II stellarator research programme towards model validation in fusion plasmas, Nuclear Fusion (2021) </ref>. The plasma scenarios where fast particle driven zonal structures would affect the nonlinear dynamics of AEs or / and turbulent transport is at present an active area of research.  

The main focus of this work is the experimental search of zonal flows and the possible influence of fast particle driven modes in the dynamics of zonal flows in the plasma core region of fusion plasmas. In this study both HIBP-I and HIBP-II systems will operate in scanning and fixed point mode to determine plasma profiles as well as plasma potential and density fluctuations in an specific radial location. This unique set-up permits the simultaneous investigation of the radial structure of fluctuations and long-range correlated scales in the whole plasma poloidal cross-section in the TJ-II stellarator.

== International or National funding project or entity ==
Eurofusion (Kharkov team)

== Description of required resources ==
Required resources:
* Number of plasma discharges or days of operation: 2
* Essential diagnostic systems: Dual HIBP
* Type of plasmas (heating configuration): NBI co & counter
* Specific requirements on wall conditioning if any: Li coating
* External users: need a local computer account for data access: yes/no
* Any external equipment to be integrated? Provide description and integration needs:

== Preferred dates and degree of flexibility ==
Preferred dates: May - June 2022

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== References ==
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