View source for TJ-II: Electric potential and turbulence studies with HIBP and LP via edge biasing

== Experimental campaign ==
2019 Autumn

== Proposal title ==
'''TJ-II: Electric potential and turbulence studies with HIBP and LP via edge biasing'''

== Name and affiliation of proponent ==
A. Melnikov, Institute of Nuclear Fusion, RNC Kurchatov Institute, Moscow, Russia (email: melnikov_07@yahoo.com) and T. Popov, NIS at St. Kliment Ohridski University of Sofia, Sofia, Bulgaria: (email: tsvpopov@yahoo.com)

== Details of contact person at LNF ==
Kieran J McCarthy
== Description of the activity ==
Biasing is very important for the transport studies since it is the only way for causality study (Er versus confinement), a historical ‘chicken and egg’ problem, still unresolved. This topic is natural for the studies in any small and medium size plasma devices. After the finish of the JE the studies on this topic could be continued in many devices of the CRP, which will help to establish the real collaborative work and to increase the CRP contribution to the mainstream plasma research. The goal is to study the effect of the Er on plasma confinement using edge biasing - an actuator for the improved confinement transition.

Biasing scenario
Low frequency meander of Ubias to measure profiles with/without biasing (normal confinement/improved confinement).
Other options?

The characteristics to be measured by HIBP and probes are the effects of biasing on plasma potential in the core and edge, the spectra of electrostatic turbulence (plasma potential and density), Zonal Flow / long-range correlations LRC, turbulence rotation VTURB, 2D turbulence spectrum S(k,f) and turbulent particle flux, ΓExB

The plasma scenarios will be to check the effect of biasing with positive and negative polarity on the global confinement of the target plasma with:
(1)	positive potential (low-density, ECRH)
(2)	negative potential (high-density, ECRH)
(3)	negative potential (low-to-high density, NBI, no ECRH)

An open question to be answered is the dependence of the biasing effect on the iota (strong rational values) – iota scan. At the moment – no idea how to realize. Scenario with iota-vac variation? It is expected to obtain knowledge of the evolution of core and edge plasma characteristics for modeling.

<ref> C.Hidalgo et al, Improved confinement regimes induced by limiter biasing in the TJ-II stellarator PPCF 2003.</ref>
<ref> A. Melnikov et al, Plasma potential measurements by the heavy ion beam probe diagnostic in fusion plasmas: biasing experiments in the TJ-II stellarator and T-10 tokamak, FS&T V.46, p.299, 2004 </ref>

== 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 o 2 days
* Essential diagnostic systems: Dual HIBP system, Plasma biasing, 
* Type of plasmas (heating configuration): ECRH & NBI
* Specific requirements on wall conditioning if any:
* External users: need a local computer account for data access: yes
* 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)

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== References ==
<references /> 

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