View source for TJ-II:Influence of positive and negative density gradients in turbulent transport using the HIBP system

== Experimental campaign ==
2018 Autumn

== Proposal title ==
'''Influence of positive and negative density gradients in turbulent transport using the HIBP system'''

== Ph. Khabanov and the HIBP team ==
Enter name and affiliation here

== Carlos Hidalgo ==


An important factor contributing to the particle transport is the density gradient localization which is closely connected to the refuelling for next step tokamaks (like ITER) and stellarators devices (W7-X). 

Refuelling of core plasma particles is foreseen by pellets that injects particles at high speed deep into the plasma. However, at reactor relevant plasma densities and temperatures, pellets are unable to reach the core plasma region. In fact, pellet ablation will take place in the plasma edge region [<ref>M. Valovic et al Nucl. Fusion 48 (2008) 075006</ref>; <ref>P. Vincenzi et al., Nuclear Fusion 55 (2015)113028</ref>], causing plasma bumps with positive and negative density gradient regions where eventually particles could be transported radially inwards by turbulence.
 
Fluid and GK simulations have investigated the level of inward turbulent particle transport in the inverted density gradient region [<ref>L. Garzotti  et al Plasma Phys. Control. Fusion 56 (2014) 035004</ref>; <ref>C. Angioni et al., Nucl. Fusion 57 (2017) 116053</ref>], but comparisons of GK with experimental fluctuation levels and fluxes are missing. 

Stellarators are well suited to investigate the influence of such positive and negative density gradients on plasmas fluctuations and transport because of its capabilities to control plasma scenarios and magnetic configuration. Recent experiments in TJ-II have shown that density fluctuations appear both at the positive and negative gradient regions in electron root ECRH plasmas, with the minimum amplitude in the zero density gradient regions [<ref>R. Sharma et al., EPS 2018 / to be submitted 2018</ref>].
 
The goal of this research proposal is to systematically investigate the influence of  on-axis / off-axis ECRH heating power on fluctuations and turbulent ExB transport in positive and negative density gradient regions.

== Collaboration with Kurchatoc and Kharkov teams==

== Description of required resources ==
Required resources:
* Number of plasma discharges or days of operation: 2 days
* Essential diagnostic systems: HIBP dual system
* Type of plasmas (heating configuration):ECRH on-axis vs off-axis and power scan
* Specific requirements on wall conditioning if any:
* 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: (format dd-mm-yyyy)

== References ==
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