High power ECRH and ECCD in moderately collisional ASDEX Upgrade Hmodes and status of EC system upgrade

C Angioni,J Stober,John Jelonnek ,Fabian Sommer ,H Zohm,E M Tai ,F Monaco,F Leuterer,D Strauß,T Scherer ,E Fable,S Münich,B Plaum ,А В Чирков ,A Bock,A G Litvak ,L G Popov ,Г Г Денисов ,H Schütz ,W Kasparek,Fabian Müller ,B Petzold,E A Soluyanova ,E Poli ,Andreas Meier ,В И Малыгин ,Manfred Thumm ,D Wágner ,M Schubert ,V.e Myasnikov ,V O Nichiporenko

doi:10.1051/epjconf/20158702004

Abstract

This contribution deals with H-modes with significant heat exchange between electrons and ions, but which can still show large differences between electron and ion-temperatures especially inside half minor radius. These conditions are referred to as moderately collisional. A systematic study shows that an increasing fraction of electron heating increases the transport in the ion channel mainly due to the dependence of the ITG dominated ion transport on the ratio Te/Ti in agreement with modeling. The rotational shear in the plasmas under study was so small that it hardly influences ITG stability, such that variations of the rotation profile due to a change of the heating method were of minor importance. These findings connect to studies of advanced tokamak scenarios using ECCD as a tool to modify the q-profile. The electron heating connected to the ECCD tends to increase the transport in the ion channel quite in contrast to the goal to operate at reduced current but with increased confinement. The confinement only increases as the fraction of ion heating is increased by adding more NBI. An ITER case was modeled as well. Due to the larger value ofei��E the ratio Te/Ti is only moderately reduced even with strong electron heating and the confinement reduction is small even for the hypothetic case of using only ECRH as additional heating. Finally the paper discusses the ongoing upgrade of the AUG ECRH-system.

Highlights

Note that for the results shown in figures 3,4 this is not an issue since the boundary conditions on the pedestal top are given in this case by the dedicated edge and pedestal diagnostics on ASDEX Upgrade (AUG)
As already discussed in the previous section, the detrimental effect of the electron heating on the transport in the ion channel is more pronounced for the case with lower collisionality since the reduced electron-ion heat-exchange allows a larger difference between Te and Ti and a larger ratio Te/Ti which reduces the critical R/LTi for the ITG-onset
For the future of the AT programme at AUG, TGLF modeling seems to be an appropriate tool to predict the effect of the ECCD on the ion temperature already in the planning phase and to add sufficient NBI heating to keep the ion temperature close to the electron temperature as it should be the case for a reactor relevant scenario

Summary

Systematic variation of the fraction of electron heating

The effect of the heating mix on the transport in the electron and ion channel has already been addressed in the EC17 meeting [1]. We see that in the experiment the Te values tend to rise initially as the electron heating is increased but drop again as Ti reduces in contrast to the model. As mentioned above it cannot be decided here if this is due to the sawtooth mismatch or to an insufficiency of the TGLF model. Note that for the results shown in figures 3,4 this is not an issue since the boundary conditions on the pedestal top are given in this case by the dedicated edge and pedestal diagnostics on AUG

Consequences for AT scenario development

Consequences for ITER

Findings

Tinit Tmodel ne ni