Impact of ICRF on the scrape-off layer and on plasma wall interactions: From present experiments to fusion reactor

Recent achievements in studies of the effects of ICRF (Ion Cyclotron Range of Frequencies) power on the SOL (Scrape-Off Layer) and PWI (Plasma WallInteractions) in ASDEX Upgrade (AUG),Alcator CMod,and JETIL Ware reviewed. Capabilities to diagnose and model the effect of DCbiasingand associated impurity production atactive antenna sandon magnetic field connections to antennas are described. The experiments show that ICRFnearfields can lead not only to E×B convection, but also to modifications of the SOL density,which for Alcator CMod are limited to anarrow regionne arantenna. On the other hand, the SOL density distribution along with impurity sources can be tail or edusing localg as injection in AUG and JET-ILW with a positive effect on reduction of impurity sources.The technique of RFimage current cancellation atantennalimiters was successfully applied in AUG using the 3-strap AUG antenna and extended to the 4-strap Alcator C-Mod field-aligned antenna.MultipleobservationsconfirmedthereductionoftheimpactofICRFontheSOLandontotalimpuritypro-ductionwhentheratioofthepowerofthecentralstrapstothetotalantennapowerisintherange0.6<Pcen/Ptotal<0.8.Near-fieldcalculationsindicatethatthisfairlyrobusttechniquecanbeappliedtotheITERICRFantenna,enablingthemodeofoperationwithreducedPWI.Onthecontrary,fortheA2antennainJET-ILWthetechniqueishinderedbyRFsheathsexcitedattheantennaseptum.Thus,inordertoreducetheeffectofICRFpoweronPWIinafuturefusionreactor,theantennadesignhastobeoptimizedalongwithdesignofplasma-facingcomponents.https://doi.org/10.1016/j.nme.2018.11.017Received26July2018;Accepted22November2018⁎Correspondingauthor.E-mailaddress:[email protected](V.Bobkov).1Seetheappendixof"A.Kallenbachetal.,2017Nucl.Fusion57102015”.2Seetheauthorlistof"H.Meyeretal.,2017Nucl.Fusion57102014”.3Seetheauthorlistof"X.Litaudonetal.,2017Nucl.Fusion57102001”.Nuclear Materials and Energy 18 (2019) 131–140Available online 20 December 20182352-1791/ © 2018 Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/).TEURATOM 633053US DoE, Office of Science,Office of Fusion Energy Sciences,User Facility Alcator C-Mod DE-FC02-99ER54512, DE-SC0010720, DE-AC05-00OR227