Modification of SOL profiles and fluctuations with line-average density and divertor flux expansion in TCV

TY - JOUR

T1 - Modification of SOL profiles and fluctuations with line-average density and divertor flux expansion in TCV

AU - Vianello, N.

AU - Tsui, C.

AU - Theiler, C.

AU - Allan, S

AU - Boedo, J A

AU - Labit, B.

AU - Reimerdes, H

AU - Verhaegh, Kevin Henricus Annemarie

AU - Vijvers, W.A.J

AU - Walkden , N.

AU - Costea, S.

AU - Kovacic, J.

AU - Ionita, C.

AU - Naulin , V.

AU - Nielsen, A.H.

AU - J. Juul , Rasmussen

AU - Schneider, B.

AU - Schrittwieser, R.

AU - Spolaore, M.

AU - Carralero, D.

AU - Madsen, Jens

AU - Lipschultz, Bruce

AU - Militello, F.

AU - The TCV Team

AU - The EUROfusion MST1 Team

N1 - © 2017 Consorzio RFX. This is an author-produced version of the published paper. Uploaded in accordance with the publisher’s self-archiving policy. Further copying may not be permitted; contact the publisher for details.

PY - 2017/8/3

Y1 - 2017/8/3

N2 - A set of Ohmic density ramp experiments addressing the role of parallel connection length in modifying scrape off layer (SOL) properties has been performed on the TCV tokamak. The parallel connection length has been modified by varying the poloidal flux expansion f x . It will be shown that this modification does not influence neither the detachment density threshold, nor the development of a flat SOL density profile which instead depends strongly on the increase of the core line average density. The modification of the SOL upstream profile, with the appearance of what is generally called a density shoulder , has been related to the properties of filamentary blobs. Blob size increases with density, without any dependence on the parallel connection length both in the near and far SOL. The increase of the density decay length, corresponding to a profile flattening, has been related to the variation of the divertor normalized collisionality ##IMG## [http://ej.iop.org/images/0029-5515/57/11/116014/nfaa7db3ieqn001.gif] {$\Lambda_{\rm div}$} (Myra et al 2006 Phys. Plasmas 13 112502, Carralero et al , ASDEX Upgrade Team, JET Contributors and EUROfusion MST1 Team 2015 Phys. Rev. Let . 115 215002), showing that in TCV the increase of ##IMG## [http://ej.iop.org/images/0029-5515/57/11/116014/nfaa7db3ieqn002.gif] {$\Lambda_{\rm div}$} is not sufficient to guarantee the SOL upstream profile flattening.

AB - A set of Ohmic density ramp experiments addressing the role of parallel connection length in modifying scrape off layer (SOL) properties has been performed on the TCV tokamak. The parallel connection length has been modified by varying the poloidal flux expansion f x . It will be shown that this modification does not influence neither the detachment density threshold, nor the development of a flat SOL density profile which instead depends strongly on the increase of the core line average density. The modification of the SOL upstream profile, with the appearance of what is generally called a density shoulder , has been related to the properties of filamentary blobs. Blob size increases with density, without any dependence on the parallel connection length both in the near and far SOL. The increase of the density decay length, corresponding to a profile flattening, has been related to the variation of the divertor normalized collisionality ##IMG## [http://ej.iop.org/images/0029-5515/57/11/116014/nfaa7db3ieqn001.gif] {$\Lambda_{\rm div}$} (Myra et al 2006 Phys. Plasmas 13 112502, Carralero et al , ASDEX Upgrade Team, JET Contributors and EUROfusion MST1 Team 2015 Phys. Rev. Let . 115 215002), showing that in TCV the increase of ##IMG## [http://ej.iop.org/images/0029-5515/57/11/116014/nfaa7db3ieqn002.gif] {$\Lambda_{\rm div}$} is not sufficient to guarantee the SOL upstream profile flattening.

KW - Tokamak

KW - filaments

KW - Transport

U2 - 10.1088/1741-4326/aa7db3

DO - 10.1088/1741-4326/aa7db3

M3 - Article

SN - 0029-5515

VL - 57

SP - 1

EP - 14

JO - Nuclear Fusion

JF - Nuclear Fusion

IS - 11

M1 - 116014

ER -