Low-recycling conditions and improved core confinement in steady-state operation scenarios in JET (Joint European Torus)

In this paper, we discuss the phenomena that link particle recycling from the vessel walls in the L-mode during discharge start-up and the core confinement in the H-mode during the subsequent main heating phase. We consider available data of JET experiments that aimed at approaching fully non-inductive ITER-relevant steady-state conditions and show that the high electron temperature produced at the edge by a low recycling during start-up tends to favour the build-up of high normalized β(βN) regimes in the H-mode, the confinement being improved in a large plasma volume. To provide an insight into this complex phenomenon we have modelled the relation between particle recycling in the scrape-off layer and the evolution of plasma transport, plasma current density and shear as well as the stability properties for such experimental conditions. The results confirm the existence of a link between the confinement in the H-mode phase and the values at the edge of electron temperature, bootstrap current density and local magnetic shear during start-up. Such a link could favour these regimes to be self-sustained in time.

[1]  G Schettini,et al.  Current drive at plasma densities required for thermonuclear reactors. , 2010, Nature communications.

[2]  Jet Efda Contributors,et al.  Development of steady-state scenarios compatible with ITER-like wall conditions. Invited Paper , 2007 .

[3]  G. Staebler,et al.  Investigations of VH-mode in DIII-D and JET , 1993 .

[4]  B. Parvitte,et al.  Atmospheric laser heterodyne detection , 1996 .

[5]  C. Kessel.  Bootstrap current in a tokamak , 1994 .

[6]  Jet Efda Contributors,et al.  Plasma edge density and lower hybrid current drive in JET (Joint European Torus) , 2011 .

[7]  J. Garcia,et al.  Critical behavior of magnetically confined plasma regimes. , 2010, Physical review letters.

[8]  Nathaniel J. Fisch,et al.  Theory of current-drive in plasmas , 1987 .

[9]  V. Parail,et al.  Effect of low magnetic shear induced by lower hybrid current drive on high performance internal transport barriers in the Joint , 2002 .

[10]  K-D Zastrow,et al.  JET quasistationary internal-transport-barrier operation with active control of the pressure profile. , 2002, Physical review letters.

[11]  J. Freidberg,et al.  Plasma Physics and Fusion Energy , 2007 .

[12]  D Mazon,et al.  Modeling of a lower-hybrid current drive by including spectral broadening induced by parametric instability in tokamak plasmas. , 2004, Physical review letters.

[13]  F. Imbeaux,et al.  Critical threshold behavior for steady-state internal transport barriers in burning plasmas. , 2008, Physical review letters.

[14]  S. Saarelma,et al.  ELM phenomenon as an interaction between bootstrap-current driven peeling modes and pressure-driven ballooning modes , 2000 .

[15]  P. C. de Vries,et al.  Development of internal transport barrier scenarios at ITER-relevant high triangularity in JET , 2005 .

[16]  Lao,et al.  Regime of very high confinement in the boronized DIII-D tokamak. , 1991, Physical review letters.

[17]  J. Garcia,et al.  Conditions for the sustainment of high-beta stationary scenarios in tokamaks , 2011 .

[18]  F. Imbeaux,et al.  Progress in internal transport barrier plasmas with lower hybrid current drive and heating in JET (Joint European Torus) , 2002 .

[19]  R. Felton,et al.  The impact of divertor detachment on carbon sources in JET L-mode discharges , 2009 .

[20]  C. Giroud,et al.  ERRATUM: Influence of the q-profile shape on plasma performance in JET , 2002 .

[21]  Douglass E. Post,et al.  Physics of Plasma-Wall Interactions in Controlled Fusion , 1986, Springer US.

[22]  W. Fundamenski,et al.  Spectral broadening of lower hybrid waves produced by parametric instability in current drive experiments of tokamak plasmas , 2006 .

[23]  F. Crisanti,et al.  Reduction of the electron thermal conductivity produced by ion Bernstein waves on the Frascati Tokamak Upgrade tokamak , 2001 .

[24]  Jet Efda Contributors,et al.  Non-inductive current drive and transport in high βN plasmas in JET , 2009 .