The role of isotope mass and transport for H-mode access in tritium containing plasmas at JET with ITER-like wall
G. Birkenmeier, E.R. Solano, I.S. Carvalho, J. C. Hillesheim, E. Delabie, E. Lerche, D. Taylor, D. Gallart, M. Mantsinen, C. Silva, C. Angioni, F. Ryter, P. Carvalho, M. Fontana, E. Pawelec, S. Silburn, P. Sirén, S. Aleiferis, J. Bernardo, A. Boboc, D. Douai, P. Puglia, Philippe Jacquet, E. Litherland–Smith, I. Jepu, D. Kos, H.J. Sun, A. Shaw, D. King, B. Viola, R. Henriques, K. Kirov, M. Baruzzo, J. García, A. Hakola, A. Huber, E. Joffrin, D. Keeling, A. Kappatou, M. Lennholm, P. Lomas, E. de la Luna, C. F. Maggi, J. Mailloux, M. Maslov, F. Rimini, N. Vianello, Geert Verdoolaege, H. Weisen, M. Wischmeier, JET Contributors
Abstract
Abstract The required heating power, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>P</mml:mi> <mml:mrow> <mml:mrow> <mml:mi>LH</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> , to access the high confinement regime (H-mode) in tritium containing plasmas is investigated in JET with ITER-like wall at a toroidal magnetic field of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>B</mml:mi> <mml:mi>t</mml:mi> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>1.8</mml:mn> </mml:mrow> </mml:math> T and a plasma current of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>I</mml:mi> <mml:mi>p</mml:mi> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>1.7</mml:mn> </mml:mrow> </mml:math> MA. <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>P</mml:mi> <mml:mrow> <mml:mrow> <mml:mi>LH</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> , also referred to as the L-H power threshold, is determined in plasmas of pure tritium as well as mixtures of hydrogen with tritium (H-T) and mixtures of deuterium with tritium (D-T), and is compared to the L-H power threshold in plasmas of pure hydrogen and pure deuterium. It is found that, for otherwise constant parameters, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>P</mml:mi> <mml:mrow> <mml:mrow> <mml:mi>LH</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> is not the same in plasmas with the same effective isotope mass, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>A</mml:mi> <mml:mrow> <mml:mrow> <mml:mi>eff</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> , when they differ in their isotope composition. Thus, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>A</mml:mi> <mml:mrow> <mml:mrow> <mml:mi>eff</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> is not sufficient to describe the isotope effect of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>P</mml:mi> <mml:mrow> <mml:mrow> <mml:mi>LH</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> in a consistent manner for all considered isotopes and isotope mixtures. The electron temperature profiles measured at the L-H transition in the outer half of the radius are very similar for all isotopes and isotope mixtures, despite the fact that the L-H power threshold varies by a factor of about six. This finding, together with the observation of an offset linear relation between the L-H power threshold, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>P</mml:mi> <mml:mrow> <mml:mrow> <mml:mi>LH</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> , and an effective heat diffusivity, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>χ</mml:mi> <mml:mrow> <mml:mrow> <mml:mi>eff</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> , indicates that the composition-dependent heat transport in the low confinement mode (L-mode) determines, how much power is needed to reach the necessary electron temperatures at the edge, and hence <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>P</mml:mi> <mml:mrow> <mml:mrow> <mml:mi>LH</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> .