Speaker
Description
See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1081.pdf
Much of the information on the isotope scaling of the L-H transition power threshold, P_LH, in JET is derived from early experiments in Hydrogen (H), Deuterium (D) and Tritium (T) with C wall (JET-C) [1]. More recent experiments have studied P_LH(H) and P_LH(D) in JET-C [2,3] and JET-ILW [4], and have shown considerable variability in P_LH associated with divertor geometry, divertor strike point configuration, Carbon vs. ILW, Neutral Beam Injection (NBI) vs. Radio Frequency heating (RF) and plasma current or q_95, particularly for Hydrogen. Here we consider the dataset with toroidal field B_tor=1.8 T of all L-H transition experiments at JET, to see what we can learn about the isotope scaling of the L-H power threshold. It contains the only n_e scan for all 3 isotopes in the old data.
Reanalysing the old P_LH data, and using P_Martin = 0.0488 n_e20^0.717 B_t^0.803 S^0.941 [5] as a convenient metric, we find that P_LH^Old(D, RF) = P_Martin, while P_LH^Old(H, RF & NBI) = 1.6 P_Martin. In Tritium the data is in a very narrow density range, (1.5-1.8)×10^19 m-3, lowest n_e with NBI, higher with RF, with different slopes, so the n_e scaling of P_LH^Old(T) is quite uncertain, with P_LH^Old(T) values falling between (0.67-0.9)P_Martin. In the JET-ILW P_LH^ILW(H, RF + NBI) = 2.6 P_Martin for the configuration (strike points in corners of divertor) most similar to the old one, but we lack data in D at this field and shape.
For scaling to high field it is especially important to investigate the low field point, which can heavily influence extrapolations. One implication of this study is that we should create a P_LH(D) dataset at 1.8 T in Corner configuration and consider studying P_LH(T) in Corner at 1.8 T in a broad density range in the forthcoming isotope campaigns at JET.
References
[1] E. Righi et al, Nucl. Fusion, 39, 309 (1999);
[2] Y Andrew et al, Plasma Phys. Control. Fusion 48 479 (2006);
[3] L. D. Horton et al, 26th EPS Conf. Contr. Fusion and Plasma Physics, Maastricht P1.021(1999);
[4] C Maggi et al Nucl. Fusion 54 023007 (2014);
[5] Y Martin et al J. Phys. Conf. Ser. 123 012033(2008)
