The H-mode pedestal, ELMs and TF ripple effects in JT-60U/JET dimensionless identity experimentsFunded under: FP7-EURATOM
This paper summarizes results of dimensionless identity experiments in JT-60U and JET, aimed at the comparison of the H-mode pedestal and ELM behaviour in the two devices. Given their similar size, dimensionless matched plasmas are also similar in their dimensional parameters (in particular, the plasma minor radius a is the same in JET and JT-60U). Power and density scans were carried out at two values of I(p), providing a q scan (q(95) = 3.1 and 5.1) with fixed (and matched) toroidal field. Contrary to initial expectations, a dimensionless match between the two devices was quite difficult to achieve. In general, p(ped) in JT-60U is lower than in JET and, at low q, the pedestal pressure of JT-60U with a Type I ELMy edge is matched in JET only in the Type III ELM regime. At q(95) = 5.1, a dimensionless match in rho*, nu* and beta(p,ped) is obtained with Type I ELMs, but only with low power JET H-modes. These results motivated a closer investigation of experimental conditions in the two devices, to identify possible 'hidden' physics that prevents obtaining a good match of pedestal values over a large range of plasmas parameters. Ripple-induced ion losses of the medium bore plasma used in JT-60U for the similarity experiments are identified as the main difference with JET. The magnitude of the JT-60U ripple losses is sufficient to induce counter-toroidal rotation in co-injected plasma. The influence of ripple losses was demonstrated at q(95) = 5.1: reducing ripple losses by ~ 2 (from 4.3 to 1.9 MW) by replacing positive with negative neutral beam injection at approximately constant P(in) resulted in an increased p(ped) in JT-60U, providing a good match to full power JET H-modes. At the same time, the counter-toroidal rotation decreased.
Bibliographic Reference: An article published in: Nuclear Fusion 47 (2007), pp. 969-983
Availability: This article can be accessed online by subscribers, and can be ordered online by non-subscribers, at: http://dx.doi.org/doi:10.1088/0029-5515/47/8/031
Record Number: 200719381 / Last updated on: 2007-09-11
Original language: en
Available languages: en