Speaker
Costanza Federica Maggi
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.101.pdf
Isotope identity experiments in JET-ILW
CF Maggi1, H Weisen2, L Horvath3, F Auriemma4, R Lorenzini4, E. Delabie5, D King1,
D Keeling1, S Menmuir1 and JET Contributors*
EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB, UK
1
CCFE, Culham Science Centre, Abingdon OX14 3DB, UK
2
SPC, Ecole Polytechnique Federale de Lausanne, Switzerland
3
York Plasma Institute, Department of Physics, University of York, York YO10 5DD, UK
4
Consorzio RFX, Corso Stati Uniti 4, I-35127 Padova, Italy
5
Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States of America
(*) See the author list of X Litaudon et al. 2017 Nucl. Fusion 57 102001
Dimensionless identity experiments test the invariance of plasma physics to changes
in the dimensional plasma parameters, e.g. ne and Te, when the dimensionless parameters are
conserved [1] [2]. However, conditions at the plasma boundary, such as influx of neutral
particles, may introduce additional physics. An isotope identity experiment was carried out
in the JET tokamak with C wall (JET-C), in which ELMy H-modes were obtained with
different hydrogenic isotopes, H and D, but with the same profiles of *, *, and q [3].
The thermal energy confinement times, ELM and sawtooth frequencies scaled as expected,
suggesting that the invariance principle was satisfied in JET throughout the plasma radius,
despite the different physical processes in the plasma centre, core confinement and edge
regions [3].
The isotope identity technique was revisited in recent experiments with H and D
plasmas in JET with the ITER-like Be/W wall materials (JET-ILW) and with improved edge
profile diagnostics. In L-mode, an isotope identity pair was achieved at IP/BT of 2.5MA/3.0T
(D) and 1.48MA/1.78T (H), q95 = 3.4, with D-NBI and H-NBI, respectively, delivering very
similar scaled power density profiles (TRANSP/NUBEAM). The line averaged Zeff, the
scaled thermal energy confinement times, B E,th /A, and core plasma effective heat
diffusivities, A eff/ B, were matched within experimental uncertainties, suggesting that the
invariance principle is satisfied in the L-mode core confinement region. In type I ELMy H-
modes the experiments were conducted at 1.7MA/1.7T (D) and 1.0MA/1.0T (H), q95 = 3,
with D-NBI and H-NBI, varying input power (Pabs ~ B5/3) and injected gas rate to achieve the
match in density and temperature profiles (n ~ A and T ~ A1/2). The scaled ELM frequencies,
A fELM/B, and the scaled E,th were not matched simultaneously in H and D discharge pairs,
unlike the JET-C case. Scaled E,th and core eff were also not matched simultaneously,
unlike the L-mode case. When the pre-ELM profiles of *, *, and q are matched in H and
D, the ELM averaged profiles are not matched and the scaled thermal energy confinement
times and ELM frequencies are larger in D than in H, suggesting that in JET-ILW H-modes
the invariance principle is not satisfied simultaneously in the core and edge regions. Atomic
physics of the edge recycling neutrals, thought to play an important role on pedestal
confinement and stability in JET-ILW [4], may invalidate the isotope identity technique in
the pedestal region.
[1] Connor J W and Taylor J B 1977 Nucl. Fusion 17 1047; [2] Luce T C, Petty C C and Cordey J G
2008 Plasma Phys. Control. Fusion 50 043001; [3] Cordey J G et al. 2000 Plasma Phys. Control.
Fusion 42 A127; [4] Maggi C F et al. 2015 Nucl. Fusion 55 113031.
