Experimental evidence of the non-local response of transport to peripheral perturbations

Abstract

Qualitatively novel results on nonlocality phenomena in perturbative transport experiments are reported. Here, nonlocality means a rapid response in the core follows an edge perturbation on a time scale far shorter than any standard approximation to the global, diffusive model confinement time. Sequential firing of SMBI on the HL-2A tokamak sustained the increase in the core temperature in response to the edge perturbation. O-mode reflectometers are introduced to measure density fluctuations and show that the central turbulence is suppressed during nonlocallity, suggesting that the interpretation of the phenomenon as due to the formation of an 'ITB-like' structure is plausible. ECH switch-off experiments on the HL-2A tokamak demonstrated that the non-local response is sensitive to the deposition location. Taken together, these results suggest that non-locality phenomena have several aspects in common which can be linked to certain simple, generic elements of tokamak turbulence physics.

Observation of non-local effects in ion transport channel in J-TEXT plasmas

“…The plasma current (I p ) and edge safety factor (q a ) are 150kA and about 3.7, respectively. The typical NLT effect in electron heat transport channel (core T e rises while edge T e drops) appears in every SMBI pulse, which is same as previous NLT experiments in other devices [1][2][3][4][5][6][7][8][9][10][11][12]. On the other hand, the prompt increasing of core ion temperature and rapid decreases of edge T i due to SMBI are also clearly shown in fig.1.…”

“…A fast increase of the central electron temperature caused by the edge cooling in Ohmic heating (OH) plasmas, the so-called non-local heat transport (NLT) [1] is one of these challenging issues. NLT was first observed in the TEXT tokamak 23 years ago, and in many fusion devices afterwards (TFTR [2], RTP [3], ASDEX UPGRAGE [4], Tore Supra [5], JET [6], LHD [7][8][9], HL-2A [10][11][12], Alcator C-Mod [13][14][15], KSTAR [16], J-TEXT [17], and EAST [18]). NLT phenomenon shows that the limitation of transport theory based on traditional local transport model.…”

A statistical analysis of avalanching heat transport in stationary enhanced core confinement regimes

“…In particular, the finding that avalanches exhibit long correlation lengths suggests a natural explanation for nonlocal heat transport, observed in the studies of response to localized perturbations. 54,55 Heat transport in ITBs is related to momentum transport, as elucidated in recent experimental 56 and simulation 35,57 studies. Recent gyrokinetic simulations also show the close connection between heat and momentum avalanches in Lmode, showing cross PDFs by which outward heat avalanches induce inward momentum avalanches.…”

Alfvénic Propagation: A Key to Nonlocal Effects in Magnetized Plasmas

“…(II) The sign of the perturbation reverses, i.e., a cooling at the edge results in heating of the core, and vice versa. Such evidence has accumulated through dedicated experiments, including edge cooling by laser blowoff (LBO) of impurities, pellets, radio frequency (RF) heating, and plasma current ramping, performed in several devices, including tokamaks and stellarators [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. The ubiquity of these phenomena calls naturally for some common fundamental physics basis.…”