Long Range Temperature Fluctuation in LHD

Abstract

We report a detailed correlation technique to identify the long-range temperature fluctuation in the Large Helical Device. Correlation hunting has successfully realized the observation of electron temperature fluctuations, which are characterized by their correlation length comparable to the plasma minor radius, with low frequency of ∼ 1-3 kHz, ballistic radial propagation (at a speed of ∼1 km/s, of the order of diamagnetic drift velocity), spatial mode number of m/n = 1/1 (or 2/1), and amplitude of ∼2% at the maximum. Bicoherence analysis confirmed their nonlinear coupling with local microscopic turbulent fluctuations. This long-range temperature fluctuation is a possible carrier of fast propagation in transport processes observed so far. We also comment on the theoretical interpretation.

An Assessment of Limit Cycle Oscillation Dynamics Prior to L-H Transition

“…The fast change of core transport at the onset of H-mode transition has been known for more than 20 years [44,45]. Recently, fluctuations that could induce rapid transmission of change of transport have been searched for [55][56][57][58][59][60][61][62]. The response of LCO provides a good opportunity to observe the response of core plasma against the change at the edge.…”

New evidence and impact of electron transport non-linearities based on new perturbative inter-modulation analysis

“…If we assume that the kernel G (2) is constant at all frequency combinations, i.e., G (2) (ρ, 9, 7) = G (2) (ρ, 9, −7) = G (2) (ρ, 7, 0) = G (2) (ρ, 9, 0), the linear response can be calculated from (8). Therefore, first the kernels G (2) are calculated to verify this assumption.…”

“…In this subsection, the linear profiles Θ lin (ρ, 7)(f 1 ) and Θ lin (ρ, 9)(f 2 ) defined in (8) are reconstructed using the temperature perturbation at T d (t) as reference. Therefore, it is assumed that G (2) (ρ, 9, 7) = G (2) (ρ, 9, 0) and G (2) (ρ, 9, −7) = G (2) (ρ, 7, 0) as was explained in Sec.…”

“…Different modulated sources can be used to perturb various transport channels such as: the electron heat transport by electron cyclotron resonance heating (ECRH) [7,8,9] or with repetitive pellet injection [10] or using a minority heating scheme [11]; particle transport using modulated gas-puffing with helium [12,13]; the momentum transport using modulated neutral beam injection (NBI) to modulate the torque [14,15,16]; the ion heat transport using ion cyclotron resonance heating [17,18]; and the analysis of impurity transport using for instance laser blow-off of boron and carbon materials [19]. This list is far from exhaustive and for a more complete overview of such experiments and its history the reader is referred to [2,3,20].…”

On Detection of a Global Mode Structure in Experiments by Use of Turbulence Diagnostic Simulator

“…Development of experimental diagnostics in fusion plasmas has made possible to measure plasma fluctuations with high spatial and temporal resolution [5,6], and spectral analyses of the data reveal the turbulent structure in linear devices [7][8][9] and toroidal devices [10][11][12][13]. Usually a limited number of lines of sight can be used for measurements in experiments, so the information of a threedimensional (3-D) structure is limited.…”