Preceding propagation of turbulence pulses at avalanche events in a magnetically confined plasma

Kinoshita, Naoki; Ida, K.; Tokuzawa, T.; Yasuhara, Ryo; Funaba, H.; Uehara, Hiyori; Hartog, D. J. Den; Yamada, I.; Yoshinuma, M.; Takemura, Y.; Igami, H.

doi:10.1038/s41598-022-10499-z

Cited by 7 publications

(7 citation statements)

References 35 publications

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“…, where v Thi is the ion thermal velocity, a is the minor radius, and ρ s is the ion gyro radius [22,40]. However, it has been reported that the model estimated velocity of turbulence spreading matches well with the heat pulse propagation.…”

Section: Discussionmentioning

confidence: 93%

“…The MHD collapse event are known to generate turbulence and heat avalanche events [22]. These turbulence and heat pulse are observed to be propagating to the peripheral region faster than the diffusion time scales, with the turbulence preceding the heat pulse.…”

Section: Discussionmentioning

confidence: 99%

“…This turbulence spreading, the propagation of turbulent fluctuation into different regions by nonlinear spectral transfer, is considered to be one of the mechanisms explaining the fast non-local heat transport. The turbulence spreading is modelled theoretically using a reactiondiffusion equation (Fisher-Kolmogorov-Petrovsky-Piskunov equation) [22,40]. The models suggest that a turbulence front propagates ballistically at a speed of V ≈ (γD)…”

Section: Discussionmentioning

confidence: 99%

“…The measured fast propagation of heat pulse with relatively higher heat diffusivity has been termed as the 'ballistic effect' [14]. To explain this fast propagation of the sawtooth induced heat pulse, several physical models are proposed invoking the role of stochastic magnetic field in region near to inversion radius [13][14][15]19], the energetic particle effect [13], the coupling of electron temperature and density [20,21], turbulence spreading [22] and the electrostatic turbulence [23]. But, the role of magneto-hydrodynamic (MHD) activity in the intermediate confinement region between the mixing radius and plasma edge in the fast propagation of heat-pulse has not been investigated systematically.…”

Section: Introductionmentioning

confidence: 99%

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Role of magnetohydrodynamic activity in sawtooth induced heat pulse propagation in ADITYA tokamak

Patel

Ghosh²,

Chowdhuri³

et al. 2023

Nucl. Fusion

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Fast propagation of sawtooth induced heat pulse propagation is observed in the magneto-hydrodynamic (MHD) active plasmas of ADITYA tokamak. The sawtooth crash deposits heat beyond the inversion radius, which gets transported to the edge region of the plasma and is, reflected as inverted sawtooth modulation in the edge channels of electron cyclotron emission (ECE) and Hα spectral line emission. The time-lag analysis on ECE signals reveals the propagation time from plasma core to edge of ~ 150 µs. From this analysis, the estimated transient electron heat diffusivity χe hp is found to be ~ 50 – 60 m2/s, which is ten times higher than that of power balance heat diffusivity, χe pb, in the MHD active discharges of ADITYA. It has been observed that the presence of MHD (m/n = 2/1, 3/1) activity in the intermediate region between the q = 1 and the edge radii, significantly influences the heat transport from the plasma core to the edge region. Stochastic magnetic field region formation with overlapping m/n = 2/1 and 3/1 MHD islands facilitates the fast heat-pulse propagation during a sawtooth crash in ADITYA tokamak. The disparity between the measured and the power-balance estimated diffusivity is significantly reduced by considering the heat-diffusivity due to stochastization of magnetic field in the intermediate region.

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Section: Discussionmentioning

confidence: 93%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Role of magnetohydrodynamic activity in sawtooth induced heat pulse propagation in ADITYA tokamak

Patel

Ghosh²,

Chowdhuri³

et al. 2023

Nucl. Fusion

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“…We are beginning design of a next generation pulse-burst laser system, aiming for a maximum rep rate of 100 kHz for 1 ms. Pulse-burst laser systems with "fast burst" rep rates in the range of 10-20 kHz have been built for the Thomson scattering diagnostics on MST [1], NSTX-U [2], and LHD. Recent measurements on LHD illustrate the new diagnostic capability to capture fast dynamics in the plasma [3,4].…”

Section: Introduction To Pulse-burst Laser Systemsmentioning

confidence: 99%

Next steps in high-repetition-rate laser development for Thomson scattering

Den Hartog,

Holly,

Thomas

2023

J. Inst.

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Design of a next generation high-rep-rate laser system is underway, aiming for a maximum rep rate of 100 kHz for 1 ms. This will be a “pulse-burst” laser, which is a type of heat-capacity laser. Heat-capacity laser operation is characterized by a burst of pulses of limited duration, with burst length ≤100 ms and pulse rep rate ≥1 kHz. Waste heat accumulates in the laser rod during the burst. This heat is deposited evenly throughout the rod volume, with very little heat removed during the burst, such that temperature rises evenly across the rod radius. Thus beam distortion due to thermal gradients is small. Heat is removed from the rod after the burst, with typically tens of seconds between bursts. Pulse-burst operation of flashlamp pumped Nd:YAG lasers is a cost-effective route to high-rep-rate capability. Pulse-burst laser systems with “fast burst” rep rates in the range of 10–20 kHz have been built for the Thomson scattering diagnostics on MST, NSTX-U, and LHD. For Thomson scattering diagnostic application, the typical requirements are 1064 nm, 1–2 J/pulse, ≤30 ns FWHM pulse, with a top-hat beam profile. A major requirement for this next generation laser system is flexibility in burst sequence programs, ranging from 1 kHz for 100 ms to 100 kHz for 1 ms, and a variety of scenarios in between so that operation can be tailored to plasma experiment requirements. Flashlamp pumping will be used for this next generation laser because it is inexpensive and flexible. A new switch-regulated flashlamp driver will provide improved flashlamp control at lower cost. Additional design issues such as the optimum flashlamp pumping spectrum and optimum Nd doping will be addressed. The use of commercial off-the-shelf components will be maximized in this laser system so that pulse-burst systems can be developed and built by others for new applications.

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Advanced operation modes relying on core plasma turbulence stabilization in tokamak fusion devices

2023

AAPPS Bull.

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Recent progress of advanced operation modes in tokamaks is addressed focusing upon internal transport barrier (ITB) discharges. These ITB discharges are being considered as one of candidate operation modes in fusion reactors. Here, “internal” means core region of a fusion plasma, and “transport barrier” implies bifurcation of transport phenomena due to suppressing plasma turbulence. Although ITB discharges have been developed since the mid-1990, they have been suffering from harmful plasma instabilities, impurity accumulation, difficulty of feedback control of kinetic plasma profiles such as pressure or current density, and so on. Sustainment of these discharges in long-pulse operations above wall saturation time is another huddle. Recent advances in ITB experiments to overcome the difficulties of ITB discharges are addressed for high βp plasmas in DIII-D, broad ITB without internal kink mode in HL-2A, F-ATB (fast ion-induced anomalous transport barrier) in ASDEX upgrade, ion and electron ITB in LHD, and FIRE (fast ion regulated enhancement) mode in KSTAR. The core-edge integration is discussed in the ITB discharges. The DIII-D high βp plasmas facilitate divertor detachment which weakens the edge transport barrier (ETB) but extends the ITB radius resulting in a net gain in energy confinement. Double transport barriers were observed in KSTAR without edge localized mode (ELM). FIRE modes in KSTAR are equipped with the I-mode-like edge which prevents the ELM burst and raise the fusion performance together with ITB. Finally, long sustainment of ITBs is discussed. EAST established electron ITB mode in long-pulse operations. JET achieved quasi-stationary ITB with active control of the pressure profile. JT-60U obtained 28 s of high βp hybrid mode, and KSTAR sustained stable ITB in conventional ITB mode as well as FIRE mode. These recent outstanding achievements can promise ITB scenarios as a strong candidate for fusion reactors.

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Preceding propagation of turbulence pulses at avalanche events in a magnetically confined plasma

Cited by 7 publications

References 35 publications

Role of magnetohydrodynamic activity in sawtooth induced heat pulse propagation in ADITYA tokamak

Role of magnetohydrodynamic activity in sawtooth induced heat pulse propagation in ADITYA tokamak

Next steps in high-repetition-rate laser development for Thomson scattering

Advanced operation modes relying on core plasma turbulence stabilization in tokamak fusion devices

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