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Title: Linking the micro and macro: L-H transition dynamics and threshold physics

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Journal Article: Publisher's Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 22; Journal Issue: 3; Related Information: CHORUS Timestamp: 2016-12-26 04:21:33; Journal ID: ISSN 1070-664X
American Institute of Physics
Country of Publication:
United States

Citation Formats

Malkov, M. A., Diamond, P. H., Miki, K., Rice, J. E., and Tynan, G. R. Linking the micro and macro: L-H transition dynamics and threshold physics. United States: N. p., 2015. Web. doi:10.1063/1.4914934.
Malkov, M. A., Diamond, P. H., Miki, K., Rice, J. E., & Tynan, G. R. Linking the micro and macro: L-H transition dynamics and threshold physics. United States. doi:10.1063/1.4914934.
Malkov, M. A., Diamond, P. H., Miki, K., Rice, J. E., and Tynan, G. R. 2015. "Linking the micro and macro: L-H transition dynamics and threshold physics". United States. doi:10.1063/1.4914934.
title = {Linking the micro and macro: L-H transition dynamics and threshold physics},
author = {Malkov, M. A. and Diamond, P. H. and Miki, K. and Rice, J. E. and Tynan, G. R.},
abstractNote = {},
doi = {10.1063/1.4914934},
journal = {Physics of Plasmas},
number = 3,
volume = 22,
place = {United States},
year = 2015,
month = 3

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1063/1.4914934

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Cited by: 11works
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  • The links between the microscopic dynamics and macroscopic threshold physics of the L → H transition are elucidated. Emphasis is placed on understanding the physics of power threshold scalings, and especially on understanding the minimum in the power threshold as a function of density P{sub thr} (n). By extending a numerical 1D model to evolve both electron and ion temperatures, including collisional coupling, we find that the decrease in P{sub thr} (n) along the low-density branch is due to the combination of an increase in collisional electron-to-ion energy transfer and an increase in the heating fraction coupled to the ions.more » Both processes strengthen the edge diamagnetic electric field needed to lock in the mean electric field shear for the L→H transition. The increase in P{sub thr} (n) along the high-density branch is due to the increase with ion collisionality of damping of turbulence-driven shear flows. Turbulence driven shear flows are needed to trigger the transition by extracting energy from the turbulence. Thus, we identify the critical transition physics components of the separatrix ion heat flux and the zonal flow excitation. The model reveals a power threshold minimum in density scans as a crossover between the threshold decrease supported by an increase in heat fraction received by ions (directly or indirectly, from electrons) and a threshold increase, supported by the rise in shear flow damping. The electron/ion heating mix emerges as important to the transition, in that it, together with electron-ion coupling, regulates the edge diamagnetic electric field shear. The importance of possible collisionless electron-ion heat transfer processes is explained.« less
  • The large amount of disposable bottles produced nowadays makes imperative the search for alternative procedures for recycling them since they are not biodegradable. This paper takes into consideration the thermomechanical recycling of post-consumed plastic bottles, especially the ones made of polyethylene terephthalate (PET) and high-density polyethylene (HDPE), and their use as composite materials for engineering applications. As changes on the composite's microstructure can have an influence on macroscopic behavior, a new type of analysis is needed. To be able to evaluate the composite performance, a dual analysis procedure was developed. It consists of a micro-mechanical analysis where the microstructure ismore » observed by optical microscopy, and variations in morphology are related to composite overall mechanical behavior. The macro-mechanical analysis is performed by ASTM D 3039/3039 M tensile tests. By doing this, the composite effective moduli can be determined. The new composite seems to be encouraging, i.e., an HDPE/PET composite with 40:60 ratio, in weight, experiments a stiffness recovery from the third to the fourth recycle. Moreover, the dual analysis was able to capture this variation.« less
  • A correlation is established between the macro-scale friction regimes of metals and a transition between two dominant atomistic mechanisms of deformation. Metals tend to exhibit bi-stable friction behavior—low and converging or high and diverging. These general trends in behavior are shown to be largely explained using a simplified model based on grain size evolution, as a function of contact stress and temperature, and are demonstrated for self-mated pure copper and gold sliding contacts. Specifically, the low-friction regime (where µ < 0.5) is linked to the formation of ultra-nanocrystalline surface films (10–20 nm), driving toward shear accommodation by grain boundary sliding.more » Above a critical combination of stress and temperature—demonstrated to be a material property—shear accommodation transitions to dislocation dominated plasticity and high friction, with µ > 0.5. We utilize a combination of experimental and computational methods to develop and validate the proposed structure–property relationship. As a result, this quantitative framework provides a shift from phenomenological to mechanistic and predictive fundamental understanding of friction for crystalline materials, including engineering alloys.« less
  • Recent high-resolution observations have revealed that subarcsecond bright dots (BDs) with sub-minute lifetimes appear ubiquitously in the transition region (TR) above sunspot penumbra. The presence of penumbral micro-jets (PMJs) in the chromosphere was previously reported. It was proposed that both the PMJs and BDs are formed due to a magnetic reconnection process and may play an important role in heating of the penumbra. Using simultaneous observations of the chromosphere from the Solar Optical Telescope (SOT) on board Hinode and observations of the TR from the Interface Region Imaging Spectrograph , we study the dynamics of BDs and their relation tomore » PMJs. We find two types of BDs, one that is related to PMJs, and another that does not show any visible dynamics in the SOT Ca ii H images. From a statistical analysis we show that these two types have different properties. The BDs that are related to PMJs always appear at the top of the PMJs, the vast majority of which show inward motion and originate before the generation of the PMJs. These results may indicate that the reconnection occurs at the lower coronal/TR height and initiates PMJs at the chromosphere. This formation mechanism is in contrast with the formation of PMJs by reconnection in the (upper) photosphere between differently inclined fields.« less