J. A. Merrifield W.-C. Müller S. C. Chapman R. O. Dendy
The statistical properties of the dissipation process constrain the analysis of large scale numerical simulations of three-dimensional incompressible magnetohydrodynamic ( MHD ) turbulence, such as those of Biskamp and Müller [ Phys. Plasmas 7 , 4889 ( 2000 )] . The structure functions of the turbulent flow are expected to display statistical self…
PublishedT.K. March S.C. Chapman R.O. Dendy J. A. Merrifield
Previous observations that suggest a substantial role for nondiffusive energy transport in tokamaks subjected to off-axis electron cyclotron heating (ECH) are compared to the output from a sandpile model. The observations considered include local and global aspects of temperature profile evolution in the DIII-D [for example, C. C. Petty and T. C. L…
PublishedR. E. Lee S. C. Chapman R. O. Dendy
The identification of preacceleration mechanisms for cosmic ray ions in supernova remnant shocks is an important problem in astrophysics. Recent particle-in-cell ( PIC ) shock simulations have shown that inclusion of the full electron kinetics yields non-time-stationary solutions, in contrast to previous hybrid ( kinetic ions, fluid electrons ) sim…
PublishedJ. Greenhough S.C. Chapman R.O. Dendy V.M. Nakariakov G. Rowlands
We investigate the distribution of fluctuations in solar irradiance when integrated over the full disk, obtained using extreme ultraviolet / soft X-ray observations from the SOHO CELIAS / SEM instrument. This time series sums over both the contributions of single distinguishable flares, and of many other processes. By detrending we select events wi…
PublishedJ. Greenhough S.C. Chapman S. Chaty R.O. Dendy G. Rowlands
Whilst direct observations of internal transport in accretion disks are not yet possible, measurement of the energy emitted from accreting astrophysical systems can provide useful information on the physical mechanisms at work. Here we examine the unbroken multi-year time variation of the total X-ray flux from three sources: Cygnus X-1, the microqu…
PublishedK. G. McClements M. E. Dieckmann A. Ynnerman S. C. Chapman R. O. Dendy
The surfatron offers the possibility of particle acceleration to arbitrarily high energies, given a sufficiently large system. Surfatron acceleration of electrons by waves excited by ions reflected from supernova remnant (SNR) shocks is investigated using particle simulations. It is shown that surfatron and stochastic acceleration could provide a s…
PublishedS. C. Chapman R.O. Dendy B. Hnat
Confinement phenomenology characteristic of magnetically confined plasmas emerges naturally from a simple sandpile algorithm when the parameter controlling redistribution scale length is varied. Close analogs are found for enhanced confinement, edge pedestals, and edge localized modes (ELMs), and for the qualitative correlations between them. These…
PublishedS. C. Chapman R. O. Dendy B. Hnat
An avalanche or ‘‘sandpile’’ model is discussed that generalizes the original self-organized criticality avalanche model of Bak, Tang, and Wiesenfeld [Phys. Rev. Lett. 59 , 381 (1987)] to include spatially extended local redistribution. A single control parameter specifies the spatial extent of local redistribution when the critical gradien…
PublishedS. C. Chapman R. O. Dendy G. Rowlands
There is increasing evidence that the Earth’s magnetosphere, like other macroscopic confined plasma systems (magnetic fusion plasmas, astrophysical accretion discs), displays sandpile-type phenomenology so that energy dissipation is by means of avalanches which do not have an intrinsic scale. This may in turn imply that these systems evolve via s…
PublishedP. Helander S. C. Chapman R. O. Dendy G. Rowlands N. W. Watkins
A simple one-dimensional sandpile model is constructed which possesses exact analytical solvability while displaying both scale-free behavior and fractal properties. The sandpile grows by avalanching on all scales, yet its shape and energy content are described by a simple, continuous (but nowhere differentiable) analytical formula. The avalanche e…
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