A global collisionless PIC code in magnetic coordinates

A global plasma turbulence simulation code, ORB5, is presented. It solves the gyrokinetic electrostatic equations including zonal flows in axisymmetric magnetic geometry. The present version of the code assumes a Boltzmann electron response on magnetic surfaces. It uses a Particle-In-Cell (PIC), δf scheme, 3D cubic B-splines finite elements for the field solver and several numerical noise reduction techniques. A particular feature is the use of straight-field-line magnetic coordinates and a field-aligned Fourier filtering technique that dramatically improves the performance of the code in terms of both the numerical noise reduction and the maximum time step allowed. Another feature is the capability to treat arbitrary axisymmetric ideal MHD equilibrium configurations. The code is heavily parallelized, with scalability demonstrated up to 4096 processors and 10⁹ marker particles. Various numerical convergence tests are performed. The code is validated against an analytical theory of zonal flow residual, geodesic acoustic oscillations and damping, and against other codes for a selection of linear and nonlinear tests.     

The nonlinear gyro-kinetic flux tube code GKW

A new nonlinear gyro-kinetic flux tube code (GKW) for the simulation of micro instabilities and turbulence in magnetic confinement plasmas is presented in this paper. The code incorporates all physics effects that can be expected from a state of the art gyro-kinetic simulation code in the local limit: kinetic electrons, electromagnetic effects, collisions, full general geometry with a coupling to a MHD equilibrium code, and E×B shearing. In addition the physics of plasma rotation has been implemented through a formulation of the gyro-kinetic equation in the co-moving system. The gyro-kinetic model is five-dimensional and requires a massive parallel approach. GKW has been parallelised using MPI and scales well up to 8192+ cores. The paper presents the set of equations solved, the numerical methods, the code structure, and the essential benchmarks.

Program summary

Program title: GKWCatalogue identifier: AEES_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEES_v1_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: GNU GPL v3No. of lines in distributed program, including test data, etc.: 29 998No. of bytes in distributed program, including test data, etc.: 206 943Distribution format: tar.gzProgramming language: Fortran 95Computer: Not computer specificOperating system: Any for which a Fortran 95 compiler is availableHas the code been vectorised or parallelised?: Yes. The program can efficiently utilise 8192+ processors, depending on problem and available computer. 128 processors is reasonable for a typical nonlinear kinetic run on the latest x86-64 machines.RAM:∼128 MB–1 GB for a linear run; 25 GB for typical nonlinear kinetic run (30 million grid points)Classification: 19.8, 19.9, 19.11External routines: None required, although the functionality of the program is somewhat limited without a MPI implementation (preferably MPI-2) and the FFTW3 library.Nature of problem: Five-dimensional gyro-kinetic Vlasov equation in general flux tube tokamak geometry with kinetic electrons, electro-magnetic effects and collisionsSolution method: Pseudo-spectral and finite difference with explicit time integrationAdditional comments: The MHD equilibrium code CHEASE [1] is used for the general geometry calculations. This code has been developed in CRPP Lausanne and is not distributed together with GKW, but can be downloaded separately. The geometry module of GKW is based on the version 7.1 of CHEASE, which includes the output for Hamada coordinates.Running time: (On recent x86-64 hardware) ∼10 minutes for a short linear problem; 48 hours for typical nonlinear kinetic run.References:

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  [1] H. Lütjens, A. Bondeson, O. Sauter, Comput. Phys. Comm. 97 (1996) 219, http://cpc.cs.qub.ac.uk/summaries/ADDH_v1_0.html.

     

Conservative global gyrokinetic toroidal full-f five-dimensional Vlasov simulation

A new conservative global gyrokinetic toroidal full-f five-dimensional Vlasov simulation (GT5D) is developed using a novel non-dissipative conservative finite difference scheme. The scheme guarantees numerical stability by satisfying relevant first principles in the modern gyrokinetic theory, and enables robust and accurate simulations of tokamak micro-turbulence. GT5D is verified through comparisons of zonal flow damping tests, linear analyses of ion temperature gradient driven (ITG) modes, and nonlinear ITG turbulence simulations against a global gyrokinetic toroidal δf particle code. In the comparison, global solutions of the ITG turbulence are identified quantitatively by using two gyrokinetic codes based on particle and mesh approaches.     

Optically transparent ZnO-based n-i-p ultraviolet photodetectors

An optically transparent tin-doped indium oxide/ZnO/NiO n-i-p heterostructure photodiode was fabricated by ion beam assisted e-beam evaporation. The diode clearly demonstrates rectifying current-voltage (J-V) characteristics with a current rectification ratio up to 10⁴ at bias ± 2 V and a low reverse current of ∼ 100 nA/cm² at − 5 V. Analysis of J-V characteristics including time dependence of the dark current shows that the leakage current at low biases is attributed to thermal generation via defect states, and at high biases, field-enhanced carrier generation from the ZnO layer dominates. Spectral response and linearity measurements indicate that such a diode is particularly suitable for low level of ultraviolet detection.     

Effect of ion irradiation on the M-Nitroaniline single crystals

In this report, the modifications in the structural, optical, mechanical, electrical and nonlinear properties of 70 MeV Li³⁺ and 100 MeV Ag⁷⁺ ion irradiated M-Nitroaniline single crystals are studied. The irradiation induced defect structures at the crystal surface which becomes more prominent at higher irradiation fluences, leading to the enhancement in the optical absorption behaviour and the nonlinear property of the irradiated crystals. The mechanism leading to the enhanced nonlinearity and the blue shift of the irradiated M-NA crystals has been discussed.     

Thickness dependence of structural, electrical and optical properties of sprayed ZnO:Cu films

ZnO:Cu thin films have been deposited by spray pyrolysis techniques within two different (450 °C and 500 °C) substrate temperatures. The structural properties of ZnO:Cu thin films have been investigated by X-ray diffraction techniques. The X-ray diffraction spectra showed that ZnO:Cu thin films are polycrystalline with the hexagonal structure and show a good c-axis orientation perpendicular to the substrate. The most preferential orientation is along the (002) direction for all spray deposited ZnO:Cu films together with orientations in the (100) and (101) planes also being abundant. Some parameters of the films were calculated and correlated with the film thickness for two different substrate temperatures. The optical properties of ZnO:Cu thin films have been investigated by UV/VIS spectrometer and the band gap values were found to be ranging from 3.29 eV to 3.46 eV.     

Inductance calculation of twisted conductors by the broken line approximation

The mutual inductance between two skew straight thin conductors is obtained as a function of two vectors corresponding to two current carrying line segments. Based on the obtained analytical expressions for the mutual inductance, the versatile calculation method for the self- and mutual inductances of various twisted conductors is studied by means of the broken line or polygonal curve approximation. In particular, it is confirmed that this numerical calculation is consistent with the analytical calculation of the self- and mutual inductances for coaxial helical conductors for the asymptotic form of the long axial length. Furthermore, for the inductances of general twisted conductors, the similar asymptotic forms of the length dependence are obtained.     

Growth and optical properties for non-catalytically grown ZnO micro-tubules by simple thermal evaporation

A simple synthesis technique to grow ZnO micro-tubules in large quantities from ZnO powders in one step at ~ 1000 °C ± 50 °C is discussed. The micro-tubules were formed in the form of small chunks or ingots as well as sticking to the walls of the crucible. Most of those micro-tubules are formed radially outwards of the ingots and that self-alignment may be attributed to the local balance of vapors as well as the steady state of vapor flow. The morphology, structure and optical properties of ZnO microtubes were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy and Photoluminescence (PL) respectively. The growth of ZnO micro-tubules would be of interest in the future for the technological revolution of useful application such as in catalytic and optoelectronics.     

Structural and optical properties of Ho2TeO6 micro-crystals embedded in tellurite matrix

In the present work, Ho³⁺ doped tellurite glasses and glass ceramics have been explored. Micro-sized Ho₂TeO₆ crystals have been successfully prepared in TeO₂ matrix using two step heat treatment method. Structural, thermal and optical properties have been investigated using different characterization techniques. Variations in above mentioned properties were observed to improve when these crystals grew in TeO₂ matrix. We have reported several anti-Stokes and Stokes emissions extended from UV to NIR region on excitation with 532 and 976 nm laser radiations. The unique structure of Ho₂TeO₆ crystal was expected to play a crucial role in enhancement of the optical properties of glass ceramics.