| 1. |
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| 2. |
- Lloyd, B., et al.
(författare)
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Overview of physics results from MAST
- 2011
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 51:9, s. 094013 (paper no.)-
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Tidskriftsartikel (refereegranskat)abstract
- Major developments on the Mega Amp Spherical Tokamak (MAST) have enabled important advances in support of ITER and the physics basis of a spherical tokamak (ST) based component test facility (CTF), as well as providing new insight into underlying tokamak physics. For example, L-H transition studies benefit from high spatial and temporal resolution measurements of pedestal profile evolution (temperature, density and radial electric field) and in support of pedestal stability studies the edge current density profile has been inferred from motional Stark effect measurements. The influence of the q-profile and E x B flow shear on transport has been studied in MAST and equilibrium flow shear has been included in gyro-kinetic codes, improving comparisons with the experimental data. H-modes exhibit a weaker q and stronger collisionality dependence of heat diffusivity than implied by IPB98(gamma, 2) scaling, which may have important implications for the design of an ST-based CTF. ELM mitigation, an important issue for ITER, has been demonstrated by applying resonant magnetic perturbations (RMPs) using both internal and external coils, but full stabilization of type-I ELMs has not been observed. Modelling shows the importance of including the plasma response to the RMP fields. MAST plasmas with q > 1 and weak central magnetic shear regularly exhibit a long-lived saturated ideal internal mode. Measured plasma braking in the presence of this mode compares well with neo-classical toroidal viscosity theory. In support of basic physics understanding, high resolution Thomson scattering measurements are providing new insight into sawtooth crash dynamics and neo-classical tearing mode critical island widths. Retarding field analyser measurements show elevated ion temperatures in the scrape-off layer of L-mode plasmas and, in the presence of type-I ELMs, ions with energy greater than 500 eV are detected 20 cm outside the separatrix. Disruption mitigation by massive gas injection has reduced divertor heat loads by up to 70%.
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| 3. |
- Sharapov, S.E., et al.
(författare)
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Energetic particle instabilities in fusion plasmas
- 2013
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 53:10, s. 104022-
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Tidskriftsartikel (refereegranskat)abstract
- Remarkable progress has been made in diagnosing energetic particle instabilities on present-day machines and in establishing a theoretical framework for describing them. This overview describes the much improved diagnostics of Alfvén instabilities and modelling tools developed world-wide, and discusses progress in interpreting the observed phenomena. A multi-machine comparison is presented giving information on the performance of both diagnostics and modelling tools for different plasma conditions outlining expectations for ITER based on our present knowledge.
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| 4. |
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| 5. |
- Anderson, D., et al.
(författare)
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A variational approach to spherical aberrations in the thermal-wave model for beam dynamics in charged particle accelerators
- 1998
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Ingår i: Physica Scripta. - : Institute of Physics Publishing. - 0031-8949 .- 1402-4896. ; 58:6, s. 608-612
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Tidskriftsartikel (refereegranskat)abstract
- A direct variational approach involving trial functions and Ritz optimization, which has previously been found very useful in nonlinear optics, is applied to analyze the effects of spherical aberrations on the focusing properties of charged particle beams in particle colliders. As compared to conventional perturbation theory, the variational approach provides a simple and physically clear analysis. Explicit expressions are given for the transverse particle beam density, the spot size, and the luminosity reduction factor at the interaction point, in good agreement with the perturbative results.
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| 6. |
- Anderson, D., et al.
(författare)
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Collapse of optical vacuum pulses due to QED nonlinearities
- 2002
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Ingår i: Nonlinear Guided Waves and Their Applications, 1–4 September 2002, Stresa, Italy. - : Optics Info Base, Optical Society of America. - 1557527237
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Due to quantum electrodynamical (QED) effects there are nonlinear corrections to Maxwell's equations in vacuum. We show that stationary two-dimensional light bullets can form, which are unstable and exhibit, the possibility of self-focusing collapse.
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| 7. |
- Dimitrevski, K., et al.
(författare)
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Analysis of stable self-trapping of laser beams in cubic-quintic nonlinear media
- 1998
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Ingår i: Physics Letters A. - : Elsevier. - 0375-9601 .- 1873-2429. ; 248:5-6, s. 369-376
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Tidskriftsartikel (refereegranskat)abstract
- A numerical and analytical analysis of two-dimensional laser beam propagation in cubic-quintic nonlinear optical media demonstrates the existence of stable stationary radially symmetric modes. By means of a variational method, involving super-Gaussian trial functions and Ritz optimization, approximate stationary solutions are obtained, showing very good agreement with numerical results, even in the strongly non-linear, almost saturated, regime. The stability of the stationary modes are verified by analytical analysis and by direct numerical simulations.
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| 8. |
- Ding, R., et al.
(författare)
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Gold-modified paper as microfluidic substrates with reduced biofouling in potentiometric ion sensing
- 2021
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Ingår i: Sensors and actuators. B, Chemical. - : Elsevier. - 0925-4005 .- 1873-3077. ; 344
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Tidskriftsartikel (refereegranskat)abstract
- Microfluidic sampling media based on paper and its modifications with either gold nanoparticles or sputtered gold were evaluated for potentiometric determination of Na+, K+, and Cl– ions in clinically relevant samples. The measurements were conducted in comparison to other commonly considered microfluidic substrates, i.e. sponge, polyester textile, and polyamide textile. Ion determination was done by using solid-contact ion-selective electrodes based on plasticized PVC membranes for Na+, K+, and Cl– ions and utilizing PEDOT(PSS) or PEDOT(Cl) as the ion-to-electron transducer. The solid-contact ion-selective electrodes and a solid-state reference electrode were placed directly on the substrate into which the sample solution was wicked. Transport of bovine serum albumin (BSA) through the paper substrate was studied by ellipsometry. Modification of the paper substrates by gold nanoparticles (AuNPs) was found to slow down the transport of BSA through the paper, when compared with unmodified paper substrates and when compared with all the other alternative sampling matrices studied. The retention of BSA obtained with AuNP-modified paper substrates significantly improved the accuracy of the potentiometric ion determinations in sweat, saliva, artificial tears, and artificial serum. The potentiometric results were validated by inductively coupled plasma optical emission spectrometry (ICP-OES) and ion chromatography (IC). The study indicates that modification of paper by AuNPs is a feasible approach to reduce biofouling of sensors that are used in the paper-based analysis of clinically relevant samples. © 2021 Elsevier B.V.
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| 9. |
- Helczynski, L., et al.
(författare)
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Cross Phase Modulation Induced Pulse Splitting - The Optical Axe
- 2000
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Ingår i: Physica scripta. T. - 0281-1847. ; 84, s. 81-84
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Tidskriftsartikel (refereegranskat)abstract
- An analytical as well as numerical analysis is made of the dynamics induced on a weak signal wave pulse by a co-propagating strong pump wave pulse in a nonlinear Kerr medium. Emphasis is given to the situation where the group velocity dispersion and the non-linearity of the signal pulse have opposite signs. In this defocusing situation, it is demonstrated that the pump splits the signal pulse into two frequency shifted pulse fragments which separate in time, asymptotically with constant separation velocity. Explicit analytical predictions for the velocity of separation are obtained and corroborated by numerical simulations.
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| 10. |
- Malomed, B. A., et al.
(författare)
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Decay of parametric solitons in a lossy medium with quadratic nonlinearity
- 1996
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Ingår i: Pure and Applied Optics (Print edition) (United Kingdom). - : IOP Publishing. - 0963-9659. ; 5:6, s. 941-946
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Tidskriftsartikel (refereegranskat)abstract
- An investigation is made into the evolution of two-wave solitons in a second-haimonic-generation system under the action of weak dissipation. Using the balance equation for the soliton energy and a previously developed variational approximation for its shape, a general evolutional equation is derived for the soliton parameters. The equation is solved explicitly for the asymptotic stage of the evolution
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