There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

A comprehensive review of zonal flow phenomena in plasmas is presented. While the emphasis is on zonal flows in laboratory plasmas, planetary zonal flows are discussed as well. The review presents the status of theory, numerical simulation and experiments relevant to zonal flows. The emphasis is on developing an integrated understanding of the dynamics of drift wave–zonal flow turbulence by combining detailed studies of the generation of zonal flows by drift waves, the back-interaction of zonal flows on the drift waves, and the various feedback loops by which the system regulates and organizes itself. The implications of zonal flow phenomena for confinement in, and the phenomena of fusion devices are discussed. Special attention is given to the comparison of experiment with theory and to identifying directions for progress in future research.

/pdf/zonal-flows-in-plasma-a-review-3byloag115.pdf

Zonal flows in plasma—a review

One of the scientific success stories of fusion research over the past decade is the development of the ExB shear stabilization model to explain the formation of transport barriers in magnetic confinement devices. This model was originally developed to explain the transport barrier formed at the plasma edge in tokamaks after the L (low) to H (high) transition. This concept has the universality needed to explain the edge transport barriers seen in limiter and divertor tokamaks, stellarators, and mirror machines. More recently, this model has been applied to explain the further confinement improvement from H (high)-mode to VH (very high)-mode seen in some tokamaks, where the edge transport barrier becomes wider. Most recently, this paradigm has been applied to the core transport barriers formed in plasmas with negative or low magnetic shear in the plasma core. These examples of confinement improvement are of considerable physical interest; it is not often that a system self-organizes to a higher energy state with reduced turbulence and transport when an additional source of free energy is applied to it. The transport decrease that is associated with ExB velocity shear effects also has significant practical consequences for fusion research. The fundamental physics involved in transport reduction is the effect of ExB shear on the growth, radial extent and phase correlation of turbulent eddies in the plasma. The same fundamental transport reduction process can be operational in various portions of the plasma because there are a number ways to change the radial electric field Er. An important theme in this area is the synergistic effect of ExB velocity shear and magnetic shear. Although the ExB velocity shear appears to have an effect on broader classes of microturbulence, magnetic shear can mitigate some potentially harmful effects of ExB velocity shear and facilitate turbulence stabilization.

/pdf/effects-of-e-b-velocity-shear-and-magnetic-shear-on-5f3wdz73f7.pdf

Effects of E×B velocity shear and magnetic shear on turbulence and transport in magnetic confinement devices

Optimal feedback control of resistive-wall modes (RWM) is of common interest for toroidal fusion concepts that use conducting walls for stabilization of ideal MHD modes. From the RWM control point of view, the RFP situation is in many respects similar to the advanced tokamak situation in the presence of very low plasma rotation, where the most effective stabilizing mechanism is the feedback action of a set of active coils. Results from EXTRAP T2R (Sweden) and RFX-mod (Italy) RFP experiments have shown that full feedback control of multiple RWMs is possible and their deleterious effects can be completely suppressed. However it is now important to optimize the RWM control systems both for the RFP and tokamak configuration for future implementation. Important aspects of optimization are effective mode identification and tracking capability, avoidance of the harmful effects of sideband modes (aliasing) in the control spectrum, minimized power requirements and robust controller stability. The paper describes collaborative work carried out on the two RFP experiments. Controller models based on the mode harmonic control concept and on a state-space multipleinput multiple-output intelligent shell concept are studied. Progress in development of optimal control schemes are presented both through experimental studies and simulations.

Reversed-Field Pinch Contributions to Resistive Wall Mode Physics and Control

ASDEX Upgrade has a large variety of technical systems, heating and fuelling as well as digital control systems needed for control and optimisation of high performance plasmas. The neutral beam injection (NBI), electron cyclotron RF (ECRF) and ion cyclotron resonance frequency (ICRF) heating systems are able to operate in heating as well as in current drive (CD) mode. One of two NBI systems has recently been redirected to allow more tangential injection to provide larger CD efficiency. With improved control procedures significant success is achieved in the optimisation of the conventional H-mode (ITER reference scenario) as well as of ‘advanced tokamak’ scenarios. The established operational boundaries encounter or exceed those of the reference scenario. H-modes showing type II ELMs with clearly reduced peak power loads on the target plates are produced at densities close to the empirical Greenwald density limit. Discharges with nearly full non-inductively driven plasma current at Greenwald densities are performed. MHD instabilities like sawteeth and neoclassical tearing modes (NTM) can be tailored and/or completely be stabilised via electron cyclotron frequency CD at relatively low injection power levels. In addition, several non-standard feedback control circuits for plasma performance improvements and machine protection circuits are devised.

Development of active control systems on ASDEX upgrade in view of ITER discharge scenarios

Where to locate DEMO in a one-step-to-an-FPP strategy H. Zohm, W. Biel, E. Fable, R. Kemp, F. Träuble, R. Wenninger Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, D-85748 Garching, Germany Institut für Energieund Klimaforschung, Forschungszentrum Jülich, D-52428 Jülich, Germany Culham Centre for Fusion Energy, Culham, Abingdon OX14 3EA, United Kingdom EUROfusion Programme Management Unit, D-85748 Garching, Boltzmannstr. 2, Germany

Where to locate DEMO in a one-step-to-an-FPP strategy

Radiating Boundary in ASDEX Upgrade Divertor Discharges

The neutron production in magnetically confined fusion plasma discharges is a measure of the discharge performance. Whereas in a reactor, D-T operation is necessary, in the medium sized ASDEX Upgrade tokamak (R0 = 1.65 m, a = 0.5 m), only H and D plasmas are used. In D-plasmas heated by D-Neutral Beam Injection (NBI) (with injection energies of 60 kev and 93 keV in ASDEX Upgrade), a significant neutron production is observed. In this paper, we analyse SDD, the neutron rate due to D-D fusion reactions, to characterise the performance of different plasma discharge scenarii. In particular, we investigate standard Hmodes, improved H-modes [1], the high βN-scenario [2] and ITB-discharges [3].

H. Zohm

Papers

Reversed-Field Pinch Contributions to Resistive Wall Mode Physics and Control

Development of active control systems on ASDEX upgrade in view of ITER discharge scenarios

Where to locate DEMO in a one-step-to-an-FPP strategy

Radiating Boundary in ASDEX Upgrade Divertor Discharges

Neutron Production in High Performance Scenarios in ASDEX Upgrade