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

Progress in the area of MHD stability and disruptions, since the publication of the 1999 ITER Physics Basis document (1999 Nucl. Fusion 39 2137-2664), is reviewed. Recent theoretical and experimental research has made important advances in both understanding and control of MHD stability in tokamak plasmas. Sawteeth are anticipated in the ITER baseline ELMy H-mode scenario, but the tools exist to avoid or control them through localized current drive or fast ion generation. Active control of other MHD instabilities will most likely be also required in ITER. Extrapolation from existing experiments indicates that stabilization of neoclassical tearing modes by highly localized feedback-controlled current drive should be possible in ITER. Resistive wall modes are a key issue for advanced scenarios, but again, existing experiments indicate that these modes can be stabilized by a combination of plasma rotation and direct feedback control with non-axisymmetric coils. Reduction of error fields is a requirement for avoiding non-rotating magnetic island formation and for maintaining plasma rotation to help stabilize resistive wall modes. Recent experiments have shown the feasibility of reducing error fields to an acceptable level by means of non-axisymmetric coils, possibly controlled by feedback. The MHD stability limits associated with advanced scenarios are becoming well understood theoretically, and can be extended by tailoring of the pressure and current density profiles as well as by other techniques mentioned here. There have been significant advances also in the control of disruptions, most notably by injection of massive quantities of gas, leading to reduced halo current fractions and a larger fraction of the total thermal and magnetic energy dissipated by radiation. These advances in disruption control are supported by the development of means to predict impending disruption, most notably using neural networks. In addition to these advances in means to control or ameliorate the consequences of MHD instabilities, there has been significant progress in improving physics understanding and modelling. This progress has been in areas including the mechanisms governing NTM growth and seeding, in understanding the damping controlling RWM stability and in modelling RWM feedback schemes. For disruptions there has been continued progress on the instability mechanisms that underlie various classes of disruption, on the detailed modelling of halo currents and forces and in refining predictions of quench rates and disruption power loads. Overall the studies reviewed in this chapter demonstrate that MHD instabilities can be controlled, avoided or ameliorated to the extent that they should not compromise ITER operation, though they will necessarily impose a range of constraints.

https://iopscience.iop.org/article/10.1088/0029-5515/47/6/S03/pdf

Chapter 3: MHD stability, operational limits and disruptions

The understanding and predictive capability of transport physics and plasma confinement is reviewed from the perspective of achieving reactor-scale burning plasmas in the ITER tokamak, for both core and edge plasma regions. Very considerable progress has been made in understanding, controlling and predicting tokamak transport across a wide variety of plasma conditions and regimes since the publication of the ITER Physics Basis (IPB) document (1999 Nucl. Fusion 39 2137-2664). Major areas of progress considered here follow. (1) Substantial improvement in the physics content, capability and reliability of transport simulation and modelling codes, leading to much increased theory/experiment interaction as these codes are increasingly used to interpret and predict experiment. (2) Remarkable progress has been made in developing and understanding regimes of improved core confinement. Internal transport barriers and other forms of reduced core transport are now routinely obtained in all the leading tokamak devices worldwide. (3) The importance of controlling the H-mode edge pedestal is now generally recognized. Substantial progress has been made in extending high confinement H-mode operation to the Greenwald density, the demonstration of Type I ELM mitigation and control techniques and systematic explanation of Type I ELM stability. Theory-based predictive capability has also shown progress by integrating the plasma and neutral transport with MHD stability. (4) Transport projections to ITER are now made using three complementary approaches: empirical or global scaling, theory-based transport modelling and dimensionless parameter scaling (previously, empirical scaling was the dominant approach). For the ITER base case or the reference scenario of conventional ELMy H-mode operation, all three techniques predict that ITER will have sufficient confinement to meet its design target of Q = 10 operation, within similar uncertainties.

https://iopscience.iop.org/article/10.1088/0029-5515/47/6/S02/pdf

Chapter 2: Plasma confinement and transport

1 The Equations of Gas Dynamics 2 Magnetoplasma Dynamics 3 Waves in Magnetoplasmas 4 Magnetoplasma Stability 5 Transport in Magnetoplasmas 6 Extensions of Theory Bibliography Index

Physics of plasmas

The advantages of nuclear fusion as an energy source and research progress in this area are summarized. The current state of the art is described. Laser fusion, inertial confinement fusion, and magnetic fusion (the tokamak) are explained, the latter in some detail. Remaining problems and planned future reactors are considered. They are the Compact Ignition Tokamak (CIT), the International Thermonuclear Experimental Reactor (ITER), and a US design called TIBER II. The design of the latter is shown. >

http://ieeexplore.ieee.org/iel1/45/1370/00031587.pdf

Nuclear fusion

A multi-channel photometer system was installed and put into operation on ASDEX Upgrade in 2008 for studying fast dynamics of broad-band plasma radiation on the microsecond time scale. Linear arrays of silicon photodiodes commonly used for Absolute power measurement in the eXtreme UltraViolet spectral range (AXUV) are encapsulated by pinhole cameras. The plasma is observed by 200 lines of sight, at four different toroidal positions. The AXUV standard detectors have been developed by International Radiation Detectors, Inc [1]. AXUV diodes are characterised by an extremely thin passivation layer, which enables photons of the vacuum-ultraviolet spectral region (VUV) to reach the depletion layer for electron-hole-pair generation. The spectral sensitivity covers the entire energy range from the X-ray down to the visible part of the spectrum. An improvement of the time resolution down to 2μs enlarges the insights into radiation dynamics of fast plasma phenomena like minor and major disruptions, sawteeth and edge localised modes, which are not accessible with usual resistive foil bolometers (1ms time resolution). In this contribution, a short introduction of the diagnostic is followed by the presentation of first measurements taken during disruption mitigation experiments. The analysis is focussed on the asymmetric evolution of toroidal and poloidal emission after the massive injection of gaseous impurities.

http://epsppd.epfl.ch/Sofia/pdf2/P1_161.pdf

Application of AXUV Diodes for Broad-Band Plasma Radiation Studies in ASDEX Upgrade

A new combined method for an investigation of the MHD activities in fusion experiments has been developed. The main advantages of this approach are the simultaneous use of several diagnostics (magnetic probes, soft X-ray cameras, electron cyclotron emission and motional Stark effect diagnostics) and the possibility for a direct comparison of theory predictions with the experimental observations. This method has been implemented into the MHD Interpretation Code (MHD-IC) and allows to investigate complicated mode structures which are not resolved by the available tools (tomography etc.). The code simulates experimental observations related to a given plasma perturbation for the diagnostics mentioned above, accounting for real plasma geometry and for measured plasma parameters. Then the calculated values are compared with the corresponding experimental data. The method has been successfully applied to different types of MHD instabilities on ASDEX Upgrade. For example, the investigation of fishbone activities in the conventional scenario shows that the displacement eigenfunction is an ideal (1,1) kink mode which get a resistive character for $\beta_{N} > 1.8$. The main analysis efforts however were focused on more demanding examples due to the more complicated mode structure in advanced tokamak scenarios. As an example, in this case the displacement eigenfunction for double tearing modes (DTM) was obtained using MHD-IC code. The growth rate of the DTM calculated from the displacement eigenfunction agrees well with numerical MHD simulations and the experiment. The time evolution of a MHD instabilities which accompanies the formation of internal transport barriers was investigated as well. It shows the behavior of two coupled (2,1) modes. Furthermore, the MHD activity causing a disruption was investigated in typical reversed shear discharges on ASDEX Upgrade. The main reason for the disruptions is an external mode or an internal (3,1) tearing mode. In addition, the structure and the position of the observed MHD phenomena are applied to improve the equilibrium reconstruction. This betterment is especially important in the plasma core region where the large error bars of the MSE measurements do not allow for an accurate determination of the q-profile.

Investigation of MHD Instabilities in Conventional and Advanced Tokamak Scenarios on ASDEX Upgrade

Seeding of neoclassical tearing modes (NTMs) by perturbations from other MHD instabilities (sawteeth, fishbones, ELMs, etc) is one of the main MHD problems which has to be avoided or controlled in ITER. NTMs can lead to strong degradation of plasma confinement or even to a disruption. This paper compares the seeding of (3,2) neoclassical tearing modes in DIII-D and ASDEX Upgrade tokamaks. It was found in both devices that a mode can start as an ideal kink mode that converts into a tearing mode on a time-scale much longer (~10) than the duration of the trigger event (~10). These findings are in good agreement with those for (2,1) mode seeding in ASDEX Upgrade as well as with non-linear MHD simulations. This result revises the simplified picture of fast island formation occurring only during the trigger event.

/pdf/seeding-of-neoclassical-tearing-modes-by-internal-crash-2rsedjnlrm.pdf

Seeding of neoclassical tearing modes by internal crash events in the ASDEX Upgrade and DIII-D tokamaks

Experimental evidence is presented demonstrating that an ion cyclotron resonance heating (ICRH) beatwave can drive toroidicity induced Alfven eigenmodes (TAEs) to a finite amplitude and also increase the amplitude of TAEs already excited by fast ions. The radial structure of a beatwave driven TAE reconstructed from soft x-ray measurements is shown to agree with simulations from the gyro-kinetic code LIGKA. Thus beatwaves provide the means to excite TAEs which can be used to diagnose the plasma's safety factor profile through MHD-spectroscopic techniques without significantly perturbing the plasma or to influence the stability of existing TAEs allowing their effect on the fast ion population to be studied.

/pdf/icrh-beatwave-excited-toroidicity-induced-alfven-eigenmodes-2hz0gyghhg.pdf

ICRH beatwave excited toroidicity induced Alfvén eigenmodes in ASDEX Upgrade

Recent analysis of the sawtooth crash in ASDEX Upgrade (AUG) tokamak suggests that stochastisation of the magnetic field occurs during the crash [1]. According to chaos theory [2] a possible cause for the transition from quasiperiodicity to chaos is the interaction of two signal components with an irrational frequency ratio. The energetically most favourable ratio is the conjugate golden mean: [2]. The appearance of these two components with the given G frequency ratio and indications of their possible interaction has been observed in different shots on AUG [3] and HT-7 [4]. One of the two components is the well-known sawtooth precursor (m,n)=(1,1) internal kink mode [1]. The other one, which appears at lower frequency in the spectrum, has an origin not explored yet.

V. Igochine

Papers

Application of AXUV Diodes for Broad-Band Plasma Radiation Studies in ASDEX Upgrade

Investigation of MHD Instabilities in Conventional and Advanced Tokamak Scenarios on ASDEX Upgrade

Seeding of neoclassical tearing modes by internal crash events in the ASDEX Upgrade and DIII-D tokamaks

ICRH beatwave excited toroidicity induced Alfvén eigenmodes in ASDEX Upgrade

Analysis of sawtooth precursor activity in ASDEX Upgrade using bandpower correlation method