Download or read book A Critical Fast Ion Beta in the Madison Symmetric Torus Reversed Field Pinch written by William Joseph Capecchi and published by . This book was released on 2017 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The first fast-ion profile measurements have been made in a reversed-field pinch (RFP) plasma. A large population of fast-ions are deposited in the core of the Madison Symmetric Torus (MST) through use of a 1 MW neutral beam injector (NBI) giving rise to a variety of beam-driven instabilities. One such mode, the energetic-particle mode (EPM) has been shown to reduce fast-ion content in MST, evident through drops in signal levels of the advanced neutral particle analyzer (ANPA). EPMs in MST appear as bursts of magnetic fluctuations at a lab frequency of ~100 kHz reaching peak amplitude and decaying away within 100 microseconds. A burst ensemble of the neutron data does not reveal a drop in neutron emission across a burst, implying the population of fast-ions transported by a burst constitute a small fraction of the total. The burst may also pitch-angle scatter out of the ANPA phase space or be transported to mid-radius where charge-exchange with the background neutrals or fast-ion orbit stochasticity may reduce fast-ion confinement. Data gathered from the expanded neutron diagnostic suite including a new collimated neutron detector (CiNDe) was used to reconstruct the fast-ion profile in MST and measure critical fast-ion beta quantities. Measurements were made in plasma conditions with varying magnetic field strength in order to investigate the interplay between the energetic particle (EP) drive and Alfven continuum damping. The measured values of the core fast-ion beta (7.5% (1.2%) in 300 (500) kA plasmas) are reduced from classical predictions (TRANSP predicts up to 10% core value) due to EPM activity. The frequency, magnitude, and rate of occurrence of the bursts depends on the tearing mode amplitude, Alfven continuum damping rate, fast-ion profile shape, and resonant orbit dynamics. Marginal stability was reached in both moderate- (300 kA) and high- (500 kA) current discharges, marked by sustained EPM activity and a saturated global neutron signal during NBI. The difference in profile shape is interpreted to be related to the core-most resonant tearing mode amplitude, as a larger core magnetic island moves the location of steepest fast-ion gradient further out in radius, resulting in lower confinement of the fast-ions. The reconstructed profile is more strongly peaked at lower current, consistent with a lower measured core-most tearing mode amplitude. A larger dataset at lower current gives enough temporal resolution to investigate the evolution of the fast-ion profile. The suppression of the core-most tearing mode amplitude during NBI results in a rapid and dynamically evolving fast-ion profile at the beginning of the NBI discharge and results in an initially broader profile early evolving into a more strongly peaked profile later in the NBI discharge.
Download or read book Reversed field Pinch Studies in the Madison Symmetric Torus written by and published by . This book was released on 1993 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt: Studies of large-size (R = 1.5 m, a = 0.5 m), moderate current (I
Download or read book Energy Research Abstracts written by and published by . This book was released on 1994-08 with total page 442 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Measured and Simulated Election Thermal Transport in the Madison Symmetric Torus Reversed Field Pinch written by Joshua Adam Reusch and published by . This book was released on 2011 with total page 222 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1994 with total page 772 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Diagnosis of Equilibrium Magnetic Profiles Current Transport and Internal Structures in a Reversed field Pinch Using Electron Temperature Fluctuations written by and published by . This book was released on 2014 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Due to long fast ion confinement times, neutral beam injection (NBI) on the Madison Symmetric Torus (MST) yields large fast ion populations with substantial density gradients. Novel application of the unique high-rep-rate (>10 kHz) Thomson scattering diagnostic on MST has enabled characterization of a newly observed beam-driven instability, and detailed measurement of equilibrium changes caused by the fast ion population. While previous work has focused on high-frequency energetic particle modes (EPMs), recent observations indicate that fast ions drive a bursting instability near the plasma rotation frequency under appropriate conditions. The mode chirps strongly, with a frequency of approximately 7 kHz in the plasma reference frame at peak amplitude. Bursts are correlated with EPM activity and core neutral particle analyzer signals drop by 30% during a burst, suggesting that this mode participates in avalanches of the higher frequency EPMs and drives enhanced fast ion transport. Electron temperature fluctuations correlated with this low-frequency mode exhibit a core-peaked structure with a sensitive dependence on the safety factor q. Although this mode has not yet been positively identified, its characteristics and internal structure are suggestive of an internal kink (fishbone) or beta-induced Alfvén eigenmode. In addition to driving EPMs, the large fast ion population also modifies the current profile. An increase in on-axis current density driven by NBI is offset by a reduction in the mid-radius, leading to net-zero current drive. This results in a slight flattening of the safety factor profile, observed by precise measurement of the rational surface locations of the dominant tearing modes; these are identified from the phase flip in correlated electron temperature fluctuations recorded by Thomson scattering. For the core n = 6 rational surface, an inward shift of 1.1 ± 0.6 cm is observed, with an estimated reduction in q0 of 5%. This technique provides a powerful tool for measuring the equilibrium magnetic field in the RFP; the phase of the temperature fluctuations also enables an estimate of pressure-fluctuation contributions to the dynamo electric field. An examination of the effect of pressure on electron momentum balance indicates that anisotropy is crucial to the kinetic dynamo.
Download or read book Physics Briefs written by and published by . This book was released on 1993 with total page 1074 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Microinstabilities and Turbulent Transport in the Reversed Field Pinch written by and published by . This book was released on 2014 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The work presented in this thesis is concerned with addressing the nature of drift wave microturbulence in the reversed field pinch (RFP). Microturbulence is an important phenomenon and contributor to heat and particle transport in tokamaks, where it has been studied for several decades, but its role in the RFP is a rather new topic of study. As such, the nature of RFP drift waves and their relationship to their tokamak counterparts is still developing, and many of the results in this work are focused on addressing this challenge. Fundamental advances in microturbulence research have been made in recent decades through two parallel developments: the theoretical framework encompassed in the gyrokinetic model, and the computational power offered by massively-parallel, high-performance computing systems. Gyrokinetics is a formulation of kinetic theory in such a way that the fast timescale gyromotion of particles around magnetic field lines is averaged out. The implementation and use of RFP equilibrium models in gyrokinetic codes constitutes the bulk of this thesis. A simplified analytic equilibrium, the toroidal Bessel function model (TBFM), is used in the gyrokinetic code GYRO to explore the fundamental scaling properties of drift waves in the RFP geometry. Two drift wave instabilities, the ion temperature gradient (ITG) mode and the microtearing mode (MTM) are found to occur, and the relationship of their critical threshold in driving gradients and plasma beta is explored. The critical values in these parameters are found to be above those of similar tokamak cases by roughly a factor of the flux surface aspect ratio. The MTM is found to be stabilized by increasing the RFP pinch parameter theta, making it unlikely for it to unstable in the high-theta improved confinement pulsed poloidal current drive (PPCD) discharges. Efforts are also made to address microinstabilities in specific experimental discharges of the Madison Symmetric Torus (MST). A semi-analytic equilibrium, the adjusted circular model (ACM), is developed and implemented in the gyrokinetic code GENE to investigate representative PPCD discharges. The flexibility of the ACM enables it to be used for the high-theta PPCD discharges where the TBFM breaks down. The dominant linear instabilites for the discharges modeled here -- ITG and the trapped electron mode (TEM) -- are studied, as are their scaling properties in the PPCD regime. It is found that these instabilities are present outside of the reversal surface, where the driving gradients are strongest. Nonlinear simulations of the TEM turbulence are performed, the first such done for the RFP, and zonal flows are found to play an important role in the nonlinear saturation mechanism. These zonal flows lead to a large Dimits-like shift and suppressed transport. There is also evidence that residual global tearing mode fluctuations are a necessary part of modeling transport in the RFP, even in improved confinement PPCD discharges, and by modeling these residual fluctuations through the use of an externally imposed perpendicular magnetic field perturbation it is possible to bring simulated fluxes into agreement with experiment. Finally, the nature of the collisionless MTM, an instability seen to arise in some parameter regimes of the RFP, is investigated analytically using a fluid expansion in the drift-kinetic framework. Particular attention is paid to the role of magnetic drifts, and some evidence for their role in the collisionless instability is presented. Comparisons are made to gyrokinetic simulations and to earlier theory on the magnetic-curvature drift instability.
Download or read book The Madison Symmetric Torus written by and published by . This book was released on 1990 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Fusion Nucl aire written by and published by . This book was released on 1996 with total page 568 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Dissertation Abstracts International written by and published by . This book was released on 1991 with total page 734 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Government Reports Annual Index written by and published by . This book was released on 1993 with total page 1200 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Fusion Energy Update written by and published by . This book was released on 1981 with total page 104 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Nuclear Fusion written by C.M. Braams and published by CRC Press. This book was released on 2002-06-20 with total page 352 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fusion research started over half a century ago. Although the task remains unfinished, the end of the road could be in sight if society makes the right decisions. Nuclear Fusion: Half a Century of Magnetic Confinement Fusion Research is a careful, scholarly account of the course of fusion energy research over the past fifty years. The authors outline the different paths followed by fusion research from initial ignorance to present understanding. They explore why a particular scheme would not work and why it was more profitable to concentrate on the mainstream tokamak development. The book features descriptive sections, in-depth explanations of certain physical and technical issues, scientific terms, and an extensive glossary that explains relevant abbreviations and acronyms.
Download or read book Plasma Science written by National Academies of Sciences Engineering and Medicine and published by . This book was released on 2021-02-28 with total page 291 pages. Available in PDF, EPUB and Kindle. Book excerpt: Plasma Science and Engineering transforms fundamental scientific research into powerful societal applications, from materials processing and healthcare to forecasting space weather. Plasma Science: Enabling Technology, Sustainability, Security and Exploration discusses the importance of plasma research, identifies important grand challenges for the next decade, and makes recommendations on funding and workforce. This publication will help federal agencies, policymakers, and academic leadership understand the importance of plasma research and make informed decisions about plasma science funding, workforce, and research directions.
Download or read book Turbulence in Space Plasmas written by Loukas Vlahos and published by Springer Science & Business Media. This book was released on 2009-06-16 with total page 332 pages. Available in PDF, EPUB and Kindle. Book excerpt: Over the years, many leading European graduate schools in the field of astrophysical and space plasmas have operated within the framework of the research network, "Theory, Observations, and Simulations in Turbulence in Space Plasmas." This text is a set of lectures and tutorial reviews culled from the relevant work of all those schools. It emphasizes applications on solar coronae, solar flares, and the solar wind. In bridging the gap between standard textbook material and state-of-the-art research, this text offers a broad flavor to postgraduate and postdoctoral students just coming to the field. And because of its unique mix, it will also be useful to lecturers looking for advanced teaching material for their seminars and courses.
Download or read book NRL Plasma Formulary written by Joseph Donald Huba and published by . This book was released on 1998 with total page 76 pages. Available in PDF, EPUB and Kindle. Book excerpt:
