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Reactor Configuration Development for ARIES-CS

Description: New compact, quasi-axially symmetric stellarator configurations have been developed as part of the ARIES-CS reactor studies. These new configurations have good plasma confinement and transport properties, including low losses of α particles and good integrity of flux surfaces at high β. We summarize the recent progress by showcasing two attractive classes of configurations — configurations with judiciously chosen rotational transforms to avoid undesirable effects of low order resonances on the flux surface integrity and configurations with very small aspect ratios (∼2.5) that have excellent quasi-axisymmetry and low field ripples.
Date: September 27, 2005
Creator: Ku LP, the ARIES-CS Team
Partner: UNT Libraries Government Documents Department

Reducing Turbulent Transport in Toroidal Configurations via Shaping

Description: Recent progress in reducing turbulent transport in stellarators and tokamaks by 3D shaping using a stellarator optimization code in conjunction with a gyrokinetic code is presented. The original applications of the method focussed on ion temperature gradient transport in a quasi-axisymmetric stellarator design. Here, an examination of both other turbulence channels and other starting configurations is initiated. It is found that the designs evolved for transport from ion temperature gradient turbulence also display reduced transport from other transport channels whose modes are also stabilized by improved curvature, such as electron temperature gradient and ballooning modes. The optimizer is also applied to evolving from a tokamak, finding appreciable turbulence reduction for these devices as well. From these studies, improved understanding is obtained of why the deformations found by the optimizer are beneficial, and these deformations are related to earlier theoretical work in both stellarators and tokamaks.
Date: April 20, 2011
Creator: H.E. Mynick, N. Pomphrey and P. Xanthopoulos
Partner: UNT Libraries Government Documents Department

Results of Compact Stellarator Eengineering Trade Studies

Description: A number of technical requirements and performance criteria can drive stellarator costs, e.g., tight tolerances, accurate coil positioning, low aspect ratio (compactness), choice of assembly strategy, metrology, and complexity of the stellarator coil geometry. With the completion of a seven-year design and construction effort of the National Compact Stellarator Experiment (NCSX) it is useful to interject the NCSX experience along with the collective experiences of the NCSX stellarator community to improving the stellarator configuration. Can improvements in maintenance be achieved by altering the stellarator magnet configuration with changes in the coil shape or with the combination of trim coils? Can a mechanical configuration be identified that incorporates a partial set of shaped fixed stellarator coils along with some removable coil set to enhance the overall machine maintenance? Are there other approaches that will simplify the concepts, improve access for maintenance, reduce overall cost and improve the reliability of a stellarator based power plant? Using ARIES-CS and NCSX as reference cases, alternative approaches have been studied and developed to show how these modifications would favorably impact the stellarator power plant and experimental projects. The current status of the alternate stellarator configurations being developed will be described and a comparison made to the recently designed and partially built NCSX device and the ARIES-CS reactor design study.
Date: September 25, 2009
Creator: T. Brown, L. Bromberg, and M. Cole
Partner: UNT Libraries Government Documents Department

Global Alfven eigenmodes in WELDELSTEIN 7-AS

Description: In the presence of fast particle populations marginally stable global modes in the shear Alfven branch can be destabilized by wave particle resonances. This is particularly of concern in future large devices, where losses of resonant particles ({alpha}-particles in a reactor) may then limit the available heating power and also may cause damage of the first wall. In tokamaks TAE modes inside toroidicity induced gaps of the shear Alfven continua have been found. In stellarators with very weak shear like W7-AS low-n TAE-gaps do not occur but gaps below the shear Alfven continua with mode numbers m and n, if the resonant values {tau} = n/m do not exist in the plasma volume (k{sub {parallel}} = (m{sm_bullet}{tau} - n )/R {ne} 0 ). Under these conditions GAE modes with frequencies {omega}{sub GAE} < (k{sub {parallel}}{sm_bullet}V{sub A}){sub min} are the favoured modes. The investigation of GAE modes could also be of relevance in the case of advanced tokamak equilibria with flat or inverted q-profiles in the central region.
Date: September 1, 1995
Creator: Weller, A.; Goerner, C. & Jaenicke, R.
Partner: UNT Libraries Government Documents Department

ATFSR: a small torsatron reactor

Description: A small (average minor radius anti a approx. = 1 m), moderate-aspect-ratio torsatron reactor based on the Advanced Toroidal Facility (ATF) is proposed as a starting point for improved stellarator reactor designs. The major limitation of the compact size is the lack of space under the helical coils for the blanket and shield. Neoclassical confinement models for helically trapped particles show that a large electric potential (radial electric field) is necessary to achieve ignition in a device of this size, although high-Q operation is still attainable with more modest potentials.
Date: January 1, 1985
Creator: Houlberg, W.A.; Lacatski, J.T. & Uckan, N.A.
Partner: UNT Libraries Government Documents Department

NCSX Construction Progress and Research Plans

Description: Stellarators use 3D plasma and magnetic field shaping to produce a steady-state disruption-free magnetic confinement configuration. Compact stellarators have additional attractive properties — quasi-symmetric magnetic fields and low aspect ratio. The National Compact Stellarator Experiment (NCSX) is being constructed at the Princeton Plasma Physics Laboratory (PPPL) in partnership with the Oak Ridge National Laboratory (ORNL) to test the physics of a high-beta compact stellarator with a lowripple, tokamak-like magnetic configuration. The engineering challenges of NCSX stem from its complex geometry requirements. These issues are addressed in the construction project through manufacturing R&amp;D and system engineering. As a result, the fabrication of the coil winding forms and vacuum vessel are proceeding in industry without significant technical issues, and preparations for winding the coils at PPPL are in place. Design integration, analysis, and dimensional control are functions provided by system engineering to ensure that the finished product will satisfy the physics requirements, especially accurate realization of the specified coil geometries. After completion of construction in 2009, a research program to test the expected physics benefits will start.
Date: September 26, 2005
Creator: Neilson, G. H.; Heitzenroeder, P.; Lyon, J.; Nelson, B.; Reiersen, W.; Zarnstorff, M. et al.
Partner: UNT Libraries Government Documents Department

Analysis of D pellet injection experiments in the W7-AS Stellarator

Description: A centrifugal injector was used to inject deuterium pellets (with 3--5 x 10{sup 19} atoms) at approx. equal 600 m/s into current-less, nearly shear-less plasmas in the Wendelstein 7-AS (W7-AS) stellarator. The D pellet was injected horizontally at a location where the non-circular and non-axisymmetric plasma cross section is nearly triangular. Visible-light TV pictures usually showed the pellet as a single ablating mass in the plasma, although the pellet occasionally broke in two or splintered into a cloud of small particles. The density evolution following pellet injection and the effect of pellet injection on energy confinement and fluctuations are discussed.
Date: July 1, 1997
Creator: Lyon, J.F.; Baylor, L.R.; Baldzuhn, J.; Fiedler, S.; Hirsch, M.; Kuehner, G. et al.
Partner: UNT Libraries Government Documents Department

On the Radial Structure of Fluctuations and Turbulence Induced Flows

Description: Comparative studies of the structure of turbulence have been carried out in stellarator plasmas with low (TJ-IU) and medium (L2-M) magnetic shear. In both devices, the value of the radial coherence of fluctuations is bursty. In the plasma edge region, the radial coherence is dominated by low frequency fluctuations ({lt}200 KHZ) in TJ-IU, whereas in L2-M, the radial coherence is due to high frequency fluctuations ({gt} 100 kHz). Numerical calculations of resistive ballooning turbulence show that in the non-linear phase, the correlation length is of the order of the width of the linear mode poloidal components, whereas in the linear phase, the correlation length is related to the width of the envelope. Toroidal coupling effects appear to be relevant in the nonlinear phase in the proximity of instability thresholds. The electrostatic Reynolds stress shows a radial gradient close to the velocity shear location in the TJ-IU torsatron, thus suggesting that this mechanism can drive poloidal flows.
Date: January 1, 1997
Creator: Hidalgo, C.; Pedrosa, M. A.; Milligen, B. V /; Sanchez, R. B.; Garcia-Cortes, I.; Batanov, G. et al.
Partner: UNT Libraries Government Documents Department

The U.S. Stellarator Power Plant Study

Description: The US Stellarator Power Plant Study (SPPS) was carried out by a national reactor study group that also conducts tokamak power plant studies (ARIES, PULSAR). The purpose was to assess the feasibility of a stellarator as a steady-state reactor and to identify critical issues for stellarator reactor design. The same system codes and assumptions (materials and costing approach) used in the tokamak reactor studies were used in this study of a 1-GW(e) stellarator power plant in order to develop a meaningful comparison between tokamak and stellarator reactors. The short time scale allowed for the study and the limited resources only permitted a first look at a stellarator reactor. Nevertheless, this study indicates that the Modular Helias-like Heliac (MHH) chosen for the SPPS could lead to an attractive steady-state reactor that is competitive with the ARIES-IV second-stability tokamak reactor. Options and tradeoffs were studied for a reference MHH case and areas needing further improvement were identified. No fatal flaws were found; solutions were found in all areas, although the design was not really optimized with respect to the magnetic configuration and reactor engineering.
Date: July 1, 1995
Creator: Lyon, J.F.
Partner: UNT Libraries Government Documents Department

Stability of local modes in low-aspect-ratio stellarators

Description: The studies of MHD stability properties of stellarator-type configurations are complicated by the three-dimensional (3-D) nature of the equilibrium of these configurations. Usually, the unstable modes are pressure-driven and very localized around the rational surface. The 3-D Mercier stability criterion for local instabilities is therefore adequate for most of the stability studies. The method has been implemented in different 3-D equilibrium codes and is widely employed in stability calculations for stellarators. We use an average method based on vacuum flux coordinates to study the equilibrium of low-aspect-ratio configurations. The specific vacuum flux coordinates (/rho/,theta,/var phi/) are those described by Boozer. The radial variable is /rho/, while theta and /var phi/ are, respectively, poloidal and toroidal-like angles. The Jacobian is D = B/sub v//sup 2///rho/B/sub 0/g/sub B/. The only vacuum magnetic field covariant component different from zero is B/sub /var phi// = g/sub B/, while B/sub 0/..pi../rho//sup 2/ is the toroidal flux. 7 refs., 1 fig.
Date: January 1, 1989
Creator: Garcia, L.; Carreras, B.A. & Dominguez, N.
Partner: UNT Libraries Government Documents Department

Ideal low-n and Mercier mode stability boundaries for /ell/ = 2 torsatrons

Description: We studied the relationship between the stability properties of ideal low-n-internal modes and the three-dimensional (3-D) ideal Mercier criterion for /ell/ = 2 torsatron configurations. For the low-n stability studies, we used the stellarator expansion as implemented in the FAR code. The 3-D Mercier criterion was applied to equilibria calculated with the VMEC code. We found that low-n modes with singular surfaces lying in a Mercier region are, in general, unstable and the critical beta given by the Mercier criterion agrees well with the critical beta for the lowest-n unstable mode. This is verified even in the case of global n = 1 modes. Therefore, the 3-D Mercier criterion is a useful guide in mapping the ideal stability beta limits for these torsatron configurations. 5 refs., 5 figs.
Date: January 1, 1989
Creator: Dominguez, N.
Partner: UNT Libraries Government Documents Department

Recent progress in stellarator reactor conceptual design

Description: The Stellarator/Torsatron/Heliotron (S/T/H) class of toroidal magnetic fusion reactor designs continues to offer a distinct and in several ways superior approach to eventual commercial competitiveness. Although no major, integrated conceptual reactor design activity is presently underway, a number of international research efforts suggest avenues for the substantial improvement of the S/T/H reactor embodiment, which derive from recent experimental and theoretical progress and are responsive to current trends in fusion-reactor projection to set the stage for a third generation of designs. Recent S/T/H reactor design activity is reviewed and the impact of the changing technical and programmatic context on the direction of future S/T/H reactor design studies is outlined.
Date: January 1, 1985
Creator: Miller, R.L.
Partner: UNT Libraries Government Documents Department

NCSX Vacuum Vessel Fabrication

Description: The National Compact Stellarator Experiment (NCSX) is being constructed at the Princeton Plasma Physics Laboratory (PPPL) in conjunction with the Oak Ridge National Laboratory (ORNL). The goal of this experiment is to develop a device which has the steady state properties of a traditional stellarator along with the high performance characteristics of a tokamak. A key element of this device is its highly shaped Inconel 625 vacuum vessel. This paper describes the manufacturing of the vessel. The vessel is being fabricated by Major Tool and Machine, Inc. (MTM) in three identical 120º vessel segments, corresponding to the three NCSX field periods, in order to accommodate assembly of the device. The port extensions are welded on, leak checked, cut off within 1&quot; of the vessel surface at MTM and then reattached at PPPL, to accommodate assembly of the close-fitting modular coils that surround the vessel. The 120º vessel segments are formed by welding two 60º segments together. Each 60º segment is fabricated by welding ten press-formed panels together over a collapsible welding fixture which is needed to precisely position the panels. The vessel is joined at assembly by welding via custom machined 8&quot; (20.3 cm) wide spacer &quot;spool pieces.&quot; The vessel must have a total leak rate less than 5 X 10-6 t-l/s, magnetic permeability less than 1.02μ, and its contours must be within 0.188&quot; (4.76 mm). It is scheduled for completion in January 2006.
Date: October 7, 2005
Creator: Viola, M. E.; Brown, T.; Heitzenroeder, P.; Malinowski, F.; Reiersen, W.; Sutton, L. et al.
Partner: UNT Libraries Government Documents Department

Overview of the US stellarator reactor study

Description: This study, which uses a cost-minimization code that incorporates the ARIES costing and reactor component models with a I-D energy transport calculation, shows that a torsatron reactor could be competitive with a tokamak reactor.
Date: December 31, 1993
Creator: Lyon, J. F.; Gulec, K.; Miller, R. L. & El-Guebaly, L.
Partner: UNT Libraries Government Documents Department

Assessment of stellarators as reactors

Description: Stellarators have significant operational advantages over tokamaks as ignited steady-state reactors: no dangerous disruptions, no need for continuous current drive and power recirculated to the plasma, less severe constraints on the plasma parameters and profiles, and access from the inboard side for easier maintenance. The US is starting a multi-year multi-institutional stellarator reactor study whose purpose is to ``identify and assess the feasibility of critical issues and their consequences for development of the stellarator concept as a steady-state fusion reactor.`` The activities during the first year are focusing on physics optimization and selection of one or more stellarator coil configurations for more detailed engineering design evaluation. The physics team is focusing on torsatron modularization, modular stellarators with lower aspect ratio, the divertor geometry, development of transport models, and overall system studies. The engineering team is studying design issues relating to minimizing the inboard thickness of the blanket and shields, the feasibility of the superconducting magnets, and maintenance schemes.
Date: July 1, 1993
Creator: Lyon, J. F.
Partner: UNT Libraries Government Documents Department

Development of Scientific Simulation 3D Full Wave ICRF Code for Stellarators and Heating/CD Scenarios Development

Description: In this report we describe theory and 3D full wave code description for the wave excitation, propagation and absorption in 3-dimensional (3D) stellarator equilibrium high beta plasma in ion cyclotron frequency range (ICRF). This theory forms a basis for a 3D code creation, urgently needed for the ICRF heating scenarios development for the operated LHD, constructed W7-X, NCSX and projected CSX3 stellarators, as well for re evaluation of ICRF scenarios in operated tokamaks and in the ITER . The theory solves the 3D Maxwell-Vlasov antenna-plasma-conducting shell boundary value problem in the non-orthogonal flux coordinates ({Psi}, {theta}, {var_phi}), {Psi} being magnetic flux function, {theta} and {var_phi} being the poloidal and toroidal angles, respectively. All basic physics, like wave refraction, reflection and diffraction are self consistently included, along with the fundamental ion and ion minority cyclotron resonances, two ion hybrid resonance, electron Landau and TTMP absorption. Antenna reactive impedance and loading resistance are also calculated and urgently needed for an antenna -generator matching. This is accomplished in a real confining magnetic field being varying in a plasma major radius direction, in toroidal and poloidal directions, through making use of the hot dense plasma wave induced currents with account to the finite Larmor radius effects. We expand the solution in Fourier series over the toroidal ({var_phi}) and poloidal ({theta}) angles and solve resulting ordinary differential equations in a radial like {Psi}-coordinate by finite difference method. The constructed discretization scheme is divergent-free one, thus retaining the basic properties of original equations. The Fourier expansion over the angle coordinates has given to us the possibility to correctly construct the ''parallel'' wave number k{sub //}, and thereby to correctly describe the ICRF waves absorption by a hot plasma. The toroidal harmonics are tightly coupled with each other due to magnetic field inhomogeneity of stellarators in toroidal ...
Date: August 15, 2005
Creator: V.L., Vdovin
Partner: UNT Libraries Government Documents Department

The Columbia Non-neutral Torus

Description: Final report for the Columbia Non-neutral Torus. This details the results from the design, construction and initial operation of the Columbia Non-neutral Torus.
Date: September 23, 2009
Creator: Pedersen, Thomas Sunn
Partner: UNT Libraries Government Documents Department

Convective equilibrium and mixing-length theory for stellarator reactors

Description: In high ..beta.. stellarator and tokamak reactors, the plasma pressure gradient in some regions of the plasma may exceed the critical pressure gradient set by ballooning instabilities. In these regions, convective cells break out to enhance the transport. As a result, the pressure gradient can rise only slightly above the critical gradient and the plasma is in another state of equilibrium - ''convective equilibrium'' - in these regions. Although the convective transport cannot be calculated precisely, it is shown that the density and temperature profiles in the convective region can still be estimated. A simple mixing-length theory, similar to that used for convection in stellar interiors, is introduced in this paper to provide a qualitative description of the convective cells and to show that the convective transport is highly efficient. A numerical example for obtaining the density and temperature profiles in a stellarator reactor is given.
Date: September 1, 1985
Creator: Ho, D.D.M. & Kulsrud, R.M.
Partner: UNT Libraries Government Documents Department

Recent progress on ATF

Description: The ATF experiment will test improvements to high-beta, steady-state toroidal confinement using external helical fields. The device design has been optimized to (1) provide direct access to the high-beta second-stability regime, (2) have sufficient flexibility to study a large range of toroidal configurations both with and without plasma current, (3) test the reduction of low-collisionality transport by EXB drifts induced by the self-consistent radial electric field, and (4) permit steady-state, high-beta operation without disruptions. Continued physics studied at ORNL and recent results from foreign stellarator experiments have increased confidence in ATF performance.
Date: January 1, 1984
Creator: Neilson, G.H.
Partner: UNT Libraries Government Documents Department

MHD stability of torsatrons using the average method

Description: The stability of torsatrons is studied using the average method, or stellarator expansion. Attention is focused upon the Advanced Toroidal Fusion Device (ATF), an l = 2, 12 field period, moderate aspect ratio configuration which, through a combination of shear and toroidally induced magnetic well, is stable to ideal modes. Using the vertical field (VF) coil system of ATF it is possible to enhance this stability by shaping the plasma to control the rotational transform. The VF coils are also useful tools for exploring the stability boundaries of ATF. By shifting the plasma inward along the major radius, the magnetic well can be removed, leading to three types of long wavelength instabilities: (1) A free boundary ''edge mode'' occurs when the rotational transform at the plasma edge is just less than unity. This mode is stabilized by the placement of a conducting wall at 1.5 times the plasma radius. (2) A free boundary global kink mode is observed at high ..beta... When either ..beta.. is lowered or a conducting wall is placed at the plasma boundary, the global mode is suppressed, and (3) an interchange mode is observed instead. For this interchange mode, calculations of the second, third, etc., most unstable modes are used to understand the nature of the degeneracy breaking induced by toroidal effects. Thus, the ATF configuration is well chosen for the study of torsatron stability limits.
Date: January 1, 1985
Creator: Holmes, J.A.; Carreras, B.A.; Charlton, L.A.; Garcia, L.; Hender, T.C.; Hicks, H.R. et al.
Partner: UNT Libraries Government Documents Department