Ultra-low Aspect Ratio Research Articles

Tokamak Startup Using Point-Source dc Helicity Injection

Startup of a 0.1 MA tokamak plasma is demonstrated on the ultralow aspect ratio Pegasus Toroidal Experiment using three localized, high-current density sources mounted near the outboard midplane. The injected open field current relaxes via helicity-conserving magnetic turbulence into a tokamaklike magnetic topology where the maximum sustained plasma current is determined by helicity balance and the requirements for magnetic relaxation.

Effect of End Wall Contouring on Performance of Ultra-Low Aspect Ratio Transonic Turbine Inlet Guide Vanes

In our previous work on ultralow-aspect ratio transonic turbine inlet guide vanes (IGVs) for a small turbofan engine (Hasenjäger et al., 2005, “Three Dimensional Aerodynamic Optimization for an Ultra-Low Aspect Ratio Transonic Turbine Stator Blade,” ASME Paper No. GT2005-68680), we used numerical stochastic design optimization to propose the new design concept of an extremely aft-loaded airfoil to improve the difficult-to-control aerodynamic loss. At the same time, it is well known that end wall contouring is an effective method for reducing the secondary flow loss. In the literature, both “axisymmetric” and “nonaxisymmetric” end wall geometries have been suggested. Almost all of these geometric variations have been based on the expertise of the turbine designer. In our current work, we employed a stochastic optimization method—the evolution strategy—to optimize and analyze the effect of the axisymmetric end wall contouring on the IGV’s performance. In the optimization, the design of the end wall contour was divided into three different approaches: (1) only hub contour, (2) only tip contour, and (3) hub and tip contour, together with the possibility to observe the correlation between hub/tip changes with regard to their joint influence on the pressure loss. Furthermore, three-dimensional flow mechanisms, related to a secondary flow near the end wall region in the low-aspect ratio transonic turbine IGV, was investigated, based on the above optimization results. A design concept and secondary flow characteristics for the low-aspect ratio full annular transonic turbine IGV is discussed in this paper.

Non-inductive Production of ST Plasmas with Washer Gun Sources on the Pegasus Toroidal Experiment

Formation of tokamak-like plasmas via electrostatic helicity injection in the ultra-low aspect ratio Pegasus Toroidal Experiment is reported. Two low-impurity, high-current (1 kA) washer gun current sources have been installed in the lower divertor region. These initially drive current along helical field lines produced by the applied toroidal and vertical fields. At sufficiently low values of externally applied vertical field, the poloidal field generated by the plasma is large enough to cause a poloidal flux reversal. In these cases the plasma relaxes into a tokamak-like configuration. Discharges with I ϕ≈ 30 kA are produced with less than 2 kA of injected current. These discharges exhibit features indicative of tokamak plasmas, including reversal of poloidal flux at the center column, strong vacuum field deformation, increased current decay times, increased core heating, and characteristic MHD modes common to other helicity-injection-driven toroidal devices.

Construction and Initial Operation of the Columbia Nonneutral Torus

We report on the results from initial testing and operation of the Columbia Nonneutral Torus, a new stellarator experiment constructed at Columbia University to study the confinement of nonneutral plasmas, electron-positron plasmas, and stellarator confinement in the presence of strong electrostatic fields. A new algorithm for automatic identification of good magnetic surfaces, island chains, and stochastic regions in Poincaré maps is also described. We present some of the details of the design of the interlocked in-vessel coils and the vacuum system and report on initial vacuum performance. Magnetic surface mapping and visualization results are also presented, confirming the existence of ultralow aspect ratio magnetic surfaces with excellent quality and good agreement with numerical calculations.

A Study on the Monitoring of Nano Scale EHL Film Formation with Ultra Low Aspect Ratio

The measurement of ultra low aspect ratio fluid film thickness is very crucial technique both for the verification of lubrication media characteristics and for the clearance design in many precision components such as MEMS, precision bearings and other slideways. Many technologies are applied to the measurement of ultra low aspect ratio fluid film thickness (i.e. elastohydrodynamic lubrication film thickness). In particular, in-situ optical interferometric method has many advantages in making the actual contact behaviors realized with the experimental apparatus. This measurement method also does the monitoring of the surface defects and fractures happening during the contact behavior, which are delicately influenced by the surface conditions such as load, velocity, lubricant media as well as surface roughness. Careful selection of incident lights greatly enhances the fringe resolutions up to ~1.0 nanometer scale with digital image processing technology. In this work, it is found that coaxial aligning trichromatic incident light filtering system developed by the author can provide much finer resolution of ultra low aspect ratio fluid film thickness than monochromatic or dichromatic incident lights, because it has much more spectrums of color components to be discriminated according the variations of film thickness. For the measured interferometric images of ultra low aspect ratio fluid film thickness it is shown how the film thickness is finely digitalized and measured in nanometer scale with digital image processing technology and space layer method. The developed measurement system can make it possible to visualize the contact deformations and possible fractures of contacting surface under the repeated loading condition.

The Columbia Nonneutral Torus: A New Experiment to Confine Nonneutral and Positron-Electron Plasmas in a Stellarator

The Columbia Nonneutral Torus is a new stellarator experiment being built at Columbia University, New York, to study the confinement of nonneutral and electron-positron plasmas. It will be a two-period, ultralow aspect ratio classical stellarator configuration created from four circular coils. The theory of the confinement and transport of pure electron plasmas on magnetic surfaces is reviewed. The guiding principles behind the experimental design are presented, together with the actual experimental design configuration.

A FINITE ELEMENT INTEGRAL METHOD FOR CALCULATING COMPLEX AXISYMETRIC PLASMA CONFIGURATIONS

International Journal of Computational Engineering ScienceVol. 05, No. 01, pp. 91-112 (2004) No AccessA FINITE ELEMENT INTEGRAL METHOD FOR CALCULATING COMPLEX AXISYMETRIC PLASMA CONFIGURATIONSFRANÇOIS ROGIER and ALESSANDRO MANCUSOFRANÇOIS ROGIERONERA, DTIM/M2SN, 2, Avenue Edouard Belin, Toulouse, FranceONERA 2, Avenue Edouard Belin, Toulouse, France. Search for more papers by this author and ALESSANDRO MANCUSOENEA/FUS, C.R.E. Frascati C.P. 65 - 00044 - Frascati, Rome, ItalyAssociazione Euratom-ENEA, C.R.E. Frascati C.P. 65 - 00044 - Frascati, Rome, Italy. Search for more papers by this author https://doi.org/10.1142/S1465876304002289Cited by:1 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail AbstractThis work aim to present a numerical method for solving ideal Magnetohydrodynamic equilibrium equations for Ultra Low Aspect Ratio Tokamak with pinch. Discretization and acceleration techniques are discussed and applications to realistic tokamak configurations are shown.Keywords:Magnetohydrodynamic equilibrium equationsFinite Element MethodGreen's functionFast Fourier TransformationUltra Low ratio Tokamak References F. Alladio, Enea Report: RT/ERG/FUS/94/26 (1994) . Google ScholarF. Alladio and P. Micozzi, Nuclear Fusion 37, 1759 (1997). Crossref, Google ScholarT. Takeda and S. Tokuda, J. Comp. Phys. 93, (1991). Google Scholar J. Blum , Numerical Simulation and Optimal Control in Plasma Physics ( Gauthier-Villars , 1989 ) . Google Scholar , T. Takeda and T. Tsunematsu, Japan Atomic Energy Research Report JAERI-M 082 (1979) . Google ScholarW. Kerner and O. Jandl, Comput. Phys. Commun. 31, 269 (1984). Crossref, Google ScholarF. Alladio and F. Crisanti, Nuclear Fusion 26, 1143 (1986). Crossref, Google ScholarF. Alladio and P. Micozzi, Nuclear Fusion 35, 305 (1995). Crossref, Google ScholarJ. C. Nedelec, Internat. J. Numer. Methods Fluids 7, 1229 (1987). Crossref, Google Scholar Hockney, Eastwood, Computer Simulation Using Particles, MacGraw-Hill, 1981 . Google Scholar FiguresReferencesRelatedDetailsCited By 1Calculation of Boozer magnetic coordinates for multiple plasma regions (with either closed or open flux surfaces) connected by magnetic separatricesF. Alladio, A. Mancuso, P. Micozzi and F. Rogier1 Nov 2005 | Physics of Plasmas, Vol. 12, No. 11 Recommended Vol. 05, No. 01 Metrics History KeywordsMagnetohydrodynamic equilibrium equationsFinite Element MethodGreen's functionFast Fourier TransformationUltra Low ratio TokamakPDF download

Highly elongated, low‐aspect‐ratio tokamak produced by negative‐biased theta pinch

Ultra Low Aspect Ratio Tokamaks (ULART) are produced by using a negative-biased theta-pinch device. A slender conducting rod which serves as a toroidal field coil is newly installed along a geometrical center axis of the theta-pinch coil. The ULART is quickly formed for about 10 μs by applying programmed current flows from three sets of fast banks and a slow bank to these coils and is sustained for about 100 μs. The plasma diagnosed from a magnetic probe array has a low aspect ratio A = 1.1 and a poloidal surface with a high elongation ratio κ = 10. The safety factor reaches about 30 near the separatrix edge when Ip = 280 kA flows in the plasma and Itfc = 30 kA in the conducting rod. A preliminary result on global MHD characteristics of the ULART is also given. The plasma is unstable with respect to a vertical displacement and a toroidal n = 1 mode. The amplitudes of these modes depend on the values of Itfc and κ. © 2001 Scripta Technica, Electr Eng Jpn, 134(4): 19–27, 2001

Engineering Design of the National Spherical Tokamak Experiment

The National Spherical Tokamak Experiment (NSTX) is an ultra low aspect ratio device with a plasma current of 1 MA. The tokamak features auxiliary heating and current drive with a close-fitting conducting shell to maximize the plasma pressure. NSTX is designed for an experimental pulse length that will demonstrate quasi-steady state non-inductively driven advanced tokamak operation. The design also takes maximum advantage of existing facilities and components from previous Princeton devices to reduce the overall program costs.

Spherical stellarator with plasma current

Recently proposed novel concept of a spherical stellarator (P. E. Moroz, ‘‘Spherical stellarator configuration,’’ to appear in Phys. Rev. Lett) is enhanced by adding the plasma current to the otherwise pure stellarator system. The coil configuration of this ultra low aspect ratio system differs from that of a spherical tokamak by inclination of external parts of the toroidal field coils. It is shown that the configuration considered possesses many attractive properties, including: wide flexibility of operating regimes, compact design and coil simplicity, good access to the plasma, closed vacuum flux surfaces with large enclosed volume, significant external rotational transform, strong magnetic well, and a high plasma β [β(0) in excess of 30%] equilibrium. It is shown that the bootstrap effect in a spherical stellarator, in principle, can supply the full plasma current required for the high-β equilibrium.

Spherical Stellarator Configuration.

A novel ultralow aspect ratio stellarator system that can be called a spherical stellarator (SS), in analogy with the spherical tokamak concept, is considered. The coil configuration of a simplest SS differs from that of a spherical tokamak by inclination of the external parts of the toroidal field coils. This system possesses many attractive properties including compact design and coil simplicity, good access to the plasma, closed vacuum flux surfaces with large enclosed volume, significant external rotational transform, strong magnetic well, and simple divertor configuration. {copyright} {ital 1996 The American Physical Society.}

Study of the Ultra Low Aspect Ratio Tokamak, ULART

We investigate experimentally and theoretically the global MHD characteristics of an ultra-low aspect ratio tokamak (ULART). Since the ULART requires a substantially smaller toroidal field current,...