Horizontal Midplane Research Articles

Pump limiter studies on the Heliotron-E device

Particle control with pump limiters has been successfully demonstrated in a variety of tokamaks. This experiment has obtained, for the first time, experimental data on pump limiter operation in a heliotron configuration. A movable pump limiter module was installed on a horizontal midplane port of Heliotron-E. The limiter module was installed on a horizontal midplane port of Heliotron-E. The limiter assembly consists of a TiC-coated graphite head with single-sided particle collection and active pumping. The location of the limiter is varied from near the vacuum vessel wall or up to 8 cm inside the last closed magnetic flux surface. This flexibility permits the study of a heliotron plasma that is limited either by the magnetic separatrix or by a material limiter. In the configuration investigated, only very low pressures are observed in the pump limiter when it is located outside the last closed flux surface, indicating that the scrape-off layer density is very low (< 5 × 10 11 cm −3). For limiter positions inside the last closed flux surface, pressures of 2–6 mTorr are observed (similar to comparable tokamak operation). Erosion patterns on the vacuum vessel, as well as hot spots on the limiter head, indicate that the particle flow out of the confined plasma exhibits complicated patterns. This suggests that for efficient particle collection in a stellarator, pump limiters must be matched to the particle flow patterns.

Electron cyclotron measurements with the fast-scanning heterodyne radiometer on the tokamak fusion test reactor

Three fast-scanning heterodyne receivers, swept between 75 and 110, 110 and 170, and 170 and 210 GHz have measured electron cyclotron emission on the horizontal midplane of the tokamak fusion test reactor (TFTR) plasma. A second-harmonic microwave mixer in the 170–210-GHz receiver allows the use of a 75–110-GHz backward wave oscillator as a swept local oscillator. Electron temperature profile evolution data with a time resolution of 2 ms and a profile acquisition rate of 250 Hz will be presented for gas-fueled and pellet-fueled ohmic and neutral beam heated plasmas with toroidal fields up to 5.2 T. Recent results from a new swept-mode absolute calibration technique which can improve the accuracy and data collection efficiency during in situ calibration will also be presented.

Passive Control of the Vertical Instability in Intor

In the international tokamak reactor (INTOR), the problem of the passive control of the vertical instability is to be solved by means of suitably shaped saddle coils to be embedded in the blanket structure. The efficiency of such a system depends on the characteristics of the passive conductors and on the plasma equilibrium as well as on the type of plasma displacement assumed. To cover the physical uncertainties caused by the model assumptions for the plasma with respect to the motion on a slow time scale (of the order of several tens of milliseconds) corresponding to efficient passive stabilization, four different plasma displacement models are considered and compared with each other. A stability analysis is performed using the energy principle, expressed in circuital form. The results of the INTOR analysis are presented and discussed showing in particular that under very general conditions the optimum stabilization efficiency is obtained for passive conductors situated at about 60 deg above and below the horizontal midplane at the outboard side. The effect of the geometric parameters of the saddle coils (e.g., area and shape of the cross section, toroidal segmentation, etc.) on the stabilization efficiency is investigated; a parametric study of these dependences ismore » presented. General conclusions applicable to INTOR are drawn.« less

Fast scanning heterodyne receiver for the measurement of the time evolution of the electron temperature profile on the Tokamak Fusion Test Reactor

Two fast scanning heterodyne receivers, swept between 75–110 and 110–170 GHz in 2 ms every 4 ms, were developed to measure the electron cyclotron emission on the horizontal midplane of the Tokamak Fusion Test Reactor (TFTR) plasma. An absolute, in situ calibration technique enables the determination of the profile of the plasma electron temperature from the fundamental ordinary mode and second harmonic extraordinary mode cyclotron emission intensity, with an accuracy of better than 10%. Temperature measurements made with the scanning receivers agree well with data from laser TV Thomson scattering and x-ray pulse-height analysis measurements. The time evolution of the temperature profile during temperature sawteeth fluctuations is well documented when the period of the fluctuation (30–100 ms) is much longer than the instrument sweep repetition time.

1-millimeter wave interferometer for the measurement of line integral electron density on TFTR

A two-pass interferometer at 285 GHz has been developed to measure the line-integrated electron density on the horizontal midplane of the toroidal fusion test reactor (TFTR). Presently, the interferometer employs a 2-mW solid-state source to supply the launch wave and a 2-mm klystron oscillator and, a harmonic mixer to provide a superheterodyne front end. The transmission system consists of 25 m of C-band rectangular waveguide, adjustable miter bends, and a spherical mirror in the vacuum vessel with a total round trip transmission loss of 21 dB. The interferometer signal to noise is ≳50 dB. Utilization of a feed forward tracking system provides long-term stable operation. The interferometer routinely provides real-time feedback control for the gas injection system and a permissive for neutral beam operation.

Fast scanning heterodyne receiver for the measurement of the time evolution of the electron temperature profile on the Tokamak Fusion Test Reactor

Two fast scanning heterodyne receivers, swept between 75–110 and 110–170 GHz in 2 ms every 4 ms, were developed to measure the electron cyclotron emission on the horizontal midplane of the Tokamak Fusion Test Reactor (TFTR) plasma. An absolute, in situ calibration technique enables the determination of the profile of the plasma electron temperature from the cyclotron emission intensity. The 4-ms repetition rate of the receiver allowed the resolution of ‘‘sawtooth’’ fluctuations of temperature, whose period was 10–100 ms, in profiles with central temperatures of 1–2.5 keV.

Symmetries and pattern selection in Rayleigh-Bénard convection

This paper describes the process of pattern selection between rolls and hexagons in Rayleigh-Bénard convection with reflectional symmetry in the horizontal midplane. This symmetry is a consequence of the Boussinesq approximation, provided the boundary conditions are the same on the top and bottom plates. All possible local bifurcation diagrams (assuming certain non-degeneracy conditions) are found using only group theory. The results are therefore applicable to other systems with the same symmetries. Rolls, hexagons, or a new solution, regular triangles, can be stable depending on the physical system. Rolls are stable in ordinary Rayleigh-Bénard convection. The results are compared to those of Buzano and Golubitsky [1] without the midplane reflection symmetry. The bifurcation behavior of the two cases is quite different, and a connection between them is established by considering the effects of breaking the reflectional symmetry. Finally, the relevant experimental results are described.

Plasma rotation in the PDX tokamak

Toroidal and poloidal rotation has been measured in the Poloidal Divertor Experiment (PDX) tokamak in Ohmic and neutral-beam heated plasmas in a variety of discharge conditions and in both circular and diverted configurations. Rotation velocities were deduced from Doppler shifts of magnetic dipole (M1) lines and lines of optically allowed transitions in the visible and UV regions, from Kα emission, and also from an array of magnetic pickup loops. Poloidal and toroidal rotation velocities in Ohmically heated discharges were usually less than 3 × 105 cm·s−1. Near the plasma edge, the toroidal rotation velocity varies with poloidal angle both before and during neutral-beam injection. No systematic poloidal rotation was observed during neutral-beam injection centred about or displaced 10 cm from the horizontal midplane, which implies that the poloidal damping time τθ < 0.5 τii consistent with theoretical estimates. The central toroidal rotation velocity during neutral-beam injection scales linearly with the quantity and is independent of plasma current and toroidal magnetic field. The toroidal rotation velocity is higher in deuterium than in hydrogen plasmas, and also in diverted discharges as compared with circular ones. Toroidal rotation decay times after injection range from 80–100 ms at the centre to 160–180 ms at half the minor radius. Modelling of the radial profile of toroidal rotation indicates a central momentum diffusivity of the order of 8 × 103 cm2·s−1. This is approximately a factor of three higher than the momentum diffusivity obtained from the decay time. All present theories are inadequate in accounting for the observed damping rate of vϕ.

Inexpensive but technically sound mine pillar design analysis : Pariseau, W G Proc 21st US Symposium on Rock Mechanics, Rolla, Missouri, 28–30 May 1980, P57–72

A simple algorithm (PILLR) for obtaining by two-dimensional analysis thee essential results that would be obtained in an actual three-dimensional finite element analysis of stress about mine pillars in flat-laying stratified rock is presented. A series of comparisons between the distributions of the local factor of safety calculated from the results of three-dimensional analysis and that obtained in the PILLR two-dimensional analyses for pillars of length/width ratio ranging from 0.33 to 8.0 shows the algorithm to be quite effective. The average vertical stress over the horizontal mid-plane of the pillar in the PILLR two-dimensional analyses is always within 0.5 per cent of the exact average; the local safety factor distribution is always within 10 per cent of the three-dimensional result. The ratio of the computer core x time product for the 2D' to 3D analyses is approimately 1/150. Additional improvements ard possible, although with the current PILLR algorithm 3D analyses require less than 1 minute for execution. This fact makes technically sound 3D mine pillar design analyses economically feasible on a routine basis.

Neonate With Abdominal Calcifications

History Progressive tympanic abdominal distension with markedly reduced chest excursions and concomitant respiratory distress developed in a neonate who was delivered by cesarean section after a prolonged labor. He became increasingly pale and shocked. He died within hours of birth. Figures 1 and 2 are flat and upright views of the abdomen without contrast medium. Diagnosis Spontaneous rupture of the gut with tension pyopneumoperitoneum in a neonate. Comment The erect film of the chest and abdomen (Fig 1) shows bilateral collapsed lungs. A long air-fluid level bisects the horizontal midplane of the distended abdomen. Air-filled bowel loops float in the midline near the top and above the fluid level. The intraperitoneal air seems to be draped over the liver and spleen, which are displaced downward and medially, leaving bilateral radiolucencies in a saddlebag configuration. The falciform ligament is outlined by air. The supine film (Fig 2) shows a large, centrally

Measurement of fission-rate distribution on a standard uranium shell

Makrofol KG solid-state track recorders (SSTRs) are used to measure the absolute fission-rate distribution in the NISUS natural-uranium shell in the three orthogonal planes. The results show that the fission-rate ratios of the outer surface to the inner surface of the shell at different positions are not constant, contrary to the prediction from the ANISN one-dimensional transport code. The minimum and maximum fission-rate ratios in the NISUS uranium shell are 7.64±0.24 and 11.58±0.27 in the horizontal midplane at θ = 30° and θ = 180°, respectively (θ = 0° is the out-of-pile direction). These ratios are compared with that of the ANISN calculation which gives the value of 10.86. The discrepancy is because of the non-uniformity of thermal neutron source distribution in the graphite cavity block.

Direct Measurement of the Ion Distribution Function in a Toroidal Octupole

The distribution function was found to be a function only of energy and canonical angular momentum Pθ thus automatically satisfying the Vlasov equation, and being consistent with the assumption of a collisionless plasma. The lifetime of the plasma was inversely proportional to ion velocity and directly proportional to accessible phase space volume. The lifetime of 40 eV ions confined in the field was about 500 μsec which is consistent with the interpretation that the plasma is gradually lost to the supports of the current-carrying hoops although it is known that other losses to walls also occur. Density and current were calculated from the appropriate moments of the measured distribution. Plasma is confined primarily in the low-field central region of the octupole, and the density drops rather sharply in the outer regions of higher field, in the horizontal midplane of the device. The only component of ion current was the azimuthal one, which had a maximum value of about 10−4 A cm−2 and indicated a net mass flow in the positive θ direction.