[en] The Tara tandem mirror program has studied anchor and ponderomotive stabilization, axicell plugging with ECH and ICRF, sloshing ion buildup in the axicells, and halo formation and stabilization by an axisymmetric divertor. Central cell plasma parameters achieved by midplane fueling and slow wave ICRF heating from a local magnetic hill are β = 1.2%, n/sub e/ = 3 x 10¹² cm^-3. The plasma is stabilized both by anchor ion β and by ponderomotive stabilization with the central cell ICRF in combination with a magnetic divertor, realizing a completely axisymmetric configuration. Anchor ICRF creates non-Boltzman potential plugging of central cell ions. Neutral beam injection establishes a sloshing ion distribution for a cold dense central cell stream; the hot ion confinement is classical and dominated by electron drag. Axicell ECH plugging experiments lead to near total reduction in endloss, but also to a decrease in the central cell density, indicating increased radial losses. Single-ended ECH plugging shows no increase in opposite endloss. Single-ended plugging with axicell ICRF produces 50% reduction in ion endloss, with about half of the reflected ions observed in the opposite endloss. In the Constance-B quadrupole mirror the hot electron pressure profile is peaked off-axis and has the shape of a baseball seam

[en] The Tara tandem mirror is typically run in an effectively axisymmetric configuration by not producing β in the quadrupole anchor cells. Slow ion cyclotron wave excitation by a slot antenna located on a midplane bump in the magnetic field of the central cell provides plasma production and heating. Ion cyclotron resonances are at the minimum central cell fields on either side of the bump. Magnetic probe measurements have identified the slow wave excited by the antenna. Effective ion and electron heating is observed with a peak β of over 2%. The ICRF also provides stabilization of an m = 1 flute mode which is otherwise unstable in axisymmetric mirror geometry. In conjunction with a magnetic divertor at the central cell midplane, the slow wave can stabilize not only the central cell plasma but additional plasma in the axisymmetric plug cells. Destabilizing β can be produced in the plug cells by neutral beam injection, ICRF, or ECRH. By maintaining the stability of the plugs and central cell, end plugging using either ICRF or ECRH in the plug cells is obtained

[en] The Tara Tandem Mirror has a 10 m long, 22 cm diameter central cell plasma heated by fundamental ion cyclotron heating. Typical central cell parameters in unplugged operation are n = 3 x 10¹²/cm³. T/sub i perpendicular/ = 300 eV, T/sub i parallel/ ≅ 75 eV. The axisymmetric plug cell incorporates sloshing ions and ECH to generate axial confining potentials. The axisymmetric central cell and plug comprise a max-B mirror which is observed to operate in both flute stable and unstable regimes. The flute instability is m = 1 and can be stabilized by an outboard anchor. The anchor plasma is formed by electron and ion cyclotron heating. Satisfactory operation of a tandem mirror requires extensive control of neutral gas from neutral beam (NB) sources and startup. Tara makes extensive use of Ti gettering in the beamlines, beam dumps and plasma surfaces for both hydrogen pumping and reflux control. A description of this technology along with its impact on plasma performance is discussed

[en] The ability of mitochondria isolated from yeast protoplasts to synthesise 6-methoxy-2-hexa-prenylphenol, 5-demethoxyubiquinone-6 and ubiquinone-6 from either 4-hydroxybenzoate and isopentenyl pyrophosphate or 3-hexaprenyl-4-hydroxybenzoate was investigated. A radiochemical assay of biosynthetic activity is reported. It uses thin-layer chromatography with silica gel (developed by different compound mixtures) as substrate

[en] For several years, Pacific Northwest National Laboratory (PNNL) has been assessing the reliability of nuclear fuel supply in support of the U.S. Department of Energy/National Nuclear Security Administration. Three international low enriched uranium reserves, which are intended back up the existing and well-functioning nuclear fuel market, are currently moving toward implementation. These backup reserves are intended to provide countries credible assurance that of the uninterrupted supply of nuclear fuel to operate their nuclear power reactors in the event that their primary fuel supply is disrupted, whether for political or other reasons. The efficacy of these backup reserves, however, may be constrained without redundant fabrication services. This report presents the findings of a recent PNNL study that simulated outages of varying durations at specific nuclear fuel fabrication plants. The modeling specifically enabled prediction and visualization of the reactors affected and the degree of fuel delivery delay. The results thus provide insight on the extent of vulnerability to nuclear fuel supply disruption at the level of individual fabrication plants, reactors, and countries. The simulation studies demonstrate that, when a reasonable set of qualification criteria are applied, existing fabrication plants are technically qualified to provide backup fabrication services to the majority of the world's power reactors. The report concludes with an assessment of the redundancy of fuel supply in the nuclear fuel market, and a description of potential extra-market mechanisms to enhance the security of fuel supply in cases where it may be warranted. This report is an assessment of the ability of the existing market to respond to supply disruptions that occur for technical reasons. A forthcoming report will address political disruption scenarios.

[en] The Tara experiment has been constructed to investigate thermal barrier tandem mirror confinement in an essentially axisymmetric system. The device consists of a 10m long central solenoid bounded by two axisymmetric mirror cells where neutral beam injection and ECH are used to build up the plug plasma. Two quadrupole mirror cells outboard from the axisymmetric plugs are used to stabilize the machine. These anchor cells should stabilize low frequency instabilities when sufficient beta is established in their good curvature regions. The machine is designed so that central cell ions trapped by potentials in the axisymmetric plugs will never see the nonaxisymmetric magnetic regions, thereby eliminating the most basic source of neoclassical radial transport. Very recently, the major systems (six 1 MW neutral beams and four 200 KW gyrotrons) required for thermal barrier experiments have begun full operation. Experiments have shown build up of the required sloshing ion population in the plugs using approximately 150 amperes (drain) injection in each plug. Plug density with sloshing beam injection is n/sub m/≅ 3 x 10/sup 12/ cm/sup -3/ and 1.5 times higher at the ion turning points. The gyrotron ECH has produced hot electron populations of a few percent beta and densities n/sub eh/ of 1- 5x10/sup 11/ cm/sup -3/

[en] The Tara tandem mirror is typically run in an effectively axisymmetric configuration by not producing β in the quadrupole anchor cells. Slow ion cyclotron wave excitation by a slot antenna located on a midplane bump in the magnetic field of the central cell provides plasma production and heating. Ion cyclotron resonances are at the minimum central cell fields on either side of the bump. Magnetic probe measurements have identified the slow wave excited by the antenna. Effective ion and electron heating is observed with a peak β of over 2%. The ICRF also provides stabilization of an m = 1 flute mode which is otherwise unstable in axisymmetric mirror geometry. In conjunction with a magnetic divertor at the central cell midplane, the slow wave can stabilize not only the central cell plasma but additional plasma in the axisymmetric plug cells. Destabilizing β can be produced in the plug cells by neutral beam injection, ICRF, or ECRH. By maintaining the stability of the plugs and central cell, end plugging using either ICRF or ECRH in the plug cells is obtained

[en] Control of the edge neutral pressure is critical for successful thermal barrier operation of tandem mirrors. High neutral pressures lead to substantial charge exchange losses of plasma ions as well as creating a population of cold ions and electrons which may be electrostatically trapped in the negative and positive confining potentials in the end cells. The primary sources of neutral gas in Tara are central cell and transition gas injection, and neutral beam injection in the plugs. In the central cell, the region of ionization is separated from the mirror-trapped hot ion region. Gettering in the region of hot ions, controls reflux and reduces the central cell gas contribution to the plug. During end plugging, the plasma stream from the central cell which is used to fuel the minimum B anchor cells is cut off, so that gas fueling must be supplied in the transition region. The beamlines and dumps use LN/Ti pumps, baffling and bakeable dumps and scrapers to limit gas penetration to the plug plasma. Gettering of the plug wall and geometric considerations are used to control reflux from charge exchange. Monte-Carlo simulations are used to analyze the plug and central cell reflux. A new central cell configuration employing a midplane magnetic divertor is now being evaluated. The halo plasma produced in the diverted magnetic flux will be used to improve shielding of the core plasma from charge exchange

[en] The Tara tandem mirror program has studied anchor and ponderomotive stabilization, axicell plugging with ECH and ICRF, sloshing ion buildup in the axicells, and halo formation and stabilization by an axisymmetric divertor. Central cell plasma parameters achieved by midplane fueling and slow wave ICRF heating from a local magnetic hill are β = 1.2%, n_e = 3x10¹²cm^-3. The plasma is stabilized both by anchor ion β and by ponderomotive stabilization with the central cell ICRF in combination with a magnetic divertor, realizing a completely axisymmetric configuration. Anchor ICRF creates non-Boltzmann potential plugging of central cell ions. Neutral beam injection establishes a sloshing ion distribution for a cold dense cell stream; the hot ion confinement is classical and dominated by electron drag. Axicell ECH plugging experiments lead to near total reduction in endloss, but also to a decrease in the central cell density, indicating increased radial losses. Single ended ECH plugging shows no increase in opposite endloss. Single-ended plugging with axicell ICRF produces 50% reduction in ion endloss, with about half of the reflected ions observed in the opposite endloss. In the Constance-B quadrupole mirror the hot electron pressure profile is peaked off-axis and has the shape of a baseball seam. (author)

[en] Plasma production and heating in the central cell of the Tara tandem mirror [Nucl. Fusion 22, 549 (1982); Plasma Physics and Controlled Nuclear Fusion Research, 1986, Proceedings of the 11th International Conference, Kyoto, Japan (IAEA, Vienna, 1987), Vol. 2, p. 251] have been studied. Using radio-frequency excitation by a slot antenna in the ion cyclotron frequency range (ICRF), plasmas with a peak β/sub perpendicular/ of 3%, density of 4 x 10¹² cm^-3, ion temperature of 800 eV, and electron temperature of 75--100 eV were routinely produced. The plasma radius decreased with increasing ICRF power, causing reduced ICRF coupling and saturation of the plasma beta. About 70% of the applied ICRF power can be accounted for in direct heating of both ions and electrons. Wave field measurements have identified the applied ICRF to be the slow, ion cyclotron wave. In operation without end plugging, the plasma parameters were limited by poor axial confinement and the requirements for maintenance of magnetohydrodynamic stability and microstability