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Beam injection in the TMX-U central cell

Description: Results pertaining to the recently modified beam-injection arrangement in the central cell of TMX-U are presented here. These modifications followed our observation that beam atoms injected perpendicular to the magnetic axis between the first two magnet-coil gaps give rise to trapped ions with midplane pitch angles lying in the intervals 68/sup 0/ < theta < 78/sup 0/ and 59/sup 0/ < theta < 65/sup 0/. These pitch-angle intervals are similar in value to the earlier arrangement of beams injected at the midplane at pitch angles of 58 and 70/sup 0/. Normal injection at an off-midplane position has two advantages when compared with off-normal injection at the midplane. First, the unattenuated beam can be dumped in the first-injector region rather than in the plasma region. Second, the beams can be oriented with their long dimension horizontal rather than vertical. The first point al
Date: June 15, 1984
Creator: Turner, W.C.
Partner: UNT Libraries Government Documents Department

Improvement of tubulars used for fracturing in hot dry rock wells

Description: Completion of hot dry rock wells as it is currently envisioned, requires that hydraulic fracturing be used to develop a heat extraction reservoir and to provide low impedance flow paths between the designated water injection and production wells. Recent fracturing operations at measured depths from 11,400 ft to 15,300 ft at the Fenton Hill Hot Dry Rock Geothermal Test Site have resulted in numerous failures of tubulars caused by the high fracturing pressures, corrosive environment and large treatment volumes at high flow rates. Two new fracturing strings were designed and purchased. Physical and chemical properties exceeding API specifications were demanded and supplied by the manufacturers. These tubulars have performed to design specifications.
Date: April 1, 1984
Creator: Nicholson, R.W.; Dreesen, D.S. & Turner, W.C.
Partner: UNT Libraries Government Documents Department

Low-energy neutral-beam injection in the central cell of TMX-U

Description: The purpose is to estimate the central-cell parameters that can be reached by injection of low-energy neutral beams. The main advantages of low energy (2-keV full-energy component) over high energy (15-keV full-energy component) are the following: (1) creation of a beam-fueled, potentially confined, central-cell plasma (n approx. = 10/sup 13/ cm/sup -3/, E/sub ic/ approx. = 1 keV, T/sub ec/ approx. = 0.4 keV) without the use of cold-gas injection or ICRH heating; and (2) reduced shielding requirement against neutrals external to the plasma. The reasons for these expectations are the larger ionization cross section and plasma radius (normalized to ion gyroradius) for low-energy compared to high-energy beams.
Date: September 24, 1984
Creator: Turner, W.C.
Partner: UNT Libraries Government Documents Department

Low energy neutral source for fueling the central cell core plasma of TMX-U

Description: The performance of a low energy neutral source formed by negatively biased plates inserted in the edge plasma of the central cell of the Tandem Mirror Experiment-Upgrade (TMX-U) is described. This technique promises to be capable of fueling the high density thermal barrier plasmas. We have found that annular ring electrodes mounted on the sides of the central cell gas box and inclined 45/sup 0/ to the plasma axis can produce about 80 A of inward-directed D/sup 0/ with an average energy E/sub 0/ approx. = 250 eV (where the plate bias = -400 V). This example was calculated for a peak plasma density n/sub e/(0) = 10/sup 13/ cm/sup -3/ and an edge plasma density n/sub L/ = 10/sup 12/ cm/sup -3/ at the limiter edge defined by the biased plates. The energetic neutrals, attenuated by about an e-fold in reaching the plasma center, are thus much more efficient in fueling the core plasma than Frank-Condon atoms, which are attenuated by greater than a factor of 100. In addition, because their energy is greater than Frank-Condon atoms their initial collisional trapping rate in the thermal barrier is reduced by a factor of approximately (100)/sup 3/2/ = 1000.
Date: April 23, 1984
Creator: Turner, W.C.
Partner: UNT Libraries Government Documents Department

Recent experimental progress in the TMX-U thermal barrier tandem mirror experiment

Description: Recent experiments on the TMX-U thermal barrier device at LLNL have achieved the end plugging of axial ion losses up to a central cell density of n/sub c/ = 2 x 10/sup 12/ cm. During these tests, the axial potential profile characteristic of a thermal barrier has been measured experimentally, indicating an ion-confining potential greater than 1.5 kV and a potential depression of 0.45 kV in the barrier region. The average beta of hot electrons in the thermal barrier has been increased to 15% and appears limited only by classical scattering and ECRH pulse duration. Furthermore, deuterium ions in the central cell have been heated with ICRF to an average energy of 1.5 keV, with a heating efficiency of 40%. During strong end plugging, the axial ion confinement time reached 50 to 100 ms while the nonambipolar radial ion confinement time was 5 to 15 ms - independent of end plugging. Radial ion confinement time exceeding 100 ms has been attained on shots without end plugging. Plates, floated electrically on the end walls, have increased the radial ion confinement time by a factor of 1.8. Further improvement in the central cell density during end plugging can be expected by increasing the ICRF, improving the central cell vacuum conditions and beam heating efficiency, and increasing the radial extent of the potential control plates on the end walls.
Date: June 22, 1984
Creator: Turner, W.C.; Allen, S.L.; Casper, T.A.; Clauser, J.F.; Coensgen, F.H.; Correll, D.L. et al.
Partner: UNT Libraries Government Documents Department