[en] The possibility of fuelling pure RF-powered tandem mirror end plugs by gas puffing is considered. It is shown experimentally that gas puffing can lead to significant increases in plug density and that the details of the plug density buildup depended on the antenna locations relative to the central cell and the plug midplane. Large charge-exchange energy loss resulting from the puff gas makes it an inefficient technique for fuelling high-temperature end plugs. The possibility of employing gas puffing for building up high-density end plugs composed of relatively cold ions is also considered as a means of achieving electrostatic confinement for an ICRF-stabilized central cell. Experimental enhancement of the central-cell density, which shows no significant cooling of the central cell by the colder plug plasmas, is demonstrated. The RF power requirements for refuelling an ICRF-powered end plug to a given density and temperature are estimated. (author)

[en] The tandem mirror Phaedrus was designed with the aim of testing RF-heating techniques for auxiliary heating, low-energy neutral-beam re-fuelling and confinement properties of tandem mirrors. Fundamental ion cyclotron heating has been used to increase plug energy content during stream gun start-up by a factor of 10. Second-harmonic ion cyclotron heating has generated strong ion-tail heating. Studies of the tandem configuration demonstrate the problem of magnetic-field error and techniques to minimize the problem. Stable tandem confinement has been achieved with fundamental heating in both end plugs. (author)

[en] Although advanced fuels with low neutron yields are very desirable, only recently are specific confinement configurations proposed which might contain such fuels reacting at much higher temperatures than DT. One axisymmetric confinement scheme is described here which has low synchrotron radiation, optimum confinement times with wall stabilization, good accessibility to beam and RF heating, steady state operation and can be constructed from modular units. The present status of physics leading to our design is summarized together with crucial problems to be investigated

No abstract available

[en] A swept frequency reflectometer based on a 26.5--40GHz YIG oscillator has been used to measure RF induced density fluctuations in the Phaedrus-T tokamak. The Phaedrus-T tokamak, is conducting experiments on Alfven wave current drive. Up to 400kW of RF are launched with a two strap fast wave antenna at frequencies between ω_ch and ω_cd. The reflectometer can be used in X or O mode, enabling the authors to cover a wide range of densities. Both modes of operation are sensitive mainly to density fluctuations. The RF component of the reflected signal, normalized to the total reflected signal, shows strong RF density oscillations in the core. Additions of impurities removes the core signal. This is in agreement with the toroidal Alfven resonance condition. In addition the signal in the core shows significant correlation with the loop volt drop observed during current drive experiments. Further data on the behavior of the density fluctuations as the magnetic field and plasma density are varied are presented, and compared with the predictions of a toroidal cold plasma wave code

[en] Rf studies in small to medium sized tokamaks requires strict attention to impurity control along with innovative antenna design. A combination of bakeable insulated antenna surrounds, graphite limiters, boroniztion, and frequent He-glow discharge cleaning has resulted in reasonable impurity levels and control of rf induced density increases. Phaedrus-T's relatively small size has allowed us to test innovative antenna designs. We found that an insulator-limiter scheme is a viable antenna construction technique. Boronization techniques have mostly involved gas phase boronization using TMB ((CH₃)₃B) although lately we have added solid state boronization using a boron-carbide rod with good results. Besides our main focus on rf issues, Phaedrus-T continues to be used as a test bed for various diagnostic techniques because of its size and accessibility. A comparison between BES (Beam Emission Spectroscopy) and probe measured fluctuations was carried out to add credence to the larger BES efforts on TFTR. Measurements of Phaedrus-T fluctuation characteristics were also made during a collaboration with the University of Texas portable probe diagnostic group. A narrow band and high throughput XUV imaging camera using layer synthetic microstructure coated optics developed by Johns Hopkins University is being tested. A Russian built Gaseous Electro-Luminescent Proportional Detector for measuring soft X-ray spectrum in the 1-10 KeV range with a spectral FWHM resolution of 8% at 6 KeV is under test. (author). 12 refs, 3 figs

[en] The Phaedrus diagnostic system makes optimum use of probes and miniature gridded energy analyzers to measure detailed parameters such as density, plasma potential, and electron and ion energy. This requires miniaturization and provision for flexible access. Other diagnostics are made as flexible as possible. A multiple-aperture, end-loss analyzer is rotatable, allowing complete mapping of the end wall loss contours. Self-emissive probes are used to measure plasma potential contours in the end plugs. A single-channel neutral energy analyzer is movable and can be swept in energy. Secondary emission detector arrays supplement the neutral energy analyzer and give a measure of the ion energy versus pitch angle. Calibrated diamagnetic loops are used to measure the total plasma energy and its axial extent in each cell. Both permanent and insertable fast ion gauges are available. Completing the diagnostic system is a computerized data-acquisition system that is flexible and receptive to the time varying demands of the many ongoing experiments

[en] The first experimental evidence of low frequency current drive in a tokamak has been observed on the Phaedrus-T tokamak. Low frequency current drive utilizes waves with frequencies below the ion cyclotron frequency to inject momentum to electrons to drive a toroidal current, and is often referred to as Alfven wave current drive (AWCD). Like other noninductive current drive techniques, AWCD would allow fusion tokamak reactors to operate as steady state devices. AWCD would also allow tailoring of the energy and current density profiles. Properly modified profiles would make the plasma less susceptible to instabilities. The presence of noninductive current is inferred from the behavior of the plasma loop voltage measured at the edge of the plasma. For the experiments presented here, the principle evidence of AWCD is a fractional loop voltage drop of 0.35 that cannot be accounted for by a decrease in plasma resistivity or stored magnetic energy. The estimated driven current is 20--35 kA out of a total 64 kA. Furthermore, the ΔV_L is approximately linear with applied RF power and ΔV_L is dependent upon the phase of the antenna

[en] Phaedrus-T is a moderate sized tokamak with low toroidal field and substantial radiofrequency power capabilities. This machine has only recently become operational and full RF power is expected in the next year. The initial studies include edge modifications due to variable phased antenna structures and RF helicity current drive experiments. The tokamak is also being used as a test site for diagnostic development. (author). 7 refs, 2 figs

[en] A tandem mirror plasma has been sustained and heated by rf alone without the need for neutral beams. End plug density and energy are maintained by ICRH which traps and heats a fraction of the central-cell loss stream. The central-cell plasma is maintained by gas fueling and rf heating. Magnetohydrodynamic stability limits the ratio of the central cell to plug plasma pressure, and the central-cell electron temperature must be kept high enough for ionization. A quasi-steady state is achieved that lasts much longer than the decay times of the plugs and central cell