Search

Advanced Tokamak (AT) research in DIII-D [K. H. Burrell for the DIII-D Team, in Proceedings of the 19th Fusion Energy Conference, Lyon, France, 2002 (International Atomic Energy Agency, Vienna, 2002) published on CD-ROM] seeks to provide a scientific basis for steady-state high performance operation in future devices. These regimes require high toroidal beta to maximize fusion output and poloidal beta to maximize the self-driven bootstrap current. Achieving these conditions requires integrated, simultaneous control of the current and pressure profiles, and active magnetohydrodynamic stability control. The building blocks for AT operation are in hand. Resistive wall mode stabilization via plasma rotation and active feedback with nonaxisymmetric coils allows routine operation above the no-wall beta limit. Neoclassical tearing modes are stabilized by active feedback control of localized electron cyclotron current drive (ECCD). Plasma shaping and profile control provide further improvements. Under these condi...

An assessment of the feasibility of installing the TEXT 2 MeV heavy-ion beam probe on the DIII-D tokamak has been completed. Detailed drawings of the machine cross section were imported into the CAD application AutoCAD. A set of programs written in AutoLisp were used to generate trajectories. Displays of the accessible cross section of the plasma, scan lines for the entire range of primary beam energy and injection angle ranges, and sample–volume dimensions can be rapidly generated. Because of the large deflection between the primary input beam and the emergent secondary beam, either the analyzer needs to be tracked over a ±20° angle or secondary poloidal deflector plates need to be installed at the exit port. Toroidal deflector plates will be installed at both the injection and exit ports to compensate for toroidal displacements and deflections. The sample volumes generated by this procedure are within a few centimeters of the locations derived from a full three-dimensional calculation.

Analysis of the circular polarization of the Lii 6708 A line emitted from a monoenergetic lithium beam provides a spatially resolved measurement of the poloidal magnetic field on the Texas experimental tokamak [Nucl. Technol. Fusion 1, 479 (1989)]. Determined from the measured magnetic field, the safety factor on the magnetic axis during Ohmically heated sawtoothing discharges is near unity.

A fast neutral lithium beam has been installed on the TEXT tokamak for beam emission spectroscopy studies of the edge plasma electron‐density profile. The diagnostic was recently upgraded from ten to twenty spatial channels, each of which has two detectors, one to measure lithium beam signal and one to monitor plasma background light. The spatial resolution is 6 mm, and the temporal resolution is designed to be as high as 10 ms for studies of transient events including plasma density fluctuations. Initial results are presented from the ten‐channel system: Edge electron densities unfolded from the LiI (2 s 2S–2 p 2P) 670.8 nm emission profile have the same general time dependence as the line‐averaged density measured by microwave interferometry.

The polarization of the π component of the Zeeman split Li2P–2S transition allows a direct spectroscopic measurement of the local magnetic pitch angle. Li atoms are injected radially into TEXT as a 95 keV beam and the intensity of the transmitted beam is detected. A polarization‐modulated, cavity‐dumped dye laser, tuned into resonance with the π line, is injected collinearly with the beam. Laser excitation of the beam results in an enhanced beam attenuation. Time‐resolved detection of the transmitted Li beam allows determination of the local magnetic pitch angle. Details of the system and results of recent measurements will be discussed.

The DIII-D Advanced Tokamak (AT) program in the DIII-D tokamak [J. L. Luxon, Plasma Physics and Controlled Fusion Research, 1986, Vol. I (International Atomic Energy Agency, Vienna, 1987), p. 159] is aimed at developing a scientific basis for steady-state, high-performance operation in future devices. This requires simultaneously achieving 100% noninductive operation with high self-driven bootstrap current fraction and toroidal beta. Recent progress in this area includes demonstration of 100% noninductive conditions with toroidal beta, βT=3.6%, normalized beta, βN=3.5, and confinement factor, H89=2.4 with the plasma current driven completely by bootstrap, neutral beam current drive, and electron cyclotron current drive (ECCD). The equilibrium reconstructions indicate that the noninductive current profile is well aligned, with little inductively driven current remaining anywhere in the plasma. The current balance calculation improved with beam ion redistribution that was supported by recent fast ion diagno...

Collisionally excited fluorescence from a low‐energy (20–30 keV) neutral lithium beam can be used to determine edge electron densities in fusion devices. A lithium beam with an equivalent neutral particle current of 2 mA has been installed on TEXT. This system can be used to measure edge density profiles, and to measure edge density fluctuations with time resolution of ∼2 μs and spatial resolution ∼0.5 cm. The observed fluorescence is not directly proportional to the underlying electron density due to the effects of beam attenuation and the finite lifetime of the radiating state. An algorithm to unfold the electron density profile, including spatial fluctuations, from the observed fluorescence signal has been developed. Results from the initial operation of the lithium beam on TEXT will be presented, and compared with data from the TEXT HIBP and IR scattering diagnostics. This work supported by U.S. Department of Energy Contract DE‐AC03‐89ER53277.

Very narrow bandpass optical fibers have been used in Zeeman polarimetry of Li I 6708 A line emission from a monoenergetic lithium beam as a spectral source makes the measurement well localized. Initial experimental results for measurements of q0 will be presented.

Ionization of xenon atoms in single highly excited states ‖nf≳ (where 25⩽n⩽40) by collisions with CCl4, CCl3F, and SF6 has been investigated. Absolute rate constants for Xe+ production are reported together with the identities of the major negatively charged species produced in the collisions. Cross sections determined from these rate constants are also given. The data lend support to the theoretical model, which views such collisions as being dominated by the interaction between the target molecules and the excited electron, with the Xe+ ion core playing a minor role.

Spectroscopy of an injected Li beam has been used to determine both the plasma density profile and the poloidal field profile on the TEXT tokamak. The neutral Li beam is injected at energies up to 95 keV and both collisional and laser‐induced fluorescence are observed during a tokamak shot. Radial and temporal profiles are obtained during a complete shot. The applicability of this technique to larger tokamaks depends on several parameters including (but not limited to) beam penetration, reliability, spatial/temporal resolution, and signal‐to‐noise ratio. Because this basic technique obtains local measurements, it is also applicable to nonsymmetric devices. Such applications will be discussed.

Crossed beams studies of chemiionization in thermal energy collisions of helium, neon, argon, and krypton metastable atoms with ground state atoms and molecules (Ar, Kr, Xe, N2, H2, O2, NO, CO, CO2, and N2O) are described. Branching ratios are presented and in some cases absolute total ion production cross sections have been measured.

The extreme wing (600

A tunable CW laser has been used to selectively remove either of the two metastable species, 3P 0,2, which are initially present in a neon metastable beam. The method is applicable to other rare gases and provides the opportunity for separate investigation of effects due to atoms in either the 3P 0 or 3P 2 state.

Fluorescence excitation spectra of uranyl formate monohydrate UO/sub 2/ (HCOO)/sub 2/xH/sub 2/O at 4.2 K show the UO/sup +2//sub 2/ asymmetric mode to be active in the vibronic absorption. This assignment is based on the measure uranium isotope shift. It is also observed that the asymmetric mode occurs with a lower frequency than the symmetric in this compound, contrary to the order reported in other uranyl compounds.

The effects of an oxidant on the optical properties of particles formed in an inert gas containing Na vapor are reported. The oxidant used was NO. Light scattering measurements are reported. (AIP).

The Zeeman current‐density profile diagnostic system installed on TEXT has observed the polarization shift of the π‐line of the Zeeman split Li D lines due to the poloidal magnetic fields. The Li is injected into the plasma as a 95‐keV neutral beam, and a cw dye laser is used to measure polarization shifts. The laser is tuned into resonance with the π‐line and the polarization vector of the laser is rotated at 50‐kHz using an electro‐optic technique. The resulting 100‐kHz laser‐induced fluorescence signal is phase analyzed in order to observe the polarization shifts due to poloidal field. The Li beam intensity into the tokamak is approximately 1 mA and the dye laser intensity is 1 W at 3 GHz bandwidth. The diagnostic system and these early results will be discussed.