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Degenerate four-wave mixing and phase conjugation in a collisional plasma

Description: Although degenerate four-wave mixing (DFWM) has many practical applications in the visible regime, no successful attempt has been made to study or demonstrate DFWM for wavelengths longer than 10..mu..m. Recently, Steel and Lam established plasma as a viable DFWM and phase conjugation (PC) medium for infrared, far-infrared, and microwaves. However, their analysis is incomplete since collisional effects were not included. Using a fluid description, our results demonstrate that when collisional absorption is small and the collisional mean-free path is shorter than the nonlinear density grating scale length, collisional heating generates a thermal force which substantially enhances the phase conjugate reflectivity. When the collisional attenuation length becomes comparable to the length of the plasma, the dominant effect is collisional absorption of the pump waves. Numerical estimates of the phase conjugate reflectivity indicate that for modest power levels, gains greater than or equal to1 are possible in the submillimeter to centimeter wavelength range. This suggests that a plasma is a viable PC medium at those long wavelengths. In addition, doubly DFWM is discussed.
Date: June 1, 1986
Creator: Federici, J.F. & Mansfield, D.K.
Partner: UNT Libraries Government Documents Department

Magneto-optically modulated CH/sub 3/OH laser for Faraday rotation measurements in tokamaks

Description: Distortion-free intracavity polarization modulation of an optically pumped CH/sub 3/OH laser is shown to be viable. The possible use of this modulation technique to make a multichannel Faraday rotation measurement on a Tokamak device is discussed. In addition, the CdTe Faraday modulator employed in this study is shown to have an anomalously large Verdet constant.
Date: July 1, 1981
Creator: Mansfield, D.K. & Johnson, L.C.
Partner: UNT Libraries Government Documents Department

Far-infrared laser scattering in the ACT-I toroidal device

Description: A far-infrared laser scattering diagnostic has been built for the ACT-I toroidal device. The optical system uses a passively stabilized 447-..mu..m CH/sub 3/I laser. A polyethylene etalon is the beam splitter. The vacuum windows are plastic (TPX), which we found has the vacuum property Q 6.5 x 10/sup -9/ torr-liter/sec/cm/sup 2/. Using paraboloidal and ellipsoidal mirrors for detection optics improves the signal strength and allows a better rf enclosure design for the detector. The diagnostic was tested by scattering from an ion Bernstein wave, a technique which can be used for ion temperature diagnostics.
Date: December 1, 1984
Creator: Goree, J.; Mansfield, D.K.; Ono, M. & Wong, K.L.
Partner: UNT Libraries Government Documents Department

Midplane Faraday Rotation: A densitometer for BPX

Description: The density in a high field, high density tokamak such as BPX can be determined by measuring the Faraday rotation of a 10.6 {mu}m laser directed tangent to the toroidal field. If there is a horizontal array of such beams, then n{sub e}(R) can be readily obtained with a simple Abel version about the center line of the tokamak. For BPX operated at full field and density, the rotation angle would be quite large -- about 75{degrees} per pass. A layout in which a single laser beam is fanned out in the horizontal midplane of the tokamak, with a set of retroreflectors on the far side of the vacuum vessel, would provide good spatial resolution, depending only upon the number of reflectors. With this proposed layout, only one window would be needed. Because the rotation angle is never more than 1 fringe,'' the data is always good, and it is also a continuous measurement in time. Faraday rotation is dependent only upon the plasma itself, and thus is not sensitive to vibration of the optical components. Simulations of the expected results show that BPX would be well served even at low densities by a Midplane Faraday Rotation densitometer of {approximately}64 channels. Both TFTR and PBX-M would be suitable test beds for the BPX system.
Date: February 1, 1992
Creator: Jobes, F.C. & Mansfield, D.K.
Partner: UNT Libraries Government Documents Department

High-energy D/sub 2/O submillimeter laser for plasma diagnostics

Description: A narrow line optically pumped D/sub 2/O laser operating at 385 ..mu..m has delivered more than 5 J in pulses longer than 3 ..mu..sec using a large aperture unstable resonator cavity design. Pulse levels which are > 1 J and 1 ..mu..sec are necessary for a single shot ion temperature measurement by Thomson scattering in large tokamaks. Experiments have, for the most part, been conducted at a 360 J, 5 ..mu..sec CO/sub 2/ laser pump level where high efficiency (approx. 2.5 J at 385 ..mu..m) has been obtained. These are the highest energies reported to date in the far infrared. In addition, the pulse length has been extended beyond the vibrational relaxation time.
Date: January 1, 1983
Creator: Semet, A.; Johnson, L.C. & Mansfield, D.K.
Partner: UNT Libraries Government Documents Department

Direct narrow line tuning of a high power CO/sub 2/ laser

Description: We report the operation of a high power, narrow linewidth CO/sub 2/ laser suitable for application as a pump for pulsed submillimeter lasers. Grating tuning and single mode cw injection have been employed in an unstable ring resonator which produces 100 nsec duration, 200 to 400 Joule pulses on the 9R(22) line with a bandwidth of less than 20 MHz.
Date: January 1, 1981
Creator: Johnson, L.C.; Mansfield, D.K. & Taylor, G.
Partner: UNT Libraries Government Documents Department

Midplane Faraday Rotation: A densitometer for BPX

Description: The density in a high field, high density tokamak such as BPX can be determined by measuring the Faraday rotation of a 10.6 {mu}m laser directed tangent to the toroidal field. If there is a horizontal array of such beams, then n{sub e}(R) can be readily obtained with a simple Abel version about the center line of the tokamak. For BPX operated at full field and density, the rotation angle would be quite large -- about 75{degrees} per pass. A layout in which a single laser beam is fanned out in the horizontal midplane of the tokamak, with a set of retroreflectors on the far side of the vacuum vessel, would provide good spatial resolution, depending only upon the number of reflectors. With this proposed layout, only one window would be needed. Because the rotation angle is never more than 1 ``fringe,`` the data is always good, and it is also a continuous measurement in time. Faraday rotation is dependent only upon the plasma itself, and thus is not sensitive to vibration of the optical components. Simulations of the expected results show that BPX would be well served even at low densities by a Midplane Faraday Rotation densitometer of {approximately}64 channels. Both TFTR and PBX-M would be suitable test beds for the BPX system.
Date: February 1, 1992
Creator: Jobes, F. C. & Mansfield, D. K.
Partner: UNT Libraries Government Documents Department

Measurements of confined alphas and tritons in the MHD quiescent core of TFTR plasmas using the pellet charge exchange diagnostic

Description: The energy distributions and radial density profiles of the fast confined trapped alpha particles in DT experiments on TFTR are being measured in the energy range 0.5--3.5 MeV using a Pellet Charge eXchange (PCX) diagnostic. A brief description of the measurement technique which involves active neutral particle analysis using the ablation cloud surrounding an injected impurity pellet as the neutralizer is presented. This paper focuses on alpha and triton measurements in the core of MHD quiescent TFTR discharges where the expected classical slowing down and pitch angle scattering effects are not complicated by stochastic ripple diffusion and sawtooth activity. In particular, the first measurement of the alpha slowing down distribution up to the birth energy, obtained using boron pellet injection, is presented. The measurements are compared with predictions using either the TRANSP Monte-Carlo code and/or a Fokker-Planck Post-TRANSP processor code, which assumes that the alphas and tritons are well confined and slow down classically. Both the shape of the measured alpha and triton energy distributions and their density ratios are in good agreement with the code calculations. The authors conclude that the PCX measurements are consistent with classical thermalization of the fusion-generated alphas and tritons.
Date: May 1, 1996
Creator: Medley, S.S.; Budny, R.V. & Mansfield, D.K.
Partner: UNT Libraries Government Documents Department

Wall conditioning experiments on TFTR using impurity pellet injection

Description: This work describes experiments intended to optimize the limiter conditioning for TFTR supershots. It is shown that deposition of thin layers of lithium on the limiters by impurity pellet injection changes the plasma-wall interaction and improves supershot performance. Series of up to ten Ohmic plasmas each with two lithium pellets were useful in preconditioning the limiter. Generally, plasma performance increased with the amount of lithium deposited up to the maximal amount which could be deposited. Experiments were performed with different materials being deposited (carbon, boron and lithium) and with different methods of deposition.
Date: November 1, 1993
Creator: Strachan, J. D.; Mansfield, D. K. & Bell, M. G.
Partner: UNT Libraries Government Documents Department

Techniques For Injection Of Pre-Charaterized Dust Into The Scrape Off Layer Of Fusion Plasma

Description: Introduction of micron-sized dust into the scrape-off layer (SOL) of a plasma has recently found many applications aimed primarily at determining dust behavior in future fusion reactors. The dust particles are typically composed of materials intrinsic to a fusion reactor. On DIII-D and TEXTOR carbon dust has been introduced into the SOL using a probe inserted from below into the divertor region. On NSTX, both Li and tungsten dust have been dropped from the top of the machine into the SOL throughout the duration of a discharge, by utilizing a vibrating piezoelectric based particle dropper. The original particle dropper was developed to inject passivated Li powder {approx} 40 {mu}m in diameter into the SOL to enhance plasma performance. A simplified version of the dropper was developed to introduce trace amounts of tungsten powder for only a few discharges, thus not requiring a large powder reservoir. The particles emit visible light from plasma interactions and can be tracked by either spectroscopic means or by fast frame rate visible cameras. This data can then be compared with dust transport codes such as DUSTT to make predictions of dust behavior in next-step devices such as ITER. For complete modeling results, it is desired to be able to inject pre-characterized dust particles in the SOL at various known poloidal locations, including near the vessel midplane. Purely mechanical methods of injecting particles are presently being studied using a modified piezoelectric-based powder dropper as a particle source and one of several piezo-based transducers to deflect the particles into the SOL. Vibrating piezo fans operating at 60 Hz with a deflection of {+-}2.5 cm can impart a significant horizontal boost in velocity. The highest injection velocities are expected from rotating paddle wheels capable of injecting particles at 10's of meters per second depending primarily on the rotation ...
Date: July 21, 2011
Creator: Roquemore, A. L.; John, B.; Friesen, F.; Hartzfeld, K. & Mansfield, D. K.
Partner: UNT Libraries Government Documents Department

Measurements of Faraday rotation in TFTR plasmas

Description: Recent results of simultaneous measurements of line electron density and poloidal field-induced Faraday rotation on the multichannel FIR interferometer/polarimeter on TFTR are presented. The procedures and results of the calibration are described in detail. The effects of various errors in the measurement, as well as the problem of cross-coupling laser beams, are studied.
Date: January 1, 1986
Creator: Ma, C.H.; Hutchinson, D.P.; Vander Sluis, K.L.; Mansfield, D.K.; Park, H. & Johnson, L.C.
Partner: UNT Libraries Government Documents Department

Calibration of the FIR polarimeter on TFTR tokamak

Description: The results of the first Faraday rotation measurement on the TFTR tokamak are presented. Data are reported on ohmic- as well as neutral-beam-heated plasmas including solid pellet injections. The procedure and the results of the calibration are described. The effects of various errors in the measurements as well as the problem of cross coupling laser beams are studied.
Date: January 1, 1985
Creator: Ma, C.H.; Hutchinson, D.P.; Vander Sluis, K.L.; Mansfield, D.K.; Park, H. & Johnson, L.C.
Partner: UNT Libraries Government Documents Department

Survey of features in radiative power loss profiles in TFTR

Description: Although the total radiated power in TFTR is often as high as 70% of the heating power, most of the radiation is concentrated near the surface of the plasma, and the interior loss is almost negligible. Fractional radiation loss declines during neutral beam heating. As the high-density limit is approached, under practically any conditions, a bright band of radiation (''marfe'') appears on the inner side of the plasma column. Marfe evolution has been tracked for various conditions of heating, magnetic field direction, and fueling. In enhanced-confinement discharges a peculiar bright band, distinct from a marfe, appears in the lower, outside part of the vacuum vessel, outside of the limiter radius. With pellet fueling, marfe evolution occurs at a higher average density, and an intense peak often appears in the plasma center, consisting of impurity radiation plus working-gas bremsstrahlung. In high density ohmically heated cases with pellet fueling radiative power loss exceeds heating power in the center. 34 refs., 19 figs.
Date: June 1, 1988
Creator: Schivell, J.; Bush, C.E.; Mansfield, D.K.; Medley, S.S.; Park, H.K. & Stauffer, F.J.
Partner: UNT Libraries Government Documents Department

A Stark-tuned, far-infrared laser for high frequency plasma diagnostics

Description: A Stark-tuned optically pumped far-infrared methanol laser operating at 119 micrometers has been built. The laser is designed to operate at high power while exhibiting a well-separated Stark doublet. At a pump power of 65 Watts and electric field of 1 kV/cm the laser has delivered over 100 mW c.w. while exhibiting a frequency splitting of 34 MHz. These parameters indicate that this laser would be suitable for use in the present generation of modulated interferometers on large thermonuclear plasma devices. The achieved modulation frequency is more than an order of magnitude higher than could be achieved using standard techniques.
Date: March 1, 1992
Creator: Mansfield, D. K.; Vocaturo, M.; Guttadora, L.; Rockmore, M.; Micai, K. & Krug, P. A.
Partner: UNT Libraries Government Documents Department

Production of high density plasma by pellet injection in TFTR

Description: High plasma densities have been produced in ohmic and neutral beam heated discharges on TFTR using a repeating pneumatic pellet injector developed at Oak Ridge National Laboratory (ORNL). Line average plasma densities as high as 1 x 10/sup 14/ cm/sup -3/ have been attained by injection of five 2.7 mm deuterium pellets ..delta..n/sub e/ = 2 x 10/sup 14/ cm/sup -3/ over a one-second interval into a stetched neutral beam pulse. Injection of a single large (4 mm) pellet in ohmic discharge has produced highly peaked profiles with nec(o) = 1.8 x 10/sup 14/ cm/sup -3/, n/sub e/(0) tau/sub E/(a) = 6.7 x 10/sup 13/ cm/sup -3/ and n/sub D/(0)Ti(0)tau/sub E/(a) = 8.8 x 10/sup 13/ cm/sup -3/ sKeV. Global confinement in these discharges approaches 0.45 seconds with a central density decay time of 2 seconds. Based on a neoclassical resistivity model and x-ray pulse-height analysis, zeff is <2 in both ohmic and beam-heated plasmas. The energy confinement properties of intermediate density (n/sub e/ (0) = 1 x 10/sup 14/ cm/sup -3/) full beam power (5.7 MW, 80 KVD/sup 0/) discharge have been studied in detail using the TRANSP code. Although the global energy confinement (approx. =2 oums at IP = 2.2 MA) is comparable to gas-fueled discharges, the confinement in the central core is considerably longer and electron heat conduction losses are smaller.
Date: January 1, 1985
Creator: Milora, S.L.; Schmidt, G.L.; Combs, S.K.; Bush, C.E.; Goldston, R.J.; Grek, B. et al.
Partner: UNT Libraries Government Documents Department

Development of lithium deposition techniques for TFTR

Description: The ability to increase the quantity of lithium deposition into TFTR beyond that of the Pellet Injector while minimizing perturbations to the plasma provides interesting experimental and operational options. Two additional lithium deposition tools were developed for possible application during the 1996 Experimental Schedule: a solid lithium target probe for real-time deposition, and a lithium effusion oven for deposition between discharges. The lithium effusion oven was operated in TFTR to deposit lithium on the Inner Limiter in the absence of plasma. This resulted in the third highest power TFTR discharge.
Date: October 1, 1997
Creator: Kugel, H.W.; Gorman, J.; Johnson, D.; Labik, G.; Lemunyan, G.; Mansfield, D. et al.
Partner: UNT Libraries Government Documents Department

Broadening and shifting of the methanol 119 {mu}m gain line of linear and circular polarization by collision with chiral molecules

Description: Evidence of circular dichroism has been observed in the spectral properties of a gas of left-right symmetric molecules. This dichroism comes about as the result of collisions of the symmetric molecules with left-right asymmetric molecules introduced as a buffer gas. In this sense, the dichroism can be said to have been transferred from the chiral buffer molecules to the symmetric, non-chiral molecules of the background vapor. This transferred dichroism appears as broadening in the gain line of the symmetric molecule which is asymmetric with respect to the right or left handedness of a circularly polarized probe. The broadening of the 119 {mu}m line of the methanol molecule was observed using infrared-far infrared double resonance spectroscopy.
Date: June 21, 2000
Creator: Bakos, J.S.; Djotyan, G.; Soerlei, Zsuzsa; Szigeti, J.; Mansfield, D. K. & Sarkozi, J.
Partner: UNT Libraries Government Documents Department

Observations Concerning the Injection of a Lithium Aerosol into the Edge of TFTR Discharges

Description: A new method of actively modifying the plasma-wall interaction was tested on the Tokamak Fusion Test Reactor. A laser was used to introduce a directed lithium aerosol into the discharge scrape-off layer. The lithium introduced in this fashion ablated and migrated preferentially to the limiter contact points. This allowed the plasma-wall interaction to be influenced in situ and in real time by external means. Significant improvement in energy confinement and fusion neutron production rate as well as a reduction in the plasma Zeff have been documented in a neutral-beam-heated plasma. The introduction of a metallic aerosol into the plasma edge increased the internal inductance of the plasma column and also resulted in prompt heating of core electrons in Ohmic plasmas. Preliminary evidence also suggests that the introduction of an aerosol leads to both edge poloidal velocity shear and edge electric field shear.
Date: December 13, 2000
Creator: Mansfield, D.K.; Johnson, D.W.; Grek, B.; Kugel, H.; Bell, M.G. & al, et
Partner: UNT Libraries Government Documents Department

MIRI: A multichannel far-infrared laser interferometer for electron density measurements on TFTR (Tokamak Fusion Test Reactor)

Description: A ten-channel far-infrared laser interferometer which is routinely used to measure the spatial and temporal behavior of the electron density profile on the TFTR tokamak is described and representative results are presented. This system has been designed for remote operation in the very hostile environment of a fusion reactor. The possible expansion of the system to include polarimetric measurements is briefly outlined. 13 refs., 8 figs.
Date: July 1, 1987
Creator: Mansfield, D.K.; Park, H.K.; Johnson, L.C.; Anderson, H.M.; Chouinard, R.; Foote, V.S. et al.
Partner: UNT Libraries Government Documents Department

Neutral beam heating of detached plasmas in TFTR

Description: Detached plasmas on TFTR have been heated with neutral beam auxiliary power for the first time. At beam powers above 2 MW the detached plasmas in TFTR expand and reattach to the limiters. Deuterium and/or impurity gas puffing can be used to maintain plasmas in the detached state at powers of over 5 MW. Transient events were observed in a number of these plasmas, including a confinement-related delay in evolution of the edge emissivity and some phenomena which appear similar to those seen in the H-mode. 16 refs., 5 figs.
Date: May 1, 1989
Creator: Bush, C.E.; Strachan, J.D.; Schivell, J.; Mansfield, D.K.; Taylor, G.; Grek, B. et al.
Partner: UNT Libraries Government Documents Department

The local density increment from an ablated deuterium pellet in the TFTR tokamak

Description: Details of the process by which ionized pellet ablatant increases the density in a tokamak have been observed for the first time. For mild ablation rates, this process is not simply diffusive. Instead, the ionized ablatant takes the form of a temporally symmetric pulse which propagates over large distances along magnetic field lines. This pulse has been observed both interferometrically and with an x-ray camera. These observations are not in qualitative agreement with models which predict a step-like densification of the plasma by the pellet. 11 refs., 4 figs.
Date: May 1, 1991
Creator: Mansfield, D.K.; Janos, A.; Owens, D.K.; Schmidt, G.L.; Bell, M.G.; Cavallo, A. et al.
Partner: UNT Libraries Government Documents Department

Submillimeter wave propagation in tokamak plasmas

Description: The propagation of submillimeter-waves (smm) in tokamak plasmas has been investigated both theoretically and experimentally to ensure successful measurements of electron density and plasma current distributions in tokamak devices. Theoretical analyses have been carried out to study the polarization of the smm waves in TFTR and ISX-B tokamaks. A multichord smm wave interferometer/polarimeter system has been employed to simultaneously measure the line electron density and poloidal field-induced Faraday rotation in the ISX-B tokamak. The experimental study on TFTR is under way. Computer codes have been developed and have been used to study the wave propagation and to reconstruct the distributions of plasma current and density from the measured data. The results are compared with other measurements.
Date: January 1, 1985
Creator: Ma, C.H.; Hutchinson, D.P.; Staats, P.A.; Vander Sluis, K.L.; Mansfield, D.K.; Park, H. et al.
Partner: UNT Libraries Government Documents Department