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  • 1
    Electronic Resource
    Electronic Resource
    Vibrational relaxation of ozone in O3–O2 and O3–N2 gas mixtures from infrared double-resonance measurements in the 200–300 K temperature range (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 5773-5780 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The relaxation of ozone laser excited to ν1 and ν3 vibrational states has been studied by means of a time-resolved infrared double-resonance technique using two CO2 lasers. Measurements have been performed in O3–M mixtures (M=O2 and N2) over the 200–300 K temperature range, as found in the upper atmosphere. Rate coefficients for the V–T,R deexcitation of the ν2 and (ν1,ν3) states and for the (ν1,ν3)→ν2 intermode transfer have been deduced from the measurements. They show a positive temperature dependence consistent with that predicted by the Landau–Teller law, which is based upon short-range repulsive interactions. These results should be useful to model more precisely the distribution of the population of ozone upon its various vibrational states in the upper atmosphere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462675
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  • 2
    Electronic Resource
    Electronic Resource
    Vibrational energy transfers in ozone from infrared double-resonance measurements (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 4212-4221 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrational energy transfer processes in pure ozone have been studied by means of a time-resolved infrared double-resonance technique using two CO2 lasers. The intermode transfer between the Coriolis-coupled ν1 and ν3 modes has been observed for the first time and its rate constant measured. The near-resonant vibrational energy transfer populating the ν2+ν3 state has been also directly observed, as well as the vibrational deexcitation of the ν1 and ν3 states including the transfer process to the ν2 mode and the direct V-T,R processes. From a kinetic analysis of the vibrational relaxation, a numerical model was formulated allowing by comparison to the experiments to determine the rate coefficients for the processes. A rate coefficient of 2.4×106 s−1 Torr−1 was obtained for the intermode transfer between the Coriolis coupled ν1 and ν3 modes. Also a rate coefficient of 7×105 s−1 Torr−1 was derived for the process populating the ν2+ν3 state. The rate coefficient corresponding to the intermode transfer from ν1 and ν3 to ν2 was found to be (2800±500) s−1 Torr−1, a value clearly smaller than that obtained in previous studies. Finally the direct deexcitation from the ν1 and ν3 states, not taken into account in previous works, was found to be rather efficient, its rate coefficient being not negligible (∼600 s−1 Torr−1) as compared to the deexcitation coefficient from the ν2 state which was found equal to (2250±300) s−1 Torr−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457779
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  • 3
    Electronic Resource
    Electronic Resource
    Vibrational relaxation of ozone in O3–O2 and O3–N2 gas mixtures from infrared double-resonance measurements (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 1875-1881 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibrational relaxation of ozone in O3–O2 and O3–N2 mixtures has been studied by means of a time-resolved infrared double resonance technique using two CO2 lasers. The collisional deexcitation of the first excited states of the stretching modes including the V–V transfer processes to the bending mode has been directly observed allowing the rate constants to be measured as a function of the O3 mole fraction in the mixtures. Finally, the rate coefficients for the intermode transfer (ν1, ν3)→ν2 and for the deexcitation from the ν2 state have been derived.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459961
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  • 4
    Electronic Resource
    Electronic Resource
    Study of the effect of compressional Alfvén modes on thermal transport in the National Spherical Torus Experiment : Review,Tutorial and Invited Papers from the 43rd Annual Meeting of the APS Division of Plasma Physics (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 2069-2076 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: With the first injection of neutral beams into the National Spherical Torus Experiment (NSTX) [Ono et al., Nucl. Fusion 40, 557 (2000)], a broad spectrum of fluctuations consisting of nearly equally spaced peaks in the frequency range from about 0.2 to 1.2 times the ion cyclotron frequency was observed. The frequencies scale with toroidal field and plasma density consistently with Alfvén waves. From these and other observations, the modes have been identified as compressional Alfvén eigenmodes (CAE). It has also recently been found that the ratio of the measured ion and electron temperatures in NSTX during neutral beam heating is anomalously high [Bell, Bull. Am. Phys. Soc. 46, 206 (2001)]. To explain the anomaly in the ratio of ion to electron temperature, it has been suggested that the CAE, driven by the beam ions, stochastically heat the thermal ions [Gates et al., Phys. Rev. Lett. 87, 205003 (2001)]. In this paper it is shown through studies of the power balance that stochastic heating of the thermal ions by the observed CAE alone is not solely responsible for the anomaly in the ion to electron temperature ratio. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1464542
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  • 5
    Electronic Resource
    Electronic Resource
    Beta-limiting instabilities and global mode stabilization in the National Spherical Torus Experiment : Review,Tutorial and Invited Papers from the 43rd Annual Meeting of the APS Division of Plasma Physics (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 2085-2092 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Research on the stability of spherical torus plasmas at and above the no-wall beta limit is being addressed on the National Spherical Torus Experiment [M. Ono et al., Nucl. Fusion 40, 557 (2000)], that has produced low aspect ratio plasmas, R/a∼1.27 at plasma current exceeding 1.4 MA with high energy confinement (TauE/TauE_ITER89P〉2). Toroidal and normalized beta have exceeded 25% and 4.3, respectively, in q∼7 plasmas. The beta limit is observed to increase and then saturate with increasing li. The stability factor βN/li has reached 6, limited by sudden beta collapses. Increased pressure peaking leads to a decrease in βN. Ideal stability analysis of equilibria reconstructed with EFIT [L. L. Lao et al., Nucl. Fusion 25, 1611 (1985)] shows that the plasmas are at the no-wall beta limit for the n=1 kink/ballooning mode. Low aspect ratio and high edge q theoretically alter the plasma stability and mode structure compared to standard tokamak configurations. Below the no-wall limit, stability calculations show the perturbed radial field is maximized near the center column and mode stability is not highly effected by a nearby conducting wall due to the short poloidal wavelength in this region. In contrast, as beta reaches and exceeds the no-wall limit, the mode becomes strongly ballooning with long poloidal wavelength at large major radius and is highly wall stabilized. In this way, wall stabilization is more effective at higher beta in low aspect ratio geometry. The resistive wall mode has been observed in plasmas exceeding the ideal no-wall beta limit and leads to rapid toroidal rotation damping across the plasma core. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1468230
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  • 6
    Electronic Resource
    Electronic Resource
    High-harmonic fast magnetosonic wave coupling, propagation, and heating in a spherical torus plasma : The 40th annual meeting of the division of plasma physics of the american physical society (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 2002-2008 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A novel rotatable two-strap antenna has been installed in the current drive experiment upgrade (CDX-U) [T. Jones, Ph.D. thesis, Princeton University (1995)] in order to investigate high-harmonic fast wave coupling, propagation, and electron heating as a function of strap angle and strap phasing in a spherical torus plasma. Radio-frequency-driven sheath effects are found to fit antenna loading trends at very low power and become negligible above a few kilowatts. At sufficiently high power, the measured coupling efficiency as a function of strap angle is found to agree favorably with cold plasma wave theory. Far-forward microwave scattering from wave-induced density fluctuations in the plasma core tracks the predicted fast wave loading as the antenna is rotated. Signs of electron heating during rf power injection have been observed in CDX-U with central Thomson scattering, impurity ion spectroscopy, and Langmuir probes. While these initial results appear promising, damping of the fast wave on thermal ions at high ion-cyclotron-harmonic number may compete with electron damping at sufficiently high ion β—possibly resulting in a significantly reduced current drive efficiency and production of a fast ion population. Preliminary results from ray-tracing calculations which include these ion damping effects are presented. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873483
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  • 7
    Electronic Resource
    Electronic Resource
    Microinstability properties of small-aspect-ratio tokamaks (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1667-1672 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Advanced tokamak configurations can have improved stability properties for high-n microinstabilities such as the toroidal drift mode (trapped-electron-ηi mode) and the kinetically-calculated magnetohydrodynamic (MHD) ballooning mode. A promising means to achieve this end involves employing tokamak configurations with very small aspect ratio, as in the proposed National Spherical Tokamak Experiment (NSTX) [M. Ono et al., Bull. Am. Phys. Soc. 40, 1655 (1995)] or the existing Small Tight Aspect Ratio Tokamak (START) experiment [R. J. Colchin et al., Phys. Fluids B 5, 2481 (1993)]. Kinetic instabilities are analyzed here using a comprehensive toroidal eigenvalue code with realistic equilibria for cases based on NSTX and START along with artificial cases to study parametric sensitivities. It is found that, as the aspect ratio decreases, the amount of "bad'' magnetic curvature decreases, causing stabilization of both electrostatic and electromagnetic high-n instabilities at sufficiently small aspect ratio. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871686
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  • 8
    Electronic Resource
    Electronic Resource
    Near-resonant vibrational energy transfer in ozone. Double-resonance measurements and calculations in the temperature range 200–300 K (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 5905-5909 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The near-resonant vibrational energy transfer mtlm;cO3(001)+O3(010)mtlm;c →mb;2qkmb;0 O3(011)+O3(000)+Δν=17 cm−1 has been investigated in the temperature range 200–300 K by means of a time-resolved double-resonance method using two CO2 lasers. The transfer rate coefficient k deduced from the measurements is compared to values calculated using a semiclassical model based on dipole (ν3)–dipole (ν3) interaction. The temperature dependences of the calculated and experimental values are in good agreement, the first ones being a little smaller than the second ones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465943
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  • 9
    Electronic Resource
    Electronic Resource
    Initial physics results from the National Spherical Torus Experiment : The 42nd annual meeting of the division of plasma physics of the American Physical Society and the 10th international congress on plasma physics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 1977-1987 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The mission of the National Spherical Torus Experiment (NSTX) is to extend the understanding of toroidal physics to low aspect ratio (R/a(similar, equals)1.25) in low collisionality regimes. NSTX is designed to operate with up to 6 MW of high harmonic fast wave (HHFW) heating and current drive, 5 MW of neutral beam injection (NBI) and co-axial helicity injection (CHI) for noninductive startup. Initial experiments focused on establishing conditions that will allow NSTX to achieve its aims of simultaneous high βt and high-bootstrap current fraction, and to develop methods for noninductive operation, which will be necessary for Spherical Torus power plants. Ohmic discharges with plasma currents up to 1 MA and with a range of shapes and configurations were produced. Density limits in deuterium and helium reached 80% and 120% of the Greenwald limit, respectively. Significant electron heating was observed with up to 2.3 MW of HHFW. Up to 270 kA of toroidal current for up to 200 ms was produced noninductively using CHI. Initial NBI experiments were carried out with up to two beam sources (3.2 MW). Plasmas with stored energies of up to 140 kJ and βt=21% were produced. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1343089
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  • 10
    Electronic Resource
    Electronic Resource
    Energetic particle orbits in the National Spherical Tokamak Experiment (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3667-3675 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The trajectories of neutral beam injected energetic ions in spherical tokamaks are examined. The large poloidal magnetic field in the outboard region of spherical tokamaks causes neutral beam injected ions to be born on trapped orbits even with cotangential injection. Numerical solutions to the equations for particle motion and for guiding center drifts are compared in several magnetic equilibria for a range of particle initial conditions. Even when rL/a∼1/4 the guiding center orbits closely resemble the path of the instantaneous center of gyration of the particle motion; exceptions occur primarily for orbits near the trapped/passing boundary. Finite Larmor radius effects are included in guiding center simulations of prompt orbit loss in the National Spherical Tokamak Experiment (NSTX) [J. Spitzer et al., Fusion Technol. 30, 1337 (1996)]. Orbit loss in the NSTX is caused primarily by collisions with the close fitting conducting shell, and severe losses would be expected with counter directed injection. While most orbits are similar to those found in conventional tokamaks, additional orbit types are possible in spherical tokamaks. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872263
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