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  • 1
    Electronic Resource
    Electronic Resource
    Improved stop cylinder loading scheme for a centrifuge pellet accelerator (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3744-3746 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In order to perform plasma refueling experiments with cryogenic hydrogen pellets at the midsize tokamak ASDEX Upgrade, a centrifuge injector was developed based on the novel stop cylinder principle. Following the demonstration of excellent performance with this instrument, similar injectors were constructed for two of the world's largest tokamaks, JET and JT-60U. The extended fuel consumption in these tokamaks enforced the employment of continuous extruders instead of a storage cryostat, requiring an increase in pellet temperature from 8 to 14 K. Degradation of the injector performance was found at these higher pellet temperatures due to increased gas evaporation rates but could be eliminated by a revised acceleration scheme. Applying the adapted setup, reliable and stable operation has been realized with JET and JT-60U injectors. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1290502
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  • 2
    Electronic Resource
    Electronic Resource
    Impact strength of cryogenic deuterium pellets for injection into tokamak plasmas (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3736-3743 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The technical implementation of the potentially very efficient inboard pellet refueling scheme in tokamaks remains so far restricted to low velocities (v=200–300 m/s) due to the fragile nature of cryogenic D2. One specific problem is practically unavoidable pellet impacts in components of the pellet guiding system: first, in a funneling adaptor installed to cope with the angular scatter of pellets from acceleration devices such as centrifuges and, second, inside variably bent guiding tubes required to access the high field side of the torus. In order to inject pellets at speeds close to those available from the ASDEX Upgrade centrifuge (v≤1200 m/s), knowledge of critical guiding system parameters such as impact angle and speed is needed. In this study design requirements for an optimized guiding scheme are derived by examining grazing incidence pellet impacts on one single and two subsequent flat, rigid plates. The survival of the pellets was found to be determined by the normal impact velocity component. After undergoing two successive collisions under the same angle a critical impact speed of v⊥=40 m/s was detected, permitting incidence angles of up to 2° at v〉1000 m/s. Studying impacts under 1°–6° reflection angles from 0.1° to 0.8° were measured, suggesting a considerable ductility of the D2 ice. This was confirmed in measurements of the plane pellet compression where irreversible deformation was found to set in well below the critical impact speed. Therefore the optimized guiding track geometry is proposed on the basis of an elliptic loop to keep the pellets as close as possible to the track and to guide the pellets through a large number of elastic small angle collisions. This makes also use of the lubricating effect of the vapor film form upon collision between the sliding pellet and the chute. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1290497
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  • 3
    Electronic Resource
    Electronic Resource
    Generation of widely tunable intense far-infrared radiation pulses by stimulated Raman transitions in methylfluoride gas (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 2576-2578 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the generation of widely tunable intense far-infrared radiation pulses by stimulated Raman transitions in methylfluoride gas. Using a tunable high-pressure CO2 laser we achieved, by P-branch tuning of stimulated Raman transitions in 12CH3F and 13CH3F gases, tunable generation of radiation in a series of intervals in the spectral range from 37 to 72 cm−1 covering 20% of this range. Possibilities of further extension of the tuning regions are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101983
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  • 4
    Electronic Resource
    Electronic Resource
    Interpretation of new 13CD3F submillimeter-wave laser lines using high resolution infrared spectroscopy (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 877-890 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A high resolution infrared spectrum of 13CD3F has been recorded in the wave number region 820–1350 cm−1 which covers four fundamentals ν2(A1), ν3(A1), ν5(E), and ν6(E). All strong and medium strong vibration-rotation lines have been assigned in terms of a model which treats simultaneously these strongly Coriolis coupled four fundamentals. Fifty-nine upper state parameters have been determined with the least squares method including 4390 infrared transitions as data. The standard deviation of the fit obtained is 0.56×10−3 cm−1. Ground state rotational parameters have been determined using ground state combination differences. Due to strong vibration–rotation interactions a large number of normally forbidden transitions have been observed which have allowed an accurate determination of the ground state axial rotational constant A0 and the centrifugal distortion constant DK0. The results of the analyzed infrared spectrum have made it possible to interpret many new laser emission lines from 13CD3F gas optically pumped with a continuously tunable high pressure pulsed CO2 laser. Making use of the coincidence of the 10 μm P and R branches of CO2 with the ν2, ν3, ν5, and ν6 bands, altogether 151 laser lines of 13CD3F between 10 and 61 cm−1 have been observed. These emission lines have been assigned as rotational transitions within the excited vibrational states and the ground vibrational state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466570
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  • 5
    Electronic Resource
    Electronic Resource
    Picosecond YBa2Cu3O7−δ detector for far-infrared radiation (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 5496-5499 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on a picosecond YBa2Cu3O7−δ detector for far-infrared radiation. The detector, consisting of a current carrying structure cooled to liquid-nitrogen temperature, was studied by use of ultrashort laser pulses from an optically pumped far-infrared laser in the frequency range from 25 to 215 cm−1. We found that the sensitivity (1 mV/W) was almost constant in this frequency range. We estimated a noise equivalent power of less than 5×10−7 W Hz−1/2. Taking into account the results of a mixing experiment (in the frequency range from 4 to 30 cm−1) we suggest that the response time of the detector was few picoseconds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351944
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  • 6
    Electronic Resource
    Electronic Resource
    High density, high performance high-confinement-mode plasmas in the Joint European Torus (JET) : 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. 2103-2112 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent experiments at the Joint European Torus [Rebut et al., Fusion Eng. Des. 22, 7 (1993)] aim to improve confinement quality in high-confinement-mode (H-mode) plasmas at high densities. Energy confinement time as predicted by the International Thermonuclear Experimental Reactor ITER-H98(y,2) scaling at densities near or in excess of 85% of the Greenwald density limit scaling has been obtained by (i) strong plasma shaping (triangularity 0.35〈δ〈0.5), or (ii) impurity seeding, or (iii) high-field side pellet injection. Slow peaking of central density without confinement degradation is observed. Loss of sawteeth and core impurity accumulation is prevented by central ion cyclotron resonance heating. In high triangularity and impurity seeded plasmas, reduction of average power loss associated with type I edge localized modes (ELMs) is found which is attributed to the occurrence of additional losses in between ELMs. Broad band magnetic fluctuations are seen which are reminiscent of regimes with small ELMs in other tokamaks. Plasma configurations have been varied to find best combinations of edge pedestal parameters and small ELM losses. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1456067
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  • 7
    Electronic Resource
    Electronic Resource
    Improvement of q-profile measurement by fast observation of pellet ablation at ASDEX Upgrade (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 4051-4060 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The q-profile measurement presented in this article is based on the observation of pellets injected into the plasma and viewed with a fast-framing camera. The pellets sublimate in the plasma and the ablated material is ionized. The ions move along the magnetic field lines, while an ablation cloud is forming. This ablation cloud contains a small fraction of neutral particles which emit visible light after collisional excitation. It is therefore possible to visualize the magnetic field lines along which the pellet passes. The inclination angle of the magnetic field lines with respect to the torus midplane can be determined from this observation. The results are compared with the inclination angles delivered by an equilibrium code. Further analysis shows that it is not meaningful to determine the q-profile from the data of only the pellet ablation, in the case of an elongated plasma as in ASDEX Upgrade. However, the accuracy of the q-profile determined by an equilibrium code, especially in the plasma center, can be greatly improved by using the pellet measurements as additional input data. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148386
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  • 8
    Electronic Resource
    Electronic Resource
    A new centrifuge pellet injector for fusion experiments (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 983-989 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This paper reports on the new pellet injection system for refueling the ASDEX Upgrade tokamak with cubic H2 or D2 pellets having alternative side lengths of 1.5, 1.75, and 2.0 mm and optional Ne doping. The system delivers series of about 100 pellets at a maximum repetition rate of more than 40 Hz. The pellets are accelerated by means of a centrifuge with an optimized straight acceleration arm. This configuration minimizes the compulsive force acting on the pellet during the acceleration process. Since this also minimizes stresses inside the pellet, high velocities—a maximum of 1211 m/s being achieved—are possible without destroying the hydrogen cubes. A special pellet feed-in technique based on a static stop cylinder interrupting the acceleration path successfully reduced the horizontal scattering angle to values of less than ±4°; a high efficiency, with more than 90% of the pellets arriving within the acceptance angle, was thus achieved. The whole system was found to work very reliably and reproducibly during the whole test operation period, covering about 105 pellet shots, and is now being integrated into the ASDEX upgrade experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144101
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  • 9
    Electronic Resource
    Electronic Resource
    High repetition inboard launch of hydrogen pellets (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 2806-2807 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The centrifuge hydrogen pellet injection system at ASDEX Upgrade was extended for inboard launching. Successful and efficient inboard pellet refueling was realized up to pellet velocities of about 400 m/s. In order to achieve maximum available pellet particle rates of the system still at the low centrifuge revolution needed in this velocity range, the injector has been modified. Thus, operational conditions have been developed yielding the potential to inject pellets at rather low speed but high repetition rate. Since pellets injected from the inboard are obviously not hampered by the low velocity but show better performance than fast pellets injected from the outside, this scheme seems to allow for an efficient and flexible particle refueling of hot plasmas. The system is now capable of launching pellet series at rates up to 60 Hz at a speed of 240 m/s. With the biggest available pellet size, this enables a pellet particle flux of 2.6×1022/s. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148983
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  • 10
    Electronic Resource
    Electronic Resource
    Compact gas gun injection system for variable sized solid pellets (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 2316-2321 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The design, construction, and the testbed results for a novel compact gas gun injector for solid diagnostic pellets of different sizes and materials is reported here. The injector was optimized for the diagnostic requirements of the ASDEX Upgrade tokamak, yielding the possibility of a widely varying deposition profile of ablated material inside the plasma. This allows variation of the pellet velocity and the total number of injected atoms. The use of spherical carbon pellets and different propellant gases (He,N2,H2) results in an accessible velocity range from about 150 m/s to more than 600 m/s and pellet masses from 2×1018 to 1020 atoms. Both the scattering angle (∼1°) and the maximum propellant gas throughput to the tokamak (less than 1016 gas particles) were found to be sufficiently low. The injector provided both high efficiency (≥85%) and high reliability during the whole testbed operation period and also during the first injection experiments performed on ASDEX Upgrade. The pellet velocities achieved for different propellant gas pressures and pellet diameters were analyzed. It was discovered that, although the pellet diameters range from 0.45 to 0.85 times the barrel diameter, the pellet acceleration is mostly caused by gas drag. Pellet velocities in excess of those calculated on the basis of the gas drag model were observed. Additional acceleration that increases with the pellet diameter contrary to the gas drag model may be explained by the influence of the pellet on the gas dynamics in the barrel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144682
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