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  • 1
    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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  • 2
    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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  • 3
    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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  • 4
    Electronic Resource
    Electronic Resource
    80 Hz repetitive centrifuge injector for hydrogen pellets (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 619-620 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The repeating centrifuge pellet injector developed for plasma fuelling experiments at ASDEX Upgrade was improved to give higher repetition rates. The system is now capable of launching pellet series at rates of up to 80 Hz and speeds of up to 1.2 km/s. Differently sized (nominal pellet masses 1.7–4.3×1020 atoms) deuterium pellets have been injected into ASDEX Upgrade. The only limitations at present derive from the pellet feed-in by a single storage cryostat. These might be overcome by using several feed-in sources © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146620
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  • 5
    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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  • 6
    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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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    Multichord calibrated bolometer array for the RFX experiment : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 665-667 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new multichord bolometer array has been installed for the first time in the RFX experiment, a large machine designed to study plasma confinement at high current in the reversed field pinch configuration. The main purpose of the diagnostic is to provide emissivity spatial profiles with good time resolution for the measurement of the total radiated power. The detectors used are miniaturized metal foil bolometers which are mounted in a water cooled pinhole camera covered by a graphite shield. The bolometers can be absolutely calibrated in situ according to a technique originally developed for the Asdex tokamak. In order to prove the electrical calibration technique a blackened bolometer was optically irradiated with a monochromatic light over a wide spectral range with wave numbers from 2.7 up to 47 000 cm−1. In the visible and UV spectral range an absorptivity of 80% was measured while in the IR and far-infrared regions only 7% of the incoming light was absorbed by the bolometer foil. In the mm wavelength range less than 1% of the radiation was absorbed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146254
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  • 9
    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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  • 10
    Electronic Resource
    Electronic Resource
    Use of high-temperature superconductors for resonators of far-infrared p-germanium lasers (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 2030-2032 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report for the first time on the use of high-temperature superconductor material for fabricating a resonator of a far-infrared solid-state laser. In our experiment the active medium consisted of a p-germanium crystal at 4.2 K in crossed electric and magnetic fields. We used a SrTiO3 plate as highly reflecting mirror and a YBa2Cu3O7−δ thin films on an MgO plate as output coupling mirror. We demonstrate highly reproducible operation of the laser.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105003
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