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  • 1
    Electronic Resource
    Electronic Resource
    Speed limit of frozen pellets (H2, D2, and Ne) through single-loop and multiloop tubes and implications for fusion plasma research (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 273-274 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Frozen pellets (H2, D2, and Ne at 8 K) of nominal 2.7 mm diam were shot through a coiled tube (single loop of (approximate)0.6 m diam and 8.5 mm bore), and the speed limit for survival was recorded for each pellet type. Intact H2 pellets were observed at speeds approaching 500 m/s; but neon pellets could not survive much more than 100 m/s. The speed limit for D2 pellets fell in the middle at (approximate)300 m/s. Some D2 pellets were also shot through a 30 m coiled tube consisting of 11 loops (average loop diameter of (approximate)0.8 m), and a speed limit of (approximate)100 m/s was observed. Injection of frozen H2 or D2 pellets is commonly used for core fueling of magnetically confined plasmas, and frozen neon pellets are sometimes used for impurity transport studies in similar experiments. The results from these tests add to a pellet database for injection lines with single- and complex multiple-curved guide tubes. All of the information to date suggests that frozen pellets can be delivered reliably from a pellet source to any accessible plasma location on a fusion device via "roller-coaster" tubes as long as the pellet speed is maintained below a threshold limit. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1331322
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  • 2
    Electronic Resource
    Electronic Resource
    Extruder system for high-throughput/steady-state hydrogen ice supply and application for pellet fueling of reactor-scale fusion experiments (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 4012-4013 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Pellet injection systems for the next-generation fusion devices, such as the proposed International Thermonuclear Experimental Reactor (ITER), will require feed systems capable of providing a continuous supply of hydrogen ice at high throughputs. A straightforward concept in which multiple extruder units operate in tandem has been under development at the Oak Ridge National Laboratory. A prototype with three large-volume extruder units has been fabricated and tested in the laboratory. In experiments, it was found that each extruder could provide volumetric ice flow rates of up to ∼1.3 cm3/s (for ∼10 s), which is sufficient for fueling fusion reactors at the gigawatt power level. With the three extruders of the prototype operating in sequence, a steady rate of ∼0.33 cm3/s was maintained for a duration of 1 h. Even steady-state rates approaching the full ITER design value (∼1 cm3/s) may be feasible with the prototype. However, additional extruder units (1–3) would facilitate operations at the higher throughputs and reduce the duty cycle of each unit. The prototype can easily accommodate steady-state pellet fueling of present large tokamaks or other near-term plasma experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149216
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  • 3
    Electronic Resource
    Electronic Resource
    Acceleration of neon pellets to high speeds for fusion applications (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 837-839 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The injection of impurity pellets into the plasmas of tokamak fusion reactors has been proposed as a technique to lessen the deleterious effects of plasma disruptions. Equipment and techniques that were previously developed for pneumatic hydrogen pellet injection systems and used for plasma fueling applications were employed for a limited experimental study with neon pellets. Isotopic hydrogen pellets doped with neon have previously been used for injection into fusion plasmas to study impurity particle transport, and pure neon pellets are applicable for disruption studies. Using a repeating pneumatic injector in the laboratory, it was found that the formation and acceleration of 2.7-mm-diam neon pellets were relatively straightforward; reliable operation was demonstrated with both a single- and a two-stage light gas gun, including velocities of ∼700 m/s with a single-stage injector and up to 1740 m/s with a two-stage injector. Based on the operating sequences and successful tests demonstrated in the laboratory experiments, a three-barrel repeating pneumatic injector installed on the DIII-D tokamak was equipped with the necessary components for neon operation and has been used in initial disruption experiments with 1.8-mm-diam neon pellets. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146819
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  • 4
    Electronic Resource
    Electronic Resource
    Pellet injection technology (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 1679-1698 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: During the last 10 to 15 years, significant progress has been made worldwide in the area of pellet injection technology. This specialized field of research originated as a possible solution to the problem of depositing atoms of fuel deep within magnetically confined, hot plasmas for refueling of fusion power reactors. Using pellet injection systems, frozen macroscopic (millimeter-size) pellets composed of the isotopes of hydrogen are formed, accelerated, and transported to the plasma for fueling. The process and benefits of plasma fueling by this approach have been demonstrated conclusively on a number of toroidal magnetic confinement configurations; consequently, pellet injection is the leading technology for deep fueling of magnetically confined plasmas for controlled thermonuclear fusion research. Hydrogen pellet injection devices operate at very low temperatures ((approximately-equal-to)10 K) at which solid hydrogen ice can be formed and sustained. Most injectors use conventional pneumatic (light gas gun) or centrifuge (mechanical) acceleration concepts to inject hydrogen or deuterium pellets at speeds of (approximately-equal-to)1–2 km/s. Pellet injectors that can operate at quasi-steady state (pellet delivery rates of 1–40 Hz) have been developed for long-pulse fueling. The design and operation of injectors with the heaviest hydrogen isotope, tritium, offer some special problems because of tritium's radioactivity. To address these problems, a proof-of-principle experiment was carried out in which tritium pellets were formed and accelerated to speeds of 1.4 km/s. Tritium pellet injection is scheduled on major fusion research devices within the next few years. Several advanced accelerator concepts are under development to increase the pellet velocity. One of these is the two-stage light gas gun, for which speeds of slightly over 4 km/s have already been reported in laboratory experiments with deuterium ice. A few two-stage pneumatic systems (single-shot) have recently been installed on tokamak experiments. This article reviews the equipment and instruments that have been developed for pellet injection with emphasis on recent advances. Prospects for future development are addressed, as are possible applications of this technology to other areas of research.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143995
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  • 5
    Electronic Resource
    Electronic Resource
    Small-bore (1.8-mm), high-firing-rate (10-Hz) version of a repeating pneumatic hydrogen pellet injector (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 2736-2737 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Repeating pneumatic pellet injectors developed at the Oak Ridge National Laboratory (ORNL) were used for plasma fueling experiments on the Tokamak Fusion Test Reactor (TFTR) and the Joint European Torus (JET). For plasma fueling on the DIII–D tokamak, a small-bore (1.8-mm) injector has been developed and tested in the laboratory at pellet rates of up to 10 Hz and speeds of ≤1 km/s (for pulse lengths of up to 15 s). This performance represents the smallest pellet size and highest repetition rate demonstrated with an ORNL repeating pneumatic pellet injector. The design has been incorporated in the three-barrel injector that was previously used on JET; the injection system, equipped with nominal pellet sizes of 1.8-, 2.7-, and 4.0-mm diameter, has been installed on DIII–D and will be used in future plasma fueling experiments. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145620
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  • 6
    Electronic Resource
    Electronic Resource
    New extruder-based deuterium feed system for centrifuge pellet injection (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 4448-4457 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The pellet injection systems for the next-generation fusion devices (such as the International Thermonuclear Experimental Reactor) and future fusion reactors will have to provide deuterium-tritium fueling for much longer pulse lengths (up to (approximate)1000 s) than present applications (typically limited to less than several seconds). Thus, a prototype pellet feed system for centrifuge pellet injection has been developed and used in long-pulse (〉100 s) tests at the Oak Ridge National Laboratory (ORNL). The new apparatus has two key components: (1) a cryogenic deuterium extruder and (2) an electromagnetic pellet punch mechanism. For maximum testing flexibility, the prototype is equipped with several other active components that allow remote adjustments, including precise positioning of the punch and the capability to index through eight different pellet lengths. The new feed system was designed to mate with an existing centrifuge accelerator facility at ORNL, and experiments in the facility were carried out to document the performance and reliability of the new feed system. With 2.3-mm-diam deuterium pellets and a catenary-shaped accelerator ((approximate)1.2 m diam), the prototype feed system was found to be capable of placing up to (approximate)90% of the punched pellets in the proper time/space window for pickup and acceleration by the high-speed rotating ((approximate)50 Hz) arbor. For these operating parameters, the pellet nominal speed was (approximate)430 m/s, and maximum pellet feed rates of 10 pellets/s and greater were tested. In this article the equipment is briefly described, and the experimental test results are summarized. Also, issues affecting overall pellet delivery efficiency are discussed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148412
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  • 7
    Electronic Resource
    Electronic Resource
    High-speed repeating hydrogen pellet injector for long-pulse magnetic confinement fusion experiments (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 1834-1841 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The projected fueling requirements of future magnetic confinement fusion devices [e.g., the International Thermonuclear Experimental Reactor (ITER)] indicate the need for a flexible plasma fueling capability, including both gas puffing and low- and high-speed pellet injection. Conventional injectors, based on single-stage pneumatic guns or centrifuges, can reliably provide frozen pellets (1- to 6-mm-diam sizes) at speeds up to 1.3 km/s and at suitable repetition rates (1 to 10 Hz or greater). Injectors based on two-stage pneumatic guns and "in situ'' condensation of hydrogen pellets can reliably achieve velocities over 3 km/s; however, they are not suitable for long-pulse repetitive operations. An experiment in collaboration between Oak Ridge National Laboratory (ORNL) and ENEA Frascati is under way to demonstrate the feasibility of a high-speed ((approximately-greater-than)2 km/s) repeating (∼1 Hz) pneumatic pellet injector for long-pulse operation. A test facility has been assembled at ORNL, combining a Frascati repeating two-stage light-gas gun and an ORNL deuterium extruder, equipped with a pellet chambering mechanism/gun barrel assembly. The main issues to be investigated were the strength of extruded deuterium ice as opposed to that produced by in situ condensation in pipe guns (hence the highest acceleration which can be given to the pellet without fracturing it), and the maximum repetition rate at which the system can operate without degradation in performance. Pellet velocities of up to 2.55 km/s have been achieved in joint experiments at ORNL. A new pressure tailoring valve was developed by the Frascati group for this application and proved to be a crucial component for good performance. Tests carried out in repeating mode, at frequencies of 0.2–0.5 Hz and speeds up to 2.2 km/s, indicate no significant degradation in performance with increasing repetition rate. Some preliminary tests using 3.7 mm pellets gave very encouraging results. The equipment and the experimental results are described in this article. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146988
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  • 8
    Electronic Resource
    Electronic Resource
    Improved core fueling with high field side pellet injection in the DIII-D tokamak : The 41st annual meeting of the division of plasma physics of the american physical society (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 1878-1885 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The capability to inject deuterium pellets from the magnetic high field side (HFS) has been added to the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)]. It is observed that pellets injected from the HFS lead to deeper mass deposition than identical pellets injected from the outside midplane, in spite of a factor of 4 lower pellet speed. HFS injected pellets have been used to generate peaked density profile plasmas [peaking factor (ne(0)/〈ne〉) in excess of 3] that develop internal transport barriers when centrally heated with neutral beam injection. The transport barriers are formed in conditions where Te∼Ti and q(0) is above unity. The peaked density profiles, characteristic of the internal transport barrier, persist for several energy confinement times. The pellets are also used to investigate transport barrier physics and modify plasma edge conditions. Transitions from L- to H-mode have been triggered by pellets, effectively lowering the H-mode threshold power by 2.4 MW. Pellets injected into H-mode plasmas are found to trigger edge localized modes (ELMs). ELMs triggered from the low field side (LFS) outside midplane injected pellets are of significantly longer duration than from HFS injected pellets. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874011
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  • 9
    Electronic Resource
    Electronic Resource
    Design considerations for single-stage and two-stage pneumatic pellet injectors (1989)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 570-575 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Performance of single-stage pneumatic pellet injectors is compared with several models for one-dimensional, compressible fluid flow. Agreement is quite good for models that reflect actual breech chamber geometry and incorporate nonideal effects such as gas friction. Several methods of improving the performance of single-stage pneumatic pellet injectors to muzzle velocities ranging from 2 to 2.25 km/s in the near term are outlined. Two-stage pneumatic injectors have the potential for much higher muzzle velocities (4–6 km/s) because of the higher gas pressures and temperatures achievable with the second-stage compression. The design and performance of two-stage pneumatic pellet injectors are discussed, and initial data from the two-stage pneumatic pellet injector test facility at Oak Ridge National Laboratory are presented. Finally, a concept for a repeating two-stage pneumatic pellet injector is described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140365
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  • 10
    Electronic Resource
    Electronic Resource
    Eight-shot pneumatic pellet injection system for the tokamak fusion test reactor (1987)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 58 (1987), S. 1195-1203 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An eight-shot pneumatic pellet injection system has been developed for plasma fueling of the tokamak fusion test reactor (TFTR). The active cryogenic mechanisms consist of a solid hydrogen extruder and a rotating pellet wheel that are cooled by flowing liquid-helium refrigerant. The extruder provides solid hydrogen for stepwise loading of eight holes located circumferentially around the pellet wheel. This design allows for three different pellet diameters: 3.0 mm (three pellets), 3.5 mm (three pellets), and 4.0 mm (two pellets) in the present configuration. Each of the eight pellets can be shot independently. Deuterium pellets are accelerated in 1.0-m-long gun barrels with compressed hydrogen gas (at pressures from 70 to 105 bar) to velocities in the range 1.0–1.5 km/s. The pellets are transported to the plasma in an injection line that incorporates two stages of guide tubes with intermediate vacuum pumping stations. A remote, stand-alone control and data-acquisition system is used for injector and vacuum system operation. The eight-shot injection system has been installed and operated on TFTR. The design features, operation, and performance characteristics of the system are described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139439
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