A tritium pellet injector (TPI) system has beea designed for the Tokamak Fusion Teat Reactor (TFTR) Q ~ 1 phase of operation. The injector gua utilizes a radial design with eight Independent barrels and a common extruder to minimize tritium inventory. The injection line contains guide tubes with Intermediate vacuum pumping stations aad fast valves to minimize propellant leakage to the torus. The vacuum system is designed for tritium compatibility. The entire injector system Is contained in a glove box for secondary containment protection against tritium release. Failure modes and effects have been analyzed, aad structural analysis has beea performed for most Intense predicted earthquake conditions. Details of the design and operation of this system are presented in this paper.

The Princeton Beta Experiment-Modified (PBX-M) Pellet Injector Project, which provides for the fabrication, installation, and operation of a pellet-injector fueling system on the PBX-M tokamak experiment, is described and its operation is discussed. The system consists of an eight-barrel pellet gun, a pellet transport facility, and a control system. The gun is an eight-shot pneumatic assembly designed and fabricated at the Oak Ridge National Laboratory (ORNL). The pellet transport and control facilities were designed, fabricated, and installed by the Princeton Plasma Physics Laboratory (PPPL). The integrated pellet-injector system has been installed on PBX-M and is operational for use in plasma experiments. Initial tokamak operation utilizing a single gun provided a high rate of successful pellet formation.<>

An eight-shot pneumatic pellet injector has been developed for routine plasma fueling and optimization studies on short-pulse fusion experiments. Such experiments will require injection sequences of several pellets of various size over the discharge period. Two eight-shot injectors that are capable of producing and firing hydrogen and deuterium pellets have been built. The injectors are based on the pipe-gun concept, which generates deuterium and hydrogen pellets by direct condensation in the barrel. One injector is in operation on the Princeton Beta Experiment, and the other is operational on the Advanced Toroidal Facility (ATF). A general overview of the gun, the ATF injection line, and the ATF diagnostic systems is given

Injection of solid tritium pellets is considered to be the most promising way of fueling fusion reactors. The Tritium Proof-of-Principle experiment has demonstrated the feasibility of forming and accelerating tritium pellets. This injector is based on the pneumatic pipe-gun concept, in which pellets are formed in situ in the barrel and accelerated with high-pressure gas. This injector is ideal for tritium service because there are no moving parts inside the gun and because no excess tritium is required in the pellet production process. Removal of 3He from tritium to prevent blocking of the cryopumping action by the noncondensible gas has been demonstrated with a cryogenic separator. Pellet velocities of 1280 m/s have been achieved for 4-mm-diam × 4-mm-long cylindrical tritium pellets with hydrogen propellant at 6.96 MPa (1000 psi).

Plasma fueling via injection of solid hydrogenic pellets has expanded the operating range for tokamaks and stellarators to higher densities than attainable with gas puffing. Pellet injection has also resulted in improved plasma energy confinement in tokamak discharges for which the pellet or pellets penetrate deep into the plasma core. The eight-shot pneumatic pellet injector described herein has been developed for use on the Princeton Beta Experiment and on the Advanced Toroidal Facility for routine plasma fueling and for confinement optimization studies. The injector is based upon the so-called ‘‘pipe-gun’’ concept, which generates deuterium and hydrogen pellets by direct condensation in the gun barrel tubes, segments of which are cooled below the hydrogen triple-point temperature by contact with a liquid-helium-cooled block. Control of the pellet length is achieved both by regulating the deuterium fill pressure and by establishing temperature gradients along the barrel tubes. This injector features eight independent gun barrel assemblies mounted around the perimeter of a single cold block, each coupled to an ORNL-designed fast propellant valve. Thus, the injector is capable of injecting arbitrarily programmable sequences of up to eight pellets of sizes ranging from 1 to 3 mm at speeds up to 1500 m/s.

Several advanced plasma fueling systems are under development at the Oak Ridge National Laboratory (ORNL) for present and future magnetic confinement devices. These include multishot and repeating pneumatic pellet injectors, centrifuge accelerators, electrothermal guns, a Tritium Proof-of-Principle experiment, and an ultrahigh velocity mass ablation driven accelerator. A new eight-shot pneumatic injector capable of delivering 3.0 mm, 3.5 mm, and 4.0 mm diameter pellets at speeds up to 1500 m/s into a single discharge has been commissioned recently on the Tokamak Fusion Test reactor. The so-called Deuterium Pellet Injector (DPI) is a prototype of a Tritium Pellet Injector (TPI) scheduled for use on TFTR in 1990. Construction of the TPI will be preceded by a test of tritium pellet fabrication and acceleration using a 4 mm bore ''pipe gun'' apparatus. A new repeating pneumatic pellet injector capable of 2.7 mm, 4 mm, and 6 mm operation is being installed on the Joint European Torus to be used in ORNL/JET collaborative pellet injection studies. A 1.5 m centrifuge injector is being developed for application on the Tore Supra experiment in 1988. The new device, which is a 50% upgrade of the prototype centrifuge used on D-III, features a pellet feed mechanism capablemore » of producing variable-size pellets (1.5 to 3.0 mm diameter) optimally shaped to survive acceleration stresses. Accelerating pellets to velocities in excess of 2 km/s is being pursued through two new development undertakings. A hydrogen plasma electrothermal gun is operational at 2 km/s with 10 mg hydrogen pellets; this facility has recently been equipped with a pulsed power supply capable of delivering 1.7 kJ millisecond pulses to low impedence arc loads.« less

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.

We have developed a prototype high-velocity pneumatic pellet injector that uses hydrogen plasma propellant generated in a high-current arc discharge. A single-barrel pneumatic pellet gun has been fitted with a cylindrical arc chamber interposed between the hydrogen propellant inlet valve and the gun breech. The chamber incorporates a ceramic insert for generating vortex flow in the incoming gas stream, which provides azimuthal arc stabilization. The arc is initiated after the propellant valve opens and the breech pressure starts to rise; a typical discharge lasts 150–300 μs with peak currents up to 2 kA. The gun has been operated with 4-mm-diam, 6- to 11-mm-long deuterium and hydrogen pellets. At 100-bar plenum pressure (hydrogen propellant), the arc characteristics are 〈V〉=350–800 V, 〈I〉=600 A, so that 60–150 J of electrical power is dissipated. Pellet speeds increase by 300 to 600 m/s depending on the projectile mass, which typically represents a 10-J increment in the pellet kinetic energy. Velocities up to 1.7 km/s for deuterium pellets and 2.0 km/s for hydrogen pellets have been achieved. Comparing these data to muzzle velocities calculated from idealized one-dimensional compressible flow gun theory demonstrates that substantial propellant heating, resulting in increased propellant sound speed, has been achieved.

A repeating pneumatic pellet injector has been developed for plasma fueling applications. The repetitive device extends pneumatic injector operation to steady state. The active mechanism consists of an extruder and a gun assembly that are cooled by flowing liquid-helium refrigerant. The extruder provides a continuous supply of solid hydrogen to the gun assembly, where a reciprocating gun barrel forms and chambers cylindrical pellet from the extrusion; pellets are then accelerated with compressed hydrogen gas (pressures up to 125 bar) to velocities ≤1.9 km/s (1.6 km/s for deuterium pellets). The gun assembly design can accommodate different pellet sizes and barrel lengths. Steady-state rates of 2 s−1 have been obtained with 2.1- , 3.4- , and 4.0-mm-diameter pellets. The present apparatus operates at higher firing rates in short bursts; for example, a rate of 6 s−1 for 2 s with the larger pellets. These pellet parameters are in the range applicable for fueling large present-day fusion devices such as the Tokamak Fusion Test Reactor (TFTR). Experimental results are presented, including effects of propellant pressure and barrel length on gun performance.

A tritium pellet injector (TPI) system has been designed for the Tokamak Fusion Test Reactor (TFTR) Q approx. 1 phase of operation. The injector gun utilizes a radial design with eight independent barrels and a common extruder to minimize tritium inventory. The injection line contains guide tubes with intermediate vacuum pumping stations and fast valves to minimize propellant leakage to the torus. The vacuum system is designed for tritium compatibility. The entire injector system is contained in a glove box for secondary containment protection against tritium release. Failure modes and effects have been analyzed, and structural analysis has been performed for most intense predicted earthquake conditions. Details of the design and operation of this system are presented in this paper.

The luminous region of the plasma cloud surrounding deuterium pellets injected into a tokamak is studied spectroscopically. At the time of peak luminosity the average electron density is 2.4 x 10/sup 17/ cm/sup -3/ to within 30% and the temperature is at most 2.0 eV. The intensity ratio of the Balmer alpha and beta light from the pellets, the total number of emitted photons, and the apparent size of the radiating region are consistent with local thermodynamic equilibrium at this temperature and density.

Pellet injectors that produce and accelerate frozen hydrogen isotope pellets are being developed at Oak Ridge National Laboratory (ORNL) for fueling of present and future plasma fusion devices. The development has focused primarily on two types of injectors: (1) gas guns, which utilize a pneumatic approach to accelerate pellets in a barrel with compressed helium or hydrogen propellant, and (2) centrifuge-type injectors, in which pellets are accelerated by centrifugal forces in a high-speed rotating track. In a single-pellet pneumatic injector, pellet speeds up to 1.4 km/s have been achieved. Three multipellet injection systems (ORNL four-pellet pneumatic design) are now functional, one each on the Poloidal Divertor Experiment (PDX), Alcator-C, and the Impurity Study Experiment (ISX-B). Currently, two repetitive devices (one of each injector type) are in operation to demonstrate steady-state fueling systems in the reactor-relevant parameter ranges of 1-km/s pellet velocity, variable pellet sizes up to 2 mm, and feed rates up to 10–40 pellets/s. The injector designs are described and operating characteristics discussed.

A pellet injector development program has been under way at the Oak Ridge National Laboratory (ORNL) since 1976 with the goals of developing D/sub 2/, T/sub 2/ pellet fuel injectors capable of reliable repetitive fueling of reactors and of continued experimentation on contemporary plasma devices. The development has focused primarily on two types of injectors that show promise. One of these injectors is the centrifuge-type injector, which accelerates pellets in a high speed rotating track. The other is the gas or pneumatic gun, which accelerates pellets in a gun barrel using compressed helium of H/sub 2/ gas.

The Oak Ridge National Laboratory single-shot pellet injector, which has been used in plasma fueling experiments on ISX and PDX, has been upgraded and extensively instrumented in order to study the gas dyamics of pneumatic pellet injection. An improved pellet transport line was developed which utilizes a 0.3-cm-diam by 100-cm-long guide tube. Pellet gun performance was characterized by measurements of breech and muzzle dynamic pressures and by pellet velocity and mass determinations. Velocities of up to 1.4 km/s were achieved for intact hydrogen pellets using hydrogen propellant at 5-MPa breech pressure. These data have been compared with new pellet acceleration calculations which include the effects of propellant friction, heat transfer, time-dependent boundary conditions, and finite gun geometry. These results provide a basis for the extrapolation of present-day pneumatic injection system performance to velocities in excess of 2 km/s.