Helium Propellant Research Articles

Development of the pellet injection system on the J-TEXT tokamak

Pellet injection is an attractive technology for core-fueling and magnetohydrodynamic study in magnetic-confinement fusion devices like tokamaks and stellarators. It can inject solid hydrogen/deuterium pellets into the plasma with deeper density deposition compared with other fueling methods, such as gas puffing. A three-barrel H2 pellet injection system was installed on the J-TEXT tokamak and experiments were carried out. The pellets are formed in three barrels cooled by a cryocooler and compressor system at around 9 K, and are 0.8 mm/1 mm diameter and 0.8 mm length. The pellet is launched by helium propellant gas and injected from the low-field side of the plasma. The normal range of pellet speed is 210–310 m s−1 for different propellant gas pressures. Due to the three-barrel structure, the number of injected pellets can be adjusted between one and three. Pellets can be launched sequentially with arbitrary time intervals, which enables flexible applications. The results of the experiments show that pellet fueling efficiency can reach 50%. The energy confinement time increased by about 7.5‒10 ms after pellet injection.

Effect of He and N2 gas on the mechanical and tribological assessment of SS316L coating deposited by cold spraying process

In this study, simulation and experimental methods were used to investigate the influence of cold spray conditions on AISI 316L stainless steel coatings. The effect of both helium and nitrogen gases used was investigated. The temperature, particle sizes of spraying powder, and distance from the nozzle throat to the impinging point were estimated by using the Kinetics Spray Solutions GmbH software. The 316L stainless steel (SS) coatings were examined by X-ray diffraction, Scanning Electron Microscopy and Energy Dispersive X-Ray Microanalysis. The tribological behavior was evaluated under different loads (2 N and 5 N) in dry conditions. It was found that the nitrogen and helium propellant gas with high speed and fine particles led to produce good coatings with dense microstructures. From the nanoindentation experiments, the Young's modulus and hardness of the SS 316L samples were enhanced of about 8% with helium due to the high particle velocity. It was shown that the wear resistance of SS 316L produced with helium was higher than that of the standard SS 316L coatings. The coatings produced with helium revealed lower friction coefficient (0.65) and wear rate (6.9 × 10–4 mm3/Nm) under 2 N applied load than that obtained nitrogen. It was also found that the SS 316L cold sprayed by helium with dense structure presents high hardness and good tribological performance that can be suggested for several applications.Graphical

Investigation into the transient flow characteristics of noble gas propellants using the pulsed inductive discharge in electric propulsion

The Pulsed Inductive Thruster (PIT) has the advantages of repeatable startup, no corruption and in-situ propellant feed. To study the flow expansion and circuit characteristics of PITs, the circuit-fluid model is developed, and the high temperature thermodynamic and transport models are combined with the circuit-fluid model to predict the critical plasma parameters. The flow fields of initial mass of 2–8 mg and charge voltages of 10–14 kV are simulated. Comparison of the flow fields of argon and helium propellants suggests that, the flow field structures are similar. Slight differences exist on the magnitude of the density and magnetic field, caused by larger velocity in lighter atom case and difference on the ionization gap between adjacent ionization levels. Analysis of the circuit characteristics by the two-dimensional results indicates that the ratio of coil inductance to circuit inductance affects both the rise rate and phase of the plasma current, the larger the ratio, the greater the rise rate and the better the following characteristic. The calculations show that the magnetic energy obtained within the decoupling distance determines the overall performance the thruster can be obtained; self-induced field maintained by the thermal motion after the main pulse leads to the long attenuation process and difference on the total impulse when the angle of conical pylon is varied under constant coil dimension.

Design of a Continuous Pellet Fueling System for Wendelstein 7-X

A continuous pellet fueling system (CPFS) is currently being designed at the Oak Ridge National Laboratory (ORNL) for the long pulse operation of the Wendelstein 7-X (W7-X) stellarator. The purpose of the CPFS is to provide deep continuous fueling for feedback-controlled high-density operation and mitigation of predicted hollow density profiles. The system will provide the capability to inject cylindrical pellets of solid hydrogen or deuterium into the plasma core, with flexibility to vary the pellet size, velocity, and injection frequency. Pellets are nominally of 3 mm in diameter and have a length between 1 and 4 mm. The heart of the CPFS is a vertically oriented, twin-screw extruder, cooled by three Gifford-McMahon cryocoolers in parallel, designed to form a continuous filament of hydrogen or deuterium. The filament width, which determines the pellet length, can be adjusted by means of a variable nozzle driven by a linear actuator at the base of the extruder. Coupled to the nozzle is a solenoid-operated gas gun and cutter assembly. A pneumatic propellant valve pulses a burst of ~60 bar helium to accelerate the cut pellet into W7-X. Three gaps in the guide tubes provide pumping locations to remove the helium propellant before it reaches the plasma. The maximum velocity of the pellet is limited by its ability to survive navigating the guide tube trajectory intact. A microwave cavity located within the guide tube provides the capability to measure the pellet size and velocity. The mechanical and thermal designs of the W7-X extruder, adjustable nozzle, and gun and cutter assembly design are described. A guide tube design and experimental pellet survivability test results are presented.

Global Energy Transfer Model of a Microwave Electrothermal Thruster Operating With Helium Propellant at 2.45-GHz Frequency

Microwave electrothermal thruster (MET) is a type of space propulsion system that uses free floating plasma to heat the propellant gas. This paper presents a 0-D model that investigates the energy transfer from the electromagnetic wave to the propellant gas via atmospheric pressure plasma, and evaluates the steady-state plasma properties of an MET thruster. In the model, governing equations for electron particle balance, electron energy, balance and heavy particle energy balance equations are solved to obtain the plasma parameters. Electron temperatures of around 1 eV, electron number densities of $10^{19}~\#/\text {m}^{3}$ , and heavy particle temperatures of about 3000 K are evaluated for the free floating plasma inside the MET resonant cavity for 1200-W delivered power at 2.45-GHz frequency. Obtained solutions are in good agreement with the experimental results from the literature. Along with the plasma parameters, rocket performance parameters, and specific impulse and thrust are computed. The developed model is also used to predict the plasma and performance parameters of a prototype MET system developed at the Bogazici University Space Technologies Laboratory.

Tribological and Corrosion Characteristics of Ti6Al4V Coatings Cold Sprayed with Nitrogen and Helium Propellant Gases

The tribological and corrosion characteristics of Ti6Al4V coatings on Ti6Al4V substrates with nitrogen (N2) and helium (He) propellant gases cold sprayed via a high pressure cold spray process were investigated because different masses of the N2 and He working gases could affect the velocities of Ti6Al4V particles during the cold spraying and consequently the properties of the coatings. The more uniform and denser structure of the Ti6Al4V coatings with a lower porosity level was achieved with He working gas. As a result, the Ti6Al4V coatings deposited with the He working gas had a higher hardness than those deposited with the N2 working gas. The tribological results showed that the use of He gas during the cold spraying produced the more wear resistant Ti6Al4V coatings associated with their higher hardness. The denser Ti6Al4V coatings deposited with the He gas had a lower anodic current density in a NaCl solution than those deposited with the N2 working gas. It is clear that the wear and corrosion resistances of the Ti6Al4V coatings were significantly influenced by the propellant gases during the cold spray deposition.

Low pressure cold spraying under 6 bar pressure deposition: Exploration of high deposition efficiency solutions using a mathematical modelling

Abstract This paper investigates the improvement of the deposition efficiency (DE) for low pressure cold spraying. In the literature, some possibilities were studied (a long preheating of the powder feedstock, the use of irregular shaped particles, the combination of metallic particle with ceramics, or the laser assisted heating) but the DE is still weak, in the range of 10%, when working at around 6 bar. In this paper, the improvement possibilities depending on the gas conditions, the particle size and the nozzle geometry are explored. The deposition of spherical copper powder onto a copper substrate is considered. Experimental investigations evidence a low DE of about 0.1 and virtual tests computing the one-dimensional flow of the gas through the nozzle and the interaction with the particles are used to identify potential solutions increasing the DE. Air or nitrogen propellant gas has led to similar DE. The highest achieved value remains low even working at the maximum capacity of the low pressure system, i.e. a gas with an inlet pressure of 12 bar and a preheating temperature of 630 °C. Factors of improvement are suggested for the specific case of the standard pressure of 6 bar. Fine particles cause clogging and larger particles are difficult to be efficiently deposited. Successful combinations promoting the DE include a nozzle expansion ratio in between 1.2 and 2, a diverging part length in between 200 mm and 300 mm and the helium propellant gas preheated at 600 °C. Hence the DE can reach up to 100% for 10 μm sized copper particles according to the computation. If using larger particles (20 μm, 30 μm or 40 μm), the maximum DE is respectively 0.7, 0.5 or 0.3 approximately. This results give indications for the suitable conditions promoting the highest achievable DE for low pressure cold spraying.

Blower Gun pellet injection system for W7-X

Foreseen to perform pellet investigations in the new stellarator W7-X, the former ASDEX Upgrade Blower Gun was revised and revitalized. The systems operational characteristics have been surveyed in a test bed. The gun is designed to launch cylindrical pellets with 2mm diameter and 2mm length, produced from frozen deuterium D2, hydrogen H2 or a gas mixture consisting of 50% H2 and 50% D2. Pellets are accelerated by a short pulse of pressurized helium propellant gas to velocities in the range of 100–250m/s. Delivery reliabilities at the launcher exit reach almost unity. The initial pellet mass is reduced to about 50% during the acceleration process. Pellet transfer to the plasma vessel was investigated by a first mock up guiding tube version. Transfer through this S-shaped stainless steel guiding tube (inner diameter 8mm; length 6m) containing two 1m curvature radii was investigated for all pellet types. Tests were performed applying repetition rates from 2Hz to 50Hz and propellant gas pressures ranging from 0.1 to 0.6MPa. For both H2 and D2, low overall delivery efficiencies were observed at slow repetition rates, but stable efficiencies of about 90% above 10Hz. About 10% of the mass is eroded while flying through the guiding tube. Pellets exit the guiding tube with an angular spread of less than 14°.

Effect of Heat Treatment on the Microstructure and Mechanical Properties of Stainless Steel 316L Coatings Produced by Cold Spray for Biomedical Applications

Abstract In this study, the effects of heat treatment on the microstructure and mechanical properties of cold sprayed stainless steel 316L coatings using N2 and He as propellant gases were investigated. Powder and coating characterizations, including coating microhardness, coating porosity, and XRD phase analysis were performed. It was found that heat treatment reduced porosity, improved inter-particle bonding, and increased ductility. XRD results confirmed that no phase transformation occurred during deposition. Significant increase in UTS and ductility was observed for the annealed specimens obtained with nitrogen propellant, whereas little changes were observed for the helium propellant produced specimen.

Development of pellet fuelling system in HL-2A tokamak

For increasing the plasma density and improving the plasma confinement, a new pellet fuelling system based on the extrusion technology has been developed successfully and set up in the low field side of the HL-2A tokamak. It is designed to produce 1–40 solid pellets of hydrogen/deuterium in one injection cycle. The pellet fuelling system consists of six main parts: (1) Vacuum system, which includes two independent sub-systems and can pump the corresponding spaces to 10 −3 Pa and below 10 −5 Pa, respectively. (2) A closed-cycle helium cryorefrigerator of 1 W power at 4.2 K, which is used for cooling of the injector and pellet production. (3) A pellet size regulator, which is used for extrusion of ice ribbon with different dimensions. (4) Electromagnetic cutter, which is used to cut the ice ribbon to pellets with high frequency (up to 30 Hz). (5) Gas supply system, it can provide the pellet material of D 2 or H 2 and propellant gas of helium, and (6) control and diagnostic system. During our 2009–2010 experimental campaign, we made some commissioning tests for the fuelling system and injected the deuterium pellets into the plasma with the typical parameters as follows: pellet size are with the diameter = 1.3 mm and length = 1.3–1.7 mm, number of pellet N p = 3–5, frequency of injection F i = 10/20 Hz , velocity of pellet V p = 200–300 m/s by helium propellant gas with pressure of 0.6–1 MPa . The injection reliability is more than 90%. This paper will describe the new pellet fuelling system in detail, and present some preliminary injection experimental results in HL-2A tokamak.

Three-Dimensional Modeling of Magnetic Nozzle Processes

Simulations of plasma flow through a magnetic nozzle were conducted using the time dependent, three -dimensional magn etohydrodynamics code, MACH3. The code’s grid generation, mesh adaptivity, initial magnetic field, and electric resistivity sub routines were upgraded to improve resolution of physical processes of varying characteristic scale. Modeling of magnetic nozzle f low using constant, classical isotropic, and classical tensor resistivity provides preliminary quantitative depiction of the core -plasma flow, evolution of the magnetic field, and conversion of stagnation enthalpy to directed exhaust thrust energy. For st agnation conditions of 100eV and 0.355MPa, steady -state modeling using helium propellant demonstrates a nearly isentropic expansion through the nozzle to exhaust speeds near 160 km/s. The extent of the contribution from the magnetic diffusion and the mass -flux penetration on the thickness of the current layer is dependent on the selection of the resistivity model. Plasma -field interaction results in a reduction of approximately 50% of the directed axial thrust when compared to a solid -wall nozzle of equiv alent Mach number design. At fixed plasma pressure and applied field the exhaust velocity scaled appropriately as the square root of the stagnation temperature.

Numerical Analysis of Free-Molecule Microresistojet Performance

The direct-simulation Monte Carlo method was used to study the flow in a free-molecule microresistojet (FMMR). The FMMR is a microelectromechanical-systems (MEMS) fabricated resistojet that operates by heating a propellant gas as it expands through a series of slots. The flow through a single heater slot of the FMMR was modeled in two dimensions for a range of chamber pressures from 50 to 200 Pa and heater chip temperatures from 300 to 573 K. Using this, the numerical performance of FMMR was computed. The resultant specific impulse was found to agree within 2% of experimental data for nitrogen propellant and within 4% for helium propellant. Then, a full three-dimensional model of the FMMR geometry was made for water vapor as propellant in two steps. First, the flow in the plenum was modeled. FMMR performance parameters were found to be 10% lower than those of the two-dimensional model. Second, the FMMR plume flow was calculated using a starting surface generated from the plenum simulation for two possible locations of the FMMR as a despin thruster on a nanosatellite. The thrust degradation caused by the resultant surface forces was examined, and the net moment of one configuration was found to be 60% higher than the other.

Experimental Target Injection and Tracking System

ABSTRACTTargets must be injected into an IFE power plant with an accuracy of ± 5 mm at a rate of approximately 5 to 10 each second. Targets must be tracked very accurately to allow driver beams to be aligned with defined points on the targets with accuracy ±200 μm for indirect drive and ±20 μm for direct drive. An experimental target injection and tracking system has been designed and is being constructed at General Atomics to investigate injection and tracking of both direct drive and indirect drive targets. The design is modular to allow testing of alternate target acceleration and tracking methods. The injector system will be used as a tool for testing the survivability of various target designs and provide feed back to the target designers. This 30 m long system will be the centerpiece of a Facility for developing IFE target fabrication and injection technologies.A high-speed high-flow gas valve (designed and built by Oak Ridge National Laboratory) will provide helium propellant gas to the targets. To avoid target damage from excessive acceleration, an 8 m gun barrel is being built to achieve 400 m/s target speed while not exceeding 10,000 m/s2 acceleration. Direct-drive targets are protected in the barrel by sabots that are spring loaded to separate into two halves after acceleration. A sabot deflector directs the sabot halves away from the target injection path. Gas expansion chambers and orifices, keep propellant gas out of the target-tracking region. Targets will be optically tracked with laser beams and line scan cameras. High-speed computations will calculate target position in less than 2 ms based on the output from the line-scan cameras. Target position and arrival time to a plane in the reaction chamber center will be predicted in real-time based on early target position measurements. The system design, construction progress, and early testing results will be presented.

Investigation of stabilized resonant cavity microwave plasmas for propulsion

Results are presented for the performance of a microwave electrothermal thruster utilizing bluff-body and swirling flow stabilized plasmas with helium and nitrogen propellent. Stabilized plasmas have been produced in the TM011 electromagnetic cavity mode with coupling efficiencies approaching 100% and specific powers up to 27.3 MJ/kg. Fluid dynamic measurements indicate specific impulses of up to 543 s, efficiencies of 44-69%, and thrusts of 0.27—0.40 N with helium propellant. Spectroscopic results indicate plasma core electron temperatures of 11,840-12,170 K with extremely flat radial profiles. Nomenclature A = orifice area, m c = speed of light, m/s cp = specific heat, J/kg K g = gravitational acceleration, m/s2 7sp = specific impulse, s k = Boltzmann's constant, J/K m = particle mass, kg m = mass flow rate, kg/s P,- = incident power, W Po = chamber pressure, Pa Pr = reflected power, W R = gas constant, J/kg K 7} = thrust, N T(k, = stagnation temperature (cold), K Tl}l, = stagnation temperature (hot), K ue = exhaust velocity, m/s y = ratio of specific heats 77 = efficiency j]c = coupling efficiency A = wavelength, A

Factors affecting gene delivery by particle bombardment ofDendrobium orchids

Five parameters were examined for their effect on transformation ofDendrobium tissues by microprojectile bombardment. The superpromoter in pBI426 produced at least 1.5 times as many transient transformants as the single cauliflower mosaic virus 35S promoter in pBI121 (37 to 69% vs. 0 to 44%) with dark and frequent GUS (β-glucuronidase) staining. Tissue, genotype, and type of microparticle significantly affected transient GUS activity. Higher expression was seen in protocormlike bodies and in hybrid UH44 compared to etiolated shoots and protocorms and to hybrids M61 and K1329-39. Microparticles of 1.6-µm Bio-Rad gold were more effective than 1.0-µm ASI gold. Transient GUS activity did not differ among protocormlike bodies bombarded using helium propellant pressures of 650, 900, or 1100 psi. Transgenic plants were recovered fromDendrobium UH800 protocormlike bodies bombarded with pBI426-coated, 1.1-µm tungsten particles using an early-model gunpowder-driven apparatus with an estimated stable transformation rate of 11.7%. One transgenic plant ofDendrobium UH44 was recovered from etiolated shoot explants bombarded with pBI121-coated, 1.1-µm tungsten particles using the Dupont PDS-1000 with a stable transformation rate of 0.17%. Positive selection results showed 100 to 200 mg·liter−1 kanamycin to be appropriate for regeneration of transgenic plants from protocormlike bodies, protocorms, and etiolated shoot explants over a 3- to 9.5-mo. period.

Use of permanent magnets to reduce anode losses in MPD thrusters

Results from previous studies indicate that the anode fall, the principal source of anode heating in MPD thrusters, increases monotonically with the electron Hall parameter calculated from electron temperature, number density, and magnetic field data obtained near the anode. In an attempt to reduce the anode fall by decreasing the local electron Hall parameter, a proof-of-concept test was performed in which an array of 36 permanent magnets were embedded within the anode of a high-power quasisteady MPD thruster to decrease the local azimuthal component of the induced magnetic field. The modified thruster was operated at power levels between 150 kW and 4 MW with argon and helium propellants. Terminal voltage, triple probe, floating probe, and magnetic probe measurements were made to characterize the performance of the thruster with the new anode. Incorporation of the modified anode resulted in a reduction of the anode fall by up to 15 V with argon and 20 V with helium, which corresponded to decreased anode power fractions of 40 and 45% with argon and helium, respectively. 26 refs.

An evaluation of the implementation of transportation systems with unconventional propellants

The paper deals with a more-dimensional evaluation of the benefits achievable by using super high energy triplet helium propellant (He∗) instead of LOX/LH 2. The evaluation criteria were, among others, technical performances, environmental aspects, risk potentials and costs. They were measured by a hierarchy of objectives. Using completely new propellants could revolutionize space travel which is up to now characterized by the use of conventional chemical systems with maximum specific impulses below 500 s at high thrust levels. The necessity of cost reductions is the most important driver. Triplet helium is considered in combination with different working fuels (liquid helium, liquid hydrogen) due to its advantages in comparison with other super high energy propellant candidates: very high specific energy, easy production, high density. It is regarded as being trapped within a cryogenic lattice of solid helium or solid hydrogen. Two different launch vehicles are analysed to deliver required data for the evaluation: a SLLV (small lift launch vehicle) carrying 7 Mg of payload, and a HLLV (heavy lift launch vehicle) carrying 120 Mg of payload. The vertically launched ballistic vehicles are fully reusable. The investigation used a long term space traffic scenario (R. E. Lo, J. Laßmann and M. Thierschmann, paper presented at the 42nd IAF Congress, Montreal[1]) as background. Degrees of goal achievement were determined with the help of a computer code using complex planning algorithms. Operational costs of the alternative concepts are presented. It is shown in the paper, that the implementation of transportation systems with super high energy triplet helium propellant is beneficial in some areas compared to conventional LOX/LH 2 systems. Vehicle volumes and masses as well as operational costs will be reduced. However, according to the present state-of-the-art, insurmountable technical problems arise against the realization of such propulsion systems.

Anode power deposition in magnetoplasmadynamic thrusters

Results of anode heat-flux and anode fail measurements from a multimegawatt self-field quasi-steady magnetoplasmadynamic (MPD) thruster are presented. Measurements were obtained with argon and helium propellants for a variety of currents and mass flow rates. Anode heat flux was directly measured with thermocouples attached to the inner surface of a hollowed section. Anode falls were determined both from floating probes and through heat flux measurements. Comparison of data acquired through either method shows excellent agreement. Anode falls varied between 4-50 V with anode power fractions reaching 70 percent with helium at 150 kW, and 50 percent with argon at 1.9 MW. The anode fall was found to correlate well with electron Hall parameters calculated from triple Langmuir and magnetic probe data collected near the anode. Two possible explanations for this result are proposed: (1) the establishment of large electric fields at the anode to maintain current conduction across the strong magnetic fields; and (2) anomalous resistivity resulting from the onset of microturbulence in the plasma. To investigate the latter hypothesis, electric field, magnetic field, and current density profiles measured in the vicinity of the anode were incorporated into Ohm's law to estimate the electrical conductivity. Results of this analysis show a substantial deviation of the measured conductivity from that calculated with classical formulas. These results imply that anomalous effects are present in the plasma near the anode.

Experimental study on a low-power direct current arcjet

An experimental investigation on a low-power dc arcjet with helium propellant was conducted. Objectives were to evaluate the thermal efficiency, to assess the performance of various cathode materials, and to investigate the effects of transpirational cooling from the electrodes. The anode was made of porous tungsten so that the propellant could be supplied through the anode. The cathode materials used in this experiment were porous tungsten, thoriated tungsten, lanthanum hexaboride, and porous tungsten impregnated with barium oxide (BaO/W). Two discharge modes of low and high voltages were found, which corresponded to low and high thermal efficiency, respectively. The BaO/W cathode was the best of all the tested materials, demonstrating a thermal efficiency as high as 64.9%. The transpirational cooling resulted in a great decrease of the thermal efficiency.

Development of Hydrogen Pellet Injectors at ORNL

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 highspeed 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 steadystate 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.