Gas-dynamic Acceleration Research Articles

Dinamika, simmetriya i udarno-indutsirovannoe «pylenie» pri kvaziizentropicheskom i izentropicheskom uskorenii tsilindricheskikh laynerov

Two devices intended for copper cylindrical liner gasdynamic acceleration to velocities of 5–7 km/s using the chemicals explosion energy have been investigated. It has been demonstrated that the acceleration of quasi-isentropically and isentropically loaded liners under the conditions of high-level dynamics, symmetry of deposition, and suppression of shock-induced dusting is feasible.

Modelling of capillary capacitively coupled radio frequency thruster

Computational fluid dynamics plasma simulations of a capillary capacitively coupled radio frequency thruster discharge with front powered electrode was performed. Good agreement with experimental results was obtained for the global parameters of the thruster. The spatial characteristics of the discharge were analyzed. DC bias is found to develop in accordance with classical theory of asymmetric capacitive discharge. The electrons temperature in the plasma bulk is ∼2 eV and increasing the sheath near the powered electrode to ∼6 eV. The plasma density is 1019 m−3 whereas excited argon species are 1020 m−3. The thrust can be completely attributed to gas dynamic acceleration.

Analysis of Energy Capabilities of Acceleration of Massive Projectiles by Gas-Dynamic Methods

The energy capabilities of acceleration devices are theoretically analyzed, including various ramjet-in-tube options for gas-dynamic acceleration of massive (1 to 40 kg) projectiles under ground conditions up to velocities of 2–3 km/s. Simple quasi-one-dimensional models for a perfect gas are used in the computations. It is demonstrated that the use of a ramjet-in-tube accelerator with a closed exit allows the velocities of acceleration of massive projectiles to be increased to 3 km/s, which is twice greater than the values that can be obtained with available gunpowder-based methods.

Theoretical Formulation for the Performance of Rectangular, Breech-Fed Pulsed Plasma Thrusters

An approach based on strong electromagnetic acceleration produced simple closed-form analytic expressions for the ablated mass and total impulse per pulse for rectangular, breech-fed pulsed plasma thrusters. The theoretical model is validated by comparisons to experiments of a wide range of geometries and operating conditions showing very good agreement. The produced expressions quantify contributions from electromagnetic and gas dynamic acceleration; confirm, explain, and generalize trends observed by experiments; and offer additional guidelines for thruster improvements.

Ignition and detonation onset behind incident shock wave in the shock tube

The paper analyses in details and describes the process of ignition kernel formation and subsequent detonation onset behind the shock wave propagating in the shock tube. To get the overall pattern of the process a series of one- and two-dimensional calculations are carried out with the use of a dissipation-free numerical technique. It is shown that one of the leading roles in the process of ignition kernel formation belongs to the non-steady flow dynamics establishing behind the shock wave. The development of the boundary layer determines both the temperature re-distribution in the near-wall region and the conditions for gas-dynamic acceleration of the flow. With an account of thermal runaway, the most intensively heated region corresponds to the area between the inner margin of the boundary layer and the contact surface separating driver gas and the test mixture. After localized ignition takes place the forming reaction wave propagates out from the ignition epicenter. Reaction wave propagates behind the outrunning compression wave through the already reacting mixture. Shock-induced compression of the test mixture provides conditions for the self-sustained acceleration of the combustion wave, and finally, the detonation onset takes place.

Gasdynamic acceleration of microparticles and their interaction with a solid body

Based on the physicomathematical model developed before, verified by comparison results of calculations with experimental data, parameters of a gas-dispersed jet, interacting with a solid body, are numerically investigated. In a wide range of temperature and pressure values in a mixing chamber, material density, the size and mass fraction of particles, the nozzle geometry and the streamlined body form, ratio of specific heat capacities, and the Mach number of carrier gas, calculations are made, which allows one to determine the impact of specified factors on the boundary of a perfectly inelastic collision of particles with the body, accompanied by different physical processes (erosion, cold deposition, ultradeep penetration). Since temperature falls below the Debye value at high expansion of flow, the impact of a significant change of the heat capacity and thermal conductivity of particles are taken into account. Radial distributions of density and velocity of the dispersed mass are plotted, which characterize the “quality” of two-phase flow as a tool for the ground modelling of interaction of a flying vehicle with a dust-laden atmosphere (containing, for example, particles of volcanic outbursts or ice crystals) as well as in technologies of surface treatment.

Relationship between nonthermal and gasdynamic processes in powerful solar flares

The relationship between gas-dynamic processes and particle acceleration is illustrated using three examples. For the flare of July 6, 2006, observations show that explosive evaporation of the chromosphere occurs in the pulse phase. In addition, the coronal mass emission (CME) related to this flare reflects the primary energy release. In the strong limb flare of July 14, 2005, the CME observed in the external layers of the corona seems to be a consequence of repeated energy releases and plasma emissions. Apparently, this is indicated by the additional emission in the decimeter range, which is typical of posteruptive processes. An example of a weak flare during the decay phase of the strong event of April 15, 2001, was also accompanied by a decimeter burst.

Study of applied magnetic field magnetoplasmadynamic thrusters with particle-in-cell and Monte Carlo collision. II. Investigation of acceleration mechanisms

The particle-in-cell method previously described in paper (I) has been applied to the investigation of acceleration mechanisms in applied-field magnetoplasmadynamic thrusters. This new approach is an alternative to magnetohydrodynamics models and allows nonlocal dynamic effects of particles and improved transport properties. It was used to model a 100 kW, steady-state, applied-field, argon magnetoplasmadynamic thruster to study the physical acceleration processes with discharge currents of 1000–1500 A, mass flow rates of 0.025–0.1 g/s and applied magnetic field strengths of 0.034–0.102 T. The total thrust calculations were used to verify the theoretical approach by comparison with experimental data. Investigations of the acceleration model offer an underlying understanding of applied-field magnetoplasmadynamic thrusters, including the following conclusions: (1) swirl acceleration mechanism is the dominant contributor to the plasma acceleration, and self-magnetic, Hall, gas-dynamic, and swirl acceleration mechanisms are in an approximate ratio of 1:10:10:100; (2) the Hall acceleration produced mainly by electron swirl is insensitive to the change of externally applied magnetic field and shows only slight increases when the current is raised; (3) self-magnetic acceleration is normally negligible for all cases, while the gas-dynamic acceleration contribution increases with increasing applied magnetic field strength, discharge current, and mass flow rate.

Physical risks of landing on a cometary nucleus

Comets originate from the outer solar system where the density and temperature of the planetary nebula were rather low. They form a distinct class of small solar system bodies and their physical properties differ considerably from those of any other known objects. The present knowledge of the cometary nucleus is cursory and driven more by imagination than by observational facts. Landing on a cometary nucleus, as planned during the ROSETTA mission, is of high scientific interest and will substantially improve our knowledge of the nature and origin of comets. However, successful landing and operating the instruments is an extraordinary challenge to engineers and scientists. Even a close approach to an inactive nucleus may jeopardize the orbiter. A wide range of uncommon and risky environmental conditions such as outgassing, a fragile surface, deposition of dust grains, extreme temperature variations, and pronounced topography have to be considered. These are described in physical terms based on model calculations ranging from simple one-dimensional heat transfer to gas-dynamic acceleration of dust particles. Environmental constraints relevant for landing and operating instruments on a cometary nucleus are presented such as sublimation and recondensation of water on the cold parts of the lander and varying illumination conditions over the extent of the mission. Aspects of risk reduction are discussed. The paper also summarizes the present knowledge about physical and structural properties of cometary nuclei relevant for the development of landing strategies.

The application of a Wien filter to mass analysis of heavy clusters from a pulsed supersonic nozzle source

A Wien filter is used for the mass analysis of small and large metal cluster ions. As the clusters are produced in a supersonic expansion source, the initial velocity obtained by gasdynamic acceleration significantly influences the measured peak positions and widths. Calculations based on the well-known theory for ions moving in crossed magnetic and electrical fields are extended to ions from supersonic expansions. They allow a mass assignment even for those (big) clusters which cannot explicitly be resolved in the Wien filter spectrum.

Gas-dynamic acceleration of ions in an inhomogeneous magnetic field

This paper evaluates the method of gas-dynamic acceleration of ions in an inhomogeneous magnetic field in two variants - a strongly scattering and nonscattering foil F. In the first variant the presence of the inhomogeneous magnetic field leads to an increase in ion current related to increase in the flux area in the acceleration region, while in the second the increase in current is insignificant, but nevertheless the efficiency of ion acceleration is increased, because all the energy of the oscillating electrons in the accelerated region will be included in a longitudinal degree of freedom. This fact leads to an increase in the rate of expansion of the plasma synthesized from ions and oscillating electrons. Because of this increase in the mean rate of plasma expansion the efficiency of acceleration increases also.

Operation of a railgun accelerator for solid projectiles powered from an explosive MHD generator

These authors investigate the possibility of using an explosive MHD generator whose electrodes consist of the rails of a railgun accelerator so that the projectile is anitially accelerated by the action of electromagnetic forces and then, once the gas-cumulative jets reach the body, it can be subjected to additional acceleration by the gas flow moving at a high rate of speed. They conclude that the proposed compounded electrodynamic and gasdynamic acceleration scheme holds promise for achieving velocities in the 5-10 km/sec range.

Spherical hydrogen pellet generator for magnetic confinement fusion research

The design and operation of a cryogenic pellet generator is described. The device is capable of producing spherical solid hydrogen pellets of sufficient size and repetition rate to meet prospective refueling requirements of near term tokamak fusion machines. It accelerates pellets to speeds in excess of 102 m/s by gas dynamic drag techniques and has achieved initial injection into the APEX tokamak at Argonne National Laboratory. A discussion of gas dynamic drag acceleration techniques is presented with an evaluation of their significance to pellet acceleration technology.

Acceleration, radiation and precession in SS 433

Some theoretical problems posed by the observations of SS 433 are considered. The monoenergetic beams point toward a gas-dynamic acceleration process. In this model the collimation implies that the acceleration occurs in a region of slab symmetry, possibly the surface layers of an accretion disk. The 164 day rotation of the beam pattern may be explained as a precession period.

Pneumatic hydrogen pellet injection system for the ISX tokamak

We describe the design and operation of the solid hydrogen pellet injection system used in plasma refueling experiments on the ISX tokamak. The gun-type injector operates on the principle of gas dynamic acceleration of cold pellets confined laterally in a tube. The device is cooled by flowing liquid helium refrigerant, and pellets are formed in situ. Room temperature helium gas at moderate pressure is used as the propellant. The prototype device injected single hydrogen pellets into the tokamak discharge at a nominal 330 m/s. The tokamak plasma fuel content was observed to increase by (0.5-1.2) x10(19) particles subsequent to pellet injection. A simple modification to the existing design has extended the performance to 1000 m/s. At higher propellant operating pressures (28 bars), the muzzle velocity is 20% less than predicted by an idealized constant area expansion process.

Effects of Propellant and Electrode Geometry on Pulsed Ablative Plasma Thruster Performance

A performance level compatible with 30% thrust efficiency at 1500 s specific impulse at 1 mlb (4.45 mN) of thrust was demonstrated with the parallel rail pulsed ablative thruster using Teflon propellant. Parametric variations of interelectrod e spacing and included angle were performed. In addition, Teflon was replaced by other thermoplastics and was also seeded with 10% and 30% LiOH and InBr in an evaluation of alternative propellants. Both the conventional breech-fed and later side-feed electrode/propellant configurations were tested. With the same initial conditions it was shown that the breech-fed geometry yields higher thrust efficiency than the side-fed geometry because of the higher specific impulse generated (i.e., up to 5300 s using Teflon). Results of parametric studies indicate that, for high thrust/power and moderately high specific impulse, virgin Teflon propellant with an interelectrode spacing of 3.0 in. (7.62 cm) and zero degree interelectrode included angle in the side-fed configuration are best. A simple semiempirical analytic model is presented where it is shown that the broad range in performance characteristic of this device is related to the degree to which magnetoplasmadynamic and ordinary gasdynamic acceleration mechanisms can be made more or less dominant in the acceleration of the ablated propellant.