Coaxial Plasma Gun Research Articles

Performance of a coaxial plasma gun

Coaxial plasma guns operating with about 20 kV applied at a peak current of approximately 80 kA are shown to produce a fast burst of clean plasma containing no other ions than H+. Densities of about 1011 cm-3 are measured at distances of 100 cm from the gun for ions of energy between 5 keV and 20 keV: peak ion energies of about 70 keV are observed. In the slow plasma following the fast burst the impurity ions are mainly copper. The ion density depends on the amount of gas admitted before firing the gun, but does not vary much with gun voltage. The measured ion velocity perpendicular to the guide field is within a factor two of the predictions of a simple theory. Discrepancies are expected because the ions do not appear in a field-free region, as the theory assumes.

Current Density Distributions in a Coaxial Plasma Gun

Current Density Distributions in a Coaxial Plasma Gun

Energy loss in pulsed coaxial plasma guns

The one-dimensional flow of a current-carry ing plasma, driven into neutral gas by its selfmagnetic field, is considered for the case where both the neutral gas and the current have arbitrary distributions in the direction of flow. The conservation laws are used to derive a simple expression for the amount of input power that goes into all forms of internal energy. It is shown that this power depends mainly on the rate at which the current sheet sweeps up neutral gas. In principle, internal energy can be converted into directed energy by expansion; however, it is argued that, in the coaxial plasma accelerators currently used in propulsion studies, most of the internal energy will be lost by excitation and subsequent radiation or ionization before expansion occurs.

Spectroscopic Measurements of the Plasma from a Plasma Gun,(I)

Line broadening of He I 4471 A and He ‖ 4686 A radiated from plasma generated in a Marshall type coaxial plasma gun are measured by a 340 cm Ebert type spectrometer. Doppler shift measurements indicates that a plasma blob is accelerated during about 5 μsec from the initiation of gun discharge and leaves the plasma gun, while an unacceleratee 1 plasma remains in the gun throughout the discharge period. Most of the line broadening on the He ‖ 4686 A is due to Doppler broadening, and Stark broadening is negligible. The accelerated plasma from the gun gradually loses the velocity component perpendicular to the axis of the plasma gun as it travels through the vacuum vessel.

Charged particle density distribution in a coaxial plasma gun

Upon measuring the magnetic field distribution and axial-electric field in a coaxial plasma gun, we could obtain the charged particles density distribution in the gun.

Spectroscopic Measurements of Impurities in The Plasma Stream (I)

The plasma stream presented by our coaxial plasma gun includes various impurity components of which copper and carbon are very serious. Emission lines from these impurities are measured by a 3. 4M Fastie-Ebert type polychrometor.In order to reduce copper ions, a longitudinal magnetic field is applied along, the passage of the plasma stream. For example, relative intensity of CuII 2247A to HeII 4686A is redu ced to 1/30 after passing through a magnetic field of 1000 gauss. Also, this relative intensity varies with operation conditions of the gun.

Spectroscopic Measurements of the Plasma from a Plasma Gun, (I)

Line broadening of He I 4471 Å and He ‖ 4686 Å radiated from plasma generated in a Marshall type coaxial plasma gun are measured by a 340 cm Ebert type spectrometer. Doppler shift measurements indicates that a plasma blob is accelerated during about 5 μsec from the initiation of gun discharge and leaves the plasma gun, while an unacceleratee 1 plasma remains in the gun throughout the discharge period. Most of the line broadening on the He ‖ 4686 Å is due to Doppler broadening, and Stark broadening is negligible. The accelerated plasma from the gun gradually loses the velocity component perpendicular to the axis of the plasma gun as it travels through the vacuum vessel.

Performance of Coaxial Plasma Gun with Various Propellants

An experimental study of a single-shot coaxial plasma gun is described. A parametric survey of the gun over the operating range is given for each of three propellants: argon, nitrogen, and hydrogen. An optimum delay time (with respect to exhaust puff energy) is described for each propellant between gas injection and bank-voltage application. Bank voltage and mass per shot were varied using the optimum delay time. Gun efficiency, system efficiency, and magnetic-front velocity in the gun were determined.

Studies of Plasma Expelled from a Coaxial Plasma Gun

An experimental study of the plasma leaving a coaxial gun is described. The plasma shows a conical shape with a central axial pinch. When a radial magnetic field is applied at the muzzle of the gun, magnetized plasma rings are formed. Under certain conditions the central pinch shows a helical instability, resulting in a considerable increase of the poloidal magnetic flux in the plasma rings. Different types of discharges are described, associated with the occurrence of a ``short-circuit'' in the gun. During the decay of the plasma, magnetoacoustic oscillations are observed.

Experimental Study of the Propagation of an Ionizing Wave in a Coaxial Plasma Gun

A coaxial plasma gun experiment is described. The gun has an azimuthal bias magnetic field, which is strong compared to the field from the discharge current. The discharge voltage is shown to depend linearly on the bias field, thus defining a velocity that is found to be almost independent of the pressure and the discharge current. This velocity is close to the ``critical velocity'' which has been found in rotating-plasma experiments. The velocity of the current layer is also measured; it is always smaller than or equal to the critical velocity and it decreases with increasing pressure and decreasing magnetic field.

Velocity Limitation of a Coaxial Plasma Gun

Arguments are cited to establish that for reasonable acceleration to occur in a pulsed coaxial plasma gun a conduction current must be drawn between electrodes in contact with the plasma. Further, under assumptions deemed justifiable for the coaxial gun it is shown that the current must consist of equal parts of ion and electron current. A drag force on the plasma then results from momentum exchange between the ions and the cathode. The equation of motion for the plasma including this drag force is solved and the results are shown to be consistent with experimental experience.

Studies of a Coaxial Plasma Gun

An experimental study of the acceleration of plasma between two coaxial electrodes is described. A high current radial discharge is obtained that is highly reproducible and axisymmetric. Particular attention has been given to the study of current distribution in the plasma. It has been found that the current layer has a complicated conical structure exhibiting closed current loops in the plasma. No pressure wave propagating in front of the current layer has been observed.

Investigation of the High-Energy Acceleration Mode in the Coaxial Gun

The amount of deuterium gas admitted to a short center electrode (1 cm) coaxial plasma gun delineates two regions of operation, depending on whether the gas is localized near the inlet port or allowed to diffuse throughout the gun length. In the former, fast deuterium ions with energy in excess of the applied voltage (V0 = 15 kV) emerge from the gun muzzle whereas in the latter, the accelerated plasma which initially starts at the breech end reaches an axial velocity of ∼2.5 × 107 cm/sec at the muzzle end and forms a high-density plasma focus on the axis in front of the central electrode. Neutron measurements show that this dense plasma is not in contact with the electrode and is most probably stagnated by the high ambient gas pressure downstream. Particle momentum analysis of the fast ion (> V0) distribution and neutron measurements downstream of the gun suggest two accelerated groups of fast ions, (1) a group of ∼1016 particles which diverge from the gun muzzle and (2) a group of ∼1014 particles which stream primarily along the axis with a radial distribution of ∼3 cm width. Multiple probes (Bθ) show an asymmetric angular distribution of the discharge current that varies as a function of time during a given discharge. A sharp break in the total gas current is accompanied by large inductive voltages. In the high-energy mode, inductive voltages up to 7V0 have been recorded at the breech end.

1086. Some characteristics of a two-stage repetitively fired coaxial plasma gun: P. Gloersen et al., Symp. on Plasma Phenomena and Measurement, San Diego, 1963, IEE Trans., Vol. NS-11, No. 1, 249–265

1086. Some characteristics of a two-stage repetitively fired coaxial plasma gun: P. Gloersen et al., Symp. on Plasma Phenomena and Measurement, San Diego, 1963, IEE Trans., Vol. NS-11, No. 1, 249–265

SPECTROSCOPIC MEASUREMENTS OF THE PLASMA FROM A PLASMA GUN I

Line broadenings of He I 4471 and He II 4686 in the plasma generated in a Marshall type coaxial plasma gun are measured by a 340cm Ebert type spectrometer. According to the Doppler shift measurement, a plasma is accelerated for about 5μ sec after the initiation ofthe gun discharge, and it leaves the plasma gun, while an unaccelerated plasma remains in the plasma gun after then during the discharge. Most of the line broadening in He II 4686 is due to Doppler broadening, and the Stark broadening is negligible. The accelerated plasma from the gun gradually loses the perpendicular component of the velocity to the axis of the plasma gun as it travels.

Impurity Content of Plasma Produced by a Coaxial Plasma Gun

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Interaction of a Plasma Stream with a Three-Dimensional Magnetic Dipole

A differentially pumped coaxial plasma gun is used as a source in studies of plasma interactions with a solenoidal coil forming a three-dimensional magnetic dipole. A cavity forms when the magnetic field is applied. The size of the cavity increases with the magnetic field, and its form is almost independent of the magnetic field. Plasma penetrates the cavity along the magnetic lines of force towards the polar regions of the day-light side of the dipole and may be the same phenomenon as the observed magnetic disturbance in the polar regions on the earth. (C.E.S.)

Measuremeints on Current Sheets in Plasmas

The acceleration of a gas undergoing ionization in a crossed electric-magnetic field leads to the formation of current sheets similar to those observed in coaxial plasma guns. The dynamics of such sheets is of great interest to workers in plasma physics in view of their application to controlled thermonuclear fusion experiments and to space propulsion. In the present paper a detailed mapping of the magnetic field in the vicinity of a current sheet is described. Conventional small search coils are used for the detection of this field. From the configuration of this field an attempt is made to understand the processes taking place in the sheet. All of the experiments described in the paper are performed on a plasma coaxial gun of mall aspect ratio.

Two High Velocity Plasma Guns

The design and operating parameters of two coaxial plasma guns are described. The high speed gun performance depends upon the use of (1) gas valve ports near the muzzle end of the central electrode, (2) an optimized gas diffusion delay time, and (3) a small injected gas load. The 10-cm-diam gun employs a low inductance power supply and a light gas load to yield a plasma containing ∼5×1016 D+ ions with a mean energy of 13 keV. The larger 25-cm-diam gun requires more energy and a larger gas load to yield a plasma containing a similar number of D+ ions but at a higher mean energy of ∼20 keV. As an example of gun performance, the 25-cm-diam gun produces a neutron yield of ≈108 when incident upon a D2O ice target located 3 m from the gun muzzle.

Current Sheet in a Coaxial Plasma Gun

Magnetic- and electric-probe measurements have been made on the thin current layer which is accelerated in a coaxial (Marshall) plasma gun. It is found that this layer does not act as a ``snowplow,'' but rather has the character of a strong shock wave.