A plasma railgun is a linear accelerator which, like a projectile
railgun
A railgun or rail gun, sometimes referred to as a rail cannon, is a linear motor device, typically designed as a ranged weapon, that uses Electromagnet, electromagnetic force to launch high-velocity Projectile, projectiles. The projectile norma ...
, uses two long parallel electrodes to accelerate a "sliding short"
armature. However, in a plasma railgun, the armature and ejected projectile consists of
plasma, or hot, ionized particles in a gas-like state, instead of a solid slug of material. Scientific plasma railguns are typically operated in vacuum and not at air pressure. They are of value because they produce muzzle velocities of up to several hundreds of kilometers per second. Because of this, these devices have applications in
magnetic confinement fusion
Magnetic confinement fusion (MCF) is an approach to generate thermonuclear fusion power that uses magnetic fields to confine fusion fuel in the form of a plasma (physics), plasma. Magnetic confinement is one of two major branches of controlled fusi ...
(MCF),
magneto-inertial fusion (MIF),
high energy density physics research (HEDP), laboratory
astrophysics, and as a
plasma propulsion engine for spacecraft.
Theory
Plasma railguns appear in two principal topologies, linear and coaxial. Linear railguns consist of two flat plate electrodes separated by insulating spacers and accelerate sheet armatures. Coaxial railguns accelerate toroidal plasma armatures using a hollow outer conductor and a central, concentric, inner conductor.
Linear plasma railguns place extreme demands on their insulators, as they must be an electrically insulating, plasma-facing vacuum component which can withstand both thermal and
acoustic shocks. Additionally, a complex triple joint seal may exist at the breech of the bore, which can often pose an extreme engineering challenge. Coaxial accelerators require insulators only at the breech, but the plasma armature in that case is subject to the "blow-by" instability. This is an instability in which the magnetic pressure front can out-run or "blow-by" the plasma armature due to the radial dependence of acceleration current density, drastically reducing device efficiency. Coaxial accelerators use various techniques to mitigate this instability. In either design, a plasma armature is formed at the breech. As plasma railguns are an open area of research, the method of armature formation varies. However, techniques including exploding foils, gas cell burst disk injection, neutral gas injection via fast gas valve, and plasma capillary injection have been employed.
After armature formation, the plasmoid is then accelerated down the length of the railgun by a current pulse driven through one electrode, through the armature, and out the other electrode, creating a large magnetic field behind the armature. Since the driver current through the armature is also moving through and normal to a self-generated magnetic field, the armature particles experience a
Lorentz force, accelerating them down the length of the gun. Accelerator electrode geometry and materials are also open areas of research.
Applications
Controlled jets from plasma rail guns can have peak densities in the 10
13 to 10
16 particles/m
3 range, and velocities from 5 to , depending on device design configuration and operating parameters, and the upper limits may be higher. Plasma rail guns are being evaluated for applications in magnetic confinement fusion for disruption mitigation and tokamak refueling.
[R. Raman and K. Itam]
Conceptual Design Description of a CT Fueler for JT-60U
2000)
Magneto-inertial fusion seeks to implode a magnetized D-T fusion target using a spherically symmetric, collapsing, conducting liner. Plasma railguns are being evaluated as a possible method of implosion linear formation for fusion.
Arrays of plasma railguns could be used to create pulsed implosions of ~1 Megabar peak pressure, allowing more access to chart this opening area of plasma physics.
High velocity jets of controllable density and temperature allow astrophysical phenomena such as solar wind, galactic jets, solar events and astrophysical plasma to be partially simulated in the laboratory and measured directly, in addition to astronomic and satellite observations.
Examples
See also
*
Helical railgun
*
Coilgun
*
Mass driver
A mass driver or electromagnetic catapult is a proposed method of non-rocket spacelaunch which would use a linear motor to Acceleration, accelerate and catapult Payload (air and space craft), payloads up to high speeds. Existing and proposed mass ...
*
Ram accelerator
*
Light-gas gun
*
Pulsed plasma thruster
*
MARAUDER
Marauder, marauders, The Marauder, or The Marauders may refer to:
* A person engaged in banditry or related activity
** Piracy
** Looting
** Outlaw
** Partisan (military)
** Robbery
** Theft
Entertainment
* ''Marauder'', the second novel in th ...
*
Combustion light-gas gun
References
{{reflist
Railguns
Plasma technology and applications