Electrothermal radio frequency thruster and components

Abstract

The invention provides an electrothermal RF plasma production system and thruster design, and associated components, that may be used in terrestrial applications and/or miniaturized to the mass, volume, and power budget of Cube Satellites (CubeSats) to meet the propulsion needs of the small satellite (˜5 to ˜500 kg) constellations and larger satellite buses.

What is claimed is: 
     
         1 . A plasma production device comprising:
 (a) a substantially cylindrical plasma production chamber having a cylinder body, a first closed end and a second open end;   (b) a magnet system comprising one or more radially-disposed magnets configured to establish a magnetic field within the plasma production chamber and oriented substantially parallel to a central longitudinal axis of the plasma production chamber such that each magnet produces a magnetic field of the same polarity within the plasma production chamber;   (c) a propellant tank and a flow regulator in communication with the plasma production chamber and configured to deliver a gaseous propellant into the plasma production chamber; and   (d) a radio frequency (RF) antenna comprising a flat spiral region external to the plasma production chamber and disposed on an external surface of the first closed end, electrically coupled to an AC power source, and configured to deliver an RF energy to an interior region of the plasma production chamber.   
     
     
         2 . The plasma production device of  claim 1 , wherein the flat spiral region has 1-10 turns. 
     
     
         3 . The plasma production device of  claim 1 , wherein the flat spiral region comprises a spiral region radius and the first closed end comprises a closed end radius, and wherein the spiral region radius is 10%-100% of the closed end radius. 
     
     
         4 . The plasma production device of  claim 3 , wherein the spiral region radius is 50%-100% of the closed end radius. 
     
     
         5 . The plasma production device of  claim 1 , wherein the spiral region is configured to cause a constructive interference in magnetic fields produced within the plasma production chamber. 
     
     
         6 . The plasma production device of  claim 1 , wherein the antenna further comprises a coiled region disposed on the external surface of the cylinder body, wherein the coiled region is selected from the group consisting of a coil, a helix, and a half-helix. 
     
     
         7 . The plasma production device of  claim 6 , wherein the coiled region has 2-50 turns. 
     
     
         8 . The plasma production device of  claim 6 , wherein the coiled region and the spiral region are wound in the same direction. 
     
     
         9 . The plasma production device of  claim 6 , wherein the coiled region and the spiral region are wound in a right-handed direction. 
     
     
         10 . The plasma production device of  claim 6 , wherein the spiral region and the coiled region are configured to cause a constructive interference in magnetic fields produced within the plasma production chamber. 
     
     
         11 . The plasma production device of  claim 6 , wherein the plasma production chamber radius (R L ) is equal to 1-7 times the skin depth (ρ s ) of the RF energy. 
     
     
         12 . The plasma production device of  claim 11 , wherein the plasma production chamber radius (R L ) is equal to 4-6 times the skin depth (ρ s ) of the RF energy. 
     
     
         13 . The plasma production device of  claim 6 , wherein the plasma production chamber radius (R L ) is equal to 1.1-5.0 times the Larmor orbit radius (ρ i ) of a plasma ion. 
     
     
         14 . The plasma production device of  claim 13 , wherein the plasma production chamber radius (R L ) is equal to 1.1-3.0 times the Larmor orbit radius (ρ i ) of a plasma ion. 
     
     
         15 . The plasma production device of  claim 6 , wherein the RF energy frequency is less than 25% of an electron cyclotron frequency (f ce ) inside the plasma production chamber. 
     
     
         16 . The plasma production device of  claim 1 , wherein the magnet system produces a first throat region within the plasma production chamber, the second radially-disposed magnet produces a second throat within the plasma production chamber, and the first throat region and the second throat region are separated by a plasma containment region having a lower magnetic field strength than either of the first throat region or the second throat region. 
     
     
         17 . The plasma production device of  claim 16 , wherein the first throat region has a higher magnetic field strength than the second throat region. 
     
     
         18 . The plasma production device of  claim 16 , wherein the magnet system produces a magnetic field strength that is continuously decreasing from the first closed end toward the second open end. 
     
     
         19 . The plasma production device of  claim 16 , wherein the magnet system device further comprises at least one planar magnet disposed behind the first radially-disposed magnet, wherein the at least one planar magnet produces a magnetic field of the same polarity within the plasma production chamber as the one or more radially-disposed magnets, and wherein the magnetic field of the at least one planar magnet is substantially parallel to the longitudinal axis of the plasma production chamber. 
     
     
         20 . The plasma production device of  claim 1 , wherein the RF energy has a frequency of 3-300 MHz. 
     
     
         21 . A plasma production device comprising:
 (a) a substantially cylindrical plasma production chamber having a cylinder body, a first closed end and a second open end;   (b) a magnet system comprising one or more radially-disposed magnets configured to establish a magnetic field within the plasma production chamber and oriented substantially parallel to a central longitudinal axis of the plasma production chamber such that each magnet produces a magnetic field of the same polarity within the plasma production chamber;   (c) a propellant tank and a flow regulator in communication with the plasma production chamber and configured to deliver a gaseous propellant into the plasma production chamber at a flow rate of 0.05-2.0 mg/second; and   (d) a radio frequency (RF) antenna external to the plasma production chamber comprising a flat spiral region disposed against the first closed end and coiled region around the cylinder body, said antenna electrically coupled to an AC power source and configured to deliver an RF energy to an interior region of the plasma production chamber.   
     
     
         22 . The plasma production device of  claim 21 , wherein the cylinder body has a length of 20-75 mm. 
     
     
         23 . The plasma production device of  claim 21 , wherein the plasma production chamber radius (R L ) is 5-20 mm. 
     
     
         24 . The plasma production device of  claim 21 , wherein the magnet system produces a minimum magnetic field strength of 250-400 Gauss. 
     
     
         25 . The plasma production device of  claim 21 , wherein the RF energy has a frequency of 3-300 MHz. 
     
     
         26 . The plasma production device of  claim 21 , wherein the AC power source has a power of 25-500 W, 
     
     
         27 . The plasma production device of  claim 21 , wherein the propellant is xenon. 
     
     
         28 . The plasma production device of  claim 21 , wherein the magnet system further comprises a planar magnet. 
     
     
         29 . The plasma production device of  claim 21 , wherein the magnet system produces a first throat region within the plasma production chamber, the second radially-disposed magnet produces a second throat within the plasma production chamber, and the first throat region and the second throat region are separated by a plasma containment region having a lower magnetic field strength than either of the first throat region or the second throat region. 
     
     
         30 . The plasma production device of  claim 21 , wherein the magnet system produces a magnetic field strength that is continuously decreasing from the first closed end toward the second open end.