Plasma accelerator with modulated thrust
The invention relates to a plasma accelerator that produces and controls a plasma stream exhaust, in particular for space propulsion. The ions are produced inside the discharge chamber by working gas collisional ionization by electrons from a single electron source placed outside, also employed for ion beam neutralization. The ion motion is directed outwards through the exit side by the electric field between a cathode grid and the walls of the plasma chamber. The acceleration voltage imparts energy to the ion flux and an electrically biased control grid modulates the ion outflow from the discharge chamber and the electron inflow from the electron source. This allows electrical control of throttle and/or modulation of thrust delivered along the longitudinal direction of the thruster axis. Several plasma accelerators could be clustered together to provide controlled non-axial thrust using the individual control of throttle.
1. A plasma accelerator comprising:
an electrically conductive discharge chamber with an open end,
means for introducing ionizable propellant inside the discharge chamber,
an active cathode configured to emit electrons for ionizing the propellant and neutralizing outflowing ions, the active cathode placed outside the discharge chamber,
a cathode grid being a passive cathode placed after the open end of the discharge chamber,
an electrically conductive control grid placed after the cathode grid,
wherein the plasma accelerator further comprises:
power supply means configured to apply:
a potential (V CT ) between the control grid and the active cathode for controlling thrust of outflowing plasma stream through the open end of the discharge chamber,
a potential (V AC ) between the active cathode and the discharge chamber for accelerating electrons into the open end of the chamber and ions towards the open end of the discharge chamber and,
a potential (V DS ) between the discharge chamber and the cathode grid for imparting an electric field between the discharge chamber and the cathode grid;
wherein the active cathode, the cathode grid and the control grid are arranged so as to introduce electrons emitted from the active cathode into the discharge chamber through the control grid and the cathode grid.
2. The plasma accelerator according to claim 1 , wherein it further comprising an inner cathode being a passive cathode electrically connected to the cathode grid, the inner cathode placed inside the discharge chamber.
3. The plasma accelerator according to claim 1 , wherein the discharge chamber extends lengthwise along an axis of symmetry.
4. The plasma accelerator according to claim 1 , wherein the cathode grid and the control grid have their open spaces aligned.
5. The plasma accelerator according to any f claim 1 , further comprising a plurality of magnets configured to confine electrons in the discharge chamber.
6. The plasma accelerator according to claim 5 , wherein the plurality of magnets is arranged concentrically around the discharge chamber with alternate magnetic poles.
7. The plasma accelerator according to claim 5 , further comprising a casing for magnetically shielding the plurality of magnets.
8. The plasma accelerator according to claim 1 , wherein the active cathode is a single one.
9. The plasma accelerator according to claim 1 , wherein the ionizable propellant is a monatomic or molecular gas.
10. Space borne vehicle comprising at least one plasma accelerator according to claim 1 .