Patent Number: 
Section: claims

1. A source of photons comprising: a discharge chamber;  first and second groups of ion beam sources in the discharge chamber, each electrostatically accelerating a beam of ions of a working gas toward a plasma discharge region, said first group of ion beam sources acting as a cathode and said second group of ion beam sources acting as an anode for delivering a heating current to the plasma discharge region; and  a neutralizing mechanism for at least partially neutralizing said ion beams before they enter the plasma discharge region, wherein the neutralized beams and the heating current form a hot plasma that radiates photons. 2. A source as defined in  claim 1 , wherein said ion beams precede said heating current. claim 1 3. A source as defined in  claim 1 , wherein said heating current is pulsed and wherein said ion beams comprise pulsed ion beams that precede said pulsed heating current. claim 1 4. A source as defined in  claim 1 , wherein said ion beam sources comprise continuous ion beam sources and wherein said heating current is pulsed. claim 1 5. A source as defined in  claim 1 , wherein said first and second groups of ion beam sources are distributed around opposite halves of the plasma discharge region. claim 1 6. A source as defined in  claim 5 , wherein said first and second groups of ion beam sources together comprise a spherical array. claim 5 7. A source as defined in  claim 1 , further comprising a transformer having a primary and a secondary, wherein a first terminal of said secondary is coupled to said first group of ion beam sources and wherein a second terminal of said secondary is coupled to said second group of ion beam sources. claim 1 8. A source as defined in  claim 7 , wherein the secondary of said transformer has a single turn. claim 7 9. A source as defined in  claim 1 , wherein said first and second groups of ion beam sources comprise concentric electrode shells having sets of apertures aligned along axes which pass through the plasma discharge region, a first voltage source for applying a voltage between said electrode shells, and a gas source for supplying the working gas to the sets of apertures in said electrode shells. claim 1 10. A source as defined in  claim 9 , further comprising a second voltage source coupled between said first and second groups of ion beam sources for supplying said heating current. claim 9 11. A source as defined in  claim 1 , wherein said neutralizing mechanism comprises resonant charge exchange in each of said ion beams. claim 1 12. A source as defined in  claim 1 , wherein said photons are in the soft X-ray or extreme ultraviolet wavelength range. claim 1 13. A source as defined in  claim 1 , wherein the working gas is xenon and wherein the radiated photons have wavelengths in a range of about 10-15 nanometers. claim 1 14. A source as defined in  claim 1 , wherein the working gas is selected from the group consisting of hydrogen, lithium, helium, nitrogen, oxygen, neon, argon and krypton. claim 1 15. A system for generating photons, comprising: a housing defining a discharge chamber;  first and second groups of ion beam sources in the discharge chamber, each electrostatically accelerating a beam of ions of a working gas toward a plasma discharge region, said first group of ion beam sources acting as a cathode and said second group of ion beam sources acting as an anode;  a first voltage source for applying an accelerating voltage to said first and second groups of ion beam sources;  a second voltage source for supplying a heating current through the plasma discharge region between said first and second groups of ion beam sources;  a gas source for supplying a working gas to the discharge chamber;  a neutralizing mechanism for at least partially neutralizing said ion beams before they enter the plasma discharge region, wherein the neutralized beams enter the plasma discharge region and form a hot plasma that radiates photons; and  a vacuum system for controlling the pressure of the working gas in the discharge chamber. 16. A system as defined in  claim 15 , wherein said first and second groups of ion beam sources comprise concentric electrode shells having sets of apertures aligned along axes which pass through the plasma discharge region, wherein at least an inner electrode shell of said concentric electrode shells is divided to form said cathode and said anode. claim 15 17. A system as defined in  claim 15 , wherein said ion beams precede said heating current. claim 15 18. A system as defined in  claim 15 , wherein said first and second voltage sources are pulsed so as to provide pulsed ion beams that precede a pulsed heating current. claim 15 19. A system as defined in  claim 15 , wherein said first voltage source produces continuous ion beams and wherein said second voltage source produces a pulsed heating current. claim 15 20. A system as defined in  claim 15 , further comprising a transformer having a primary coupled to said second voltage source and a secondary coupled between said first and second groups of ion beam sources. claim 15 21. A method for generating photons, comprising the steps of: electrostatically accelerating a plurality of beams of ions of a working gas toward a plasma discharge region;  at least partially neutralizing said ion beams before they enter the plasma discharge region; and  supplying a heating current through the plasma discharge region, wherein the neutralized beams and the heating current form a hot plasma that radiates photons. 22. A method as defined in  claim 21  wherein the step of electrostatically accelerating a plurality of beams of ions precedes the step of supplying a heating current through the plasma discharge region. claim 21 23. A method as defined in  claim 21  wherein the step of supplying a heating current comprises supplying a pulsed heating current and wherein the step of electrostatically accelerating a plurality of beams of ions comprises accelerating a plurality of pulsed ion beams that precede the pulsed heating current. claim 21 24. A method as defined in  claim 21  wherein the step of supplying a heating current comprises coupling the heating current to a spherical electrode array through a transformer. claim 21 25. A source of photons comprising: a discharge chamber;  a plurality of ion beam sources in the discharge chamber, each electrostatically accelerating a beam of ions of a working gas toward a plasma discharge region;  a neutralizing mechanism for at least partially neutralizing said ion beams before they enter the plasma discharge region; and  an external electrode spaced from the plasma discharge region and biased with respect to the ion beam sources for delivering a heating current to the plasma discharge region, wherein the neutralized beams and the heating current form a hot plasma that radiates photons. 26. A source as defined in  claim 25  wherein said ion beam sources comprise concentric electrode shells having sets of apertures aligned along axes which pass through the plasma discharge region, a first voltage source for applying a voltage between said electrode shells, and a gas source for supplying the working gas to the sets of apertures in said electrode shells. claim 25 27. A source as defined in  claim 26  further comprising a second voltage source coupled between said ion beam sources and said external electrode for supplying said heating current. claim 26 28. A source as defined in  claim 25  wherein said external electrode has a cylindrical configuration. claim 25 29. A source of photons comprising: a housing that defines a discharge chamber;  a first group of ion beam sources directed toward a plasma discharge region in the discharge chamber, wherein a component of said first group of ion sources constitutes a first electrode;  a second electrode spaced from the plasma discharge region;  a first power supply for energizing the first group of ion beam sources to electrostatically accelerate, from the first group of ion beam sources toward the plasma discharge region, ion beams which are at least partially neutralized before they enter the plasma discharge region; and  a second power supply coupled between the first and second electrodes for delivering a heating current to the plasma discharge region, wherein the ion beams and the heating current form a hot plasma that radiates photons. 30. A source of photons as defined in  claim 29 , wherein the ion beam sources of said first group of ion beam sources are distributed around the plasma discharge region. claim 29 31. A source of photons as defined in  claim 29 , further comprising a second group of ion beam sources directed toward the plasma discharge region, wherein a component of said second group of ion beam sources constitutes said second electrode. claim 29 32. A source of photons as defined in  claim 31 , wherein said first and second groups of ion beam sources together comprise a spherical array of ion beam sources. claim 31 33. A source of photons as defined in  claim 31 , wherein the ion beam sources of said first and second groups of ion beam sources are distributed around the plasma discharge region. claim 31 34. A source of photons as defined in  claim 31 , wherein said first and second groups of ion beam sources comprise inner and outer electrode shells having sets of apertures aligned along axes which pass through the plasma discharge region, and wherein said first power supply is coupled between said inner and outer electrode shells. claim 31 35. A source of photons as defined in  claim 34 , wherein said inner shell comprises a first inner shell portion and a second inner shell portion and wherein said second power supply is coupled between said first and second inner shell portions. claim 34 36. A source of photons as defined in  claim 31 , wherein said first group of ion beam sources includes a first inner shell portion and said second group of ion beam sources includes a second inner shell portion, and wherein said second power supply is coupled between said first and second inner shell portions. claim 31 37. A source of photons as defined in  claim 31 , wherein said first group of ion sources includes a first inner shell portion and said second group of ion sources includes a second inner shell portion, said source further comprising a transformer having a primary and a secondary, wherein said primary is coupled to said second power supply, wherein a first terminal of said secondary is coupled to said first inner shell portion and wherein a second terminal of said secondary is coupled to said second inner shell portion. claim 31 38. A source of photons as defined in  claim 37 , wherein the secondary of said transformer has a single turn. claim 37 39. A source of photons as defined in  claim 29 , wherein a photon beam is emitted from the plasma discharge region in a beam direction and wherein said second electrode is spaced from the plasma discharge region in a direction opposite the beam direction. claim 29 40. A source of photons as defined in  claim 39 , wherein said first group of ion beam sources comprises inner and outer electrode shells having sets of apertures aligned along axes which pass through the plasma discharge region and wherein said second power supply is coupled between said inner electrode shell and said second electrode. claim 39 41. A source of photons as defined in  claim 39 , wherein said second electrode comprises a ring. claim 39 42. A source of photons as defined in  claim 39 , wherein said second electrode comprises a cathode for delivering a heating current to the plasma discharge region. claim 39 43. A source of photons as defined in  claim 29 , wherein the ion beams precede the heating current. claim 29 44. A source of photons as defined in  claim 29 , wherein the heating current is pulsed and wherein the ion beams comprise pulsed ion beams that precede the pulsed heating current. claim 29 45. A source of photons as defined in  claim 29 , wherein the ion beams are continuous and wherein the heating current is pulsed. claim 29 46. A source of photons as defined in  claim 29 , wherein the ion beams are at least partially neutralized by resonant charge exchange. claim 29 47. A source of photons as defined in  claim 29 , wherein the radiated photons are in the soft X-ray or extreme ultraviolet wavelength range. claim 29 48. A source of photons as defined in  claim 29 , wherein the ion beams comprise xenon ions and wherein the radiated photons have wavelengths in a range of about 10-15 nanometers. claim 29 49. A source of photons as defined in  claim 29 , wherein the ion beams comprise ions of a working gas selected from the group consisting of xenon, hydrogen, lithium, helium, nitrogen, oxygen, neon, argon and krypton. claim 29 50. A source of photons as defined in  claim 29 , wherein said first group of ion beam sources comprises a first hollow ring electrode and an inner shell that at least partially encloses the plasma discharge region. claim 29 51. A source of photons as defined in  claim 50 , wherein said first power supply is connected between said first hollow ring electrode and said inner shell. claim 50 52. A source of photons as defined in  claim 50 , further comprising a second group of ion sources, said second group of ion sources comprising a second hollow ring electrode and said inner shell. claim 50 53. A source of photons as defined in  claim 52 , wherein said first power supply has a first terminal connected to said first and second hollow ring electrodes and a second terminal connected to said inner shell. claim 52 54. A source of photons as defined in  claim 50 , wherein said first hollow ring electrode and said inner shell have a plurality of hole pairs which define plasma channels from the first hollow ring electrode to the plasma discharge region. claim 50 55. A source of photons as defined in  claim 52 , wherein said first hollow ring electrode and said inner shell have a plurality of hole pairs which define plasma channels from the first hollow ring electrode to the plasma discharge region and wherein said second hollow ring electrode and said inner shell have a plurality of hole pairs which define plasma channels from the second hollow ring electrode to the plasma discharge region. claim 52 56. A source of photons as defined in  claim 29 , wherein said second power supply is triggered to deliver a heating current about 0.1 to 10 microseconds after said first power supply is triggered to energize said first group of ion beam sources. claim 29 57. A source of photons as defined in  claim 29 , further comprising a gas source for supplying a working gas to the discharge chamber, wherein the working gas is ionized to form the ion beams. claim 29 58. A source of photons as defined in  claim 29 , wherein said first and second electrodes are configured such that the heating current is conducted along the ion beams to the plasma discharge region. claim 29 59. A source of photons comprising: means for accelerating a group of ion beams toward a plasma discharge region in a discharge chamber, wherein the ion beams are at least partially neutralized before they enter the plasma discharge region; and  means for supplying a heating current to the plasma discharge region, wherein the ion beams and the heating current form a hot plasma that radiates photons. 60. A method for generating photons, comprising: accelerating a group of ion beams toward a plasma discharge region in a discharge chamber, wherein the ion beams are at least partially neutralized before they enter the plasma discharge region; and  supplying a heating current to the plasma discharge region, wherein the ion beams and the heating current form a hot plasma that radiates photons. 61. A system for generating photons, comprising: a housing defining a discharge chamber;  a first group of ion beam sources directed toward a plasma discharge region in the discharge chamber, wherein a component of said first group of ion sources constitutes a first electrode;  a second electrode spaced from the plasma discharge region;  a first power supply for energizing the first group of ion beam sources to accelerate, from the first group of ion beam sources toward the plasma discharge region, beams of ions of a working gas, wherein the ions are at least partially neutralized before they enter the plasma discharge region;  a second power supply coupled between the first and second electrodes for delivering a heating current to the plasma discharge region;  a gas source for supplying the working gas to the discharge chamber; and  a vacuum system for controlling the pressure of the working gas in the discharge chamber.