Patent Number: 
Section: claims

1. An extreme ultra violet light source device of a laser produced plasma type comprising:a target supply unit configured to supply a target material;a chamber in which plasma is generated by irradiating the target material with a laser beam;collector optics configured to collect extreme ultra violet light radiated from the plasma; anda magnetic field forming unit including (1) plural coils configured to form, when applied with electric currents, magnetic fields having different intensity from each other at both sides of a position where the target material is irradiated with the laser beam and (2) a shielding unit configured to shield a part of the magnetic fields formed by said plural coils. 2. The extreme ultra violet light source device according to claim 1, wherein said magnetic field forming unit includes plural magnetic cores having different shapes from each other and/or different sizes from each other and inserted into central openings of said plural coils, respectively. 3. The extreme ultra violet light source device according to claim 1, wherein said plural coils includes superconducting coils. 4. The extreme ultra violet light source device according to claim 1, wherein said magnetic field forming unit is configured to apply electric currents having different magnitudes from each other to said plural coils, respectively. 5. The extreme ultra violet light source device according to claim 1, wherein said magnetic field forming unit is configured to apply electric currents in different directions from each other to said plural coils, respectively. 6. The extreme ultra violet light source device according to claim 1, wherein numbers of turns and/or diameters of turns of winding wires in said plural coils are different from each other. 7. The extreme ultra violet light source device according to claim 1, wherein said magnetic field forming unit is configured to form asymmetric magnetic fields in which a central axis of lines of magnetic flux is not a straight line. 8. The extreme ultra violet light source device according to claim 7, wherein said plural coils are provided to face each other at a predetermined angle. 9. The extreme ultra violet light source device according to claim 1, wherein said magnetic field forming unit is configured to form asymmetric magnetic fields with respect to a surface perpendicular to a central axis of lines of magnetic flux. 10. The extreme ultra violet light source device according to claim 9, wherein said magnetic field forming unit is configured to form asymmetric magnetic fields having a higher magnetic flux density at one side of a central axis of lines of magnetic flux and a lower magnetic flux density at the other side thereof. 11. The extreme ultra violet light source device according to claim 1, further comprising:an ion ejection port provided in a direction from a higher magnetic flux density to a lower magnetic flux density of the magnetic fields formed by said magnetic field forming unit. 12. The extreme ultra violet light source device according to claim 1, further comprising:an electric field forming unit configured to form an electric field in the magnetic fields formed by said magnetic field forming unit. 13. The extreme ultra violet light source device according to claim 1, wherein a central axis of said target supply unit is oriented in a direction perpendicular to a central axis of lines of magnetic flux of the magnetic fields formed by said magnetic field forming unit. 14. The extreme ultra violet light source device according to claim 1, wherein said shielding unit contains one of iron, cobalt, nickel and ferrite. 15. An extreme ultra violet light source device of a laser produced plasma type comprising:a target supply unit configured to supply a target material;a chamber in which plasma is generated by irradiating the target material with a laser beam;collector optics configured to collect extreme ultra violet light radiated from the plasma; anda magnetic field forming unit including (1) plural permanent magnets configured to form magnetic fields having different intensity from each other at both sides of a position where the target material is irradiated with the laser beam and (2) a shielding unit configured to shield a part of the magnetic fields formed by said plural permanent magnets. 16. The extreme ultra violet light source device according to claim 15, wherein said shielding unit contains one of iron, cobalt, nickel and ferrite. 17. The extreme ultra violet light source device according to claim 15, wherein said magnetic field forming unit is configured to form asymmetric magnetic fields in which a central axis of lines of magnetic flux is not a straight line. 18. The extreme ultra violet light source device according to claim 17, wherein said plural permanent magnets are provided to face each other at a predetermined angle.