Patent Number: 
Section: claims

1. A target supply unit mounted to a chamber, comprising:a nozzle unit having a through-hole to allow a target material to be outputted therethrough;a cover provided to define a first space inside the cover and to cover the nozzle unit, the cover having a through-hole to allow the target material to pass therethrough from the first space to a second space inside the chamber; anda device configured to pump out gas inside the first space. 2. The target supply unit according to claim 1, further comprising:an electrode provided to face the nozzle unit; anda voltage generator configured to apply a voltage between the target material and the electrode. 3. The target supply unit according to claim 1, wherein the cover is formed of an electrically conductive material. 4. The target supply unit according to claim 1, whereinthe nozzle unit is disposed in the chamber,the cover is disposed in the changer to form together with the nozzle the first space which is a closed space inside the chamber. 5. A target supply unit mounted to a chamber, comprising:a nozzle unit having a through-hole to allow a target material to be outputted therethrough;a plurality of electrodes provided in a direction in which the target material travels;an electrical insulator for holding the plurality of electrodes;at least one voltage generator configured to apply a voltage between the plurality of electrodes;a cover provided to define a first space inside the cover and to cover the nozzle unit, the plurality of electrodes, and the electrical insulator, the cover having a through-hole to allow the target material to pass therethrough from the first space to a second space inside the chamber; anda device configured to pump out gas in the first space. 6. The target supply unit according to claim 5, whereinthe nozzle unit is disposed in the chamber, andthe cover is disposed in the changer to form the first space in the chamber, the first space is a closed space containing the nozzle unit, the plurality of electrodes, and the electrical insulator. 7. An extreme ultraviolet light generation apparatus, comprising:a chamber provided with a window through which a pulse laser beam travels into the chamber; anda target supply unit mounted to the chamber, the target supply unit comprising:a nozzle unit having a through-hole to allow a target material to be outputted therethrough;a cover provided to define a first space inside the cover and to cover the nozzle unit, the cover having a through-hole to allow the target material to pass therethrough from the first space to a second space inside the chamber; anda device configured to pump out gas inside the first space. 8. The extreme ultraviolet light generation apparatus according to claim 7, wherein the device is configured to pump out gas in the first space so that a gas pressure in the first space be lower than that in the second space. 9. The extreme ultraviolet light generation apparatus according to claim 7, whereinthe nozzle unit is disposed in the chamber,the cover is disposed in the changer to form together with the nozzle the first space which is a closed space inside the chamber. 10. An extreme ultraviolet light generation apparatus, comprising:a chamber provided with a window through which a pulse laser beam travels into the chamber; anda target supply unit mounted to the chamber, the target supply unit comprising:a nozzle unit having a through-hole to allow a target material to be outputted therethrough;a plurality of electrodes provided in a direction in which the target material travels;an electrical insulator for holding the plurality of electrodes;at least one voltage generator configured to apply a voltage between the plurality of electrodes;a cover provided to define a first space inside the cover and to cover the nozzle unit, the plurality of electrodes, and the electrical insulator, the cover having a through-hole to allow the target material to pass therethrough from the first space to a second space inside the chamber; anda device configured to pump out gas in the first space. 11. The extreme ultraviolet light generation apparatus according to claim 10, wherein the device is configured to pump out gas in the first space so that a gas pressure in the first space be lower than that in the second space. 12. The extreme ultraviolet light generation apparatus according to claim 10, whereinthe nozzle unit is disposed in the chamber, andthe cover is disposed in the changer to form the first space in the chamber, the first space is a closed space containing the nozzle unit, the plurality of electrodes, and the electrical insulator.