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EP-3496111-B1 - ROTARY CHARGE STRIPPING FILM IN CHARGE STRIPPING DEVICE OF ION BEAM AND CHARGE STRIPPING METHOD OF ION BEAM

EP3496111B1EP 3496111 B1EP3496111 B1EP 3496111B1EP-3496111-B1

Inventors

  • MURAKAMI, MUTSUAKI
  • TACHIBANA, MASAMITSU
  • TATAMI, Atsushi
  • HASEBE, HIROO

Dates

Publication Date
20260506
Application Date
20170727

Claims (14)

  1. A rotary charge stripping film for use in a device which strips a charge of an ion beam, wherein the rotary charge stripping film comprises a carbon film having a circular shape and wherein the rotary charge stripping film has a jig serving as the axis of rotation at the center thereof, characterised in that the carbon film has a thermal conductivity of 500 W/mK or more in a film surface direction at 25°C, and in that a film thickness of the carbon film is 0.2 µm or more and less than 10 µm.
  2. The rotary charge stripping film according to claim 1, wherein the film thickness of the carbon film is 0.2 µm or more and 9 µm or less.
  3. The rotary charge stripping film according to claim 1 or 2, wherein the ion beam is an ion beam of an atom having an atomic number of 6 or more.
  4. The rotary charge stripping film according to any one of claims 1 to 3, wherein the film thickness of the carbon film is more than 3 µm and is 9 µm or less.
  5. The rotary charge stripping film according to any one of claims 1 to 4, wherein the carbon film is a graphite film having a carbon atomic concentration of 97% or more.
  6. The rotary charge stripping film according to any one of claims 1 to 5, wherein the carbon film has an area of 4 cm 2 or more.
  7. The rotary charge stripping film according to any one of claims 1 to 6, wherein a density of the carbon film is not less than 0.90 g/cm 3 and not more than 2.26 g/cm 3 .
  8. The rotary charge stripping film according to any one of claims 1 to 7, wherein the density of the carbon film is not less than 2.0 g/cm 3 and not more than 2.26 g/cm 3 .
  9. The rotary charge stripping film according to any one of claims 1 to 8, wherein the carbon film is a film produced by a polymer annealing method.
  10. A charge stripping method of an ion beam, comprising irradiating the rotary charge stripping film according to any one of claims 1 to 9, which is rotating, with an ion beam.
  11. The charge stripping method according to claim 10, wherein a rotation speed of the rotary charge stripping film is not less than 1 rpm and not more than 3000 rpm.
  12. The charge stripping method according to claim 10 or 11, wherein a charge stripping of the ion beam is performed in a vacuum environment of 1 × 10 -3 Pa or less.
  13. The charge stripping method according to any one of claims 10 to 12, wherein the ion beam is an ion beam of an atom having an atomic number of 6 or more.
  14. The charge stripping method according to any one of claims 10 to 13, wherein an arrangement of the charge stripping film is determined such that the charge stripping film always intersects the ion beam path during rotation, preferably wherein the ion beam is irradiated to the peripheral edge portion of the charge stripping film.

Description

TECHNICAL FIELD The present invention relates to a rotary charge stripping film used in a charge stripping device of an ion beam and a charge stripping method using the rotary charge stripping film. BACKGROUND ART In order to efficiently accelerate a beam in an ion beam accelerator, it is necessary to strip electrons from ions to adjust into an intended valence. A charge stripping film plays an important role for stripping electrons from ions to adjust into an appropriate valence. Liquid lithium, beryllium, a carbon film, a carbon-boron composite film, a carbon nanotube composite film, and a carbon-organic composite film have been reported as charge stripping films (Non-Patent Document 1). Patent Document 1 also reports that a carbon film is vapor-deposited on a vapor-deposited substrate obtained by vacuum-depositing nickel chloride on a glass substrate by arc discharge or the like, and the film is used as a charge stripping film. In addition, Patent Document 2 also reports a carbon-boron composite film as a charge stripping film. Although carbon nanotube (CNT) composite films as disclosed in Patent Document 3 have high physical strength, they may be broken due to a long-time operation because of a low heat resistance, so that there is a problem in reliability such as necessity to stop the operation of the accelerator at each time (Non-Patent Document 2). Further, in order to prevent a beam energy after passing through a charge stripping film from decreasing too much, a film thickness of the charge stripping film should be reduced, but on the other hand, when the film thickness becomes thin, a beam after passing through the film is difficult to be made multivalent. Furthermore, since an ion beam has high energy, a load applied to the charge stripping film is large, so that the charge stripping film is required to have durability. In order to improve the durability, attempts have been made to prevent the beam from being intensively irradiated to a specific portion of the charge stripping film by rotating the charge stripping film (Non-Patent Document 2). Non-Patent Document 3 discloses the use of a gas stripper of hydrogen or helium for charge stripping. PRIOR ART DOCUMENTS PATENT DOCUMENTS [Patent Document 1] JP55-23035A[Patent Document 2] WO2007/058224[Patent Document 3] JP2009-87581A Further related art may be found in US 8432090B2, which discloses a stripping member for stripping electrons off a negatively charged particle beam, and in WO 2013/043930 A1. NON-PATENT DOCUMENTS [Non-Patent Document 1] 27th International Conference of the International Nuclear Target Development Society (INTDS-2014) Tokyo, Japan, August, 2014.[Non-Patent Document 2] Hasebe H.et al, DEVELOPMENT OF NEW FOIL COMPOUNDED FROM CARBON NANOTUBE AND SPUTTER-DEPOSITION CARBON, Journal of Radioanalytical and Nuclear Chemistry,2014, 299,1013-1018.[Non-Patent Document 3] Hiroshi Imao et.al, STUDY OF GAS CHARGE STRIPPER FOR ACCELERATION OF HIGH-INTENSITY HEAVY ION BEAM, Proceedings of the 8th Annual Meeting of Particle Accelerator Society of Japan, August 1-3, 2011, Tsukuba, Japan SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION Since lithium reacts with water, a charge stripping film produced from liquid lithium disclosed in Non-Patent Document 1 is very expensive and becomes complicated because a special device is required under a rare gas atmosphere not containing any moisture. Beryllium of Non-Patent Document 1 has been frequently used as a target material because it is a light element and it has a high charge stripping efficiency. However, beryllium is very expensive, and beryllium-containing dust is toxic to the human body, so there is a problem that it may cause a fatal chronic disease called chronic beryllium disease. The deposited carbon film disclosed in Patent Document 1 has problems such as a weak physical strength and a low heat resistance. Further, the carbon-boron composite film of Patent Document 2 has serious problems such that impurities such as sodium contained in the reagent used for film formation are activated by beam irradiation. In addition, the CNT composite film of Patent Document 3 contains iron and silicon at the time of film formation. For this reason, the charge stripping film after the beam irradiation has been activated and there was a problem that it takes several months before such a charge stripping film can be carried out from the radiation control area. In addition, as described above, a thin charge stripping film is advantageous for preventing reduction in beam energy after charge stripping but on the other hand, making the beam multivalent after passing the charge stripping film is difficult, and it is difficult to use a thin charge converting film as a rotary type. Furthermore, the gas stripper disclosed in Non-Patent Document 3 is preferable from the viewpoint of durability and stability, but a large-scale device is necessary. In view of the above circumstances, an object of the pres