JP5751538B2 - Method for controlling critical current density of bulk superconductor and method for producing bulk superconductor for undulator - Google Patents

Description

  The present invention can improve the critical current density control of a superconductor, more specifically, improve and control the critical current density of the entire bulk body, and can be implemented by an existing accelerator. Moreover, the present invention relates to a method for controlling the critical current density of a bulk superconductor capable of suppressing variations in critical current density among a plurality of bulk bodies, and a method for manufacturing a bulk superconductor for an undulator.

  As is well known, bulk superconductors have been put into practical use in a wide range of fields (for example, pseudo-permanent magnets and current leads) by utilizing their characteristics, and in recent years, they are used as insertion light sources for synchrotron radiation. Research is also underway to use bulk superconductors instead of permanent magnets in undulators (electronic meandering devices).

  For bulk superconductors, the critical current density (the maximum current value that can flow through the superconductor per unit cross section with zero resistance) is an important factor that affects performance. The current density can be increased to a practical level by forming pinning centers (defects such as impurities and vacancies) inside the bulk body.

  Therefore, when manufacturing bulk superconductors, in the case of REBaCuO-based (RE: rare earth element) superconductors, the 211 phase which is the normal conduction phase is dispersed in the 123 phase which is the superconducting phase, or the rare earth element is dispersed. The pinning center is introduced by replacing a part of the material with a material exhibiting non-superconductivity (see, for example, Patent Document 1).

  However, not only is the above method difficult to control the critical current density, but also the critical current density tends to vary among a plurality of superconductors manufactured by the same method. Then, the variation in the critical current density becomes the variation in the undulator magnetic field amplitude as it is and leads to a decrease in the performance of the undulator (see Non-Patent Document 1).

  On the other hand, as a method of forming the pinning center, a method of introducing a columnar defect by irradiating a superconducting thin film with high-energy heavy ions is known (see Non-Patent Document 2). In the case where a bulk material having a thickness of 2 is intended, it is not a realistic method because it requires irradiation with an extremely high energy beam.

  Conventionally, a technique for increasing the critical current density by irradiating an electron beam to a bulk superconductor has also been disclosed (see Patent Document 2). Since defects are generated only in a shallow range of about 1 mm from 1 mm, a large performance improvement cannot be expected in a pseudo permanent magnet having a large volume effect or a current lead whose performance is determined by critical current density × cross-sectional area.

JP 2009-280424 A (page 1-16, FIG. 1-4) Japanese Unexamined Patent Publication No. 64-33006 (page 14, FIGS. 32-33)

L. Civale, et al., Phys. Rev. Lett. 67 (1991) 648. T.Kii, et al., “VARIATION OF UNDULATOR FIELD IN BULK HTSC STAGGERED ARRAY UNDULATOR”, In Proceedings of Particle Accelerator Society Meeting 2009, pp.344-346

  The present invention has been made in view of the problems as described above, and the object thereof is to greatly improve the performance of a pseudo permanent magnet and the like by improving and controlling the critical current density of the entire bulk body. The method of controlling the critical current density of a bulk superconductor that can be implemented by an existing accelerator and that can improve the performance of the undulator by suppressing variations in the critical current density of a plurality of bulk bodies, and of the bulk superconductor for an undulator It is to provide a manufacturing method.

  Means adopted by the present inventor for solving the above-described problems will be described as follows.

That is, the present invention irradiates the entire bulk type II superconductor with a particle beam having a size that allows energy to pass through the bulk body and lower than the threshold value for generating columnar defects , or Prior to the irradiation, a critical energy density can be partially increased by intensively irradiating a part of the bulk body with a particle beam having a predetermined energy.

On the other hand, in the present invention, in the method for manufacturing a bulk superconductor installed in a plurality of undulators, the bulk of the second type superconductor is in a size that allows energy to pass through the bulk body, and Prior to or before irradiating the entire bulk body with a particle beam that is lower than the columnar defect generation threshold, focus the particle beam of a given energy on a part of the bulk body placed near the electron beam path of the undulator. The critical current density can also be partially increased by irradiation.

Furthermore, in the present invention, in order to further improve the performance of the undulator , the particle beam is focused on a portion from the outer peripheral surface of the bulk body arranged toward the electron beam path to a predetermined depth in the above means. Can do.

  In the present invention, by adopting a method of irradiating a particle beam that can be transmitted through the bulk body in the control and improvement of the critical current density of the bulk superconductor, the pinning center is set in the bulk body by a model as shown in FIG. Since it can be formed entirely, it is possible to greatly improve the performance of a pseudo permanent magnet in which a super permanent current flows through the whole and a magnetic field is generated, and a current lead through which a current flows.

  In the present invention, it is also possible to partially or intensively irradiate the bulk superconductor with the above particle beam to improve a part of the performance, and thereby to shape the bulk body where a certain material strength is required. The distribution of the magnetic flux density can be changed without performing it.

  Moreover, if the critical current density is controlled by irradiating the particle beam as described above, the variation in the critical current density between the plurality of bulk superconductors can be suppressed. Therefore, in an undulator using a plurality of superconductors. However, it is possible to improve the device performance by making the periodic alternating magnetic field distribution uniform.

  In addition, since the particle beam used in the present invention does not require such a large amount of energy that a columnar defect is generated, even when a bulk material having a certain thickness is targeted, an existing accelerator can sufficiently cope with it.

  Therefore, according to the present invention, it is possible to improve the performance of the bulk superconductor and its application products, and further, it is possible to expand the use of the bulk superconductor to application fields that require precise magnetic field generation. Since the method for controlling the critical current density of the conductor can be provided, the practical utility value of the present invention is very high.

It is comparison data of the maximum capture magnetic field in Example 1 of this invention. It is explanatory drawing showing the undulator using the bulk superconductor in Example 2 of this invention. It is explanatory drawing showing the production | generation model of the pinning center in this invention.

“Example 1”
First, Example 1 of the present invention will be described below. In Example 1, a proton beam is selected as the particle beam, and a semicircular bulk superconductor (composition: DyBa ₂ Cu ₃ O ₇ -δ) having a thickness of 2.5 mm and a diameter of 25.2 mm from an accelerator (synchrotron). The whole was irradiated with 200 MeV proton beam. The ambient temperature during irradiation was 25 ° C. (room temperature), and the irradiation particle density was 1.0 × 10 ¹² particles / cm ² .

The proton beam energy (200 MeV) is selected after confirming that it has a size that transmits several _centimeters of the bulk material having the same composition and does not generate columnar defects.

  And after irradiating the said proton beam, the bulk superconductor was cooled in liquid nitrogen and the maximum capture magnetic field was measured. As a result, it was observed that the maximum trapping magnetic field was improved from 0.11T to 0.19T as shown in FIG. This result means an improvement of 70% or more in terms of the critical current density at 77K.

  From the above results, not only can the critical current density of bulk superconductors be significantly improved by particle beam irradiation, but also precise control of the critical current density can be expected by adjusting the energy, intensity, and dose of the particle beam. .

“Example 2”
Next, Example 2 of the present invention will be described below. In Example 2, after irradiating the entire bulk superconductor with a proton beam as in Example 1, a particle beam is further applied to a part of the bulk body arranged near the electron beam path of the undulator shown in FIG. Irradiation partially improved the critical current density.

  Further, when the particle beam was intensively irradiated, beam irradiation was performed so that defects were generated from the outer peripheral surface of the bulk body to a portion having a depth of about 2 mm. As a result, the periodic magnetic fields of a plurality of bulk superconductors were made uniform, and the trapped magnetic field distribution of each bulk superconductor was optimized to improve the performance of the undulator.

  The present invention generally employs the above-described method, but is not limited to the above-described embodiments, and various modifications can be made within the description of “Claims”. For example, superconductor is irradiated. As the particle beam to be used, an electron beam other than a proton beam, a neutron beam, a heavy ion beam or the like can be adopted. In addition, regarding the bulk superconductor, other high-temperature superconductors and low-temperature superconductors can be targeted even if they are not REBaCuO-based superconductors.

  On the other hand, for the energy of the particle beam, the energy range that can be set varies depending on various conditions such as the type of particle beam and the density and composition of the bulk body. However, the energy can be any size as long as it can penetrate the bulk body and does not generate columnar defects. Can be set.

  On the other hand, partial irradiation of a particle beam is also effective when changing the generated magnetic field distribution without machining, or when injecting magnetic flux from an arbitrary place (low performance place) in the pulse magnetization method. May be performed before the whole irradiation, both of which belong to the technical scope of the present invention.

  In recent years, superconducting technology has become more important from the viewpoint of energy problems, and the development of technology that contributes to performance improvement is indispensable for practical use. In the staggered array undulator (Bulk HTSC Staggered Array Undulator) that controls the trajectory of an electron beam using a bulk superconductor, the control of the critical current density is an important issue for improving the device performance.

  Under such circumstances, the method for controlling the critical current density of the bulk superconductor and the method for manufacturing the bulk superconductor for the undulator of the present invention can greatly improve the performance of the pseudo permanent magnet and the current lead, and the period in the undulator. Since it is a useful technology that can overcome the problem of magnetic field variation, the industrial utility value is very high.

Claims (3)

Overall bulk of the two superconductors to, energy of permeable size of the bulk body, and, after irradiation with low particle beam than generating threshold columnar defects throughout the bulk body, or before irradiation In addition, a critical current density control method for a bulk superconductor characterized in that a critical current density is partially increased by intensively irradiating a part of the bulk body with a particle beam having a predetermined energy . In the manufacturing method of bulk superconductors installed side by side in the undulator, the bulk type II superconductor has a size that allows energy to pass through the bulk body and is less than the threshold for columnar defects. After irradiating a low particle beam or before irradiating, a part of the bulk body placed near the electron beam path of the undulator is focused on the particle beam of a predetermined energy, and partly critical current density A method for producing a bulk superconductor for an undulator, characterized in that 3. The method for producing a bulk superconductor for an undulator according to claim 2 , wherein the particle beam is intensively irradiated to a portion from the outer peripheral surface of the bulk body arranged toward the electron beam path of the undulator to a predetermined depth. .