| Summary: | 碩士 === 國立清華大學 === 先進光源科技學位學程 === 104 === Insertion device (ID) is the key devices in the facilities of synchrotron radiation and free electron laser. In order to enhance the brightness of synchrotron radiation and minimize the size of accelerator facilities, the development of a short-period undulator with strong magnetic field was launched. For this purpose, we used high-temperature superconducting (HTS) YBCO bulks with diameter of 32 mm and thickness of 2.5 mm as the magnet pole to generate a strong periodic magnetic field in the longitudinal axis.
The HTS bulks were constructed and assembled as the staggered undulator that the period length and magnet gap were 5 mm and 4 mm, respectively. So as to obtain the trapped magnetic field, the staggered undulator with HTS bulks was magnetized at 77 K and 7 K in a 3.5 T solenoid system. The peak field of this HTS bulk staggered undulator is obtained around 0.015 T and 0.3 T at 77 K and 7 K, respectively. Meanwhile, both field cool (FC) and zero field cool (ZFC) were used to analyze properties of trapped magnetic field and uniform field of magnetized HTS bulk staggered undulator (HTSBSU). For low-temperature environment, we used SolidWorks to design a new cryogen-free system which cooled down the HTS bulks to 7 K by cryocooler.
In order to optimize the HTSBSU to let the first field integral (i.e. electron angle) and the second field integral (electron position) be zero, we needed to obtain the exact magnet field strength and the field distribution. Therefore, it was necessary to develop a simulation code to find out the trapped field strength and the field distribution of the HTSBSU magnet. Meanwhile, this simulation code was also used to optimize the end pole configuration and to maximize the homogeneity field range. So, we use the energy minimization method (EM Method) which based on Bean’s model theory to simulate the trapped field on the HTS bulks. This simulation code was developed through the application program of Mathematica and Radia. Consequently, this simulation code was applied to calculate the distribution of induced current density on the bulk array and then to simulate not only the longitudinal periodic fielddistribution, but the magnetic field strength.
In the end, the key to successful construction of HTSBSU is the uniformity of all HTS bulks. If the field homogeneity of all HTS bulks is not good enough, we have to find a solution to solve the issue of non-uniform trapped field. If the quality of all HTS bulks is different, the field-cooled is selected for the magnetized method and bulks are maintained at unsaturated state, then it is able to reduce the effect from the non-uniformity of each HTS bulks. Consequently, there is opportunity to get better homogenous trapped magnetic field on each bulk and good period field in the longitudinal axis.
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