With the development of basic research and applied research of nuclear physics, the construction of high energy and high current accelerator has become a research hotspot in particle accelerator field. Due to the excessive resistance loss of oxygen-free copper, the traditional copper RF cavity can not operate under high gradient and high duty ratio, which limits the improvement of accelerator energy. In the liquid helium environment (2K or 4K), niobium metal is in a superconducting state, and its surface resistance is 10-5 times that of oxygen-free copper, so the RF cavity fabricated by niobium metal can operate stably under high acceleration gradient and high occupancy ratio, thus greatly improving the accelerator energy.
The processing technology of the superconducting cavity requires that the superconducting cavity is composed of a high-purity niobium plate with an RRR value greater than 300 (resistivity ratio under 300K environment to that under 4K environment) and a high-purity niobium tube with an RRR value greater than 300. The production of niobium materials with a high RRR value has a more complex production process than that of ordinary niobium plates, resulting in a higher cost (4200 yuan per kg). Therefore, the reduction of the production cost of high purity niobium material can reduce the construction cost of the accelerator.
In the existing technology, the high purity niobium tube at home and abroad is realized by the high purity niobium rod machine and the high purity niobium plate coil. The disadvantage of the high purity niobium rod machine is that a large amount of niobium material is wasted, which leads to high production cost. The disadvantages of high purity niobium plate winding are the existence of weld and large roundness tolerance, which leads to low machining accuracy of cavity. Therefore, it is of great practical significance to develop a new preparation method of high purity niobium tube which can not only reduce the production cost of niobium tube but also improve the machining precision of the cavity.
The objective is to provide a fabrication method of high purity niobium tube for multiple stretch forming. This method can not only ensure the excellent superconductivity of high purity niobium tube and reduce the cost, but also provide a feasible technical route for the acceleration structure selection of China's accelerator large science equipment.
