The superconducting niobium cavity has a plurality of openings that require a flange structure for vacuum or connection to other equipment. In order to enable the flange to be welded with the niobium tube of the superconducting niobium cavity, the flange material of the superconducting niobium cavity is titanium niobium material which can be directly welded with electron beam. And the hardness of niobium titanium itself is not high, flange gasket more choose the hardness than niobium titanium also low material processing. At present, gasket materials can be divided into two categories, magnesium aluminum alloy and indium wire, but also two different niobium titanium flange structure corresponding to it. Among them, the niobium titanium flange structure suitable for magnesium aluminum alloy ring is mostly the lower groove structure, which is used for fixing magnesium aluminum alloy ring; The flange structure suitable for the indium wire is usually a large flat surface to facilitate the removal of indium wire after use. These two flange structures cannot be used interchangeably.
At present, the biggest disadvantage of niobium titanium flange structure using magnesium aluminum alloy gasket is the low success rate of vacuum seal, which cannot guarantee the high vacuum degree.
The sealing surface of the flange shall be smooth to maintain a vacuum in close contact with the magnesium aluminum alloy gasket. The superconducting cavity will undergo many other surface treatments before testing, and the niobium titanium material is very soft and can easily scratch the sealing surface of the flange. The vacuum degree of the superconducting cavity is not high due to minor scratches, and the vacuum cannot be sealed directly due to serious scratches.
The biggest defect of niobium titanium flange sealed with indium wire is the huge amount of work required to clean indium wire during disassembly.
Indium wire is soft, similar to chewing gum. Indium wire squashed after use is difficult to remove from the flange plane. Since the flange is a planar structure, it is easy to bring the indium wire into the superconducting cavity when removing the used indium wire, thus making the cavity unusable.
