6 GHz cavities: a method to test A15 intermetallic compounds rf properties

We needed a fast, easy and performing way to produce and measure A15 superconducting resonators. The idea is to build micro-cavities completely equal in shape to the real scale model. 6 GHz resonators can become our cavity shaped samples. Since the International Committee for Future Accelerators recommended that the Linear Collider design has to be based on the superconducting technology, the scientifc world interest is now focused on further developments of new resonant cavities fabrication techniques and cost reduction. It is important to pursue research on new materials: the goal will be the achievement of superconducting cavities working better than the Nb ones at 4.2 K. For superconducting alloys and compounds, at a given operating temperature, the best rf performances (low surface resistance and ?, high relevant critical fields) are obtained for high Tc and low ?n materials. Among the possible candidates, A15 compounds appear to be the most promising. Two of them were chosen: V3Si that has a really high RRR value and Nb3Sn that is the only A15 material already used for a resonant accelerating structure. The process parameters optimization necessary to improve the A15 phase superconducting properties, crystal structure and morphology is going on through the small samples production: this is fundamental but still not enough. We are perfectly aware that having satisfactory results with A15 samples, doesn't mean obtaining good superconducting cavities with ease. That's why we decided to look for the best way to overcome this problem. Our solution is to work directly with cavities. Obviously it would be foolish to use 1.5 GHz resonant structures: it would be too onerous both for the material cost and the cryogenic expense. The idea is to build 6 GHz cavities. They are made from larger cavities fabrication remaining material, they don't need welding (even for flanges) and they can be directly measured inside a liquid helium dewar. Finally it is possible to perform more than one rf test per day. We can check the A15 production experimental procedure directly on a small resonator without modifying the apparatus and shortly verify its quality.