COMPLETION OF THE FIRST SUPERCONDUCTING RFQ AT INFN-LNL

The construction of SRFQ2, the first built superconducting RFQ for the low velocity accelerator PIAVE (injector of the SC linac ALPI at INFN-Legnaro) was completed. It resonates at 80 MHz, it is made of full niobium and it is mechanically stiffened by a titanium jacket which is welded by electron beam welding on the tank. The cavity is about 0.8 m both in length and in diameter. After completion of the mechanical construction, the structure went under a number of experimental tests, which are reported in the paper, in order to check: voltage unbalance among the four quadrants through bead-pulling; vacuum tightness; frequency change under vacuum and additional external pressurization; frequency change between 300 and 77 K; frequency change given by stepwise chemical etching of the internal surface. The paper reports as well the most recent achievements obtained when the resonator was mounted into the cryostat, purpose-built to test it in the superconducting regime, and cooled down to the working temperature.