Superconducting RFQs

At INFN-Legnaro the heavy ion injector PIAVE, based on two superconducting RFQ and eight quarter wave resonators (QWR), is at an advanced stage of beam commissioning. The RFQs (SRFQ1 and SRFQ2), built in full Nb within a stiffening Ti jacket, are 0.8 m in diameter and 1.4 and 0.8 m long respectively, with a resonant frequency of 80 MHz. The PIAVE beam is bunched by a normal conducting 3-harmonic buncher upstream the SRFQs. The SRFQs are specified to work at a peak surface field of 25.5 MV/m, a value which was exceeded in the test phase and has been recently confirmed in on-line tests. Phase and amplitude locking, versus both microphonics and pressure variations of the liquid helium bath, is the main issue. Since November 2004, the two SRFQs have been used quite extensively, for beam acceleration tests in PIAVE, showing a high degree of reliability. A 16O3+ pilot beam, received from an ECR ion source located on a high voltage platform, was used in the tests. The typical ion beam current was a few hundreds nA, even though it could be raised up to a few μA without any inconveniences. Beam tests with 132Xe18+ were made too. The paper reports the more recent results of on-line SRFQ tests and beam operation.