Status of the spallation neutron source

The superconducting linac for the spallation neutron source is being commissioned. Seventy seven of the 81 niobium cavities resonating at 805 MHz have been installed in the SNS tunnel in 11 medium beta (0.61) cryomodules each containing three cavities and 11 (presently) high beta (0.81) cryomodules each with four cavities. The niobium cavities and cryomodules were designed and assembled at Jefferson Lab to operate at 2.1 K. The central helium liquefier has been tested to 2.1 K but is routinely operated at 4.2 K. At this temperature, all but four cavities have been tested, mostly at 10 pulses per second and at a full pulse length of 1.3 ms. Shorter periods of operation at 2.1 K have also been implemented, with results similar to those at 4.2 K. Beam commissioning is under way and operation with beam at both temperatures has been demonstrated. Negative hydrogen ion energies of 865 and 907 MeV have been reached at 4.2 and 2.1 K respectively, even with a few cavities not being operated. Further beam commissioning is under way.