Testing of the SNS Superconducting Cavities and Cryomodules

The superconducting linac for the Spallation Neutron Source is in the process of being commissioned. Eightyone niobium cavities resonating at 805 MHz are being installed in the SNS tunnel in 11 medium beta (. 61) cryomodules each containing 3 cavities and 12 high beta (. 81) cryomodules each with 4 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, 70 of the 81 cavities have been tested, mostly in open loop at 10 pulses per second and at a full pulse length of 1.3 msec. The results indicate that high gradients can be reached even at 4.2 K (average value of 17.8 MV/m) and that operation of the superconducting linac at that temperature may be possible.

INTRODUCTION

The Spallation Neutron Source will start producing neutrons for materials science research in less than a year [1]. A central feature of the accelerator, designed to generate the 1 GeV protons for the spallation process, is the superconducting part of the H⁻ linac. This section of the accelerator will accelerate the H ions from 187 MeV up to 1 GeV with two types of superconducting cavities, matched to and. 81 respectively. The use of superconducting elliptical cavities for particles at makes this accelerator a very important prototype for learning operating conditions of this type of cavities. Another important aspect of the superconducting linac is the fact that it is operated under pulsed conditions, for which only the Tesla Test Facility at DESY has extensive experience for electron acceleration [2].