Quench Protection Studies on CBA Magnets

Results from quench studies on both short cable samples and prototype Colliding Beam Accelerator project magnets are presented. The quantity of paramount interest is ¿I2dt which is a monotonic function of the maximum conductor temperature obtained in a quench. Conductor damage in short samples has been observed for ¿I2dt ¿ 8.4 × 106 amp2-sec at 50 kG and 4.2° K. Each magnet is equipped with spot heaters in various locations so that systematic studies of quench propagation under controlled conditions can be made. Values of ¿I2dt as a function of current, location, bath temperature, and cooling mode (single phase helium versus two phase helium) are presented. The magnets are able to absorb their own energy with a modest margin of safety for the type of quenches expected in an accelerator environment. In order to obtain an additional margin of safety, a quench protection scheme which employs current shunting diodes across each magnet half has been adopted.