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.