  A new approach for selection of Silicon-Controlled Rectifier (SCR) for
switching high pulsed currents in the septum magnet power supply is described.
In this approach, an attempt is made to select the SCR from its I2t rating
given in data sheet. For this, a factor which we have called I2t derating
factor is defined as the ratio of I2t rating of SCR to the I2t value of current
pulse to be switched. Thus, the SCR to be used in power supply is selected from
its I2t derating factor. Three different experiments were performed using SCR
of different manufacturers, to estimate the value of I2t derating factors. In
these experiments, the SCR was subjected to maximum thermal stress till SCR
started showing degradation. The forward blocking voltage and the leakage
current are the parameters used for characterizing the SCR before and after the
stress. The results of these experiments are presented and discussed. This
approach will be of great help when pulse rating of SCR, like, transient
thermal impedance is not available. Finally, a method is presented which can
contribute to design low-cost and high-reliability septum magnet power supply.
