ION SWITCH FOR EXCITING AN ACCELERATOR ELECTROMAGNET WITH UNIPOLAR PULSES

V. A. KONEGUROV, V. M. KUZNETSOV, I. P. CHUCHALIN

For pulsed excitation of an accelerator electromagnet, the discharge of a capacitor bank is widely used [1–6]. In order to reduce the power consumed, the capacitors are usually recharged either through the electromagnet [1] or through an additional choke [2]. In both cases, the discharge circuit has additional energy losses associated with recharging the capacitors, since no particle acceleration occurs during the recharge.

In a betatron with an accelerated-electron energy of 80 MeV and pulsed excitation of the electromagnet [3], the polarity of the capacitor bank is switched after each discharge cycle by means of a mechanical switch, with the intention of using both the discharge and recharge cycles for acceleration. However, at high pulse-excitation frequencies of the electromagnet, mechanical switching presents considerable difficulties and is sometimes entirely impracticable.

Fig. 1.

In the present article a more advanced ion switch is proposed for unipolar pulsed excitation of an accelerator electromagnet.

The idea of the ion switch is very simple. The capacitor bank \(C\) (Fig. 1) is charged from controlled rectifier 1 to a positive voltage \(+U_c\). Then, through the switching devices

$L_1$ and $L_2$, during the interval $t_1—t_2$ the battery is discharged into the electromagnet $L$ and is recharged to the voltage $-k U_c$, where $k$ is a coefficient that takes account of losses in the circuit. Rectifier 2 during the time $t_2—t_3$ tops up the capacitors to the voltage $-U_c$.

After the recharging and top-up charging of the capacitor battery, during the interval $t_3—t_4$ it is again discharged into the electromagnet through the devices $L_3$ and $L_4$ to the voltage $+kU_c$. Subsequently the battery is again topped up from rectifier 1, the capacitors are discharged through $L_1$ and $L_2$, and so on. In this way, current pulses of one polarity are excited in the winding of the electromagnet $L$.

The use of an ion switch leads to a certain complication of the electromagnet power-supply circuit in comparison with the circuits [1, 2, 4–6].

First, the number of switching devices is doubled. However, the operating conditions of these devices in the present circuit are considerably eased owing to the halving of the anode voltage on each device. Second, the control circuit of the rectifier, which must top up the capacitors alternately with voltages of different polarity, becomes somewhat more complicated. But, along with the indicated disadvantages, the ion switch makes it possible to use both half-waves of the current for accelerating particles, both the discharge and the recharge half-wave, i.e., to double the number of acceleration cycles, which in turn doubles the average radiation intensity of the accelerator at the same power consumption.

The schematic diagram of the rectifiers for the case of three-phase full-wave rectification has the form shown in Fig. 2, where the valves of the direct bridge charge the capacitor battery to a positive voltage, while the valves of the reverse bridge charge it to a negative voltage.

Fig. 2.

The proposed circuit for obtaining unipolar current pulses is suitable not only for exciting accelerator electromagnets, but may also find application in other physical installations where the creation of unidirectional pulsed magnetic fields is required.

References

1. Getting J. A. Engineer, 191, No. 4967, 440, 1951.

2. Jones W. B., Kratz H. R., Lawson J. L., Miller D. H., Miller R. D., Ragan G. L., Rouvina J. and Voorhies H. C., R.S.I., 26, No. 9, 809, 1955.

3. Kerst D. W., Adams G. D., Koch H. W. and Robinson G. S., R.S.I., 22, 462, 1950.

4. McFarlane W., Barden S. E. and Oldroyd D. L., Nature, 176, No. 4484, 666, 1955.

5. Goward F. K., Lawson J. D., Wilkins J. J. and Carruthers, Proc. of the Inst. El. Eng., 97, No. 108, 329, 1950.

6. Grauer C. T., El. Eng., 72, 212, 1953.