Energy control system for electrons accelerated in a betatron based on deflection
Abstract Generated abstract
The paper addresses the problem of controlling the energy of electrons accelerated in a betatron when direct measurement at the end of acceleration, or simple accurate measurement of maximum bremsstrahlung energy, is not practically available. It proposes an indirect deflection-based control scheme in which the voltage from turns in the working zone is integrated from the zero magnetic-field point until a radiation pulse marks electron dumping, so that the resulting signal is proportional to the electron energy at the dumping moment and can be compared with a reference value to adjust the displacement phase in the next acceleration cycle. The authors argue that this approach accounts for the finite and potentially unstable dumping process better than conventional phase-control methods, while noting that true deviation-based energy regulation would require direct bremsstrahlung-energy sensors that were not yet practically available.
Full Text
Proceedings of the Tomsk Order of the Red Banner of Labor Polytechnic Institute named after S. M. Kirov
Vol. 156 1969
Energy Control System for Electrons Accelerated in a Betatron by Deflection
A. A. Vorob'ev, V. M. Razin
At present there are no practical methods for directly measuring the energy of electrons at the end of the betatron acceleration process. For measuring the maximum energy of bremsstrahlung after the accelerated electrons are dumped onto a target, there are likewise no sufficiently simple and accurate sensors. Here, apparently, the so-called gamma quantometers considered in works [1, 2] may prove promising. In view of the circumstances indicated above, the methods that have found the greatest practical application are indirect methods of measuring energy by integrating the voltage from windings located in the working zone or on the yoke of the betatron electromagnet. Existing methods for controlling the displacement phase have the disadvantage that they do not in any way take into account the dumping process itself, which does not occur instantaneously, but over a finite interval of time. Instabilities of the dumping process itself are not taken into account in this case, and this leads to the appearance of additional errors in energy control.
Since it does not appear possible to measure, even indirectly, the energy of the electrons at the moment of dumping, these measurements should be made in the preceding acceleration cycle and, on the basis of the results of these measurements, energy control should be carried out in the subsequent acceleration cycle. In this case the control is obtained with an inevitable delay of at least one period of the mains alternating voltage. The operating principle of a control system based on deflection with indirect energy measurement can be clarified with the aid of the block diagram of Fig. 1. In this diagram the betatron $B$ has a zero magnetic-field sensor $D_1$, turns $V$ in the working zone, and a radiation sensor $D_2$ (pulse-type). A photomultiplier or a pulse ionization chamber with an electron collector may be used as the pulse-radiation sensor.
The system operates as follows. At the moment when the magnetic field passes through zero at the beginning of the acceleration cycle, the time sensor $D_1$ is triggered and unlocks the switching element $K_1$, through which the voltage from the turns in the working zone begins to be supplied to the integrator $K_2$. At the moment when the displacement circuit $SS$ is triggered, a radiation pulse is generated. This pulse is recorded by the sensor $D_2$ and, through a shaper, acts on the switching element $K_2$, locking it. Locking should occur somewhere in the middle part of the radiation pulse, when its magnitude reaches a maximum. From the output
during the operation of the element, the integrated voltage, proportional to the energy of the accelerated electrons precisely at the moment of dumping, is fed to the comparison circuit \(C\), where it is compared with the specified reference voltage \(E^\circ\). The mismatch signal is amplified and shaped in the shaping amplifier \(U\Phi\) and is subsequently used to control the displacement phase in the displacement circuit \(CC\).
Fig. 1. Block diagram of the control of the betatron radiation energy
We note that, with the proper choice of the parameters of the integrating circuit and provided that these parameters and the parameters of the equivalent circuit of the betatron electromagnet are highly stable, the sensor \(D\) and the switching element \(K_1\) can be excluded from the system, since at any moment in time and for any laws of variation of the line voltage the signal at the output of the integrator will be proportional to the magnetizing current and, accordingly, to the magnetic induction on the equilibrium orbit.
The idea of such a method of regulation was first considered, as far as we know, in work [3]. It is also indicated there that positive results were obtained in an experiment with such a system. Undoubtedly, only direct methods of measuring the maximum energy of the bremsstrahlung radiation of a betatron make it possible to create systems for regulating the energy by deviations in the direct sense of this term.
Practical attempts in this direction have not yet been made because of the absence of the sensors required for this purpose.
REFERENCES
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