Pulsed Excitation System for a 300 MeV Synchrotron Electromagnet
Abstract Generated abstract
This paper describes the pulsed power supply and electronic control system for the electromagnet of a 300 MeV synchrotron. The system uses a controlled thyratron rectifier, a 1770 microfarad capacitor bank charged to 8.7 kV, switching thyratrons, capacitor recharging through the magnet windings, and a saturable reactor to shape the magnetic field pulse and reduce the field rise rate during injection. The authors outline the timing and circuitry for rectifier blocking, delayed thyratron firing, phase control, and stabilization of the capacitor charging voltage, reporting voltage stability no worse than 0.3 percent. They also analyze transient overvoltages in the discharge circuit and describe the use of a parallel damping resistance to reduce voltage stress on the electromagnet.
Full Text
PULSED EXCITATION SYSTEM FOR THE ELECTROMAGNET OF A 300 MeV SYNCHROTRON
I. A. Gabrusenko, V. A. Kocheturov, V. M. Kuznetsov, A. A. Tereshchenko
I. P. Chuchalin
Figure 1 shows the schematic diagram of the pulsed power supply of the synchrotron electromagnet. The circuit includes a three-phase transformer TM 50/10, a controlled thyratron rectifier assembled according to the Larionov circuit, a storage capacitor bank with a capacitance of 1770 μF, TP1-85/15 switching thyratrons, and also an electronic control system. The circuit operates as follows. The storage capacitors of the controlled rectifier are charged to a voltage of 8.7 kV. After this the rectifier is locked, and a firing pulse is applied to the grid of the switching thyratron. The thyratron opens and the capacitor bank discharges into the electromagnet. In this process, a sinusoidal magnetic-field pulse with an amplitude of 10,700 gauss and a duration of 63 μs is excited in the gap of the electromagnet. To reduce the power drawn from the mains, recharging of the capacitors through the electromagnet windings is used [1]. Periodic supplemental charging of the capacitors is carried out in the interval between discharge pulses.
To reduce the rate of rise of the magnetic field during the injection period to 180 kG/s, a saturable reactor is connected in series with the electromagnet [2]. Figure 2 shows the current and voltage curves in the power-supply circuit of the synchrotron electromagnet.
The reliability of operation of the synchrotron pulsed power-supply system depends largely on the precision of operation of the electronic control circuits. The control circuits must be simple and reliable in operation.
The complete electronic control circuit of the power-supply system includes:
1) control of the switching devices of the discharge circuit;
2) control of the operation of the rectifier.
Figure 3 presents a block diagram of the electronic control and shows the timing of the control pulses.
The circuit operates as follows. The rectifier control circuit keeps it open; during this time the capacitors are charged. When a pulse from master oscillator 1, synchronized with the mains, is applied to shaping circuit 2, the latter produces a negative pulse that locks the rectifier. The duration of the negative pulse is chosen to be somewhat greater than the time of discharge and recharge of the capacitor banks. Simultaneously with the triggering of the negative-pulse shaping circuit, circuit 3 is triggered, provid-
Fig. 1.
Visible labels in the circuit diagram:
- From starting transformer TM 60/10
- Tr 1-15/15
- \(R_c\)
- \(-U_c\)
- From the electrical control circuit
- \(500\,\mathrm{m}\)
- \(150\,\mathrm{m}\)
- \(C\)
- \(L_{\mathrm{em}}\), \(1000\,\mathrm{m}\)
- \(L_{\mathrm{nd}}\)
- Electrical control circuit
- To the rectifier grids
- To the grid of the commutating thyratron
- Tr 1-85/15
- \(R_c\)
- \(-U_c\)
- From the electrical control circuit
providing the delay of the pulse fed to the firing circuit of the switching thyratron TR1-85/15. The delay time is determined by the time required for complete blocking of the rectifier from the moment a negative pulse is applied to the grids of its tubes, and is equal to 10 μsec.
Figure annotations: \(U_{\mathrm{em}}\), \(i_{\mathrm{em}}\), \(q = 0.63\ \mathrm{cm}\), \(U_c\), \(i_{\mathrm{ch}}\), 10 μsec.
Fig. 2
Figure annotations: master generator; shaping circuit; rectifier system; to the rectifier grids; delay circuit; firing circuit; to the grid of TR 85/15; 0.2 sec; 10 μsec.
Fig. 3
In Fig. 4 a schematic circuit diagram is given for the electronic control of the power-supply system of the 300 MeV synchrotron.
The master generator is made in the form of series-connected trigger cells, which provide division of the mains frequency by a factor of 64. The stage for shaping the negative pulse that blocks the rectifier is assembled on tubes L\(_1\)—L\(_4\) and includes a phantastron
\((L_1—L_2)\) and three amplifiers \((L_3—L_4)\). Tubes \(L_9—L_{11}\) form the firing pulses for the rectifier. The mean voltage of the rectifier is regulated by shifting a series of firing pulses by the phase regulator.
Delay circuit 3 is assembled on tubes \(L_7\) (a blocked multivibrator) and \(L_8\) (an amplifier).
A circuit assembled on the thyratron TG1-2.5/4 forms the firing pulses of the switching thyratron.
To stabilize the charging voltage on the capacitor bank, a differential amplifier \((L_5)\), a trigger \((L_6)\), and a reference-voltage source are introduced into the electronic control circuit of the rectifier. Part of the voltage from the capacitor banks is applied to the input of the differential amplifier and compared with the reference voltage. At the moment when the value of the input voltage is close to the reference voltage, the trigger \((L_6)\) switches over; the voltage from its anode is applied to amplifier \(L_3\). In this case, regardless of the state of the phantastron, tube \(L_3\) is cut off and, correspondingly, tubes \(L_9—L_{11}\), which form the firing pulses of the rectifier, are cut off. Thus the charging of the capacitors ceases. The circuit ensures stability of the capacitor charging voltage no worse than \(0.3\%\).
Fig. 5
Since the supply of the electromagnet is pulsed, transient processes naturally occur in the circuit; in the present case these are especially dangerous because of their comparatively frequent repetition.
The capacitor-discharge circuit into the electromagnet can be represented in the form of the equivalent circuit (Fig. 5), where
\(L_{\rm em}\) is the inductance of the electromagnet;
\(L_k\) is the equivalent capacitance of the lead-in cable;
\(R_k\) is the active resistance of the lead-in cable.
At the initial stage of discharge of capacitance \(C\), the conductivity of the electromagnet inductance may be neglected. Then the transient values of the voltage and current in the circuit are determined by:
\[ U' = U_m - \frac{U_m}{\omega_0\sqrt{L_k C_k}} e^{-bt}\sin(\omega_0 t+\chi), \]
\[ I' = \frac{U_m}{\omega_0 L_k} e^{bt}\sin\omega_0 t, \]
where
\[ \omega_0=\sqrt{\frac{1}{L_k C_k}-\frac{R_k^2}{4L_k^2}},\qquad b=\frac{R_k}{2L_k},\qquad \tg\chi=\frac{\omega_0}{b}. \]
The voltage \(U'\) oscillates about its forced value with frequency \(\omega_0\) and reaches almost twice the value approximately half a period after switching on. To reduce the transient voltage on the electromagnet, an active resistance \(R=1600\ \Omega\) is connected in parallel with the electromagnet windings.
REFERENCES
- V. A. Kochegurov. Dissertation, TPI, 1960.
- V. A. Kochegurov. Izv. vuzov, “Fizika,” 1, 1957.
Fig. 4.
Visible inscriptions in the schematic:
- Mains, \(\sim 0.3\ \mathrm{V}\)
- \(-150\ \mathrm{V}\)
- \(+200\ \mathrm{V}\)
- \(200\ \mathrm{V}\)
- \(150\ \mathrm{V}\)
- \(6.4\ \mathrm{V}\)
- \(A\)
- H.F.
- Output \(F\)
- MR
- To the grids of the F.D. rectifier
- H.F.
- SHR
- Strobe input
- Control rectifier
Visible tube and component designations include: \(T_1\)--\(T_{14}\), \(P_1\)--\(P_{16}\), 6N8S, 6P3S, GM-4S, 6Ts5S, and the resistance/capacitance values shown in the circuit.