JPS6056391B2 - High voltage pulse generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a high-power magnetron used as a power source for a high-power magnetron of a medical linear particle accelerator, for example.

This invention relates to a voltage pulse generator. As is well known, medical linear particle accelerators accelerate charged particles (electrons) on microwave waves to obtain radiation such as high-energy electron beams and X-rays, and irradiate patients with this radiation to treat cancer, etc. This is one of the so-called radiation therapy equipment that treats.

In this type of device, high-energy microwaves are required to accelerate charged particles to near the speed of light, so a high-power magnetron is generally used as the microwave generator.

As the power supply supplied to this magnetron, a high voltage pulse power supply with an extremely short pulse width and high duty is required, so a line type pulse generator (line type pulse generator) as shown in Fig. 1 is generally used. A high-voltage pulse generator is used. That is, a DC power source, for example, IOKV, which is obtained by rectifying and smoothing an AC voltage that has been appropriately stepped up through a transformer (not shown), is connected to a pulse forming circuit PFN, which will be described later, through a resonant inductance Lo and a reverse current blocking diode Do. Charge all capacitors Co.

Thereafter, the pulse forming circuit PFN is activated by igniting the thyratron TT via a trigger pulse source (not shown).
is discharged, and a pulse with an extremely short pulse width of, for example, 2 μs as shown in FIG. 2A is generated in the pulse transformer PT, and the magnetron M is
supplied to T. When the capacitor Co of the pulse forming circuit PFN finishes discharging, the thyratron Π is instantly extinguished due to the phenomenon described later, but at this time, a series resonant circuit is formed by the inductor resistance and the capacitor Co, and the frequency F0=1/ Resonance occurs at 2π/LoCo (H2), and the capacitor Co is charged with a charging current 10 that draws a resonance curve as shown in FIG. 2B, and a charging force as shown in FIG. It attempts to be charged to twice the voltage (2E).

As this charging progresses, the voltage detected via the bleeder resistors R, R2 increases, and when the voltage corresponding to the charging voltage reaches the charging set voltage Vs, the comparator CM outputs the charging and disconnection thyristor SCR. A trigger pulse as shown in Fig. 2D is supplied to the gate terminal of the thyristor SCR.
fires. As a result, the energy stored in the resonance inductance LO flows through the secondary coil Ls as a secondary current 1S as shown in FIG. , is consumed by the resistor Rs. Therefore, the Q of the inductance LO (Q
ualtyfactOr) value is reduced all at once, the resonance due to fat CO stops, and the current charge voltage is held in the capacitor CO by the diode DO, and the voltage of the capacitor CO is shown in Fig. 2C. It is stabilized as follows. In this case, the thyratron T
There has been a problem in that T commutation failure is likely to occur, and a phenomenon of continuous energization, that is, a short-circuited high-voltage power supply, causing an overcurrent to flow and tripping a breaker in a backup circuit (not shown) frequently occurs.

That is, normally the thyratron TT is fired, the capacitor CO of the pulse forming circuit PFN is discharged, and the magnetron M
After a pulse I as shown in FIG. 2A is supplied to the thyratron TT, a reverse bias voltage similar to a reflected wave due to the leakage inductance of the pulse transformer PT is applied to the thyratron TT, and the arc is automatically extinguished.

On the other hand, at the same time that thyratron TT starts conducting, capacitor C
Charging starts at O, but at this point the charging current value is regulated by the inductance and is small until it overcomes the reverse bias applied to the thyratron TT and maintains the conductive state of the thyratron TT. Therefore, the arc of the thyratron TT is surely extinguished. However, as the set value of the charging voltage is lowered, the point at which the charging current 10 to the capacitor CO is cut off by the firing of the thyristor SCR, that is, the point in FIG. 2B becomes large. Therefore, the secondary current 1s also becomes large.

As shown in Figure 2E, the secondary current 1s gradually decreases, drawing a discharge force determined by the time constant of the coil Ls and the resistor Rs, but it remains until the conductive operation of the thyratron TT. Therefore, when the secondary current h becomes large, the secondary current 1s as shown in H in FIG. 2E during the conduction operation also becomes large. As a result, the impedance of the resonant inductance b becomes equivalently very small, so that the charging current b as shown in Figure 2 B when charging starts to the capacitor CO after ignition of the thyratron ■ is generated. This inrush current becomes a transiently flowing inrush current, and this inrush current becomes the extinction current of the thyratron TT.It overcomes the aforementioned reverse bias, prevents the commutation of the thyratron, and causes a continuous conduction state. Become. Therefore, when the set value of the charging voltage is low, the value of the current consumption resistor Rs in the secondary circuit of the inductance b is increased, and when the secondary current 1s discharges when the thyristor SCR is fired, It is conceivable to shorten the constant so that the tail does not remain until the next ignition of the thyratron ■, but in that case, the rate at which the inductance LO(7)Q value is reduced will decrease, and the This has the drawback that the charging current 10 becomes more gradual and the stability of the charging pressure becomes worse.
The present invention has been made in view of the above circumstances, and is a high voltage pulse generator that ensures commutation of the thyratron even if the set value of the charging voltage to the capacitor is low. The purpose is to provide

An embodiment of the configuration of a high voltage pulse generator according to the present invention will be described below with reference to FIG. Note that the same parts as in FIG. 1 are given the same reference numerals. That is, DC is a high-voltage direct current power supply, which is composed of a rectifier DH to which an alternating current power supply AC is connected to the input side, and a smoothing inductance IL and a smoothing capacitor C connected to the output side of the rectifier DH.

The positive terminal of this DC current PC is the resonant inductance LO
At one end of each, the negative terminal is connected to ground.
One end of the inductance LO is connected to the ground through the bleeder resistor 11/LRl, R2 for detecting charging pressure, and
Pulse forming circuit P via reverse current blocking diode DO
Connected to one end of FN. Further, a thyratron TT whose grid is connected to a trigger pulse generator (not shown) is connected in the forward direction between the cathode of the diode DO and the ground. A primary winding of a pulse transformer PT is connected between the pulse forming circuit PFN and ground, and a magnetron MT is connected to a secondary winding of the pulse transformer PT. The pulse forming circuit PFN is a line charging type pulse generator.
In principle, by charging a coaxial cable with a DC voltage through a charging impedance (inductance LO), a signal voltage is transmitted between the inner and outer conductors of the coaxial cable when it is discharged, and the pulse width is determined by the length of the coaxial cable. The device generates a pulse voltage having a value of 0.2, and is actually composed of a coil and a number of capacitors, but during charging, the entire charging capacity is expressed as the capacitor CO.

CO is a charging current or disconnection circuit for reducing the Q value of the resonant inductance LO (7) and, as a result, cutting off the charging current to the capacitor CO. The following circuit consists of a coil Ls, a gate turn-off thyristor GTO (hereinafter simply referred to as GTO) connected in the forward direction between one end of the coil h and the ground, and a gate turn-off thyristor GTO (hereinafter simply referred to as GTO) connected between the other end of the coil Ls and the ground. It is composed of a secondary current consumption resistor Rs. As is well known, the GTO is a thyristor that fires when a positive pulse voltage is applied to its gate terminal and then extinguishes when a negative pulse voltage is applied. The CC is a charging voltage control circuit consisting of a charging voltage setting circuit for the capacitor CO and a gate control circuit for the GTO, and has the following configuration.

That is, the inverting input terminal is connected to the junction point of the bleeder resistors Rl and R2 for detecting the charging voltage. and input resistor R4
The non-inverting input terminal is connected to the variable resistor VR for setting the conduction time of the GTO, and its output terminal is connected to the positive feedback capacitor. It is connected to the non-inverting input terminal via C1 and to the base of the transistor Trl via a base resistor R5. The transistor Trl is a first GTO gate driving transistor, and its collector is connected to the base of the second GTO gate driving transistor Tr2, and its emitter is connected to the base via a protection diode D1 and is grounded. transistor T
The collector of r2 is connected to the DC power supply +Vc for supplying the gate voltage of the GTO via the collector resistor R6, the base resistor R7 is connected between the collector and the base, the protective diode D2 is connected between the emitter and the base, and the emitter is connected to the DC power supply +Vc for supplying the gate voltage of the GTO. It is connected to the gate terminal of the GTO via a gate current limiting resistor R8 and a gate driving capacitor C2. Next, the operation of the above configuration will be explained with reference to FIG. 4. First, for convenience of explanation, the capacitor C of the pulse forming circuit PFN will be described.

The operation will be explained from the point in time when the thyratron TT is charged to a predetermined voltage and then discharged once by ignition of the thyratron TT, and a pulse as shown in FIG. 4A is supplied to the magnetron MT. That is, when the thyratron TT is ignited, a DC power supply DC of, for example, 10 KV, which is obtained by rectifying the AC power supply AC which has been appropriately stepped up by a power transformer (not shown) by a rectifier DH and smoothing it by an inductance L and a capacitor C, is supplied to the inductance LO. Due to the resonant current 10 as shown in FIG. 4B of the capacitor CO and the capacitor CO, charging is started through the diode DO toward twice the voltage (20 KV) as shown in FIG. 4C. On the other hand, a voltage corresponding to the charging voltage is generated via the bleeder resistors Rl and R2. via amplifier AP
Appears at the inverting input terminal of the DC power supply for setting the charging voltage.
■When the absolute value becomes larger than S, the output of the amplifier Oki is reversed from positive to negative. As a result, the transistor Trl, which had been conductive until then, becomes non-conductive, and conversely, the transistor Tr2, which had been non-conductive, becomes conductive, so that it is connected to the GTO gate terminal via the resistor R8 and the capacitor C2, as indicated by the symbol N in FIG. 4D. A positive pulse voltage such as this is applied, and the GTO is ignited. The energy accumulated in the inductance b due to the ignition of the GTO is transferred through the coil and the resistor Rs to E in Fig. 4.
The secondary current flows as a secondary current 1s as shown in FIG. the result,
The Q value of the inductance LO is reduced all at once and the LOCO
The resonance stops, and the charging current 10 to the capacitor CO is reduced to the fourth
It is cut off at the point shown in Figure B, but the diode DO
As a result, the charging voltage of the capacitor CO is held at the voltage when the capacitor CO is cut off, as shown by C in FIG. On the other hand,
Since the amplifier AP is subjected to positive feedback via the capacitor C1 at the same time as the inverting operation, the predetermined time T determined by the time constant of the capacitor C1 and the resistor 2R.

When , the amplifier Oki is reversed from negative to positive, making the transistor Trl conductive and conversely making the transistor Tr2 non-conductive. As a result, the charge of the capacitor C2 is discharged through the transistor Tr2, and a negative pulse voltage as shown by the line D in FIG. 4 is applied to the gate terminal of the GTO. Therefore, the GTO is extinguished, and the secondary current 1S that had been flowing until then is cut off at the point indicated by H in Figure 4D without leaving a tail until the next conduction operation of the thyratron TT. At this point, the impedance of the inductance LO returns to its original predetermined value. Therefore, when the thyratron TT is subsequently turned on by a gate pulse from a trigger pulse generator (not shown), the charge in the capacitor CO is instantly discharged, and a pulse voltage as shown by A in FIG. 4A is applied to the pulse transformer PT. The reverse bias current to the thyratron (2), which is supplied to the magnetron MT via the magnetron MT and appears immediately thereafter, is regulated by the original impedance of the inductance b and is canceled out by the charging current 10 that flows from the point of "R" in FIG. 4B. It reliably extinguishes the Thyratron ■ without causing any damage.

As described above, according to the present invention, the secondary current that flows when the circuit is closed reduces the Q value of the resonant inductance and stops the charging current to the capacitor of the pulse forming circuit. In the circuit, by using an element such as a GTO as an on-off circuit switching part whose firing and extinguishing can be controlled arbitrarily, commutation of the thyratron for discharging the capacitor of the pulse forming circuit can be reliably performed. .

Furthermore, since the value of the resistor that consumes the secondary current of the secondary circuit can be reduced, the rate at which the Q value of the resonant inductance is reduced can be increased, and the current of charge to the capacitor can be abruptly interrupted. This has the advantage of increasing the stability of charging pressure. It should be noted that the present invention is not limited to the above-mentioned embodiments, and for example, GTO is used as a switching element for switching between the charging current and the disconnection circuit.
It goes without saying that the same operation can be performed by adding a known commutation circuit to a conventional thyristor (SCR) or thyratron.

Generally, the primary side of the resonance impedance used in this embodiment is 10KV. ．． 3A, 300V on the secondary side
The current capacity is approximately 1100A, and switching elements capable of satisfying this capacity would have been thyristors (SCRs), thyratrons, etc., but these were only used as examples due to the recent development of large-capacity GTOs. .

In addition, in the above embodiment, a thyratron is used as an element for discharging the charge and voltage of the capacitor of the pulse forming circuit, but this is not limited to thyratrons, and as many capacitance-satisfactory numbers are connected in series. It goes without saying that other suitable implementations may be made without changing the gist, such as using a thyristor (SCR) or the like (an element that operates similarly to a thyratron).

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram showing the configuration of an example of a conventional high voltage pulse generator, FIG. 2 is a signal waveform diagram for explaining the operation of the electric circuit in FIG. 1, and FIG. 3 is a high voltage pulse generator according to the present invention. FIG. 4 is an electric circuit diagram showing the configuration of one embodiment of the voltage pulse generator, and FIG. 4 is a signal waveform diagram for explaining the operation of the electric circuit of FIG. 3.

Claims (1)

[Claims] 1. A DC power supply, a capacitor that is charged by the DC power supply through an inductance and a reverse current blocking diode and generates a pulse voltage when discharging, and a discharge element that discharges the charge charged in the capacitor. , a charge flow or disconnection that reduces the Q value of the inductance for an arbitrary predetermined period to stop the charge flow of the capacitor, and a charge flow or disconnection that reduces the charge flow of the capacitor when the charge pressure of the capacitor reaches a set value. A high-voltage pulse generator comprising: a charging voltage control circuit having a time limit means for operating the circuit and outputting an operation stop signal for charging and circuit disconnection after the predetermined period has elapsed. 2. The high-voltage pulse generator according to claim 1, characterized in that a gate turn-off thyristor is used as the charging/disconnection switching means.