JP3594536B2 - Beam chopper - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a beam chopper for splitting a beam in a short time, and more particularly to a beam chopper suitable for use when a beam accelerated by a linear accelerator is supplied to a synchrotron or a storage ring.
[0002]
[Prior art]
When a beam accelerated by a linear accelerator is supplied to a synchrotron or a storage ring, a section without a beam is required to perform incidence and extraction of the beam. The time is approximately several hundred ns. Therefore, it is necessary to divide a pulse-like beam of several ms as shown in FIG. 1 into a shorter time as shown in FIG. For this purpose, a beam chopper is used.
[0003]
The beam chopper is roughly classified into an electrostatic type, a transmission line type, and an RF type.
[0004]
As shown in FIG. 3, the electrostatic type is provided with a long plate-like chopper electrode 12 in a beam axial direction (referred to as a beam line) 10 and applying a high voltage to the electrode 12 to form a beam trajectory. To deflect.
[0005]
However, since the electrode 12 is long in the beam axis direction, it takes time for the beam to pass through the electrode. Therefore, there is a problem that sharp chopping cannot be performed, and the beam passing through the slit 14 arranged on the exit side of the electrode 12 is also deflected.
[0006]
That is, even when it is desired to pass only the beam bunch at point a in FIG. 3 through the slit 14 and block all the beam bunches at points b to e, the beam bunch at point b at the start of voltage application will Since the time affected by the electric field E formed therebetween is short and only slightly deflects, it passes through the slit 14 at the next moment of the chopping process as shown in FIG. The beam bunches at points c and d also cannot be sufficiently deflected. The beam bunch that has passed through the slit 14 despite being deflected collides with a vacuum box or the like during acceleration, and causes activation of equipment.
[0007]
Therefore, when high-precision chopping is required, the above-mentioned electrostatic type cannot be used, and the transmission line type described below is used.
[0008]
As shown in FIG. 5, the transmission line type beam chopper includes a large number of short plate-shaped chopper electrodes 20 arranged in the beam axis direction 10 and applies a high voltage to the electrodes 20 to deflect the beam trajectory. The electrodes are connected by a delay circuit 22 such as a coaxial cable, and a voltage is applied to the electrodes 20 in synchronization with the beam speed. The final end is connected to a terminator 24 made of a resistor having the same impedance as the delay circuit 22.
[0009]
In this transmission line type beam chopper, the delay circuit 22 (the length of the coaxial cable) is adjusted so that a voltage is generated at the short electrode in the beam axis direction in synchronization with the beam speed. For this reason, as shown in FIGS. 6 to 8, the beam bunch is not affected by the electric field E generated by the chopper at all (a) or is sufficiently affected (b, c...) A beam deflected halfway will not pass through the slit. That is, the beam bunches at points b and c in FIG. 6 at the start of voltage application are sufficiently affected by the electric field E of the next electrode at the next instant, as shown in FIG. 8, the beam bunch at the point b, which has been bunched, is not affected by the electric field E generated by the chopper electrode at all, but the beam bunch after the point b is sufficiently affected by the electric field E. To receive it.
[0010]
Therefore, if impedance matching can be performed with high accuracy, fine chopping can be performed.
[0011]
[Problems to be solved by the invention]
However, since the termination is terminated by the same 50Ω pure resistance as that of the delay circuit (coaxial cable) 22, a large-capacity pulse power supply is required. In addition, it is difficult to perform impedance matching at the connection between the electrode 20 and the delay circuit 22, and adjustment is troublesome. Furthermore, at present, high capacity high speed switches are not reliable. In addition, there is a problem that the voltage contact (ringing) is large particularly when the voltage applied to the electrode is turned off.
[0012]
Note that the last RF beam chopper is used when one RF beam bunch is required, and has a different purpose from the electrostatic type or the transmission line type.
[0013]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a beam chopper capable of performing sharp chopping without requiring a large-capacity power supply.
[0014]
[Means for Solving the Problems]
The present invention provides a beam chopper for splitting a beam in a short time, a plurality of mutually independent electrodes arranged in parallel in a beam axis direction, and a number of mutually independent power supply lines connected to each electrode. This problem is solved by providing a power supply-side switch disposed on each power supply line and sequentially turned on and off in accordance with the timing at which a beam passes through each electrode.
[0015]
Further, a resistor is inserted between the power switch and the electrode.
[0016]
Furthermore, when turning off the voltage applied to the electrodes, each electrode is provided with a ground-side switch for dropping to ground via a resistor and a capacitor, thereby preventing ringing when turning off the voltage. Things.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0018]
As shown in FIG. 9, the chopper pole portion in the present embodiment has a large number of short electrodes 30 arranged in the beam axis direction, like the conventional transmission line type. However, each electrode is not connected to the adjacent electrode, and the power supply line 32 is individually connected. This eliminates the need to lower the impedance by terminating with a pure resistor as in the related art, and enables driving with a small-capacity power supply, thereby reducing the required power supply capacity. Further, since the electrodes are short in the beam traveling direction, sharp chopping can be performed.
[0019]
Further, similarly to the transmission line type, it is possible to supply power to a large number of electrodes by one power supply 34. Further, by disposing the bank capacitor 36 near the chopper main body, the power supply capacity can be further reduced.
[0020]
Between each electrode 30 and the power supply 34, there is provided a power supply side switch 38 which is sequentially turned on and off in accordance with the timing at which the beam bunch passes through each electrode. Further, a resistor 40 is inserted between the power switch 38 and the electrode 30. Further, a ground-side switch 42 for grounding each electrode 30 via a resistor 44 and a capacitor 46 is also provided.
[0021]
As shown in FIG. 10, the power-supply-side switches 38 are sequentially turned on (open) at the timing when each beam bunch passes through the electrode. In this way, as shown in FIGS. 6 to 8, the beam bunch (a) running in front of the beam bunch (b) is not affected at all by the electric field E generated by the chopper electrode, and is now focused on. The beam bunches (c...) Subsequent to the beam bunches (b) can be maximally affected by the electric field E generated by the chopper electrode.
[0022]
Considering the beam trajectory, the voltage oscillation when turning off is more important than when applying voltage. In order to solve this problem, when turning off the applied voltage, the electrode 30 is grounded via the resistor 44 and the capacitor 46 by the earth switch 42.
[0023]
Each switch is turned on and off by the switch control circuit 50 as shown in FIG.
[0024]
FIG. 11 shows a simulation result of the electrode voltage in the embodiment. Voltage oscillation when turning off the voltage applied to the electrode can be finely adjusted.
[0025]
In the present embodiment, since the resistor 40 is inserted between the power switch 38 and the electrode 30, the characteristic can be adjusted to the optimum by selecting the value of the resistor 40 according to the capacitance of the power source 34. It is.
[0026]
In the present embodiment, a ground-side switch 42 is provided so that each electrode 30 is grounded via a resistor 44 and a capacitor 46 when the voltage applied to the electrode 30 is turned off. Therefore, the voltage oscillation at the time of cutting off the voltage can be minimized.
[0027]
In the present embodiment, since the bank capacitor 36 is disposed near the chopper main body, the power supply capacity can be further reduced. Note that the bank capacitor 36 can be omitted.
[0028]
【The invention's effect】
According to the present invention, the reliability of the system can be improved without requiring a large-capacity power supply. Also, sharp chopping is possible. Further, the capacity of the high-speed switch is small, and there is a switch that operates at about 3 ns even at the present time. In addition, the delay time can be easily changed.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a pulse beam chopped by a beam chopper. FIG. 2 is a diagram showing an example of a beam similarly chopped at 400 ns. FIG. 4 is a cross-sectional view showing a state at the start of voltage application for explaining a problem of the conventional electrostatic beam chopper. FIG. 4 is a cross-sectional view showing a chopping process similarly. FIG. FIG. 6 is a cross-sectional view showing a force applied to a beam at the start of voltage application in a conventional transmission line beam chopper and an embodiment of the present invention. FIG. 8 is a cross-sectional view showing a force applied to a beam when a voltage is applied to all the electrodes. FIG. 9 is a perspective view showing a configuration of an embodiment of a beam chopper according to the present invention. Diagram showing a simulation of electrode voltage results in Figure 11 the embodiment shown the OFF state of the power-side switch and the ground-side switch in the form [Description of symbols]
DESCRIPTION OF SYMBOLS 10 ... Beam line a, b, c, d, e ... Beam bunch 30 ... Electrode 34 ... Power supply 36 ... Bank capacitor 38 ... Power supply side switch 40, 44 ... Resistance 42 ... Earth side switch 46 ... Capacitor 50 ... Switch control circuit

Claims (3)

In a beam chopper for splitting a beam in a short time,
A plurality of independent electrodes arranged side by side in the beam axis direction,
A number of independent feeders connected to each electrode,
A power-supply-side switch disposed on each power supply line and sequentially turned on and off in accordance with a timing at which a beam passes through each electrode;
A beam chopper comprising: The beam chopper according to claim 1, wherein a resistor is inserted between the power switch and the electrode. The switch according to claim 1 or 2, further comprising a ground-side switch for dropping each electrode to ground via a resistor and a capacitor when turning off the voltage applied to the electrodes. Beam chopper.

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