JPH10233298A - Control device for high-frequency acceleration cavity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable acceleration/deceleration control wherein particle loss of an orbiting beam is suppressed, by controlling a phase of a high-frequency voltage with high accuracy and at a high speed by using a direct digital waveform synthesizing oscillator as an oscillator of the high-frequency voltage. SOLUTION: A high-frequency voltage to be applied to a high-frequency acceleration cavity 1 is generated by an oscillator 7 using a direct digital waveform synthesizing oscillator and amplified by a power amplifier 8. The oscillator 7 controls a frequency, an amplitude, and a phase of the high-frequency voltage in keeping with an energy increase of an orbiting beam in the course of acceleration of the orbiting beam. The frequency, the amplitude, and the phase of the high-frequency voltage are beforehand prepared in an operation pattern data base 6 and renewed synchronously with a deflection magnetic field intensity change.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a control device for a high-frequency acceleration cavity.

[0002]

2. Description of the Related Art In order to accelerate a proton or heavy ion beam with an ion synchrotron, the magnetic field strength of a bending electromagnet in the synchrotron is increased so that the beam orbits on a fixed orbit, and a high-frequency accelerating cavity (hereinafter, referred to as "acceleration") is used. The frequency and amplitude of the high-frequency voltage applied to the accelerating cavity) are controlled. The control of the high-frequency voltage updates a set value of the output frequency and amplitude of the oscillator based on a magnetic field strength change detection signal (hereinafter, a magnetic field clock) output in synchronization with the deflection magnetic field strength change. In the process of accelerating the beam, the frequency set value of the high-frequency voltage must be changed by a factor of 5 to 10 from the start to the end of the acceleration as the energy increases. This change in the frequency of the high-frequency voltage changes the impedance characteristics of the acceleration cavity, causing a shift between the circulating phase of the beam and the high-frequency voltage phase generated in the acceleration cavity. If the deviation is to be corrected in advance, a stable frequency output is required for the oscillator. When a plurality of accelerating cavities are installed in the synchrotron, the high-frequency voltage is applied to the beam as the sum of the output voltages from the cavities. It is necessary to control the phase of the high-frequency voltage when passing through the acceleration gap (hereinafter, synchronous phase).

Conventionally, as shown in FIG. 6, one oscillator using a VCO (Voltage Controlled Oscillator) for outputting a frequency corresponding to an analog input voltage is prepared for one synchrotron, and the frequency is set and set. After the output, a phase shifter that changes in the high-frequency accelerating cavity and an initial phase of the high-frequency voltage of each cavity prepared in the synchrotron are corrected in advance by the phase shifter.

[0004]

In the above prior art, when a VCO is used as a high frequency voltage oscillator, the output of the oscillation frequency becomes unstable due to a change in ambient temperature. It has been found that with this frequency change, the phase of the high-frequency voltage with respect to the circulating phase of the beam also changes, resulting in an increase in particle loss of the beam. In order to suppress this, it is necessary to precisely and quickly control the phase of the high-frequency voltage during the acceleration operation.
However, with the phase shifter conventionally used, the set phase change amount can be obtained only at a certain point of the changing oscillation frequency, and the response speed to the frequency change is not enough to suppress the increase of the particle loss of the beam. It is enough.

An object of the present invention is to provide control means capable of adjusting the phase of a high-frequency voltage applied to a high-frequency accelerating cavity at high speed and with high accuracy.

[0006]

To achieve the above object, the present invention provides an oscillator for oscillating a reference signal of a high-frequency voltage applied to a high-frequency accelerating cavity by providing digital data of an oscillating frequency, amplitude and phase by oscillating. It uses a direct digital waveform oscillator (Direct Digital Synthesizer, DDS) to provide the same number of high-frequency voltage controllers and operation patterns and databases as the number of accelerating cavities together with this oscillator. Output control.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of a high-frequency accelerating cavity and its control device according to a first embodiment of the present invention. A digital waveform oscillator (DDS) is used directly as an oscillator 7 for generating an acceleration voltage to be supplied to the high-frequency accelerating cavity 1, and the setting data of the frequency, amplitude, and phase of the high-frequency voltage is adjusted in advance to the operation pattern of the accelerating cavity. It is prepared in the operation pattern database 6 as time series data.

FIG. 5 shows a DDS used for the oscillator. The DDS includes a frequency setting register 11, a phase setting register 12, an amplitude setting register 13, a look-up table 14, a D / A converter 15, and a low-pass filter 1
6 is comprised. Lookup table 14 contains si
The amplitude-phase information of the n-wave or the cos-wave is prepared as digital data. The phase register determines the reading start phase of the amplitude-phase information, and the frequency register determines the reading interval of the amplitude-phase information. After the read data is amplitude-modulated by the set value of the amplitude register, D / A conversion,
A desired waveform is output by filtering. DD
The oscillation frequency stability of S is about 1 / 100,000, the output response speed is several μs, and the phase setting resolution is about 0.1 degree, which enables precise phase control of the high frequency voltage.

In the process of accelerating the beam, the high-frequency voltage setting data detects a change in the magnetic field strength of the bending electromagnet 2 by the magnetic field detecting element 3 and synchronizes the magnetic field clock output from the magnetic field synchronous clock generator 4 with the high frequency voltage. Input to the voltage control device 5. The data is read from the operation pattern database 6 in synchronization with the magnetic field clock, and the set value is output to the oscillator 7. At this time, the characteristic impedance of the cavity changes with the frequency change of the high-frequency voltage applied to the high-frequency acceleration cavity, and the phase of the high-frequency voltage applied to the high-frequency acceleration cavity,
The phase of the high-frequency voltage actually applied to the beam is shifted. Therefore, the frequency-phase characteristics of the high-frequency accelerating cavity are measured in advance, and the result is set in addition to the phase setting data, whereby the phase can be controlled accurately and at high speed in the operating frequency range. The oscillator 7 outputs a waveform based on the set data, amplifies the waveform with the power amplifier 8, and applies the amplified waveform to the high-frequency acceleration cavity 1. The orbiting beam is accelerated by an electric field generated in the acceleration gap of the high-frequency acceleration cavity.

FIG. 2 shows the configuration of a high-frequency accelerating cavity and its control device according to a second embodiment of the present invention. In this embodiment, in addition to the configuration of the embodiment shown in FIG. 1, a cavity voltage monitor 9 is provided in the high-frequency accelerating cavity 1, and a beam monitor 10 is provided near the cavity. The high-frequency voltage controller 5 calculates the actual phase of the orbiting beam with respect to a preset acceleration voltage based on the detection signals from these monitors, and determines the feedback correction amount.
The result is set in the oscillator 7 as phase setting data, and feedback control is performed. By performing this feedback control, it is possible to reduce the orbital displacement of the orbiting beam and reduce the beam loss during acceleration.

FIG. 3 shows the configuration of a high-frequency accelerating cavity and its control device according to a third embodiment of the present invention. To stably accelerate the orbiting beam with a synchrotron, it is necessary to orbit around the central orbit. At this time, the orbiting beam is

[0013]

The condition P = eBρ (Equation 1) must be satisfied. Here, P is the momentum of the orbiting beam, e is the charge amount of the orbiting beam, B is the intensity of the bending magnetic field on the central orbit, and ρ is the radius of curvature of the central orbit of the bending electromagnet. Even if the momentum increases due to the acceleration of the beam, the magnetic field strength must be increased to maintain the center orbit of the orbiting beam constant,

[0014]

The following relationship holds: ΔP = eΔBρ (Expression 2) Here, when ΔB is considered as an increase in the magnetic field strength per one revolution of the orbiting beam, ΔP is an increase in the momentum around one circumference. Here, when ΔP is converted into energy change ΔE around one side,

[0015]

(3) eVp sinφs = ΔE (Expression 3) Here, Vp is the amplitude of the high-frequency voltage, φs
Is the synchronization phase. From Equation 3, it is possible to control the energy change of acceleration / deceleration of the beam by setting the synchronization phase φs. In this embodiment, two high-frequency accelerating cavities 1 are installed in the synchrotron.
By controlling the term φs, an arbitrary high-frequency voltage can be generated. Here, the beam energy ΔE1, ΔE2 that changes in each accelerating cavity is expressed according to Equation 1.

[0016]

(Equation 4) eVp1 sin (φs1 + δφ) = ΔE1 (Equation 4)

[0017]

EVp2 sin (φs2−δφ) = ΔE2 (Equation 5) Here, Vp1 and Vp2 are the amplitudes of the high-frequency voltage applied to each high-frequency acceleration cavity, φs1 and φs2 are the synchronization phases of the high-frequency acceleration cavities, and δφ is the phase correction amount set for each cavity. Here, the synchronous phases φs1 and φs2 are controlled together with the change in the high-frequency voltage frequency so that the orbiting beam does not cause particle loss due to orbital displacement during acceleration. In addition, by correcting the set phase amount with δφ, it is possible to control the effective voltage amplitude of the high-frequency voltage applied to the circulating beam while keeping the high-frequency voltage amplitude constant. These φs1, φs2, and δ
φ is prepared in the operation pattern database 6 in advance. The configuration of the other devices and the method of outputting the high-frequency voltage setting data to the oscillator are the same as in the first embodiment.

FIG. 4 shows the configuration of a high-frequency accelerating cavity and its control device according to a fourth embodiment of the present invention. In this embodiment, in addition to the configuration of the embodiment shown in FIG. 3, a cavity voltage monitor 9 is provided in the high-frequency accelerating cavity 1, and a beam monitor 10 is provided near the cavity. The high-frequency voltage control device 5 of each high-frequency acceleration cavity 1 calculates the actual phase of the orbiting beam with respect to the acceleration voltage applied to the preset data based on the detection signals from these monitors,
Each feedback correction amount is determined. The result is set in the oscillator 7 as phase setting data, and feedback control is performed. By performing this feedback control,
It is possible to reduce the phase displacement of the orbiting beam and reduce the particle loss of the beam. The configuration of the other devices and the method of outputting the high-frequency voltage setting data to the oscillator are the same as in the first embodiment.

[0019]

According to the present invention, the phase of the high-frequency voltage applied to the high-frequency accelerating cavity can be controlled accurately and at high speed. Further, according to the present invention, by adjusting the phase of the high-frequency voltage applied to the high-frequency accelerating cavity, it is possible to perform acceleration / deceleration control while suppressing the particle loss of the orbiting beam.

[Brief description of the drawings]

FIG. 1 is a block diagram of a high-frequency acceleration cavity and a control device thereof according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a high-frequency acceleration cavity and a control device thereof according to a second embodiment of the present invention.

FIG. 3 is a block diagram of a high-frequency acceleration cavity and a control device thereof according to a third embodiment of the present invention.

FIG. 4 is a block diagram of a high-frequency acceleration cavity and a control device thereof according to a fourth embodiment of the present invention.

FIG. 5 is a block diagram of a direct digital waveform oscillator used in the present invention.

FIG. 6 is a block diagram of a conventional high-frequency acceleration cavity control device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... High frequency acceleration cavity, 2 ... Bending electromagnet, 3 ... Magnetic field detection element, 4 ... Magnetic field clock generator, 5 ... High frequency voltage controller, 6 ... Operation pattern database, 7 ... Oscillator, 8
... power amplifier.

Claims (3)

[Claims] An apparatus for controlling a high-frequency acceleration cavity for accelerating a beam with an ion synchrotron, wherein the phase of a high-frequency voltage applied to the high-frequency acceleration cavity is controlled by an oscillator. apparatus. 2. A high frequency accelerating cavity control device for accelerating a beam with an ion synchrotron, wherein at least one high frequency accelerating cavity and the same number of oscillators are provided in the synchrotron, and the high frequency accelerating cavity is provided in the high frequency accelerating cavity. A control device for a high-frequency accelerating cavity, wherein a phase of a high-frequency voltage to be applied is controlled by an oscillator. 3. The control apparatus for a high-frequency acceleration cavity according to claim 1, wherein a digital waveform synthesis oscillator is used directly as an oscillator for a high-frequency voltage applied to said high-frequency acceleration cavity.