Accelerator system and discharge detector

Abstract

To provide an accelerator system and a discharge detector that can suppress the impact of discharge on the inside of an accelerator.SOLUTION: An accelerator system 100 includes a discharge detector 60 that detects discharge inside an accelerator 1. On the basis of the detection of continuous discharge, the discharge detector 60 cuts off the discharge at a stage before the discharge has an effect inside the accelerator 1. Therefore, even when continuous discharge occurs inside the accelerator 1, the discharge can be cut off early to prevent the discharge from having an effect. As described above, the effect of the discharge on the inside of the accelerator 1 can be suppressed.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an accelerator system and a discharge detector.

Background Art

[0002] Conventionally, as a technology in such a field, an accelerator system described in Patent Document 1 below is known. The accelerator system accelerates particles by generating a high-frequency electric field in a cavity inside the accelerator.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, in the accelerator system as described above, discharge may occur inside the accelerator (for example, in a cavity). Among such discharges, when continuous discharge occurs, effects due to discharge such as discharge marks, current paths, and damage to the inner wall occur inside the accelerator. When such effects due to discharge occur, problems such as damage to components inside the accelerator and deterioration of performance occur. Conventionally, a method of confirming discharge by using the increase and decrease of the degree of vacuum inside the accelerator has been adopted for such problems. Since such a method detects based on an indirect index generated by the occurrence of continuous discharge, there is a large time lag from the occurrence of continuous discharge to detection. Therefore, there has been a problem that the effects occurring inside the accelerator caused by continuous discharge cannot be sufficiently suppressed.

[0005] An object of the present invention is to provide an accelerator system and a discharge detector that can suppress the influence of discharge on the inside of the accelerator.

Means for Solving the Problems

[0006] The accelerator system of the present invention includes an accelerator that accelerates particles and a discharge detector that detects discharges inside the accelerator. The discharge detector shuts off the discharge at a stage prior to the occurrence of an impact due to the discharge inside the accelerator based on detecting a continuous discharge.

[0007] The accelerator system according to the present invention includes a discharge detector that detects discharges inside the accelerator. Based on detecting a continuous discharge, this discharge detector shuts off the discharge at a stage prior to the occurrence of an impact due to the discharge inside the accelerator. Therefore, even when a continuous discharge occurs inside the accelerator, the impact due to the discharge can be suppressed by shutting off the discharge early. From the above, the impact on the inside of the accelerator due to the discharge can be suppressed.

[0008] The discharge detector may shut off the discharge based on the electrical waveform of the cavity of the accelerator. Different from the degree of vacuum inside the accelerator, etc., the electrical waveform of the cavity can directly detect the occurrence of a discharge. Therefore, when a continuous discharge occurs, the discharge detector can quickly detect the discharge.

[0009] The accelerator system includes a host system that controls the accelerator and a control unit that controls the application of voltage to the cavity of the accelerator, and the control unit may have a discharge detector. In this case, the discharge detector can detect the discharge by the control unit that controls the cavity without going through the host system. Therefore, the discharge detector can quickly detect the discharge.

[0010] The discharge detector may shut off the discharge when it detects that the number of discharges within a predetermined time in the cavity of the accelerator is equal to or greater than a predetermined number. In this case, the discharge detector can detect a type of continuous discharge in which single discharges occur repeatedly.

[0011] When the discharge detector detects that the discharge in the cavity of the accelerator lasts for a predetermined time or longer, it may cut off the discharge. In this case, the discharge detector can detect continuous discharges of the type in which the discharge persists.

[0012] When the electrical waveform of the cavity of the accelerator is shorted for a predetermined time, the discharge detector may cut off the discharge. In this case, the discharge detector can detect continuous discharges due to the short circuit.

[0013] The discharge detector according to the present invention is a discharge detector that detects discharges inside an accelerator that accelerates particles, and based on detecting continuous discharges, it may cut off the discharge at a stage prior to the occurrence of an influence due to the discharge inside the accelerator.

[0014] According to this discharge detector, the same operations and effects as those of the above-described accelerator system can be obtained.

Advantages of the Invention

[0015] According to the present invention, it is possible to provide an accelerator system and a discharge detector that can suppress the influence of discharges on the inside of the accelerator.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the description of the drawings, the same or equivalent elements are denoted by the same reference numerals and redundant descriptions are omitted. Also, the positional relationships such as up, down, left, and right are based on the positional relationships in the drawings.

[0018] FIG. 1 is a block diagram showing an accelerator system 100 according to this embodiment. As shown in FIG. 1, the accelerator system 100 includes an accelerator 1 and a control system 101. The accelerator 1 is a device that accelerates particles to generate a beam. The control system 101 controls the accelerator 1.

[0019] Referring to FIG. 2, the accelerator 1 will be described. FIG. 2 is a perspective view showing the inside of the accelerator 1. In FIG. 2, a state is illustrated in which the upper side of the accelerator 1 is removed and the built-in components can be seen. In this embodiment, a cyclotron is exemplified as the accelerator 1.

[0020] The accelerator 1 generates a proton beam, accelerates the positive ions (particles) of hydrogen supplied from an ion source (not shown) inside the vacuum vessel 3, generates a proton beam, and emits it. The vacuum vessel 3 is formed of, for example, stainless steel or the like. Also, a vacuum pump (not shown) is connected to the vacuum vessel 3. The vacuum vessel 3 forms a vacuum environment inside where ions are accelerated.

[0021] The accelerator 1 includes a yoke 4 arranged to face each other vertically and an exciting coil 5 that forms a magnetic field inside the vacuum vessel 3. Also, the accelerator 1 includes a cavity 6 that generates a high-frequency electric field and an RF tuner 11 that adjusts the resonance frequency of the cavity 6 in order to impart energy to the proton beam.

[0022] A magnetic field is formed in the vacuum vessel 3 by the yoke 4 and the exciting coil 5, and a high-frequency electric field is formed by the cavity 6, so that the proton beam orbits in a spiral trajectory, and the traveling speed of the proton beam increases as the radius of the orbiting trajectory increases. In FIG. 2, the lower yoke 4 is shown, and the illustration of the upper yoke 4 is omitted.

[0023] In addition, the accelerator 1 is provided with a deflector 7 installed on the inner surface side of the side wall of the vacuum vessel 3 for extracting the accelerated proton beam, a gradient collector 8 for correcting the magnetic field gradient, a collimator 9 for emitting the proton beam in a predetermined direction (horizontal direction), and a permanent quadrupole magnet 10 for adjusting the focus of the emitted proton beam. The proton beam accelerated in the vacuum vessel 3 is extracted by the deflector 7, the magnetic field gradient is corrected by the gradient collector 8, and the emission direction is adjusted by the collimator 9. The focus of the emitted proton beam is adjusted by the permanent quadrupole magnet 10.

[0024] FIG. 3 is a schematic cross-sectional view of the cavity 6. In the accelerator 1, a pair of cavities 6 are provided above and below with the passage of the proton beam B therebetween. As shown in FIG. 3, the pair of cavities 6 are substantially vertically symmetric to each other and have the same or equivalent structures. Therefore, hereinafter, in order to omit duplicate explanations, only the structure of the lower cavity 6 will be described.

[0025] The cavity 6 has a Dee electrode 21, a ground plate 23, and a stem 27. The ground plate 23 is spaced apart from the Dee electrode 21, forms a bottomed cup shape that houses the Dee electrode 21 inside, and is fitted into the recess of the yoke 4. The ground plate 23 is made of, for example, oxygen-free copper. A stem 27 extends upward from the bottom surface of the ground plate 23, and the Dee electrode 21 is fixed to the upper end of the stem 27.

[0026] The upper edge of the ground plate 23 constitutes the counter-dee 29. Also, a gap is provided between the upper edge of the ground plate 23 and the dee electrode 21, and this gap constitutes the acceleration gap G between the dee electrode 21 and the counter-dee 29. A high-frequency electric field corresponding to the rotational phase of the proton beam B is generated between the dee electrode 21 and the counter-dee 29, so that the proton beam B is accelerated every time it passes through the acceleration gap G.

[0027] Returning to FIG. 1, the control system 101 includes a host system 50, a control unit 51, and an amplifier 52. The host system 50 is a system that controls the accelerator 1. The host system 50 controls the operation of the entire accelerator 1. The control unit 51 controls the voltage application to the cavity 6 of the accelerator 1. The control unit 51 receives a control signal from the host system 50 and controls the cavity 6 based on the control signal. The amplifier 52 is a device that amplifies the input signal to the cavity 6 from the control unit 51.

[0028] The control unit 51 has a discharge detector 60. The discharge detector 60 detects discharges inside the accelerator 1. The discharge detector 60 is a device that interrupts discharges at a stage prior to the occurrence of an impact due to the discharge inside the accelerator 1 based on the detection of continuous discharges. Here, since the cavity 6 has an electrode to which a high electric field is applied, a discharge phenomenon occurs. The discharge phenomenon includes single discharges and continuous discharges. A single discharge is a discharge phenomenon in which the discharge occurs once and is completed in a short time. A continuous discharge is a discharge phenomenon in which the discharge is continuously performed. The continuous discharge includes a type of discharge in which single discharges are repeated multiple times within a short period (indicated by "TP1" in FIG. 4) and a type of discharge in which the discharge continues for a predetermined time (indicated by "TP2" in FIG. 4).

[0029] Continuous discharge generates effects such as internal discharge marks, current paths, and damage to the inner wall of the cavity 6 (effects caused by discharge), including the possibility of causing damage to the cavity and deterioration of performance. Therefore, when continuous discharge occurs, the discharge detector 60 performs an interlock and cuts off the discharge before the effects of discharge occur inside the accelerator 1 to protect the cavity 6. Fig. 8(a) is a photograph showing the inside of the cavity 6 before continuous discharge occurs and before the effects of discharge appear. Fig. 8(b) is a photograph showing the inside of the cavity 6 after continuous discharge occurs and after the effects of discharge appear without the protection by the discharge detector 60 of this embodiment. As shown by "A" in Fig. 8(b), it is shown that there are discharge marks as an effect of continuous discharge. The discharge detector 60 cuts off the discharge at a stage before such discharge marks occur.

[0030] Here, if the discharge detector 60 cuts off the discharge in response to a single discharge, it will perform an interlock at a high frequency even for a discharge that does not cause the effects of discharge. Therefore, the discharge detector 60 does not respond to single discharges and performs an interlock only when continuous discharge occurs. The discharge detector 60 cuts off the discharge based on the electrical waveform of the cavity 6 of the accelerator 1. For example, as shown in Fig. 4, the discharge detector 60 detects the occurrence of continuous discharge based on the waveform of the cavity voltage obtained by detecting the cavity voltage of the cavity 6. Then, when the discharge detector 60 detects the occurrence of continuous discharge based on the waveform, it performs an interlock to interrupt the voltage application to the cavity 6, thereby cutting off the discharge.

[0031] Specifically, when the discharge detector 60 detects that the number of discharges in the cavity 6 of the accelerator 1 within a predetermined time is equal to or greater than a predetermined number, it interrupts the discharge. As shown in FIG. 4, when no discharge occurs, the cavity voltage becomes a constant voltage. In contrast, when a discharge occurs, the cavity voltage drops below the discharge threshold TH. When the discharge detector 60 detects a discharge below the discharge threshold TH, it starts measuring time. In the case of continuous discharge of the type where single discharges are repeated, the cavity voltage immediately returns, but then the next single discharge immediately occurs. The discharge detector 60 counts the number of discharges. The discharge detector 60 counts the number of discharges for a preset predetermined count time T1. If the number of discharges that occur during the count time T1 is equal to or greater than a preset predetermined count number, the discharge detector 60 detects that continuous discharge is occurring. Alternatively, the discharge detector 60 may detect continuous discharge when the number of discharges reaches the predetermined count number before the count time T1 has elapsed. When the discharge detector 60 detects continuous discharge, it outputs an interlock signal to interrupt the application of voltage to the cavity 6. Thereby, the discharge in the cavity 6 is interrupted. The length of the count time T1 is not particularly limited and can be set arbitrarily, but for example, it may be set to about 2 μs to 65000 μs. Note that the discharge period PD during continuous discharge is about 2 μs.

[0032] Further, when the discharge detector 60 detects that the discharge in the cavity 6 of the accelerator 1 continues for a predetermined time or longer, it shuts off the discharge. That is, the discharge detector 60 shuts off the discharge when the electrical waveform of the cavity 6 of the accelerator 1 is shorted for a predetermined time. As shown in FIG. 4, although a predetermined voltage is applied to the cavity 6, the cavity voltage may remain below the discharge threshold TH and the waveform may be shorted (see "TP2" in FIG. 4). When the discharge detector 60 detects a discharge below the discharge threshold TH, it starts measuring time. In the case of continuous discharge of the type in which the discharge continues, the cavity voltage continues to be below the discharge threshold TH without returning. The discharge detector 60 determines whether or not the state continues for a preset predetermined duration T2. When the discharge detector 60 detects that the state in which the cavity voltage is below the discharge threshold TH has continued for a duration T2 or longer, it detects that continuous discharge has occurred. When the discharge detector 60 detects continuous discharge, it outputs an interlock signal to interrupt the application of voltage to the cavity 6. Thereby, the discharge in the cavity 6 is interrupted. Note that the length of the duration T2 is not particularly limited and can be arbitrarily set, but may be set to about 2 μs to 65000 μs, for example.

[0033] Next, with reference to FIG. 5, an example of a specific configuration of the discharge detector 60 will be described. FIG. 5 is a circuit diagram showing the circuit configuration of the discharge detector 60. As shown in FIG. 5, the discharge detector 60 includes a discharge detection circuit 61, a discharge duration detection circuit 62, an interval discharge count confirmation circuit 63, latches 64A and 64B, and an OR circuit 65.

[0034] The discharge detection circuit 61 is a circuit that monitors the cavity power and detects the occurrence of a discharge. Before the operation of the accelerator 1, the value of the discharge threshold TH is input to the discharge detection circuit 61 in advance. Thereby, the discharge detection circuit 61 sets the input value as the discharge threshold TH. During the operation of the accelerator 1, the cavity voltage is input to the discharge detection circuit 61. Thereby, the discharge detection circuit 61 detects a discharge by comparing the input cavity voltage with the discharge threshold TH. The discharge detection circuit 61 outputs the detection result of the discharge to the discharge duration detection circuit 62 and the interval discharge count confirmation circuit 63.

[0035] The discharge duration detection circuit 62 is a circuit that detects continuous discharges of the continuous type (TP2). Before the operation of the accelerator 1, the value of the duration T2 is input as a parameter to the discharge duration detection circuit 62 in advance. The discharge duration detection circuit 62 sets the input value as the duration T2. When the discharge duration detection circuit 62 detects that the discharge has continued for a duration of T2 or more, it outputs an interlock command signal to the OR circuit 65 via the latch 64A.

[0036] The interval discharge count confirmation circuit 63 is a circuit that detects continuous discharges of the single-shot discharge repetition type (TP1). Before the operation of the accelerator 1, the values of the count number and the count time T1 are input as parameters to the interval discharge count confirmation circuit 63 in advance. The interval discharge count confirmation circuit 63 sets the input values as the count number and the count time T1. When the interval discharge count confirmation circuit 63 detects that discharges equal to or more than the count number have continued for a duration of T2 or more during the count time T1, it outputs an interlock command signal to the OR circuit 65 via the latch 64A.

[0037] The latches 64A and 64B are devices having the function of maintaining the states of the circuits 62 and 63. When the latches 63A and 64 receive an interlock command signal from each of the circuits 62 and 63, they output the command signal to the OR circuit 65. When the OR circuit 65 receives an interlock command signal from at least one of the discharge duration detection circuit 62 and the interval discharge count confirmation circuit 63, it outputs the command signal to the interlock section (not shown) of the control unit 51.

[0038] Next, the operations and effects of the accelerator system 100 and the discharge detector 60 according to the embodiments of the present invention will be described.

[0039] First, with reference to FIGS. 6 and 7, the accelerator system 200 according to the comparative example will be described. The accelerator system 200 according to the comparative example uses a vacuum control panel 70 to detect continuous discharge instead of the above-described discharge detector 60. The vacuum control panel 70 is a device that detects the degree of vacuum inside the cavity 6. The vacuum control panel 70 receives the degree of vacuum inside the cavity 6 and outputs it to the upper system 50. The upper system 50 detects the occurrence of continuous discharge based on the received degree of vacuum, and implements an interlock when continuous discharge is detected. The upper system 50 outputs a command signal for stopping the voltage application to the cavity 6 to the control unit 51. Based on the command signal, the control unit 51 interrupts the voltage application to the cavity 6 to cut off the discharge.

[0040] For example, in the accelerator system 200 according to the comparative example, as shown in FIG. 7, the upper system 50 performs detection based on a timing signal. When the upper system 50 detects a deterioration in the degree of vacuum, it monitors for a predetermined time T3. When the upper system 50 detects that the state of deteriorated degree of vacuum continues for the predetermined time T3, it detects continuous discharge. The timing signal of the upper system 50 has a period of 1 Hz to 10 Hz, and it takes about 1 s to 0.1 s for one cycle. Therefore, the time T3 is set to about several seconds. Also, in FIG. 7, for the sake of convenience, the state where the degree of vacuum changes rapidly is shown, but even when continuous discharge occurs, the degree of vacuum changes gradually. Therefore, it takes a certain amount of time until the deterioration of the degree of vacuum can be detected. From the above, in the accelerator system 200 according to the comparative example, it takes about several seconds from the occurrence of continuous discharge to the implementation of the interlock. Therefore, the cavity may be affected by the discharge before the interlock is implemented.

[0041] In contrast, the accelerator system 100 according to this embodiment includes a discharge detector 60 that detects discharge inside the accelerator 1. Based on detecting continuous discharge, this discharge detector 60 shuts off the discharge at a stage prior to the occurrence of an impact due to the discharge inside the accelerator 1. Therefore, even when continuous discharge occurs inside the accelerator 1, by shutting off the discharge at an early stage, it is possible to suppress the occurrence of an impact due to the discharge. As described above, it is possible to suppress the impact on the inside of the accelerator 1 due to the discharge.

[0042] The discharge detector 60 may shut off the discharge based on the electrical waveform of the cavity 6 of the accelerator 1. Unlike the degree of vacuum inside the accelerator 1, the electrical waveform of the cavity 6 can directly detect the occurrence of discharge. Therefore, when continuous discharge occurs, the discharge detector 60 can quickly detect the discharge.

[0043] The accelerator system 100 includes a host system 50 that controls the accelerator 1 and a control unit 51 that controls voltage application to the cavity 6 of the accelerator 1, and the control unit 51 may include the discharge detector 60. In this case, the discharge detector 60 can detect the discharge by the control unit 51 that controls the cavity 6 without going through the host system 50. Therefore, the discharge detector 60 can quickly detect the discharge.

[0044] When the discharge detector 60 detects that the number of discharges within a predetermined time in the cavity 6 of the accelerator 1 is equal to or greater than a predetermined number, the discharge detector 60 may shut off the discharge. In this case, the discharge detector 60 can detect continuous discharge of the type in which single discharges occur repeatedly.

[0045] When the discharge detector 60 detects that the discharge in the cavity 6 of the accelerator 1 continues for a predetermined time or longer, the discharge detector 60 may shut off the discharge. In this case, the discharge detector 60 can detect continuous discharge of the type in which the discharge continues.

[0046] The discharge detector 60 may interrupt the discharge when the electrical waveform of the cavity 6 of the accelerator 1 is shorted for a predetermined time. In this case, the discharge detector 60 can detect continuous discharges due to the short.

[0047] The discharge detector 60 according to the present embodiment is a discharge detector 60 that detects a discharge inside the accelerator 1 that accelerates particles, and may interrupt the discharge at a stage prior to the occurrence of an influence due to the discharge inside the accelerator 1 based on detecting continuous discharges.

[0048] According to this discharge detector 60, the same operations and effects as those of the accelerator system 100 described above can be obtained.

[0049] The present invention is not limited to the above-described embodiments.

[0050] The type of accelerator is not limited to a cyclotron. For example, as the accelerator, various accelerations such as a linac or a synchrotron may be employed. Further, the object for which the discharge is detected is not limited to the cavity, and can be appropriately applied to devices that use high frequencies, such as a deflector or an ion source. Further, the present invention can be applied to the entire DC power supply of the accelerator 1.

Description of Reference Numerals

[0051] 1... Accelerator, 6... Cavity, 60... Discharge detector, 100... Accelerator system.

Claims

1. An accelerator system comprising an accelerator for accelerating particles and a discharge detector for detecting a discharge inside the accelerator, wherein the discharge detector interrupts the discharge at a stage prior to the occurrence of an influence due to the discharge inside the accelerator based on detection of continuous discharges.

2. The accelerator system according to Claim 1, wherein the discharge detector interrupts the discharge based on an electrical waveform of a cavity of the accelerator.

3. The accelerator system according to Claim 1, further comprising a host system for controlling the accelerator and a control unit for controlling voltage application to the cavity of the accelerator, wherein the control unit includes the discharge detector.

4. The accelerator system according to Claim 1, wherein the discharge detector interrupts the discharge when detecting that the number of discharges within a predetermined time in the cavity of the accelerator is equal to or greater than a predetermined number.

5. The accelerator system according to Claim 1, wherein the discharge detector interrupts the discharge when detecting that a discharge in the cavity of the accelerator continues for a predetermined time or longer.

6. The accelerator system according to Claim 1, wherein the discharge detector interrupts the discharge when the electrical waveform of the cavity of the accelerator is short-circuited for a predetermined time.

7. A discharge detector for detecting a discharge inside an accelerator for accelerating particles, wherein the discharge detector interrupts the discharge at a stage prior to the occurrence of an influence due to the discharge inside the accelerator based on detection of continuous discharges. ​ ​

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