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H-mode drift-tube linac and design method therefor

外国特許コード F100002315
整理番号 244US
掲載日 2010年12月2日
出願国 アメリカ合衆国
出願番号 06514505
公報番号 20090261760
公報番号 7868564
出願日 平成17年10月31日(2005.10.31)
公報発行日 平成21年10月22日(2009.10.22)
公報発行日 平成23年1月11日(2011.1.11)
国際出願番号 JP2005019990
国際公開番号 WO2007034573
国際出願日 平成17年10月31日(2005.10.31)
国際公開日 平成19年3月29日(2007.3.29)
優先権データ
  • 特願2005-277426 (2005.9.26) JP
  • 2005JP19990 (2005.10.31) WO
発明の名称 (英語) H-mode drift-tube linac and design method therefor
発明の概要(英語) A linearity of a voltage change to a tuner insertion amount is verified for at least one of a plurality of tuners. Based on the voltage change linearity, individual voltage change data corresponding to respective insertion amounts are calculated for each of the plurality of tuners through a proportional calculation. A combination of auto-tuners and a combination of respective insertion amounts of the auto-tuners are determined using the individual voltage change data, and an adequacy of the determined combinations is verified through a direct three-dimensional electromagnetic field calculation. The combinations are determined on a condition that, when the individual voltage change data of nominated tuners are added together, respective voltage changes attributed to the nominated tuners are cancelled out to allow an entire voltage distribution to have substantially no change.
従来技術、競合技術の概要(英語) BACKGROUND ART
A drift-tube linac (i.e., drift-tube linear accelerator) designed to accelerate charged particles by utilizing a transverse electric (TE) wave (i.e., H mode) where a current flows in a direction perpendicular to a beam axis (i.e., an axis of a charged particle beam) is known as an H-mode drift-tube linac. In the H-mode drift-tube linac, a large number of drift tubes are arranged in a cavity resonator along the beam axis in the resonator, and a predetermined voltage is applied between respective adjacent ones of the drift tubes so that particles are accelerated according to the voltage (i.e., potential difference) successively every tine the particles pass through each of the drift tubes.
One type of H-mode drift-tube linac using an interdigital H-mode (IH) resonator is known as an IH linac. The IH resonator typically has a structure in which a pair of upper and lower plates, called “ridges”, are mounted (in a vertically opposed arrangement) inside a cylindrical-shaped resonator (although the ridges are not essential to the IH linac). A plurality of drift tubes are alternately attached to the upper and lower ridges through respective stems in such a manner as to be aligned in an axial direction of the resonator. Particles will travel in the axial direction while passing through the drift tubes.
Generally, a linac is equipped with a tuner for adjusting a resonant frequency and a voltage distribution in an entire cavity of a resonator. The finer includes a plurality of fixed tuners and a manually-operated tuner. The fixed tuners are installed in a lateral portion of a wall of a resonator tank and adapted to be used for roughly adjusting the voltage distribution and the resonant frequency. The fixed tuners are immovably welded after the rough adjustment. The manually-operated tuner is adapted to be used for fine adjustment to set a final voltage in the cavity.
During operation of the linac, the resonant frequency is likely to vary due to thermal expansion of the tank and other factor. An auto-tuner is an effective means to compensate or correct such a variation in the resonant frequency caused by temperature change, during the linac operation. Specifically, a slight resonant frequency shift on the side of the tank due to temperature change and other factor is detected by measuring a phase difference between a traveling-wave component in an output of a high-frequency amplifier, and a monitoring signal picked up inside the tank. Then, an automatic frequency control (AFC) circuit performs a calculation based on the measured phase difference to drive the auto-tuner in such a manner as to correct the slight resonant frequency shift.
The H-mode drift-tube linac employs a plurality of tuners, wherein some of the tuners are selectively used as an auto-tuner, and the remaining tuners are used as manually-operated and fixed tuners. The plurality of tuners are arranged in an axial direction of a resonator and along an outer surface of a resonator tank, and each adapted to allow an end member thereof to be inserted into a cavity through a lateral portion of a wall of the resonator tank so as to change a circuit constant of the resonator to modify a resonant frequency or a voltage distribution, as will be described later. Among the tuners, one type configured to change an inductance of the resonator is an inductive tuner, i.e., L tuner, and another type configured to change a capacitance of the resonator is a capacitive tuner, i.e., C tuner.
The auto-tuner is required to have a function of changing only a frequency without changing a voltage distribution. In reality, if one of the tuners is changed in position, a voltage distribution in the entire resonator tends to be changed. It is known that this tendency becomes prominent, particularly, in the IH linac. Thus, two or more of the tuners different in position have to be selectively used as auto-tuners in such a manner that respective voltage changes attributed thereto are cancelled out to keep the voltage distribution from being changed. For this purpose, a three-dimensional electromagnetic field calculation is essential to accurately figure out the voltage distribution, because the voltage distribution in the resonator is dependent on an entire structure of the resonator. However, if the three-dimensional electromagnetic field calculation is performed for each of the tuners while finely changing an insertion amount thereof, to figure out a relationship between a tuner insertion amount and a voltage change, a considerable time has to be spent therefor. As a way for evaluating a combination of tuners suitable for auto-tuners, such a repetitive three-dimensional electromagnetic field calculation is not realistic.
Non-Patent Publication 1: Satoshi YAMADA, et al., “Integrated Report on Construction of Heavy Particle Beam Cancer Therapy Equipment”, May/1995, National institute of Radiological Sciences
特許請求の範囲(英語) [claim1]
1. A method of designing an H-mode drift-tube linac utilizing a TE wave (H mode) generated inside a resonator, said method comprising:
nominating at least two tuners from among a plurality of tuners arranged along an axial direction of said resonator; and
selecting said nominated tuners as auto-tuners through evaluation in terms of whether only a frequency is changed without changing a voltage distribution in said resonator, using a combination of respective positions of said nominated tuners in the axial direction of said resonator and respective insertion amounts of said nominated tuners into said resonator.

[claim2]
2. The method as defined in claim 1, wherein said step of selecting includes:
calculating or measuring individual voltage change data corresponding to respective insertion amounts, for each of said plurality of tuners, based on a given relationship between a tuner insertion amount and a voltage change; and
determining a combination of at least two auto-tuners and a combination of respective insertion amounts of said at least two auto-tuners, using said individual voltage change data.

[claim3]
3. The method as defined in claim 2, which said step of selecting further includes the sub-step of verifying said given relationship between a tuner insertion amount and a voltage change.

[claim4]
4. The method as defined in claim 2, which said step of selecting further includes the sub-step of verifying whether said determined combinations are adequate.

[claim5]
5. The method as defined in claim 2, wherein said given relationship is a linear relationship between a tuner insertion amount and a voltage change, wherein said individual voltage change data corresponding to respective insertion amounts, for each of said plurality of tuners, are calculated through a proportional calculation based on said linear relationship.

[claim6]
6. The method as defined in claim 2, wherein said sub-step of determining a combination of at least two auto-tuners and a combination of respective insertion amounts of said at least two auto-tuners comprises determining said combinations on a condition that, when the individual voltage change data of said nominated tuners are added together, respective voltage changes attributed to said nominated tuners are cancelled out to allow an entire voltage distribution to have substantially no change.

[claim7]
7. An H-mode drift-tube linac utilizing a TE wave (H mode) generated inside a resonator, said linac comprising a plurality of tuners which are arranged along an axial direction of said resonator, and partly used as an auto-tuner, wherein:
said auto-tuner consists of at least two tuners which are nominated from among said plurality of tuners, and selected through evaluation in terms of whether only a frequency is changed without changing a voltage distribution in said resonator, using a combination of respective positions of said nominated tuners in the axial direction of said resonator and respective insertion amounts of said nominated tuners into said resonator.

[claim8]
8. The H-mode drift-tube linac as defined in claim 7, which includes insertion-amount adjustment means adapted to adjust respective insertion amounts of said selected at least two auto-tuners without changing a ratio between said respective insertion amounts.

[claim9]
9. The H-mode drift-tube linac as defined in claim 8, wherein said insertion-amount adjustment means includes storage means adapted to store said ratio between the respective insertion amounts of said at least two auto-tuners.

[claim10]
10. An auto-tuner selection process for use in a method of designing an H-mode drift-tube linac utilizing a TE wave (H mode) generated inside a resonator, said process comprising:
nominating at least two tuners from among a plurality of tuners arranged along an axial direction of said resonator; and
selecting said nominated tuners as auto-tuners through evaluation in terms of whether only a frequency is changed without changing a voltage distribution in said resonator, using a combination of respective positions of said nominated tuners in the axial direction of said resonator and respective insertion amounts of said nominated tuners into said resonator.

[claim11]
11. A method of adjusting at least two auto-tuners employed in an H-mode drift-tube linac utilizing a TE wave (H mode) generated inside a resonator, said auto-tuners being selected by nominating at least two tuners from among a plurality of tuners arranged along an axial direction of said resonator, and evaluating said nominated tuners in terms of whether only a frequency is changed without changing a voltage distribution in said resonator, using a combination of respective positions of said nominated tuners in the axial direction of said resonator and respective insertion amounts of said nominated tuners into said resonator, said method comprising adjusting respective insertion amounts of said auto-tuners without changing a ratio between said respective insertion amounts.
  • 発明者/出願人(英語)
  • IWATA YOSHIYUKI
  • YAMADA SATORU
  • National Institutes for Quantum and Radiological Science and Technology
国際特許分類(IPC)
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