Patent Application
20180192506
Embodiments of the present invention generally relate to the field of cyclotron resonators. More specifically, embodiments of the present invention relate to systems and methods for tuning RF cyclotron resonators.
Standard radiation therapy using X-ray beams deposit their energy along the path of the beam to a target tumor. Particle therapy with protons or other ions is a type of radiotherapy that uses an external beam to provide targeted ionizing radiation to a tumor. Protons or other charged ions are sent to an accelerator to bring the particles' energy to a predetermined value. The protons or other ions then move through a beam-transport system, where magnets are used to shape, focus and/or direct the proton or other ion beam as necessary.
Traditionally, one of the key design aspects of particle therapy is the use of symmetrical tuners in a cyclotron resonator. The cavities of cyclotrons, called Dees, are tuned for matching the cavity eigenmode to the RF-Signal of the RF-Power supply system and to preserve the field balance between the cavities. Some proton therapy systems use Hill-Number Ford rotational symmetry. In addition, all cyclotron are designed to obtain Top-Bottom mirror symmetry, where the mirror plane coincides with the beam plane. A RF resonator is used to produce a voltage to accelerate particles. Within the resonator tuners are used to control the resonance frequency. The maximum accelerating voltage is expected to be in the middle of the distance between two tuners. If only one of the tuners is moved, the maximum accelerating voltage moves away from the median plane which negatively affects acceleration performance of a cyclotron.
The complexity of the cyclotron is increased greatly when both tuners need to be moved to maintain symmetry. For example, moveable sliding seals are used to separate atmospheric pressure from evacuated portions of the cyclotron. The use of a great number of moving parts increases the design complexity and the risk of failure of a moving part. Additionally, cyclotrons having symmetrical tuners require complex control software, especially when feedback loop algorithms are used for multi-dee cyclotrons. What is needed is a simplified high performance cyclotron that does not require complex control software and moving parts to reduce material, operation, and service costs of the cyclotron.
Methods and systems for tuning a cyclotron resonator using asymmetrical tuners are disclosed herein.
According to one disclosed embodiment, a cyclotron is disclosed. The cyclotron includes a main coil for producing a magnetic field, an iron magnet surrounding the main coil for shaping the magnetic field, and a radio frequency resonator for producing an alternating electric field using the vacuum chamber. The resonator includes, a fixed short stem coupled to a vacuum chamber disposed within the cyclotron, a movable short stem coupled to the vacuum chamber, and a tuner plate disposed within the movable short stem, where the tuner plate asymmetrically tunes the RF resonator to accelerate particles.
According to another disclosed embodiment, fixed short stem for tuning an RF cyclotron resonator is disclosed. The fixed short stem includes a first shorting plate disposed within the fixed short stem, and an inner conductor disposed within the fixed short stem and in contact with the shorting plate. The inner conductor contacts an outer surface of a dee, a moveable short stem comprising a second shorting plate tunes the resonator by changing a distance between the second shorting plate and the first shorting plate, and the dee performs particle acceleration.
The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention:
Reference will now be made in detail to several embodiments. While the subject matter will be described in conjunction with the alternative embodiments, it will be understood that they are not intended to limit the claimed subject matter to these embodiments. On the contrary, the claimed subject matter is intended to cover alternative, modifications, and equivalents, which may be included within the spirit and scope of the claimed subject matter as defined by the appended claims.
Furthermore, in the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the claimed subject matter. However, it will be recognized by one skilled in the art that embodiments may be practiced without these specific details or with equivalents thereof. In other instances, well-known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects and features of the subject matter.
Portions of the detailed description that follows are presented and discussed in terms of a method. Although steps and sequencing thereof are disclosed in a figure herein describing the operations of this method, such steps and sequencing are exemplary. Embodiments are well suited to performing various other steps or variations of the steps recited in the flowchart of the figures herein, and in a sequence other than that depicted and described herein.
Some portions of the detailed description are presented in terms of procedures, steps, logic blocks, processing, and other symbolic representations of operations on data bits that can be performed on computer memory. These descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. A procedure, computer-executed step, logic block, process, etc., is here, and generally, conceived to be a self-consistent sequence of steps or instructions leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated in a computer system. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like.
It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussions, it is appreciated that throughout, discussions utilizing terms such as “accessing,” “writing,” “including,” “storing,” “transmitting,” “traversing,” “associating,” “identifying” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.
Some embodiments may be described in the general context of computer-executable instructions, such as program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Typically, the functionality of the program modules may be combined or distributed as desired in various embodiments.
Cyclotron Rf Resonator Tuning With Asymmetrical Fixed Tuner
The following description is presented to enable a person skilled in the art to make and use the embodiments of this invention; it is presented in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present disclosure. Thus, the present invention is not limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.
With regard to
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Although the fixed shorting plate 235 and fixed short stem 230 are depicted below dee 225, according to some embodiments, fixed shorting plate 235 and fixed short stem 230 are located in another position (e.g., above dee 225). Fixed short stem 230 further includes inner conductor 220. In some of the embodiments, the voltage distribution does not change, and the voltage maximum remains in middle position despite asymmetrical movement of the shorting plate tuner. Voltage is bound by capacitance of the accelerating surfaces, and a very small distance between dee 225 and an outer structure or liner of the resonator yields a relatively high capacitance.
Cyclotron 200 further includes an iron magnet for shaping a magnetic field, a magnetic coil 255, an upper ion source 260, and a lower ion source 265. Specifically, according to some embodiments, the iron magnet includes iron yoke ring 240, upper iron pole cap 245, and lower iron pole cap 250. The coil and iron components are used to produce and shape the magnetic field needed to accelerate particles inside the cyclotron. Upper pole cap 245 and lower pole cap 250 work in conjunction with yoke ring 240 to return the magnetic field lines. The ion sources 260 and 265 may comprise any particle source that produces charged particles for the accelerator, such as an external ion source with an injection system or an Electron Cyclotron Resonance (ECR) Ion Source.
According to some embodiments, magnetic coil 255 is constructed from annealed copper, insulated with fiber-glass and covered with an epoxy resin.
According to some embodiments, fixed tuner stem 215 comprises a sliding shorting plate. According to other embodiments, fixed tuner stem 215 comprises a bellowed stem. According to other embodiments, fixed tuner stem 215 comprises a telescopic tube.
With regard to
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With regard to
Like with symmetrically fixed tuners, for asymmetrically fixed tuners, no unusual behavior of the tuner positioning was caused by the field balance loop or the matching loop. At the 14:28 timestamp, half of the tuners are static. At timestamp 14:56, the field balance loop was activated and regulated the dee voltages in balance within five minutes. Regulation behavior from the field balance loop shows no negative effects caused by fixed tuners. Performing particle acceleration using asymmetrical tuning reduces design complexity, the cost of maintenance, fabrication and installation complexity, failure rate, and software complexity (e.g., control software), for example.
With regard to
For an Asum of 0.51 V, the system took an average of 350 seconds for the tuners to reached stable relative positions after a restart of the RF system to full power. After that time the system reached a balanced field across the dees 1-4. For an Asum of 0.78 V, the System took an average of 350s until the tuners reached stable positions relative to each other after a restart of the RF system to full power.
With regard to
At step 702, the charged particles are accelerated using a magnetic field. According to some embodiments, the magnetic field is shaped using a magnet, and field lines of the magnet field are returned using an upper pole cap, a lower pole cap, and a yoke ring.
At step 703, a first tuner disposed within a moveable tuner stem is moved to asymmetrically tune the cyclotron for preserving a field balance between cavities of the cyclotron. As described above, a distance between the first tuner and a fixed tuner defines a resonance frequency of the cyclotron, and a maximum field produced by the cyclotron is independent from an asymmetrical movement of the tuner plate.
Embodiments of the present invention are thus described. While the present invention has been described in particular embodiments, it should be appreciated that the present invention should not be construed as limited by such embodiments, but rather construed according to the following claims.
