RU2792835C1 - Accelerating module of a linear resonance accelerator with tuner patches for drift tube supports - Google Patents

Abstract

FIELD: linear accelerators of charged particles.

SUBSTANCE: invention relates to the field of creation of linear accelerators of charged particles and is an accelerating module of a linear resonant accelerator. The design of the module is represented by a cylindrical resonator housing made of materials characterized by strong electrical conductivity, such as copper, aluminum. Drift tubes are placed inside the resonator housing using a system of direct supports for drift tubes without changing the angle of installation of the supports. The drift tube supports have an increased diameter and a cylindrical shape due to the installation of a cylindrical tuner patch on each of the said supports, consisting of two parts, cut in a plane along the axis and forming a cylinder and connected to each other for fixing on the specified support.

EFFECT: simple setting up of the distribution of the accelerating field of the module of the developed accelerating structure without a significant reduction in energy efficiency.

3 cl, 5 dwg, 1 tbl

Description

The invention relates to the field of creation of linear accelerators of charged particles. It can be used in the development of new and modernization of existing linear charged particle accelerators.

State of the art

As analogues, one can choose known designs of accelerating structures, for example, those described in the report by Kurennoy S., O'Hara J., Rybarcyk L, Compact Linac for Deuterons (Based on IH Structures with PMQ Focusing), LANL, Los Alamos, Proceedings of Hadron Beam 2008, Nashville, Tennessee, USA NM, High-Intensity Linacs & Rings: New Facilities and Concepts, WGE13, 2008, p. 428-430 [1]. The proposed report presents a comparison of the design parameters of accelerating structures for resonant accelerators on a standing wave based on H-resonators. Common to all designs is the presence of a cylindrical body that acts as a high-frequency screen with drift tubes placed inside it, which are supported by supports. The supports are made in the form of cylinders of the same diameter and are attached to the resonator body on one side and support the drift tube on the other. One of the close analogs is the design called "IH with vanes", shown in fig. 1. As shown in fig. 1, the supports (3) supporting the drift tubes (2) are attached to the resonator body (1) through a conductive stand (4) made in the form of a pylon - a rectangular plate installed along the longitudinal axis of the resonator body, while all supports (3) are the same. This design has the best energy efficiency parameters.

The disadvantage of this design is the complexity of tuning the distribution of the accelerating field, which is discussed below.

Known design of the accelerating structure, shown in Fig. 2 disclosed in copyright certificate SU 728684, publ. 03/30/1984 [2], in which part of the supports (3) of the drift tubes (2) is attached to the resonator body (1), and part to the conductive stand (4), made in the form of a pylon, this design allows to reduce high-frequency power losses, for by increasing the surface area through which high-frequency currents flow, and to adjust the distribution of the accelerating field by attaching an additional conductive rod (5). Rod (5) is a conductive rod attached on one side to the drift tube support, and on the other side to the side wall of the resonator housing.

A common disadvantage of the above analogs of the present invention is the complexity of adjusting the distribution of the accelerating field formed between the drift tubes. The distribution of the accelerating field is tuned by adjusting the natural frequency of the cells of the accelerating system, since a resonator with drift tubes is a system of resonant circuits (cells) connected by an electromagnetic field. Under the cell of the accelerating system is meant the region of the resonator between the planes perpendicular to the axis of the resonator and passing through the midpoints of the supports of the drift tubes. The presence of a single conductive stand, made in the form of a pylon, complicates the tuning process, since the tuning of each cell of the accelerating system must be done individually, and due to the fact that all cells are covered by a common single longitudinal magnetic field that creates a strong magnetic connection between the cells, a satisfactory tuning can be achieved. difficult due to the influence of cells on each other (i.e. due to the feedback effect). As a result, even a slight rearrangement of one cell leads to a rearrangement of others. Although some simplification of the cell adjustment is carried out by installing additional rods, the installation of such rods in one row of drift tube supports does not provide a sufficient range of cell adjustment, because the opposite row of drift tube supports, attached to a conductive support made in the form of a pylon, is still covered by a strong magnetic connection due to the presence of a common pylon.

The closest analogue (prototype) of the invention is known from the copyright certificate SU 588887, publ. 11/05/1979 [3], the accelerating structure of a linear accelerator of charged particles, operating on the type of oscillations H and made in the bidet of a cylindrical resonator (1) with a system of straight lines (3a) and angular supports (36), called in [3] pins, at the ends which the drift tubes (2) are reinforced, the diagram of which is shown in fig. 3.

The advantage of the prototype over the analogues discussed above is a significant simplification of setting the required distribution of the accelerating field. In such an accelerating system, the drift tube supports are located in such a way that the projections of the supports of each two adjacent tubes, except for the first two, onto a plane perpendicular to the resonator axis, form angles less than 180°, and with increasing distance between the geometric centers of the drift tubes, the value of these angles decreases. .

The prototype, like the proposed invention, has a cylindrical resonator housing with a system of drift tubes supported by supports.

The disadvantage of the prototype is that it has less energy efficiency compared to other designs [1, 2]. This is probably due to the fact that the design of the prototype used the fastening of the supports to the resonator body directly and without the use of any pylons.

Disclosure of the essence of the invention

Technical problem

Accelerators used for applied purposes, and in particular, to accelerating structures, are subject to a number of specific requirements that are closer to industrial ones. First of all: ease of maintenance, efficiency, reliability. These requirements are especially important in the case when the accelerating structure of a linear accelerator is built according to a modular scheme, i.e. the accelerating structure consists of a sequence of separate resonators (modules). In this case, the design of each module of the accelerating structure must be unified. Moreover, the technical problem lies in the absence of such a unified module of the accelerating structure, the design of which will reduce the time for setting up the distribution of the accelerating field of the module and not significantly reduce its energy efficiency.

The solution to this problem is to create a design of the accelerating structure module, which makes it possible to combine the conditions of ease of tuning the distribution of the accelerating field in it without a significant decrease in its energy efficiency.

In the context of the proposed invention, energy efficiency is understood as the generally accepted effective energy consumption (see, for example, https://ru.wikipedia.org/wiki/Energy Efficiency [4]), which for resonator accelerating structures can be determined by the value of the shunt resistance. Comparison of the energy efficiency of resonator accelerating structures is carried out in terms of high-frequency power P (the actual order of magnitude is hundreds of kW), which must be introduced into the accelerating structure in order to obtain the voltage U (the actual order of magnitude is hundreds of kV) between the drift tubes required to accelerate and acquire a given particle energy . This power is defined as:

where _Rsh is the shunt resistance, a value characterizing the efficiency of accelerating structures (the current order of magnitude is tens of MΩ) [5]. Because Since this value depends on the design of the accelerating structure, it is possible to compare the energy efficiency of accelerating structures using it. A higher value of shunt resistance at the same voltage between the drift tubes for different designs of accelerating structures means higher energy efficiency.

It is proposed to adjust the distribution of the accelerating field in each accelerating gap between the drift tubes without violating the preliminary adjustment of the drift tubes, which is achieved by changing and redistributing the electric potentials on the drift tubes by the unique design of the tuning device disclosed in the present invention. Ease of setup is ensured by the design of such a device. At the same time, such a device does not significantly affect the high-frequency losses in the resonator and is suitable for reliable long-term operation.

[5], где

- продольная составляющая напряженности ускоряющего поля между трубками дрейфа,

- собственная частота ячейки ускоряющей системы, а относительное изменение собственной частоты ячейки ускоряющей системы

где ΔV - изменение объема ячейки ускоряющей системы [5], то процесс настройки распределения ускоряющего поля вдоль резонатора сводится к процессу изменения объема каждой ячейки.As mentioned above, the distribution of the accelerating field is tuned by adjusting the natural frequency of the cells of the accelerating system, because

[5], where

is the longitudinal component of the accelerating field strength between the drift tubes,

is the natural frequency of the cell of the accelerating system, and the relative change in the natural frequency of the cell of the accelerating system

where ΔV is the change in the cell volume of the accelerating system [5], then the process of tuning the distribution of the accelerating field along the resonator is reduced to the process of changing the volume of each cell.

Technical result

The technical result of the proposed invention consists in a significant simplification of the adjustment of the distribution of the accelerating field of the module of the developed accelerating structure without a significant reduction in energy efficiency.

[6], где, J - амплитуда поверхностного тока. Исходя из того, что

где D - внешний диаметр цилиндрических опор трубок дрейфа [7], т.е. обратно пропорционально диаметру D и, следовательно, чем меньше потерь, тем выше энергоэффективность.The technical result is achieved due to the proposed design of the module of the accelerating structure, in which drift tube supports of a special design are used, which include the function of special tuning devices and allow, by increasing the volume of each of the drift tube supports along their length, to ensure the adjustment of the distribution of the accelerating field in each gap between drift tubes. An increase in the volume of drift tube cylindrical supports due to an increase in their lateral area leads to a decrease in the surface resistance R _s of the supports, which, in turn, reduces the high-frequency losses dP _n per element of the lateral surface dS, since:

[6], where, J is the amplitude of the surface current. Based on the fact that

where D is the outer diameter of the cylindrical supports of the drift tubes [7], i.e. inversely proportional to the diameter D and, therefore, the lower the losses, the higher the energy efficiency.

The diagram of the module of the accelerating structure proposed in this application is shown in fig. 4 (A - front view, B - side view). The proposed module is a cylindrical product made of materials characterized by strong electrical conductivity, such as copper, aluminum, etc. The design of the accelerating structure module according to the present invention consists of a resonator body (1) with drift tubes (2) placed in it, which are supported by supports (3), on which cylindrical tuners (6) are attached, as shown in Fig. 4 (A, B).

Inside the resonator case, a system of only direct supports of the drift tubes is installed without using the placement of the drift tubes at an angle (angular supports (3b) of the drift tubes in the prototype in Fig. 3), i.e. all drift tubes in the proposed invention are installed only using a system of straight supports. In the proposed invention, the drift tube supports, in contrast to the prototype, have an increased diameter, while the increase depends on the specific distribution of the accelerating field and can reach four, five or more times, which is achieved by installing cylindrical tuner pads on them, cut into two parts by a plane along axis and generatrix of the cylindrical surface and connected to each other for fixing in this way on the specified supports, for example, using a screw, bolt or other connection.

.The height of the cylindrical overlays-tuners is selected on the basis of design considerations when calculating the tuning devices, as a rule, it is not higher than R, determined by the formula H=R-r; where R is the radius of the resonator housing; r is the radius of the drift tube. The distribution of the accelerating field is adjusted by changing the volume of the cells of the accelerating system by installing cylindrical tuner pads on the supports, each of which is fixed on the support and consists of two parts cut by a plane along the axis and forming a cylinder and connected to each other. The diameter of cylindrical overlays-tuners and their height are calculated after finding the magnitude of the change in the volume of the cell of the accelerating system, which depends on the specific frequency of the resonator, the distribution of the accelerating field, the diameter, length of the tubes, etc. The relationship between the change in the volume of the cell of the accelerating system and the change in the frequency of the resonator is determined by the method of small perturbations [5], numerical simulation using the CST-studio program [8], which is widely used in the field of resonator calculation.

Below is the calculated ratio of frequency change for small deviations of the resonator parameters resulting from the placement of a small metal body into the resonator volume. In the context of the present invention, cylindrical tuners mounted on supports act as a small metal body that changes the internal volume of the resonator. The shape of such overlays-tuners is chosen as cylindrical, because, firstly; this simplifies the process of numerical simulation, and secondly; simplifies their production.

где D и RThe volume V of these tuner overlays is defined as

where D and R

- respectively, the diameter and height of the cylindrical overlays-tuners. Frequency change is defined as:

- относительное изменение частоты резонатора,Where

- relative change in the frequency of the resonator,

W is the stored energy in the resonator,

ε ₀ - vacuum permittivity,

dv - differential of the integration argument,

E ₀ - electric field strength before tuning the resonator,

R ₀ - magnetic field strength before resonator tuning;

μ ₀ - vacuum magnetic permeability

V is the volume of the cylindrical overlays-tuners installed on the supports of the drift tubes, by changing which the volume of the resonator changes.

Thus, according to the present invention, an accelerating system of a linear resonant accelerator is proposed, made in the form of a cylindrical resonator with a system of counter supports of drift tubes, at the ends of which drift tubes are fixed. At the same time, a system of direct supports of the drift tubes is installed inside the resonator housing without changing the angle of installation of the supports, and the supports of the drift tubes have an increased diameter and a cylindrical shape due to the installation of a cylindrical tuner lining on each of these supports, consisting of two parts, cut in a plane along the axis and generatrix of the cylinder and connected to each other for fixing on the specified support.

Brief description of the drawings Figure 1. Accelerating structure "IH with vanes", described in [1], where:

1 - resonator body;

2 - drift tubes;

3 - drift tube supports;

4 - conductive stand.

Figure 2. Accelerating structure with a longitudinal plate according to [2], where:

1 - resonator body;

2 - drift tubes;

3 - drift tube supports;

4 - conductive stand;

5 - additional conductive rod.

Figure 3. Accelerating structure of the counter pin type according to [3], where:

1 - resonator body;

2 - drift tubes;

3 - straight (a) and angled (b) drift tube supports.

Figure 4 (A, B). The module of the accelerating structure according to the present invention, where: A - front view, B - side view,

1 - resonator body;

2 - drift tubes;

3 - drift tube supports;

6 - overlays-tuners for drift tube supports;

Figure 5. Dependence of the relative change in the electric field strength in the accelerating gap on the change in the diameter of the drift tube support in a five-gap resonator.

Implementation of the invention (examples)

Example 1. Comparative, showing the setting of the distribution of the accelerating field, carried out according to the prototype.

Setting the required distribution of the accelerating field in the prototype is due to the installation of drift tube supports at angles less than 180° on a plane (for example, as indicated, from 0 to 180 degrees) perpendicular to the axis of the resonator. The required angle of installation is determined by the selection, and a more accurate installation of the support is determined in the process of setting the accelerating field.

In this case, it is very important not to disturb the alignment of the drift tubes, if it is violated, then a very laborious procedure for its restoration will be required, since the accuracy of the alignment of the drift tubes of modern accelerators is required at least +/- 25 μm. Installing supports at an angle, moving them around the resonator housing and fixing them in the desired position all require the use of complex fixtures. For example, specially designed devices that allow simultaneous movement along the angle with a step of no more than 1 degree, adjustment in three planes of drift tubes with an accuracy not less than the specified one, as well as reliable electrical contact with the resonator housing. For the manufacture of such devices, the use of high-precision machines is required, and their operation also requires high precision in the manufacture of the resonator housing, relative to the geometric axis along which the position of the drift tubes should be adjusted. With an increase in the dimensions of the resonator housing, the degree of accuracy of linear dimensions decreases. So, according to GOST 25346-89, the required diameter of the resonator case for the meter wavelength range is 300-500 mm. The parameters of the accelerating resonator according to the prototype: the diameter of the resonator housing 420 mm; resonator length 434 mm; drift tube diameter 100 mm; clearance between drift tubes 46 mm; drift tube length 46 mm; drift tube support diameter 20 mm; drift tube aperture diameter 50 mm; resonant frequency 162 MHz. In such an accelerating five-gap resonator with drift tubes, the installation of two supports with a diameter of 20 mm drift tubes at an angle of 2.5 degrees each to the normal leads to a change in the electric field strength by 5% in the accelerating gap between this drift tube and the previous drift tube, and the allowable Accelerating field tuning error in modern accelerators is no more than 2%. This imposes increased requirements on the accuracy of the installation of the supports in terms of the angle, while simultaneously ensuring the accuracy of the spatial adjustment, which has to be achieved in order to ensure the operation of the accelerator.

Example 2. The use of the design of the accelerating module according to the proposed invention, demonstrating the simplification of setting the distribution of the accelerating field and the increase in energy efficiency compared to the prototype.

According to the proposed invention, it is possible to simplify the process of fine tuning the distribution of the accelerating field, if we use the design of the accelerating structure module, which uses supports with attached cylindrical tuner pads and which do not need to be moved at an angle along the resonator housing, it is enough just to install them in their regular place and in If the result is unsatisfactory, it will be necessary to replace the tuner pad. As was found, for example, in an accelerating five-gap resonator with drift tubes. Parameters of the accelerating resonator according to the invention: resonator case diameter 450 mm; resonator length 420 mm; drift tube diameter 100 mm; clearance between drift tubes 46 mm; drift tube length 50 mm; diameter of supports for drift tubes of increased diameter 96 mm; drift tube aperture diameter 50 mm; resonant frequency 162 MHz. Changing the diameter of the tube support from 80 mm to 96 mm (by 16 mm) leads to a change in the electric field strength by 2% in the accelerating gap between this drift tube and the previous drift tube, which can be seen from Fig. 5 dependences of the relative change in the electric field strength in the accelerating gap on the change in the diameter of the tube support. The energy efficiency (shunt resistance R _W ) of the accelerating structure module with special cylindrical overlays-tuners, according to the results obtained (see Table 1), is higher by 19% in comparison with the prototype, and lower by no more than 5% in comparison, if pylon stands as in "IH with vanes" [1]. Shunt resistances were calculated using the CST-studio program [8], which is widely used in the field of calculating resonator parameters.

Thus, the proposed invention makes it possible to abandon the complex process of setting the drift tube supports to the required angle, as in the prototype [3], and use a simpler and less laborious process of selecting the diameters of cylindrical tuner pads, while maintaining the required energy efficiency, surpassing the energy efficiency indicators of the prototype and only slightly inferior to "IH with vanes" according to [1], which is characterized by an even more complex setting of the distribution of the accelerating field formed between the drift tubes than in [3]. In addition, based on the results of the studies presented in Fig. 5, the requirements for the accuracy of selecting the diameters of tuner overlays are not high, for example, if you need to change the field strength in the accelerating gap by 2%, it is enough to make the diameter of the tuner overlay with an accuracy of ±1 mm).

Literature

[1] paper by Kurennoy S., O'Hara J., Rybarcyk L, Compact Linac for Deuterons (Based on IH Structures with PMQ Focusing), LANL, Los Alamos, Proceedings of Hadron Beam 2008, Nashville, Tennessee, USA NM, High -Intensity Linacs & Rings: New Facilities and Concepts, WGE13, 2008, p. 428-430.

[2] copyright certificate SU 728684, publ. 03/30/1984.

[3] copyright certificate SU 588887, publ. 11/05/1979.

[4] Wikipedia article “Energy Efficiency”, posted at https://ru.wikipedia.orq/wiki/Energy Efficiency, as amended on 12/11/2021.

[5] Sobenin N.P., Milovanov O.S., "Technique of microwave frequencies" Energoatomizdat, Moscow 2007

[6] "Radio waveguides and cavity resonators" Shirman Ya.D., Svyazizdat, Moscow 1959

[7] "Fundamentals of radio engineering" Amalitsky M.V., Svyazizdat, Moscow 1949

[8] CST Studio Suite (https://www.3ds.com/ru/).

Claims (14)

1. The accelerating system of a linear resonant accelerator, made in the form of a cylindrical resonator with a system of counter supports of the drift tubes, at the ends of which the drift tubes are fixed, characterized in that a system of direct supports of the drift tubes is installed inside the resonator body without changing the angle of installation of the supports, while the supports of the tubes drift have a cylindrical shape due to the installation on each of the said supports of a cylindrical lining-tuner, consisting of two parts, cut in the plane along the axis and generatrix of the cylinder and connected to each other for fixing on the specified support, where the diameter of the specified support is selected in accordance with the formula :

Where

- relative change in the frequency of the resonator, W is the stored energy in the resonator, ε ₀ - vacuum permittivity, dν - differential of the integration argument, E ₀ - electric field strength before tuning the resonator, H ₀ - magnetic field strength before tuning the resonator, μ ₀ - vacuum magnetic permeability, V=πD ² H/4, where V is the volume of the drift tube support in the form of a cylinder, by changing which the volume of the resonator changes, D and H are, respectively, the diameter and height of the drift tube supports in the form of a cylinder. 2. The accelerating system according to claim 1, where the drift tube support is a cylinder with a height not exceeding H, where H is determined by the formula: H=R-r, where R is the radius of the cavity body, r is the radius of the drift tube. 3. Accelerating system according to any one of paragraphs. 1, 2, where the drift tube support has a diameter of 96 mm.

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