DE1199901B - Linear accelerator - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

LIBRARY

OF THE GERMAN

PATENT OFFICE

Int. α .:

Number:
File number:
Registration date:
Display day:

H05h

German class: 21g-36

V 22720 VIII c / 21,

June 29, 1962

September 2, 1965

The invention relates to a linear accelerator for charged particles, in which the particle beam a Waveguide traverses that of high frequency vibrations with one for the acceleration of the particles suitable phase velocity is excited and at the end of a device for absorption, which there incoming high frequency power is provided.

At the end of the device mentioned, another electrode for the purpose of generating X-rays can be provided; the accelerated particles can also be guided out of the vacuum vessel and aimed at an object to be irradiated.

For the purpose of the most favorable formation of the accelerator, it has been found to be desirable to train the device so that about 10% of the high frequency power at the end of the accelerating Waveguide remain and are destroyed there in an absorption device. In certain circumstances however, there may be even higher remaining high-frequency powers at the end of the accelerator than desirable result.

The high-frequency power remaining at the end of the accelerator is either available in an external one Absorption resistance destroyed or by means of a feedback to the input of the accelerator fed back. Such devices require a high frequency transition at the end of the accelerator device and an external absorption resistor or a device to return the high-frequency power removed at the end The input of the accelerator.

For many purposes the devices are for relaying or destroying the high frequency power undesirable because of their considerable space requirements. Especially when it comes to particle accelerators acts that are used for medical therapy, the accelerator should take up as little space as possible occupy, especially if the accelerator assembly is arranged on a crane, to a To be able to irradiate patients from different angles.

In the known accelerator arrangements, the focusing device is between the high-frequency coupling device and the high-frequency decoupling device provided at the end of the accelerator leading to the feedback branch or the absorption resistor provided, wherein the accelerator device is located inside the vacuum vessel and the focusing device around the Vacuum vessel is arranged around. Under such linear accelerator

Applicant:

Varian Associates, Palo Alto, Calif. (V. St. A.)

Representative:

Dr. phil. G. B. Hagen, patent attorney,

Munich-Solln, Franz-Hals-Str. 21

Named as inventor:

Jacob Haimson, Palo Alto, Calif. (V. St. A.)

Claimed priority:

V. St. v. America June 29, 1961 (120 597)

There may be difficulties in carrying out repair and monitoring work. It is undesirable if the vacuum vessel can only be completed after the focusing device has been applied to the accelerator device is. Under certain circumstances there is also the need to open the vacuum vessel, if for a repair the focusing device should be removed.

The invention avoids these disadvantages. A linear accelerator for charged particles with a traversed by the particle beam and by high-frequency oscillations for the acceleration of the Particles of suitable phase velocity excited waveguide and one connected to the end of the waveguide A device for absorbing the high-frequency power still arriving there is characterized according to the invention in that the absorbing device is a collinear with the waveguide, is terminating part having damping walls.

The linear accelerator according to the invention has the advantage of requiring little space and also allows there is a coupling-out conductor leading to an external absorption resistance at the end of the waveguide it is not necessary that from the rear end of the absorbing device or of the waveguide the focusing device can easily be pushed on.

According to a preferred embodiment of the invention, the absorbent closure part is designed so that it reflects any remaining high-frequency energy at its end, so that it is reflected

509 659/380

3 4

Waves pass back through the terminating section and this high frequency source becomes synchronous with the

be dampened again. Pulsed impulses, which the electrodes of the emitter

The absorbent closure can be supplied from a generator.

There are series of cavity resonators, whose In the packetizing section 13, which in typical

Walls at least partially with a material of 5 wise be a waveguide loaded with disks

high specific electrical resistance, can have various dimensions, such as the

are, where at least a portion of the cavity resonant inner diameter of the waveguide, the diameter

nators can have corrugated inner surfaces. Should that of the beam opening or the distance and the thickness

beam consisting of the accelerated particles on the disks, different along its length

End of the absorbing device to be led out io, so that the passing electron beam in

are, the end wall is expediently speed-modulated in such a way that the

of the end part with a beam for the high frequency waves has electron bunches when it enters the

Provided throttle acting particle outlet opening. uniformly accelerating section 14 occurs.

In view of the heat that occurs during operation, the packaging section can also be different

It is recommended that the waveguide be designed in a lengthwise manner or, in certain cases, at all

of the vacuum vessel only rigidly attached at one point not be present.

is, so that an expansion is possible when heated. The acceleration section 14 consists of a typical

The ability of the waveguide in the vacuum vessel to be guaranteed by a waveguide loaded with disks,

is performing. of a series of coupled cavity sonators

With reference to the drawings, the invention is intended to include 20 in more detail, the disks having an opening more constant

explained. It shows size and evenly spaced

F i g. 1 is a schematic view of a particle arranged along the length of the waveguide,

accelerator according to the invention, In the packetizing section 13, the electrical

F i g. Figure 2 is an enlarged side view of a portion of the packetized beam. These packages arise

the in F i g. 1 shown device, but 25 towards the apex of the high-frequency wave, the

certain parts have broken away, spread through the accelerating device.

F i g. 3 shows a cross-section through part of the

F i g. 2 pass along the line 3-3 shaped accelerating section 14,

in the direction of the arrows, is constantly carried by the high frequency wave on the

F i g. 4 shows a side view of another embodiment 30 electron bunches transfer energy so that these

example of the invention that a part of the packets are greatly accelerated.

F i g. 2 corresponds to, with typical linear accelerators they reach

F i g. 5 a fig. 4 similar side view of an emerging from the accelerating device

Another embodiment of the invention and electrons that form the beam, very high energies

F i g. 6 a fig. 4 similar side view of a 35 of, for example, many millions of electron volts,

another embodiment of the invention. To achieve maximum efficiency in generation

F i g. 1 shows a schematic view of an evacuation of X-rays, which can be raised Linear accelerator 10, in which a particle frequency power that is in the accelerating wave beam can be accelerated. Although the remains in the conductor when the passing through the following described particle accelerator to the 40 frequency wave the end of the accelerating Acceleration of an electron beam formed device has reached on the order of 10% the invention is also based on high-frequency power supplied to particle accelerators. These Less applicable in which other particles, such as when- power is usually played over an output transition Positrons, are accelerated. Furthermore, the formator is discharged and either through a single die Device according to the invention both for a 45 direction with a vacuum window for high frequency Impulse operation as well as constant currents of the energy supplied to a water-cooled load or Particle beam suitable. via a waveguide to the entrance of the

The particle accelerator 10 has a particle-nigging device returned,

source 11, for example an electron beam generator. The end section 15 according to the invention of FIG

ger, on and an accelerating device, which will be described in more detail 50 below, is located

z. B. a packetizing section 13, a steady at the output end of the uniformly accelerating

accelerating section 14 and an end section 14 and not only serves as an end section for

Contains section 15, which are all designed so that the high-frequency wave, but also as a single

from the source 11 coming electron beam direction, through which the electron beam continues,

can pass through it. 55 after leaving the accelerating section 14

In one for the impulse operation of a particle emerges, accelerated to the desired energy In a typical manner, a square-shaped becomes, or leaves, depending on the present usage impulse high voltage is supplied to the electrodes, the purpose of which is to change or reduce the entry energy are provided in the electron gun 11, the beam energy. In general, however, it is so that the electron beam in a corresponding manner 60 desirable to continue the beam in the end portion pulsates. To supply energy.

A voltage source, not shown, for high- The outer wall of the waveguide of the packetizing frequency High power shafts, e.g. B. a KIy section 13, the acceleration section 14 and power amplifier, serves to accelerate the end section 15 itself the vacuum envelope Device via an input coupling 12 to represent one for 6g for the particle accelerator 10. As in Acceleration of the beam serving high frequency is shown the embodiment of the invention, power, for example of about 1.75 MW with a vacuum envelope 16 can also use the wave frequency of for example 2,988 MHz. Head for the high frequency waves surrounding which

5 6

is then provided with openings for pumping out, so during the review of the accelerator or

that the waveguide can be evacuated. to feed.

The high energy packetized particle beam, the final cavity resonator 22 in the final building the end section of the particle accelerator 10 section 15 causes a reflection of the high frequency exiting, can either by an approach of the evacuated 5 waves that run along the accelerator

ierte envelope can be continued or run directly through, so that the remaining high-frequency power exit a vacuum window 20, like the simplicity at the end of the particle accelerator 10 along the

sake is shown. In any case, the particle accelerating device can be opposed to the

beam can be deflected onto or over a target, the direction of the beam is reflected.

to produce X-rays, or in any i ° due to the construction of the above described known way to be exploited. A particle accelerator can accelerate the process The coil 17, which focuses the beam, surrounds the device in a vacuum envelope 16 which accelerates it Facility can be arranged along the length of the, with only the entrance end of the Particle accelerator 10. Since, according to the invention, packetizing section 13 on the vacuum envelope 16 does not exist Coupling device for high-frequency waves 15 is anchored, while the rest of the accelerated The device facing the exit end of the particle accelerator 10, which apart from the packaging must be, the focusing coil 17 can cut 13, the accelerating section 14 and the in a simple manner over the output end of the loading end section 15, in the longitudinal direction in the accelerating device pushed onto this sleeve 16 can move when the accelerating will. This is a very desirable benefit of the device expanding due to heating. Invention, by the special cost and a The particle accelerator 10 operates in the folloW more complicated Construction of the vacuum envelope 16 avoided lowing manner: When the high-frequency waves, will. Another advantage of this arrangement consists in the accelerating device through the due to the omission of the external connections coupling device 12 are coupled by in that the accelerating device is located within the packaging section 13 and the accelerating device of the vacuum vessel expand freely and propagate the supply section 14, transmit the waves can pull together, as will be explained in more detail later, energy on the electrons passing through to the shall be. Packetizing and accelerating particles of the beam in FIG. 2 and 3 is a typical design. From the accelerating section 14 spreads Example of the end section 15 according to the invention 30, the high-frequency wave in the end section 15 shown. The end portion 15 has a with. where continues to interact with the Slices loaded waveguide 18, which takes place a particle beam and an energy transfer, high frequency power delay device When the high frequency wave passes through the endin represents the accelerator and spreads the same dimension section, it is also strongly attenuated, sings like the waveguide of 35, which is loaded with disks, in particular through the walls 21 of the spacers, having uniform accelerating portion 14. which have a high specific resistance. The loaded waveguide 18 consists of a number. Therefore, the high frequency wave continues to emit of conductive discs 19, which have a central opening to transfer energy to the electron beam while they are themselves have and for example consist of copper. is dampened. In the last cavity resonator 22 of the Each disc 19 is by means of a hollow cylindrical 40 end section 15, the high-frequency wave reflector spacer 21 at a distance from the ant and runs backwards in the end section 15 adjacent disc 19 arranged. The walls of the opposite to the direction of the electron beam Spacers 21 consist of a magnetic one and are in turn damped. The length of the Resistance material, for example from magnetic end section, is selected so that the damping stainless steel. 45 functional properties of the end section 15 in the direction of the alternately one behind the other arranged splitting of the beam together with the damping planes 19 and spacers 21 form a number of properties of the end section 15 compared to the Cavity resonators 22, which via central opening-reflected wave in the opposite direction gene 23 in the disks 19 are coupled. A number the correct amount of damping the remaining of openings 24 for pumping out 50 high-frequency power is produced in each wall 22, which in the end abder Spacers are provided to facilitate evacuation of the cut 15 from the accelerating section 14 of a waveguide 18 in the sleeve 16 to enable. occurs to an interaction of the reflected wave A cooling device for the waveguide, as with both the packetization and acceleration properties cooling pipes through which water flows, can th of the packetizing section 13 and the Schleuauf the outer surface of the waveguide provided 55 inclination section 14 as well as a disadvantageous frequency, because to prevent a large amount of heat in the final change of the high frequency generator, section is generated in which the remaining high frequency is the most convenient in a typical particle accelerator Performance is destroyed. When the wall of the kind written start the phase positions of the Elek waveguide 18 is the vacuum envelope, it can electrify in an undesirable way from its circles, the always be surrounded by a coolant. A 60 are determined by the embodiment in which Number of radial supports 25 are provided to deviate the packetizing section when the waveguide is available 18 to be held in the sheath 16. A high output in the direction of the beam reduced by 8% Frequent throttle device 26 is at the end of the will. Also becomes the property of the packetizing waveguide 18 provided in the end section 15, in sections with regard to the generation of a focus the passage of high-frequency waves is influenced by the 65 ization of the energy when the reflected To prevent the end of the waveguide 18. This one-time performance is high.

direction 26 can, however, also from the end of the shaft although the end section 15 has the remaining power

conductor must be removed in order to attenuate high-frequency power of the high-frequency wave in the beam direction,

In some cases it is not desirable to have the remaining high frequency power at the end of the end section is so low that the particle beam regeneratively supplies high-frequency power and energy the high frequency device emits. According to the invention, the length of the termination can be selected that the attenuation in the beam direction can be reduced to zero if necessary. For practical purposes, however, this damping is chosen so that in combination with the attenuation in the opposite direction reduces the amount of reflected power sufficiently is, thereby reducing the packaging and accelerating properties of the accelerating device are not affected and the high frequency generator is not adversely affected.

The following two tables show the manner in which the remaining high frequency power in a typical particle accelerator can be damped in the accelerating device. Of the special particle accelerator is specially designed for therapeutic purposes. The delivered peak power the high frequency energy is about 1.75 MW. The result is electron energies of about 6 MeV. However, much higher energies can be achieved

ίο be. The tables show damping properties of particle accelerators of the same length, in which the lengths of the acceleration section are along the accelerator axis 14 and of the end section 15 are different in order to increase the amount of damping change to which the remaining high frequency power is exposed.

Table I.

Distance along the
Acceleration Z Power in beam direction (MW) burdened Reflected Power (MW) burdened Energy of
Electrons device in Fig. 1 (cm) unencumbered 1.75 unencumbered 0.091 ray (MeV) O 1.75 1.60 0.176 0.095 * 0.08 W. 10 1.15 0.112 X 55 1.41 0.61 0.225 0.147 2.8 Y 130 1.07 0.28 0.30 0.28 5.9 Z 150 0.56 0.56 6.5

d. H. 6% of the power in the direction of the beam.

Table II

Distance along the
Acceleration Z Power in beam direction (MW) burdened Reflected Power (MW) burdened Energy of
Electrons device in Fig. 1 (cm) unencumbered 1.75 unencumbered 0.027 ray (MeV) 0 1.75 1.60 0.064 0.028 * 0.08 W. 10 1.15 0.034 X 55 1.41 0.73 0.079 0.041 2.8 Y 110 1.15 0.15 0.096 0.150 5.3 Z 150 0.32 0.32 6.4

d. H. 1.75% of the power in the direction of the beam.

The amount of attenuation applied to the residual high frequency power that causes the uniform accelerating section 14 leaves can be changed in various ways. The cushioning / is given by the following formula:

π · c

IFvj

where c is the speed of light, Q is 2π times the ratio of the energy stored in the cavity resonators of the waveguiding device to the energy that is dissipated in the cavity resonators of the device during one cycle, Vg is the group speed of the high-frequency wave traveling along the Device, and λ is the wavelength of the high frequency wave in vacuum. Therefore, at a given operating frequency, the damping in the end portion 15 can be increased over the damping that occurs in the uniformly accelerating portion 14 by decreasing Q and / or Vg . Q can be decreased by decreasing the ratio of the effective void volume to the effective electrical surface area. Another way of lowering the ß-factor of a cavity is that the permeability and / or the specific resistance are increased.

In the embodiment described above, the cavity walls of the resonator were raised from magnetic Material with high specific resistance, such as made of magnetic stainless steel, the attenuation of one end section is strong, the cavity resonators with the same dimensions like that of the accelerating section. For example, acceleration sections would have spacers made of copper have a ß-factor of about 12,500, while the Hohlraumresonatoreri of the end portion 15 described above is similar in size to that of the uniformly accelerating one Section, but with walls 21 made of magnetic stainless steel, a ß-factor of about 1400 would own. Even if the walls are made of a non-magnetic material with a high specific Resistance rather than a magnetic material would still have the Q-factor be around 2500.

9 10

In another exemplary embodiment of the single-space resonators of the acceleration section 14 "

Both the panes 19 and the walls21 are the case.

the spacer made of material with high specificity Resistance to find even greater attenuation can be the desirably low ß-factor iür the high-frequency wave in the end section 15 5 of the cavity resonators achieved in the end section to achieve. Everyone will be erected in such an establishment, although the hollow space is appropriately executed the heat generated in the panes 19 is not so walls and panes of the same dimensions and well fed to the cooling device, which feeds the shafts - the same materials as the uniform 18 as used in the accelerating section described above. Through this Embodiment is the case in which the Schei- io will weave the manufacture of the particle accelerator 19 made of a highly conductive material such as copper, is much favored. According to FIG. 6 is at the end of one exist. In this embodiment, uniform accelerating portion 30 can have an end therefore Cooling devices, such as, for example, water section 33, which has a series of cavity channels, In the disks 19 are provided to contain resonators 43, which are alternately arranged from these Slices 19 to cool better. 15 Neten discs 35, which have openings and from

In Fig. 4 is another embodiment of the copper made, as well as walls 36 are made,

Invention illustrated in which a number of which can also be made of copper.

Grooves 27, which give a non-planar surface, transversely adjacent cavity resonators are through the

Openings 37 in the disks 35 are coupled to the flow path along the surface of the disk 19 ′. The last

and the walls 21 'are provided, whereby the remaining ao side wall 36, on which a throttle device 40 for

borrowed high frequency power in the waveguide 15 can be attached in high frequency at the end,

to a much greater extent the same can be made of stainless steel to an increased extent

axial length of the waveguide can be attenuated. Strength and increased cushioning of the last

To achieve the incised in this way transversely to the current path cavity resonator. Metal powder 38 with

tenen grooves lower the ß-factor of the cavity- 35 high specific resistance is applied to parts of the

resonator sprayed on by increasing the ratio of the end section to reduce damping

effective void volume for effective elec- tric increase. A well-suited material for this is a

tric surface area. The cavity resonance metal powder, which is sold under the trade name »Kanthai«

goals one trained in this way, is known with. In several ways it is such a thing

Discs 19 provided closure, the example 30 material ideal to dampen the cavity resonance

wise made of copper, as well as with walls 21 ', nators and the relevant device to increase,

which can consist of non-magnetic stainless steel, It has a high specific resistance ρ and

have a β factor of about 1600. If the high magnetic permeability μ. Furthermore results

Walls are also magnetic, the ß-factor would affect this on the inner surfaces of the cavity resonators

be around 1100. 35 sprayed material has a very uneven surface,

In the end section there is much more power, increasing the ratio of the void volume to

per unit length absorbed than is reduced by the acceleration-effective area size. A hollow

undulating waveguide. Although the device cooled room resonator with the same dimensions as the

the temperature of the facility will increase. The cavity resonators described above, the

Cavity resonators expand so that the 40 has the walls made of copper and with the

The wavelength of the cavity resonators changes, what the said material is sprayed has a ß-factor

a phase shift between the electron of 300. An even lower ß-factor can

ray and the high-frequency wave. be achieved when Kanthai on the discs 35 and

This results in an undesirable contribution to being sprayed onto the side walls 36.

Spreading the electron beam. 45 As in Fig. 6 is the amount of

It is therefore advantageous to have a very high damping kanthai, which in successive cavity resonators

fung factor so that the end portion is very short nators along the length of the end portion 33

can be, whereby the contribution to the spectral output is provided, gradually increased so that no very

spread of the electron beam due to large thermal discontinuity at the front end of the

Operational fluctuations are considerably reduced. 50 end section 33 of the accelerating device

If the end section is made of a material with due to a very large difference between the

a low coefficient of expansion, there is damping in the last cavity of the uniformly

and / or when Vg is less than the uniformly accelerating portion 30 and the damping in that

accelerating section is, so that the frequency first cavity of the end section 33 is present.

change for a given rise in temperature 55 Kanthai can also affect parts of the end section

is not so great then the phase shift- 'will be applied after the area on which

even less. this material is applied, first sandblasted

Another embodiment of the invention was shown. This results in an even rougher surface

F i g. 5, where the last cavity resonator 28 of the surface, while the Kanthai better at the base

uniformly accelerating section 14 "and the 60 adhered.

first cavity resonator 29 of the end section 15 ″ represents other materials that are to be erected in addition to Kanthai are. In this embodiment, the sprays on the terminal are used central openings 23 "of the disks 19" smaller than can, are highly lossy materials, such as the central openings 32 of the discs 31 in the stainless steel, iron, kovar, etc.

uniformly accelerating section, 65 The following table shows how the remaining high-

so that the cavity resonators in the end section frequency output in a typical particle accelerator

a high-frequency wave with a lower group niger of the embodiment shown in FIG

speed than is the case with the hollow ones.

. .. ". . , .-., .. ■., Ν 509659/380

Table III

distance JLi Power in beam direction (MW) burdened Reflected Power (MW) burdened Energy of along axis (cm) 100 ma pk lOOmapk Electrons in Fig. 1 0 unencumbered 1.75 unencumbered 0.0143 ray (MeV) 10 1.75 1.60 0.031 0.015 * 0.08 W. 55 1.15 0.018 X 140 1.41 0.55 0.038 0.024 2.80 Y 150 1.04 0.11 0.050 0.110 6.25 Z 0.23 0.230 6.47

* 0.94% of the power in the direction of the beam.

VSWR (mismatch) in a high frequency generator without ferrite insulator and without radiation exposure = 1.31;

VSWR for a high-frequency generator without ferrite insulator and with a peak load of 100 mA = 1.186;

VSWR with a high frequency generator with 5 db Isolation and with 100 mA peak load = 1.106;

VSWR for a high frequency generator with 10 db isolation and 100 mA peak load = 1.060;

Optionally, the attenuation that extends through the end section 15 for the remaining high-frequency power at the end of the uniform accelerating section results, are increased by loading the cavity resonators of the end portion by z. B. with a Resistive coated ceramic members can be used or by increasing the thickness of the discs in the end portion opposite the thickness of the disks in the uniformly accelerating. Section increased will.

35

Claims (8)

Patent claims: 1. Linear accelerator for charged particles with one traversed by the particle beam and high-frequency vibrations with a phase velocity suitable for the acceleration of the particles excited waveguide and a device connected to the end of the waveguide for the absorption of the high-frequency power still arriving there, characterized in that that the absorbing device has a terminating part which is collinear with the waveguide (14) and has damping walls (15) is. 2. Linear accelerator according to claim 1, characterized in that the terminating part so is designed that he still existing high frequency energy for the purpose of further at its end Attenuation reflected. 3. Linear accelerator according to claim 1 or 2, characterized in that the terminating part consists of consists of a series of cavity resonators, the walls of which are at least partially covered with a material are clad with high specific electrical resistance. 4. Linear accelerator according to claim 3, characterized in that at least some of the cavity resonators Has corrugated inner surfaces coated with a material of high specific electrical strength Resistance are clothed. 5. Linear accelerator according to claim 1 or one of the following, characterized in that the terminating part is or rather a hollow cylinder, which is divided into a plurality by a plurality of transverse disks is divided by cavity resonators, the discs through openings for the from charged particles have existing beam. 6. Linear accelerator according to claim 1 or one of the following, characterized in that the end wall of the end part has a particle outlet opening acting as a throttle for the high-frequency waves Has. 7. Linear accelerator according to claim 1 or one of the following, characterized in that the damping material has both a high specific resistance and a high magnetic resistance Has permeability. 8. Linear accelerator according to claim! or one of the following, characterized; that the waveguide is only rigidly attached at one point along the vacuum vessel, so that when heated an expansion possibility of the waveguide in the vacuum vessel is guaranteed. Considered publications:
U.S. Patent No. 2,920,228. 1 sheet of drawings 509 659/380 8.65 © Bundesdruckerei Berlin