DE3601271A1 - LINEAR ACCELERATOR FOR LOADED PARTICLES - Google Patents

Description

description

The invention relates to a linear accelerator for charged particles, with the particle beam short duration in an accelerator for converter shafts are to be accelerated. Such linear accelerators are in different Areas used, for example for scientific purposes. As an example, reference is made to the injection of electrons or positrons into rings to generate synchrotron radiation.

In linear accelerators, the bundle of charged particles is injected into an accelerator by placing it under accelerated by the action of an electric field developed by a high frequency electromagnetic wave which is also injected into the accelerator. In general, the accelerators have a sequence of cavities that are dimensioned so that they cooperate, for example, with a high frequency wave, whose frequency is 3,000 MHz (S-band).

For a given electron beam energy, it is always interesting to reduce the length of the accelerator. This length can be reduced by increasing the power of the electromagnetic wave or that of acceleration serving high frequency wave enlarged. The magnification however, the high-frequency performance has its limits.

\ ^r In recent years, a high frequency compressor called SLED has been developed. This abbreviation stands for "Standord Linear Engergy Doubler". Compare this to ZD Farkas et al., "SLED: a Method of Doubling SLACs Energy", Proc. 9 Int. Conf. on High Energy Accelerators, SLAC, Stanford, CA, May 2-7, 1984. This high-frequency

The frequency compressor enables increased performance for short periods of time. One can therefore practically the communicated to the particles Double the energy, based on a unit of length of the linear accelerator.

A high frequency wave source operates in this system together with the SLED compressor. The high frequency source emits a high frequency wave after a pulse, which is corrected by the compressor SLED so that during a For a short time the power is concentrated which corresponds to the first pulse emitted by the high-frequency source will. The high-frequency pulse or the power high-frequency pulse corrected by the compressor SLED is used by the accelerator fed at a first end, where the bundle to be accelerated also enters the accelerator.

After compression in the SLED, the high-frequency power pulse is emitted with a very rapidly increased power peak. The impulse then drops again very quickly. This limits the duration T (HF) of this pulse and you have to use an accelerator "whose charging time T (S) is short. The duration T (F) of the electronic pulse or of the bundle to be accelerated should be such that the following equation is satisfied:
T (HF) = T (S) + T (F).

The high frequency power pulse must initially be the second Reach the end of the accelerator before the bundle to be accelerated arrives there. The duration T (F) of the bundle must be the shorter as the charging time T (S) is longer, and between a given duration T (H.F) of the power high-frequency pulse.

The residence time of the high frequency wave in a transducer wave type accelerator corresponds to the charging time TS this accelerator, contrary to the case of a standing wave accelerator.

For this reason, high-frequency compressors are used only with accelerators for converter shafts in the real sense. The accelerators for converter shafts have one Charging time T (S), which, compared to the charging time of an accelerator with resonance waves or standing waves, is short.

This solution is only partially satisfactory, in particular because the coupling between the accelerator cavities depends on the interaction between the High frequency waves and the bundles is dependent. the Coupling between two successive acceleration cavities takes place via a central aperture, through which the bundle to be accelerated also passes through. In particular, this leads to only mediocre quality the energy transfer of the high frequency wave to the bundle, based on an accelerator for standing waves, in which the shape of the accelerating cavities allows a lot between the high frequency wave and the beam achieve better synchronization.

The invention relates to a linear accelerator which makes it possible to use in an accelerator for a transducer shaft To accelerate bundles which take less time than the charging time T (S) of the accelerator. A linear accelerator according to the invention allows, compared with the prior art, that communicated to the bundle To increase energy, calculated on the length

unit of the accelerator. In particular, the benefits of a high frequency pulse compressor of the SLED type and the advantages that come with the shape of the cells or accelerating cavities the accelerators for standing waves are connected to be exploited together.

In particular, this allows the energy transfer to the Bundle and the shunt impedance of the accelerator can be improved. The energy of the accelerated Bundle can be raised and the global efficiency of the linear accelerator can be improved. Alternatively the charging time TS can be reduced with the same gain in energy per meter of the accelerator.

The invention is based on a linear accelerator for charged particles

- an accelerator for advancing waves with a specified loading time ζ to accelerate a bundle that takes less than the loading time,

- with a generator for an accelerating high frequency wave, which emits the high frequency wave after a pulse, wherein

- The accelerator has a series of accelerating cavities, which are on a longitudinal axis of the accelerator are arranged and have axial openings through which the bundle passes, which is attached to a first end enters the accelerator and progresses in the accelerator along its longitudinal axis, and from the first end to a second end of the accelerator.

To solve the problem of the invention, this is characterized by that the high frequency wave at the second end into the

Accelerator occurs in such a way that the interaction between the radio frequency source and the bundle at each other opposite directions of propagation takes place and that the accelerator has magnetic couplings, which couple the acceleration cavities with each other at high frequencies and which are independent of the axial openings.

The invention is explained in more detail below using an exemplary embodiment from which further important ones Characteristics. It shows:

1 - schematically, a linear accelerator according to the invention;

Figures 2a and 2b - pulses containing the accelerating high frequency wave;

Fig. 3 Fig. 4 -

schematically a segment of an accelerator, that of the linear accelerator is used according to the invention;

a detail of elements that form a segment according to FIG.

Fig. 1 shows schematically a particle accelerator according to the invention.

The particle accelerator 1 has an accelerator for advancing waves and a generator 4 for High frequency waves. The generator is indicated in a dashed box. He gives a high frequency wave which forms the electromagnetic acceleration wave.

The accelerator 2 makes it possible to accelerate a bundle of charged particles, for example electrons. That The bundle is indicated in FIG. 1 by the arrow 5 which coincides with a longitudinal axis 6 of the accelerator 2. The bundle 5 is emitted in the form of a pulse with a duration T (F) via conventional means, not shown Middle. The accelerator 2 has a sequence η of acceleration cavities Cl, C2, ..., Cn, the are arranged along the longitudinal axis 6. It has on this longitudinal axis 6 axial openings 9 through which the electron beam 5 passes through. The electron beam 5 enters the accelerator 2 at a first end 7 of the Accelerator and moves in the accelerator along its longitudinal axis 6, in the direction of arrow 5, which at the same time symbolizes the bundle. So the direction of propagation of the bundle is from this first end 7 to a second end 8 of the accelerator 2.

In a non-limiting example, the generator 4 has means 10, 11 for generating the high frequency wave after a pulse which is not shown in FIG. This has a duration T (HF), which is essentially equal to one Charging time or filling time T (S) of accelerator 2 is plus the duration T (F) of bundle 5:

T (HF) = T (S) + T (F).

It should be noted that the charging time of a standing wave accelerator is much longer than the charging time TS of an accelerator for converter shafts. This has already been pointed out at the beginning. With the mentioned and Non-limiting example show the Means 10, 11 for emitting the high frequency wave, a high frequency source 10 on, for example a klystron, the

no

cooperates with a compressor 11 for high frequency pulses. The compressor is, for example, a SLED compressor as mentioned above.

Figures 2a and 2b show a first pulse 20 and a second pulse 21. Both pulses contain the High-frequency wave (not shown). This changes the instantaneous amplitude or power P as a function of time t illustrated. In Fig. 2a, the first pulse 20 has a first part 20- and a second part 20+. These Parts are negative or positive. The part of the impulse that can be used to accelerate the bundle is through the second, positive part 20+ is formed. This reaches a performance level Pl. The first impulse 2 0 decreases Correction by the high-frequency compressor 11 essentially takes the form of FIG. 2b. You can see that the negative part 21- of the second pulse 21, compared with the first pulse 20, has an area S which is much smaller is. The difference Sd is essentially shifted to the second, positive part 21+ of the second pulse, that can be exploited. Its power level P2 is much higher than the first power level Pl.

This instantaneous amplification of the power of the high frequency wave is used in the prior art to reduce the energy of the accelerated bundle per unit length of the To increase accelerator by using a conventional accelerator for transducer shafts in the direct sense will. This selection of the accelerator line is made possible by the short duration T (HF) of the usable high-frequency pulse 21+ dictates.

In practice, the duration T (HF) is always less than 1.5 microseconds. With the mentioned and not limited

ί kend the example to be understood, the duration is of the order of magnitude one microsecond (working range in the S-band at 3000 MHz). This duration essentially corresponds to Accelerator 2 charging time T (S) plus first duration T (F). The accelerated bundle forms an impulse, its Duration T (F) is on the order of 0.1 microseconds.

In Fig. 1, the generator 4 emits a high frequency wave after a high frequency pulse which is similar to the pulse 21 of Figure 2b. This high-frequency power pulse, which is not shown in FIG. 1, is transmitted via a transmission line 15 and into the accelerator 2 injected by means of a known high frequency input coupling 16.

According to the invention, the high-frequency pulse is on the second The end 8 of the accelerator 2 is injected into it, i.e. at the end opposite the end at which the bundle 5 enters the accelerator. The high frequency wave therefore proceeds in the accelerator 2 in the direction of the second arrow 17, i.e. in a second direction, which is anti-parallel to the direction of propagation of the bundle 5 to be accelerated. The coupling between the resonance cavities Cl, C2, ..., Cn is realized via magnetic couplings.

In an exemplary embodiment that is not to be understood as limiting, these couplings are made via aperture openings 18 realized, which are arranged substantially on the periphery of the acceleration cavities Cl, C2, .., Cn and the are provided in walls 19 which separate two adjacent acceleration cavities from one another.

This arrangement offers, compared to the prior art, being an accelerator for advancing Waves use finds the advantage that the couplings 18 between the cavities Cl, ..., Cn and the axial openings 9 or passage openings for the bundle from each other become separate and independent of each other. This makes it possible for the accelerator 2 additional sliding tubes 31 which are connected to the passage openings 9 and which provide better synchronization allow between the high frequency wave and the beam 5.

The first end 7 of the accelerator 2 can also have a short Have end 23, which is formed by the wall 9 of the first cavity Cl. The short circuit acts opposite the high frequency. The high frequency wave is therefore reflected to the second end 8. This reflection takes place after passage and acceleration of the bundle 5. The accelerator 2 is therefore for the bundle 5 in this case a structure for advancing waves.

A simultaneous power supply for the accelerator 2 and a second one, identical to this and shown in the drawing accelerator, not shown, can be achieved by means of a 3 dB high-frequency hybrid coupler take place. This coupler is known. He has a known burden that those of the Accelerators absorbed reflected high frequency waves

The accelerator 2 can have a high frequency output coupling at its first end 7, towards which the high frequency wave is directed have and a high frequency load thereby conventionally the high frequency wave which comes to this first end 7 is absorbed.

It should be mentioned that the arrangement of the short circuit 23 is particularly advantageous because it allows the coupler and the burden become superfluous.

The resonance or working wave "] \ · ~ of the accelerator is preferably chosen in such a way that the quotient -

2 ^m

is equal to or greater than ■ =. A frame 40 in FIG. 1 shows a segment 25 of the accelerator structure 2. 3 shows a preferred resonance wave of this segment 25.

In Fig. 3 the segment 25 of the accelerator 2 is shown in a preferred embodiment.

4 "T \

The resonance wave used corresponds to wave ■.

The segment 25 has a length L1 corresponding to two wavelengths 2 ^ of the high frequency wave, i.e. in this example the length Ll is essentially 200 mm. at this length Ll, the segment 25 has five cavities C2, C3, C4, C5, C6. These have the same length as one another L2. They are coupled to one another via the aperture openings 18.

The cavities Cl, C2, ..., Cn always have the same structure and the same length. This is different from the case an accelerator for stationary waves. The cavities can be produced economically. They are proportionate long, based on the wavelength. They result in a raised overvoltage coefficient that reduces the shunt impedance improved. As a result, the energy of the accelerated bundle 5 can also be increased.

It is estimated that in an S-band there is a shunt impedance of 5 0% (60 MOhm to 90 MOhm per meter). Corresponds to this value

an increase in the energy of this bundle of the order of 22%.

The couplings between the cavities Cl, ..., Cn are separated from the through openings 9 for the bundle 5. Therefore, on the one hand, one can determine the diameter d of the diaphragm openings 18 to further reduce the charging time Ts of the accelerator without the Impedance shunt value is excessively decreased. This separation of functions enables, on the other hand, the Interaction between the high frequency waves and the Optimizing bundles by using the sliding tubes 31 which are provided at the passage openings 9 for the bundle are. These passage openings 9 can furthermore have a second, reduced diameter d2.

4 shows in particular in a schematic longitudinal section an accelerating cavity, for example the third accelerating cavity C3. This cavity is described in detail and is designed for an operating frequency of approximately 3000 MHz.

The acceleration cavities are obtained by rotating about the longitudinal axis 6. In Fig. 4 is therefore only the upper one Part of the cavity C3 is shown, i.e. above the longitudinal axis 6. In the mentioned and non-limiting example the walls 19 have along a transverse axis 35 which extends perpendicular to the longitudinal axis 6, e: r, en part 36 which has a reduced thickness E. On one side of this thinner section E is the iris or diaphragm opening 18 and on the other side tips 30, which form the ends of the sliding tubes 31. The passage opening 9 has in these, not limited to-

BATH ORIGINAL

The example to be taken has a radius r of 4.5 mm. The tips 30 are circular in shape. They connect the sliding tube 31 with a part 19a which is inclined to the wall 19, in relation to the transverse axis 35. This inclined part 19a forms an angle of approximately with the transverse axis 35 45 ° from such that an inner length L3 of the cavity C3 between the tips 30 is smaller than a larger one Inner distance L4 of this cavity C3. This greater length L4 is at the level of the smaller wall thickness E of the wall 19.

In this exemplary embodiment, which is not to be understood as limiting, the sliding tubes 31 have a length L5 of 14 mm, measured between the tips 30. The shorter inner distance L3 is of the order of 26 mm and the longer inner distance L4 is on the order of 37.5 mm. The smallest wall thickness E of the wall 19 is 2.5 mm.

With this configuration it is advantageous to use the components, For example, the components El, E2 between the dashed Lines 37 are provided to be produced identically to one another and then to be assembled.

The above description of an accelerator 1 according to the invention is not intended to be construed in a restrictive manner. The accelerator structure 2 is designed so that it operates with high-frequency pulses 21 which are short Have duration T (HF). The duration is incompatible with the charging time of conventional accelerators for stationary Waves. The accelerator 2 according to the invention has a reduced charging time T (S), which makes it suitable for such high-frequency pulses becomes suitable. Furthermore, the charging

time T (S) can be reduced compared to the charging time of a conventional structure for transducer shafts. However, certain advantages are retained that provide accelerator structures for standing waves.

It should be mentioned that in the example, which is not to be understood as limiting, the high frequency wave generator has a compressor 11 for Hochfreuqenzimpulse, the emits a rapidly increasing high frequency pulse. However, the present invention can generally be used in conjunction with High frequency wave generators work, the high frequency pulses short duration T (HF) as described above

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Claims (9)

PRINZ, LEISER, BUNKE & PARTNER Patent Attorneys · European Patent Attorneys Ernsbergerstrasse 19 8000 Munich 60 3 6 U I 27 I 17th January 1986 C.G.R.-MeV 551, Route de la Miniere 78530 BUC / France Our reference: C 3428 Claims /1. Linear accelerator for charged particles with - An accelerator structure (2) for converter shafts, with a given charging time T (S) and for acceleration a bundle (5) whose duration T (F) is shorter than the charging time T (S), - A generator (4) for an accelerating high-frequency wave, which the high-frequency wave as a pulse (21) gives, where - the accelerator structure (2) a sequence of loading acceleration cavities (Cl, ..., Cn) which are arranged on a longitudinal axis (6) of the accelerator structure (2) and have axial openings (9), through which the bundle (5) passes and enters the accelerator structure (2) at a first end (7) and in this along its longitudinal axis (6) from the first end (7) to a second end (8) of the accelerator structure (2) progresses, characterized in that the high frequency wave at the second end (8) of the Be-Schleuniger structure (2) enters this in such a way that the interaction between the high frequency wave and the bundle (5) takes place in opposite directions of propagation (5, 17), and that the accelerator structure (2) has magnetic couplings (18), which the acceleration cavities (Cl, ..., Cn) couple with each other at high frequencies and which are independent of the axial openings (9). 2. Linear accelerator according to claim 1, characterized in that the generator (4) has means (10, 11) through which the high-frequency pulse (21) is approximately the same length as the sum of the charging time (T (S)) and the duration (T (F)) of the bundle 3. Linear accelerator according to claim 1 or 2, characterized in η e t, that the means (10, 11) for generating the pulse (21) have a high frequency source (10) which is connected to a High-frequency pulse compressor (11) is connected. 4. Linear accelerator according to one of claims 1-3, characterized in that the Accelerator structure (2) has sliding tubes (31) and that the couplings (18) are formed by aperture openings (18) are, which are provided in transverse walls (19), the two adjacent acceleration cavities (Cl, ..., Cn) are common. 5. Linear accelerator according to one of claims 1-4, characterized in that that the acceleration cavities (Cl, ..., Cn) have the same length (L2). 6 · Linear accelerator according to one of claims 1-5, characterized in that the resonance or working wave of the accelerator structure (2) •> Y - corresponds to - ^ - ■ =. Π m ... m 3 7. Linear accelerator according to one of claims 1-6, characterized in that the working shaft corresponds to the shaft 4 fr. 8. Linear accelerator according to one of claims 1-7, characterized in that that the accelerator structure (2) is short-circuited in terms of high frequency at its first end (7) (short circuit 23). 9. Linear accelerator according to one of claims 1-8, characterized in that two identical accelerator structures (2) are provided that are connected to the same generator (4) via a 3 dB hybrid coupler to which a load is assigned which absorbs the high-frequency waves reflected by the accelerator structures (2).