RU136669U1 - FOCUSING DEVICE OF THE SYNCHROCYCLOTRON - Google Patents

Abstract

A synchrocyclotron focusing device, including a duant, a Penning-type ion source with a system of focusing central and side electrodes and their power supply units, characterized in that an additional deflector is introduced into the device, consisting of two half-ring plates surrounding the side focusing electrode plates, and a generator is introduced radio pulses with a filling frequency equal to the frequency of the betatron vertical oscillations of protons in an accelerated bunch, and the generator’s bipolar output is connected to the plates of the reflector, and its input is connected to the dowant, ensuring the inclusion of the radio pulse at the moment when only part of the proton bunch with large amplitudes of radial vibrations is between the deflector plates.

Description

The utility model relates to accelerator technology, directly to the focusing device of the synchrocyclotron, and is intended to coordinate the radial size (emittance) of the accelerated proton bunch with the radial size (acceptance) of the output channel of the synchrocyclotron, thereby ensuring the proton output from the accelerator chamber without radiation effect on the output system.

The focusing device of the 680 MeV synchrocyclotron at JINR, Dubna, RF: “Focusing device” was chosen as an analog device. Proceedings of the international conference on accelerators, Dubna, 1963, M., "Atomizdat", 1964, [1].

An analog device consists of a duant, an open source Penning type ion source, and a focusing side electrode connected to their power sources.

The analog device works as follows. A negative potential of the required magnitude is applied to the side electrode, as a result of this, an electric field is created between the duant and the side electrode around the ion source, which focuses the protons in the vertical direction and determines the vertical size of the proton bunch and the density of protons in it, i.e., the intensity of the synchrocyclotron.

The disadvantage of the analogue is the inability to influence the radial amplitude spectrum of betatron vibrations of protons in an accelerated bunch and to regulate the radial size (emittance) of a proton bunch, which leads to inconsistency with the radial size (acceptance) of the output channel, to the loss of protons when they are removed from the accelerator and, as a result, to radiation activation of the output channel by the accelerated beam.

As a prototype, the focusing device of the world's largest synchrocyclotron for proton energy of 1000 MeV of the St. Petersburg Institute of Nuclear Physics, A.S. N743243 [2].

The focusing device consists of a duant, an open source of Penning type protons, and focusing side and central electrodes located in the central region of the accelerator. The duant, source and electrodes are connected to their respective power sources.

The prototype device operates as follows. Corresponding voltages are applied to the duant, ion source, and focusing electrodes, as a result of which an electric field is created in the central region of the accelerator, which focuses protons in the vertical direction to the median plane of the magnetic field and determines the amplitude spectrum of betatron vibrations of protons, as well as the density and transverse dimensions of the bunch accelerated protons and thereby the intensity of the proton beam of the synchrocyclotron. (The prototype device used at the PNPI synchrocyclotron leads to a 10-fold increase in the intensity of the synchrocyclotron. Proceedings of the VI All-Union Conference on Charged Particle Accelerators, Dubna, October 11–13, 1978, M., 1979, v. 3 [3]) .

The disadvantage of the prototype is the inability to change the spectrum of amplitudes of radial betatron oscillations of protons in an accelerated bunch and to regulate the radial size (emittance) of an accelerated bunch of protons, which leads to inconsistency with the radial acceptance of the output channel, to the loss of part of the protons when they are removed from the accelerator and, as a result , to radiation activation of the output channel by protons accelerated to high energy. This shortcoming, in turn, leads to significant negative consequences for the operation of the synchrocyclotron itself.

Explain this disadvantage of the prototype in detail. The capture of protons in the mode of their acceleration by a dount and the formation of a spectrum of amplitudes of vertical and radial vibrations of protons and the size of a bunch occurs in the central region of the synchrocyclotron. The focusing device mainly affects only the vertical spectrum of amplitudes and the vertical size of the bunch 2A _Z , (where A _Z is the maximum amplitude in the spectrum of vertical betatron vibrations), and the radial spectrum of amplitudes and the radial size of the bunch 2A _R , (where A _R is the maximum the amplitude in the spectrum of radial betatron vibrations) is determined by the process of proton capture in the separatrix and is practically independent of the parameters of the focusing device. A bunch of protons with transverse dimensions 2A _Z × 2A _R formed in the center of the synchrocyclotron with its further acceleration and increase in energy practically does not change its amplitude spectrum of betatron vibrations and reaches the output channel with the same dimensions. Typical transverse clot sizes in synchrocyclotrons 2A _Z ≈ 2-4 cm; 2A _R ≈20-40 cm. The output of an accelerated proton bunch from the synchrocyclotron chamber for its use is carried out using a regenerative output magnetic system (output channel). However, it is known that in all Penning-type open-source synchrocyclotrons, the proton extraction coefficient from the accelerator chamber is only 5% -30%, the remaining 95% -70% of protons die on the elements of the output channel: Proceedings of the II All-Union meeting on charged particle accelerators M ., November 11-18, 1970; M., 1972, vol. II, [4].

It is also known that one of the main causes of losses is a too wide spectrum of radial betatron vibrations of protons in a bunch. These losses can be significantly reduced by narrowing the spectrum of radial vibrations of protons in an accelerated bunch, that is, by reducing the radial size of the bunch.

Thus, since in the prototype device the radial size (emittance) of the accelerated bunch is several times larger than the radial size (acceptance) of the output channel (conventionally called the “window” of the output channel), a significant part of the accelerated protons die on the channel structure elements, producing it radiation activation: Sat reports of the XV Conference on charged particle accelerators. Protvino October 22-24. 1996 Protvino, 1996, vol. II 5]. Due to this drawback, the level of induced radioactivity of the output channel of the synchrocyclotron is close to the maximum permissible values, and the dose load on the maintenance personnel and the necessary radiation protection of the synchrocyclotron itself is a significant cost for the operation of the accelerator. It is also important to note that this disadvantage of the prototype is a limiting factor for the intensity of the synchrocyclotron. At an energy of 1000 MeV, the intensity limit of the accelerator is ~ 1 μA, since with an increase in the intensity and, consequently, an increase in the radiation load, it would be necessary to switch to the use of remote manipulators when servicing the radioactive systems of the synchrocyclotron.

Thus, in the synchrocyclotron when working with the prototype, the radial emittance of the beam is not consistent with the radial acceptance of the output channel and is much larger than it, which leads to the loss of a significant part of the protons on the structural elements of the output channel and to radiation activation of the output channel by the accelerated beam.

The objective of the invention is the creation of a new focusing device of the synchrocyclotron, which not only vertically focuses the protons as in the prototype, but also simultaneously generates and adjusts the radial size (emittance) of the bunch of accelerated protons to match it with the radial acceptance of the output channel of the synchrocyclotron.

The technical effect is to ensure the removal of protons from the accelerator chamber without radiating them to the output channel while maintaining the number of protons extracted from the accelerator chamber, that is, at the same intensity of the synchrocyclotron beam.

The technical effect is achieved by the fact that in the focusing device of the synchrocyclotron, including the duant, a Penning-type ion source with a system of focusing central and side electrodes and their power supply units, it is new that an additional deflector is introduced into the device, consisting of two plates in the form of half rings surrounding plate of the side focusing electrode, and a radio pulse generator is introduced with a filling frequency equal to the frequency of betatron vertical oscillations of protons in an accelerated bunch, moreover, The bright output of the generator is connected to the plates of the deflector, and its input is connected to the dowant for temporary synchronization and the inclusion of a radio pulse at the moment when only part of the bunch of protons having large radial oscillation amplitudes is between the plates of the deflector.

The essence of the proposed device is illustrated in figure 1a, b, where 1a is a diagram of the device is a side view, 1b is a top view.

1. The vacuum chamber of the synchrocyclotron.

2. The Duant.

3. An ion source with central focusing electrodes.

4. Side focusing electrode.

5. Deflector plates.

6. The generator of radio pulses.

7. The synchronization circuit of the generator of radio pulses 6 with 2.

8. The bipolar outputs of the generator 6 are connected to the plates of the deflector 5.

9. The position and size of the accelerated proton bunch at the moment of supply of the radio pulse t *. (The shaded part of the bunch is the protons exposed to the deflector and dropping from the accelerated bunch).

10. The position and size of the proton bunch, continuing further acceleration.

11. The direction of the extracted protons from the chamber of the synchrocyclotron 1.

12. A schematic representation of a radio pulse supplied to the plates of the deflector 5 produced by the radio pulse generator 6.

13. Schematic representation of the output channel.

Figure 1 introduced the following notation.

0 is the center of symmetry of the magnetic field of the synchrocyclotron.

XYZ - coordinate system.

OXY is the median plane of the accelerator’s magnetic field.

R is the acceleration radius.

R _df is the radius of the deflector plates 5.

b is the width of the plates of the deflector 5.

R ₀ (t) is the equilibrium radius of the bunch (center of the bunch) at time I of its acceleration.

A _Z is the maximum amplitude of the vertical betatron vibrations of protons in a bunch.

2A _Z - the vertical size of the bunch.

A _R is the maximum amplitude of radial betatron vibrations of protons in a bunch.

2A _R is the radial size of the bunch.

2a _R is the radial size of the bunch 10 continuing acceleration after applying to the deflector plates 5 of the radio pulse 12.

U _dF - voltage amplitude on the plates of the deflector 5.

f _df is the frequency of the voltage of the radio pulse 12 supplied to the plate of the deflector 5.

f _Z - the frequency of vertical oscillations of protons.

t is the current time of acceleration of the bunch

t * is the time instant of the appearance of the radio pulse 12 on the plates of the deflector 5.

τ is the duration of the radio pulse 12.

The proposed focusing device (Figure 1) consists of a deant 2 located in the vacuum chamber 1, an ion source 3, and focusing central 3 and side 4 electrodes. (The system of their fastening and power are not shown in FIG. 1).

A deflector 5 is additionally introduced into this focusing system. The deflector 5 consists of two plates in the form of half rings surrounding the lateral focusing electrode 4. (The attachment diagram of it in FIG. 1 is not shown).

A radio pulse generator 6 is also introduced into the focusing system; moreover, the filling frequency of the radio pulses is equal to the frequency of the betatron vertical oscillations of the protons in the accelerated bunch. The bipolar outputs 8 of the generator 6 are connected to the plates of the deflector 5. The input of the generator 6 is connected to the dual 2 to temporarily synchronize the operation of the generator 6 with the cycle and the frequency RF program of the dual 2.

The proposed device operates as follows.

At each accelerating cycle, an accelerated bunch (bunch) of protons is formed in the vacuum chamber of the synchrocyclotron 1. The formation of a bunch occurs in the central region of the median plane of OXU at radii of 5-15 cm as a result of the action of the focusing forces of the magnetic field and electrostatic fields when the ion source operates with the central focusing electrodes 3, the lateral focusing electrode 4, and the RF field of the duant 2.

The size of this bunch is 2A _Z ≈ 2-4 cm, 2A _R ≈20-40 cm, angular size Δφ≈40-60 °. In the process of its further acceleration by the second 2 and movement along the radius R, the size of the bunch practically does not change.

At some point in the acceleration cycle t *, the center of the bunch reaches a radius R ₀ (t *) exceeding the radius of the deflector plates R _df and the bunch occupies position 9, in which only its left shaded part will be between the plates of the deflector 5. At this moment t * on the deflector plates 5 are supplied with a radio pulse 12 generated by a radio pulse generator 6. The shape of this radio pulse 12 is conventionally shown in Fig. 1b. Between the plates of the deflector 5, a high-frequency electric field arises, which acts on the protons located in the hatched parts of the bunch 9, both to the left and to the right of its center R ₀ . Since the filling frequency of the radio pulse f _{df is} chosen equal to the frequency of vertical betatron vibrations of protons in the bunch f _Z , this effect is resonant in nature, the amplitudes of the vertical vibrations of protons in the shaded areas of the bunch 9 increase, and the protons fall on the plates of the deflector 5 and drop out of the process of further acceleration . A bunch of the remaining protons 10 with a shortened radial size of 2a _R continues to further accelerate, reaches the output channel 13 and with virtually no loss and radiation exposure to the output channel, the bunch is removed from the accelerator chamber in direction 11.

Let us explain the operation of the proposed device in detail.

It is known that a proton bunch accelerated in a synchrocyclotron has an equilibrium radius R ₀ , the position of which is unambiguously related to the parameters of the accelerator’s magnetic field and the frequency of the decelerating accelerating field f ₀ (t). The accelerated bunch rotates around the center of accelerator 0 in a spiral with a revolution frequency equal to the frequency of the douant f ₀ (t), and as it moves along the radius R it increases its energy. "Fundamentals of physics and technology of accelerators." M., Energoatomizdat, 1991 [6],

,

, где n(R) - показатель спада магнитного поля. Спектр амплитуд бетатронных колебаний формируется в центральной области ускорителя и определяет размеры сгустка 2A_R×2A_Z, где A_R и A_Z - максимальные радиальные и вертикальные амплитуды колебаний протонов в ускоряемом сгустке. В процессе дальнейшего ускорения сгустка эти размеры остаются практически неизменными. Все выше перечисленные величины известны и могут быть определены экспериментально.Protons in an accelerated bunch make free harmonic oscillations near the equilibrium radius (center of the bunch) R ₀ both in the vertical Z and horizontal R directions, which are called betatron vibrations. In the synchrocyclotron, these oscillations are independent of each other. The frequencies of these oscillations are related to the parameters of the magnetic field and the frequency of the douant by the known relations

,

where n (R) is the index of magnetic field decline. The amplitude spectrum of betatron vibrations is formed in the central region of the accelerator and determines the size of the bunch 2A _R × 2A _Z , where A _R and A _Z are the maximum radial and vertical amplitudes of proton vibrations in the accelerated bunch. In the process of further acceleration of the bunch, these sizes remain almost unchanged. All of the above values are known and can be determined experimentally.

It is known that if the entire bunch in the process of its acceleration and movement along the radius R completely falls into the electric field of the deflector plates 5, to which a voltage is applied in the form of a radio pulse 12 with a filling frequency equal to the frequency of proton vertical vibrations in the bunch f _df = f _z , then all protons in a bunch undergo resonant vertical buildup, increase their amplitudes of vertical vibrations, fall on the deflector plates and all drop out of further acceleration: Auth. testimonial. No. 997593 [7].

In the proposed device, not all protons, but only part of the protons from the shaded parts of the bunch 9, having large amplitudes, are subjected to resonance action by the deflector 5 and are eliminated from further acceleration. This happens as follows.

The radio pulse 12 is fed to the plates of the deflector 5 at the moment t *, when the center of the bunch R ₀ (t *) is outside the radius of the plates of the deflector R _df , and between the plates in the electric field of the deflector 5 there will be only the shaded left side of the bunch 9, with radial amplitudes The proton vibrations are larger than the amplitudes a _R necessary for the derivation.

However, since the protons in the bunch simultaneously with vertical Z-oscillations independently make radial R-oscillations relative to the center of the bunch 0, not only the protons in the left, but also in the right hatched part of bunch 9 are subjected to resonant influence. As a result of such exposure to the deflector, the bunch it is shortened along the radius on both sides, and protons having large amplitudes of R - vibrations fall on the deflector plates and drop out of further acceleration.

Thus, the bunch 10 formed and shortened along the radius R from size 2A _R to size 2a _R continues to accelerate further, reaches output channel 13 and, with almost no loss and radiation exposure, is brought out of the accelerator chamber outward in direction 11.

The time t * supply of the radio pulse to the deflector 5 is determined in the following way. The input of the radio pulse generator 6 is connected to the dual 2 circuit 7 to temporarily synchronize the operation of the generator 6 with the cycles and frequency of the RF program of the dees. Since the radial position of the bunch is uniquely related to the frequency of the douint R ₀ = R ₀ (f ₀ ), the generator 6 “monitors” the frequency of the douint f ₀ (t) and at the right time t * “turns on” the radio pulse 12 on the plates of the deflector 5. This moment t * depends on the spectrum of amplitudes of the proton radial vibrations in the bunch and is selected experimentally from the minimum loss signal from the output channel.

Thus, in the proposed focusing device, using the introduced deflector 5 and the radio pulse generator 6, the excess part of the spectrum of large radial oscillation amplitudes is “cut off” and the necessary radial bunch size (2a _R ) is formed, the emittance of which corresponds to the acceptance of the output channel for lossless output.

The advantages of the proposed device compares it favorably with the prototype and all known devices similar to it.

The proposed focusing device passed prototype tests at the FSBI PNPI named after B.P. Konstantinov at the synchrocyclotron 1000 MeV.

We give the necessary parameters of the PNPI synchrocyclotron [7] and the calculated parameters of the proposed focusing device.

The diameter of the magnet pole is 685 cm

The gap between the poles - 50 cm

Decline indicator n≈0.01

The frequency of the duant f ₀ (t) = 30-13 MHz.

Intensity - 1.8 10 ¹³ proton / s

The size of the bunch is along the radius 2A _R ≈32 cm, along the vertical 2A _Z ≈4 cm, along the azimuth ~ 30 ° -40 °.

Dee frequency f deflector at the radius ₀ (R _DB) ≈28 MHz

Deflector radius R _df ≈30 cm

Deflector width - 6 cm

The gap between the deflector plates - 6 cm

Pulse parameters:

Amplitude U _df - up to 300 V.

Radio pulse filling frequency - f _Z = 3 MHz

The filling frequency deviation is 5% f _Z.

Duration of a radio pulse τ≈0.5 ms

In FSBI PNPI, work is underway to introduce the proposed device into continuous operation.

Information sources

1. Danilov V.I. and others. "Focusing device." Proceedings of the international conference on accelerators, Dubna, 1963, M, Atomizdat, 1964, p. 591-594. The analogue.

2. Abrosimov N.K. and others. "Focusing device synchrocyclotron." A.S. 743243. The prototype.

3. Abrosimov N.K. et al. "An increase in the beam intensity of the PNPI synchrocyclotron B.P. Konstantinova ANSSSR due to the improvement of electrostatic focusing in the central region. " Proceedings of the VI All-Union meeting on charged particle accelerators. Dubna, October 11-13, 1978, M, 1979, v. 1, pp. 277-280.

4. Abrosimov N.K. et al. “Conclusion of the proton beam of the synchrocyclotron of the Physicotechnical Institute of the Academy of Sciences of the USSR to an energy of 1 GeV”. Proceedings of the II All-Union meeting on charged particle accelerators. M., November 11-18, 1970, M, 1972, vol. II, pp. 182-184.

5. Mironov Yu.T. “Radiation consequences of the loss of a proton beam with an energy of 1 GeV.” Collection of reports of the XV Conference on charged particle accelerators. Protvino, October 22-24. 1996 Protvino, 1996, vol. II, p. 275-278.

6. Lebedev A.N. and others. "Fundamentals of physics and technology of accelerators." M., Energoatomizdat, 1991

7. Abrosimov N.K. and others. "A method of forming a pulse of secondary particles on the internal targets of the synchrocyclotron." A.S. 997593, publ. Bulletin No. 25, part II, p. 433, 2000

8. G.F. Mikheev. "Synchrocyclotron on the proton energy of 1 GeV PNPI RAS". Bibliography. Gatchina. 2000 year

Claims (1)

A synchrocyclotron focusing device including a duant, a Penning type ion source with a system of focusing central and side electrodes and their power supply units, characterized in that an additional deflector is introduced into the device, consisting of two half-ring plates surrounding the side focusing electrode plates, and a generator is introduced radio pulses with a filling frequency equal to the frequency of the betatron vertical oscillations of protons in an accelerated bunch, and the generator’s bipolar output is connected to the plates of the reflector, and its input is connected to the dowant, ensuring the inclusion of the radio pulse at the moment when only part of the proton bunch with large amplitudes of radial vibrations is between the deflector plates.

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