The method of acceleration and focusing of charged particles in a constant electric field and the device for its implementation

 

The invention relates to techniques of charged particle acceleration constant electric field, solves the problem of acceleration and simultaneous strong focusing of charged particles and can be used in electric direct action accelerators to obtain a particle beam of great intensity. The method of acceleration includes formation through electrostatic electrodes constant longitudinal acceleration and linearly focusing the transverse components of the electric field. Field is implemented using the extended electrodes quasicylindrical quadrupole shape, the inner profile which in cross section is described by four branches raveboy of hyperbole and longitudinally as the square root of the values of the longitudinal coordinate. The potential values and parameters of electrodes set in accordance with the requirements for acceleration and focusing of charged particles. The technical result is the possibility of acceleration, focusing and formation of a beam of accelerated charged particles with a large intensity increase of the voltage gradient at the accelerator tube and reducing the size and cost of the accelerator. 2 S. p. f-crystals, 2 Il.

In modern accelerators for beam shaping and increasing the intensity of ions use their focusing using various techniques, retaining the particles in the accelerator. Known principles of strong focusing of charged particles, based on the use of azimuthal variations of the magnetic field in a circular circular accelerators, on the application of spatial periodic gradient magnetic field and, in particular, fokusirale-defocusing quadrupole magnetic field in the cyclic ring accelerators and, finally, on the application of time-varying electric quadrupole field (high-frequency quadrupole focusing in linear resonance accelerators. All these techniques allow you to get by means of accelerators these types of reasonably well-formed beams of accelerated charged particles with an average intensity of up to several tens of mA.

In direct action accelerators, i.e., the CSOs step-up transformer and rectifier, or by means of an electrostatic generator for generating a beam of charged particles is mostly weak electric focusing, due to the action of multiple regional electric field [1], [2]). For this purpose, the accelerator creates or breaks in the flat electric field accelerating tube, dissecting the continuous tube into sections, or change the longitudinal gradient of the accelerating electric field, specify a special way, the potential of the accelerating electrode. Section of the accelerator tube with open ends into force of solenoidality electric field acts on the particles as collecting a single lens at the entrance to the section, and as a diverging lens on the exit section. As a result, the difference between the actions of the scattered field at the two ends of the section creates a weak focusing effect.

Weak electric focusing does not provide effective retention of charged particles in the beam with high spatial density of electric charge. Therefore, in the direct action accelerators for effective transaction of the beam through the accelerator introduce additional focusing elements, such as short solenoidal lenses of the permanent magnets on krichesky cylindrical quadrupole lenses for focusing more stringent heavy ions with energies of hundreds of MeV [4] . The requirement of strong focusing action is especially important in electrostatic tandem using to increase the energy of ions in the Stripping of their electronic shells of strippers. However, even with the use of cylindrical quadrupole lenses transported the current of accelerated heavy ions [4] does not exceed a few μa, whereas the supply current of the electrostatic conductor accelerator, which determines the maximum value of the current of accelerated particles is several mA. In addition, the extra focus, but not accelerating cylindrical quadrupole lens between the accelerating electrodes and the sharing of a common accelerating tube on a separate partition, leading to the formation of so-called "dead" zones, increases the length of the accelerator tract, reduces the average acceleration rate and thereby increases the overall size of the accelerator and the external tank with gas under pressure of 10-15 bar, increasing the cost of the accelerator.

In an electrostatic tandem type 25URC of the two accelerators on the total voltage of 25 MB [4], produced by the National electric company of the USA and designed for acceleration of heavy ions, installed in four breaks accelerating tube multi the second tube is only 1.6 MV/m, while other similar accelerators it is considerably higher (up to 2.2 MV/m).

The above mentioned method and device for focusing and forming a beam of ions accelerated in an electrostatic accelerator direct action [4], which contains additional cylindrical quadrupole lens between the sections of the accelerator tube, taken here as a prototype of the invention.

The present invention solves the problem of creating a static electric field for use in high-voltage linear accelerator direct action, effectively accelerating and at the same time focusing charged particles using a particular device - accelerating-focusing electrodes of a special form. This method and device solves the problem of acceleration, focusing and formation of a beam of accelerated charged particles with a large intensity increase of the voltage gradient at the accelerator tube and thereby reducing the size and cost of the accelerator. This goal is achieved by the formation of a constant electric field with a constant longitudinal accelerating component and transverse linearly increasing component of the electric field defined by the Sol in a cylindrical coordinate system r,, z, Ez- accelerating the DC component of the electric field, directed along the longitudinal axis z of the electric field in the entire region of the cross section z= const, Grthe gradient is radial (transverse) or focusing defocusing component of the electric field intensity, V(0, 0, z0- the potential at the point z0on the axis of the field.

The device for realization of the field (1) is a system monopolistically electrodes, the internal profile which is made in accordance with the formulawhere re(, z) is the radius-vector of the internal profile of the electrode, Ve- potential electrode, and the electrodes are arranged in the sequence of their focusing and defocusing actions as defined by the sign of the radial gradient field strength Gr.

Accelerating-focusing a static electric field (1) found the proposed method of solving electrical problems, reverse the traditional method of directly solving the problems of electrostatics on the basis of the Laplace equation. Reverse method is that based on the requirements to the structure of the electric field in any physical or technical the Electric field in the remaining space of the aperture of the device is determined by integration of the Maxwell equationsTo solve this problem set the base field in the plane of symmetry=0 and the z-axis in the form ofAs you can see, the conditions (5) represent the electric field accelerating charged particles along the z-axis DC component of tension Ezand focusing (defocusing) particle transverse linearly increasing component of the electric field gradient Grin the plane=0, Gr<0 or Gr>0. From equation (3) are equalE(r,z)/=[rEr(r,z)]/r = -2Grr, integrating whichfrom 0 toand using the initial conditions (5), we get
E(r,,z) = -2Grr. (6)
Substituting the result (6) in equation (4), we come tointegrating that againreceived
Ecome to
E(r,,z) = -Grr[(2)-(2)3/3!].
Continuing so on an infinite number of times and using the decomposition formula of trigonometric functions sinand cosin the ranks, eventually find

Integrating the expression (8), we obtain the formula (1) for the potential field V(r,, z) at any point.

Electric potential (1), as it is easy to directly verify that satisfies the Laplace equation.

At the transition of the azimuthal anglethrough the values of/2, 3/2, 5/2 and 7/2, as follows from formula (1), the potential field changes sign on the back. With it changes sign on the back and the gradient of the radial component of the electric field strength Gr. This corresponds to the axial symmetry of the fourth order structure of the electric field, enabling them to provide focusing of charged particles in two mutually perpendicular planes by alternately focusing and defocusing a continuous longitudinal acceleration of charged particles axial component of the tension Fzand alternate transverse focusing of the radial component of Erin all its volume.

Field potential (1), like any other electrostatic field may be formed by the local electrodes of relatively small size with the corresponding values of potential, located on the border of the aperture device. However, it is more convenient for practical use in high-voltage accelerators of charged particles of direct action are monopolistically extended electrodes of a special form. From (1) follows equation (2) internal profile re(,z) equipotential electrode under potential Ve.

From the formula (2) implies that in any cross section z=const profile electrode is described by four branches raveboy hyperbola, and in section= const is the square root of the difference of the coordinates (z-z0).

The General scheme of the system of the four electrodes (2), forming the field (1), shown in Fig. 1, where 1 and 2 - "quasicylindrical" hyperbolic electrodes, made of sheet metal trough-shaped electrodes, as shown in Fig. 1, or in the form of a solid rod electrodes, with the sustained fashion the tube and the feed electrode electric potential. In the upper part of Fig.1 shows the projection electrodes on a planein the first quadrant. The azimuthal profiles of the electrodes in the other three quadrants are mirror reflection symmetry in the horizontal and vertical planes. In the lower part of Fig.1 shows the projection of the electrode 1 on the half-plane=0, z and the electrode 2 on the half-plane=/2, z, andminandmax- the minimum and maximum distances from the optical axis z to the crest quasicylindrical hyperbolic electrode, L is the length of the electrode.

The parameters of the electrodes are chosen according to (2) in accordance with the requirements for acceleration and focusing of ions and with regard to the size and beam current on the specific area of the accelerating tube. For example, demanding the tension of the longitudinal accelerating field equal to Ez=22 kV/cm (2, 2 MV/m), and setting the dimensions of the electrodes and= 1.5 cm (defines the minimum clearance in the aperture system of electrodes equal to 3.0 cm), andmax=2.5 cm and 1=3.5 cm, from the formula (2), we obtain the radial field gradient equal to Gr=38,5 kV/cm2in the upper and lower quarters quasicylindrical of the quadrupole (focusing positively the charger, side buttons the species in relation to the potential axis field at the point of least distance of the electrode from the axis equal to Ve=43,3 kV, respectively. The maximum intensity elektrycznego fields on the inner surface of the considered quasicylindrical quadrupole electrodes is equal to Ee= (E2r+E2&phis;+E2z)1/2don't exceed in vacuum at 100 kV/cm. The maximum electric field intensity Eset, as in the known cylindrical quadrupoles, the choice of the azimuthal dimension of the hyperbolic electrode.

The desired electric potentials of the electrodes for accelerating and focusing of charged particles served with divider full voltage on the conductor of the accelerator through the electrode holders 3 and do not require other sources of power.

In Fig. 2 shows the relative placement of two quasicylindrical quadrupoles in focusing doublet with the initial potential of a doublet, is equal to, for example, v0=-1000 kV accelerator direct action for positively charged particles with a grounded source of ions. The doublet is built on the principle of FD and DF-focus, respectively, in planes= 0,=, z and==0,=z is equal to - 956.7 and - 1000.7 kV and in the plane=/2,=3/2, z - 1120,3 and - 1077,7 kV. Electric strength of vacuum between the electrodes is provided with a choice of sizes and radii of rounding boundaries of the electrodes, are also presented in Fig.2.

The calculation of the focus continuously accelerated particles is possible with known methods of calculation, including analytical. Numerical estimates show that the doublet quasicylindrical quadrupoles with the above parameters has a focal length defined by the transformation of the beam particle type "Parallels in point" and is measured from the exit boundary of the doublet equal to15 cm in the plane of the FD and equal70 cm in the plane DF excluding defocusing action space charge of the beam. The wave number of each of the two quasicylindrical quadrupole lenses about 0.13 cm-1. Taking into account the spatial charge determined by the Maxwell's equation divD = 4where- the density of the space charge of the beam is the super linear field gradientwhere j is the beam current density, v is the velocity of the accelerated particles. For example, the rigidity of the above quadrupoles with respect to ions with respect to the ion charge to mass number of the ion Q/M= 1/30 at the current density of the beam j10 mA/cm2dropping just two times in the focusing plane and increases three times in defocusing. It does not interfere with still acceptable focusing the ions.

Found accelerating-focusing field in the acceleration of positive ions eliminates the counter-current of secondary electrons, knock of electrodes and molecules of the residual gas, due to the strong differences of the focusing action of the field in relation to ions and electrons, due to the significant difference in their energies. This eliminates the so-called "effect of full voltage, which in the existing high-voltage electrostatic accelerators excluded tilt flat accelerating electrodes to the axis of the system and the withdrawal of electrons from the optical axis of the accelerator.

Quasicylindrical the quadrupoles can be used to sort the ion charges after Stripping of ions of the strippers in the accelerator as used cylindrical quadrupoles by their transverse offset.

the modern nuclear physics, requiring high currents and high precision energy from the accelerated ions, and in some applications that require cost-effective methods of charged particle acceleration with high intensity beam (ion propulsion for spacecraft, electronuclear generating neutrons for energy purposes). The most attractive seems to be the application of the proposed method for electronuclear generate intense neutron fluxes, for example, in the reaction D+9Be at an energy of datanow about ten MeV for economically viable energy production method controlled by the accelerator safe subcritical nuclear reactor proposed by Rubbia.

References
1. A. P. Greenberg "Methods of charged particle acceleration", M. L., Gill, 1950. C. 27-58.

2. That Is, The Mosquito. "Fundamentals of accelerator physics", M., Atomizdat, gittl. 1950. C. 27-58.

2. That Is, The Mosquito. "Fundamentals of accelerator physics", M., Atomizdat, 1975, S. 33-47,
3. E. A. Abrahamian and C. A. Gaponov. A. E. 1966. so 20, vol.5, S. 385.

4. Heavy Ion Laboratory, Newsletter, (Oct.-Dec. 1975) no. 4, Oak Ridge National Laboratori.

5. J. B. Ball et al. Journ. de Phys. 1976, vol. 37, n. 11, p. S-227.


Claims

1. The method of acceleration and focusing of charged particles constant electric the who field, created by a system of electrodes mounted on passing through the wall of the accelerating tube metal holders, through which the electrodes serves electric potentials, characterized in that the charged particles simultaneously accelerate and focus quasicylindrical quadrupole field generated in accordance with the formula

where V(r,, z) is the electric potential field in the cylindrical coordinate system r,and z;
Ez- constant accelerating component of the electric field strength;
Gr- the gradient of the radial component of the electric field strength;
V(0, 0, z0- field potential on its axis at the starting point of z0.

2. Device for acceleration and focusing of charged particles in a constant electric field that contains a system of electrodes mounted on passing through the wall of the accelerating tube metal holders, through which the electrodes serves electric potentials, characterized in that the electrodes made with quasicylindrical hyperbolic profiles in accordance with the formula

where otential, supplied through the metal holder with divider full accelerating potential,
and the electrodes are arranged in the order of alternation of the sign of the gradient of the radial component of the electric field strength.

 

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