SU1170948A1 - Device for generating shaped radiation fields - Google Patents

Description

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00 The invention relates to the field of accelerator technology and can be used to form irradiating fields of random shape and intensity distribution at the output of accelerators used for applications, for example, in medicine. The purpose of this invention is to improve the accuracy of obtaining the irradiation field of a given shape by introducing a doublet with adjustable orientation of the quadrupole fields, which improves the characteristics of the irradiation field being formed and simplifies the process of obtaining a given law of intensity change. . FIG. 1 is a diagram of the device j in FIG. 2 shows the beam shape in the case of a constant bo time for the feeding mode of the quadrupoles} in FIG. 3 shows the beam section in the proposed device, where the feeding mode of the quadrupoles is consistent with the transverse deflection of the beam. The device contains a deflecting dipole 1, in front of which two lenses 2 and 3 are installed, each of which consists of a PM4 and two four-pole windings 5 and 6, shifted one relative to the other by 45 so that a pair of poles alternates from the same polarity. The windings of the dipole and octupole are powered by six Independent sources 7. The current in each winding is a function of the coordinates of the irradiation field. The device, the formation works as follows. Particle beam is focused by quadrupole fields of octupole lenses 2 and 3 and then deflected by dipole 1, i.e. scanned by irradiation field. Since each winding 5 and 6 near the field creates a qua-thru field in the lens aperture, the superposition of these fields will also be quadrupole, and depending on the ratio of the winding currents, the orientation of the total field gradients will change by rotating around the angle i45. In the proposed device, the rotation of the quadrupole fields of the lenses is synchronized with the rotation of the dipole field H. To clarify the positive effect of the proposed solution, consider a device with fixed and quadrupole fields. FIG. Figure 2 shows the beam section shapes, the name of which is the spread in the pulses of others at three points of the irradiation field: point 8 in the center, 9 on the ij axis, 10 on the diagonal of the first quadrant. We introduce an estimate of the beam quality in the irradiation field according to two criteria: the radius of the circle described around the section, and the beam filling factor of the area of the circumscribed circle. One of the main requirements for the beam, as mentioned, is the constant size of the cross section or the constant radius of the circumcircle. Obviously, its minimum radius is determined for the most distant, from the center of point 10, since the dispersion in it is maximum. From FIG. 2, it can be seen that the largest fill factor at this point is the irradiation field for the case of a circular cross section of a monoenergy beam. The radius of the minimum circumscribed circle is determined from the expression 4 1 where Oj is the dispersion of the formation system when the beam is deflected to point 10; the minimum possible radius of the monoenergy beam at point 10. The filling factor for the beam section at point 10 is determined by the relation: Ift) The filling factor can be increased by increasing g, but the radius will increase for the section at point 9, the filling factor can be significantly increased the same H value by imparting an elliptical shape to the beam cross section, since in this case the axes of the ellipse are oriented along the axes of the irradiation field. In this case, we have: l (fi K, A | (+ The ratio of the coefficients of filling coefficients is determined by the formula:

./(.ii GL

where r is the small axis of the ellipse. From (3) it follows that with finite Р and well focused beam

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With the introduction of quadrupole fields rotating synchronously with the dipole field, the azimuthal variation of the fill factor disappears (see FIG. 3), and. 5 for any point of the irradiation field, it is determined from relation (2),

TpatKfnopuv pdchka .Y) 7 If (X.y) G2 (X.

Claims (1)

DEVICE FOR FORMING PROFILE IRRADIATED FIELDS, containing a coaxially located source of charged particles with adjustable energy and intensity and deflecting a dipole magnet with an orientation in the plane perpendicular to the axis of the device, the orientation of the polarity, characterized in that, in order to improve the accuracy of obtaining radiation fields of a given shape, four independent power sources and an oak-tree of lenses are introduced into the device, each of which is made in the form of combined in a plane perpendicular to the axis of the device, shifted in azimuth by 45 ° two quadrupole lenses, wherein each winding of the quadrupole lenses are connected to independent power sources.