SU191010A1 - - Google Patents

Description

When focusing beams of charged particles with different energies, the chromatic aberration of the focusing system plays a weird role. The resolution of various electronic and ion-optical devices essentially depends on its size. It has been proven that the chromatic aberration commonly used for focusing axially-symmetric systems can be reduced to pool.

The proposed system of two non-axially symmetric elements (combined electrostatic and magnetic quadrupole lenses) has zero chromatic aberration and allows to obtain a stigmatic image, while each lens is individually astigmatic. In one plane, the lens focuses the nooch, in the perpendicular one it scatters.

In order to obtain the achromatic mode, the voltage b and the ampere-turns of excitation of the p1 lens must be interconnected by the following relation

(from C + E) U E (2tC2 -f E) 25

0.4.

TO,

 -) - (gS2 - g) s

nitric lenses (distance from the optical axis to the electrode or pole); K-coefficient depending on the shape of electrodes and zeroes (with hyperbolic poles K.E / ().

The distribution of the electric and magnetic fields along the axis should be the same, and the effective lengths of the lenses are equal.

The lenses are coaxial and rotated one relative to the other by 90 °, so that the focusing plane of one lens coincides with the scattering plane of the other, and vice versa. With an appropriate selection of modes and distances using lenses to achieve that the lens focuses in all planes and gives an accurate image of a point source. Moreover, between the geometric and electrical parameters the following relations are established:

20

five;

-r- s,

b and d are the effective lengths of the lenses; a and g are the distances from the object to the first lens n from the second lens to the image, respectively; 5 — distance between lenses (all distances are calculated taking into account the effective lengths of the lenses); tick is the mass of the rest and energy of the charged particle; C is the speed of light; E and yy, "- the radii of the aperture of the electrostatic and magnetic lenses (the distance from the optical axis to the electrode or pole); K is the coefficient depending on the shape of the electrodes and poles (with hyperbolic poles KE Kt 1); - for example on the lens electrodes; n is the number of ampervices on one pole of the gth lens.

The increase created by the proposed system is different in different planes.

Subject invention

Achromatic anamorphic doublet for focusing charged particles from quadrupole lenses that are rotated 90 ° relative to each other; characterized in that, in order to provide both stigmatic and achromatic modes, an achromatic combined quadrupole lenses are used in the doublet, and the following are set between the geometric and electrical parameters of the system

ratios:

-tgl.b

li

-five;

/ Iflfg / li-l

g + i-id

 - th

M

+ 5,

kgigkd - l

lia th lib - 1 of which:

 ,

0 ,, (nI) i

 2

rlcyi

Iwe

b and d are the effective lengths of the lenses; a and g are the distances from the object to the first lens and from the second lens to the image, respectively; 5 — distance between lenses (all distances are calculated taking into account the effective lengths of the lenses); m and e are the mass of the rest and energy of the charged particle; C is the speed of light; and the r-radii of the aperture of the electrostatic and magnetic lenses (the distance from the optical axis to the electrode or pole); K is the coefficient depending on the shape of the electrodes and poles (with hyperbolic poles); + t / f voltage on the lens electrodes; / is the number of ampere turns on one pole of the gth lens.