Short Magnetic Lens Research Articles

Моделювання електродних систем газорозрядних гармат з фокусуванням електронного пучка в магнітному полі короткої лінзи

In the article, based on the analysis of the basic provisions of the theory of high - voltage glow discharge (HVGD), a method of modeling electrode systems of gas discharge guns with focusing of the electron beam in the field of a short magnetic lens is proposed. To calculate the electric field in the electrode system the finite-difference Poisson equation has been used, which, to simplify its using in the software, is written in the form of an arithmetic-logical expression. Analysis of the guiding of the electron beam in the free drift region was performed with using a system of equations of discrete mathematics based on the Rutherford scattering model. A numerical algorithm for calculating the focus position of the electron beam and its focal diameter is also proposed. To estimate the position of the plasma boundary, a simulation method based on the conversion of the anode plasma volume from a one-dimensional system to the actual spatial geometry of the electrodes was used. In this case, the calculation of the height of the anode plasma in a real electrode system is reduced to the analytical solution of the cubic equation. The calculation of the magnetic field of a short lens was performed using the Yavor model. To implement the proposed methods of modeling HVGD guns, it is proposed to use arithmetic and logical expressions and methods of matrix programming. The obtained results of calculations on the distribution of the electric field in the electrode system, the boundary trajectories of the electron beam in the field of magnetic lense, as well as the distribution of the current density in the focal plane of the hollow electron beam with the ring focus are presented.

Simulation of a pulse-dilation framing tube with sensitive diameter of 60 mm using large aperture short magnetic lens

A pulse-dilation framing tube with large aperture short magnetic lens is simulated by using Monte Carlo method. The photo-cathode (PC) sensitive diameter is 60 mm, and the image ratio is 2:1. While a -3.15 kV dc voltage overlap by an excitation pulse with gradient of 3 V/ps are applied on PC, a gating pulse with width of 225 ps and amplitude of -1.3 kV plus a −100 V dc bias are for the microchannel plate (MCP), the temporal resolution and spatial resolution are 7.8 ps, 11 lp/mm, respectively. The electron beam temporal magnification factor is about 10.3. The relationship between the spatial resolution and the PC electron beam emitting point is obtained. The variation of the temporal magnification factor and temporal resolution with the PC excitation pulse gradient is also given. Furthermore, the connection between the spatial resolution and the PC excitation pulse gradient is acquired.

Achieving a large detector sensitive area of short magnetic focusing pulse-dilation framing tube using a combination lens

A modified short magnetic focusing pulse-dilation framing tube was developed base on imaging characteristic of solenoid lens and short magnetic lens, by which a combination lens composed of two magnetic lenses with a soft iron shield. The spatial performance is simulated by Runge–Kutta method and the imaging distribution of electrons. The detector sensitive area and spatial resolution is measured using Au photocathode with a UV-ray mask and ultraviolet source. When the magnetic field strengths on the axis close to photocathode and microchannel plate were 31 and 56 G, respectively, and the electron image had 2:1 demagnification, the measured detector sensitive area is Φ45 mm and the spatial resolution is about 207 μm. The spatial performance parameter was satisfied the ICF requirement.

Combined focusing of an uncharged particle beam by axially symmetric magnetic and electric fields in a vacuum

A way of simultaneously focusing a circular uniform beam of fine uncharged diamagnetic particles in the longitudinal and transverse directions is explored. Focusing is performed by a short magnetic lens and a diaphragm providing a time-dependent electric field. The size of the particles is within the range of 10−4–10−1 cm.

Magnetic lens analysis of fast electrons in the negative glow

The short magnetic lens technique used in beta-ray spectroscopy is applied to the fast electrons entering the negative glow from the cathode dark space in a helium glow discharge. Information can be obtained about the decrease of electron energy and number density through the negative glow. The method also gives information about the range of the fast electrons.

Absolute measurements of longitudinal β-polarization in 32P decay

The longitudinal β-polarization P has been absolutely measured for five β-enegies in the 32P spectrum. The β-momenta were modified by electrostatic accelaration of the emitted β-particles and were separated by a short magnetic lens with a relative momentum spread of 6%. Crossed electric and magnetic fields were used to rotate the β-spin by 90° relative to the β-direction, and the transverse β-polarization was determined by the analysis of Mott scattering asymmetries. The results, i.e. − P/( v/ c) = 1.00±0.04 (230 keV); 1.00±0.04 (290 keV); 1.01 ±0.03 (349 keV); 1.02±0.03 (410 keV); 1.00±0.03 (481 keV); give a mean value between 200 keV and 500 keV of 1.00±0.01 and show that the longitudinal β-polarization coefficient equals unity for β-particles in 32P decay.

A magnetic lens spectrometer for electron-gamma and electron-electron directional correlation measurements

A magnetic lens spectrometer has been adapted for electron-gamma and electron-electron directional correlation measurements. One electron channel has magnetic momentum selection provided by a medium short magnetic lens spectrometer. The lens spectrometer is iron-free with the exception of two steel end plates which decouple the already weak magnetic field in the lens from the electron detector and from the movable gamma or electron detector. The source sits outside the magnetic field and is accessable through 180° to a movable detector. Directional correlations of electrons with gamma-rays or electrons have been carried out by using a NaI(Tl) detector or an anthracene scintillation detector, respectively. A special source holder was designed for the electron-electron work. Electron energies down to 20 keV have been measured in the lens. A proportional counter may be used to lower energies. The maximum lens energy is ≈ 5 MeV. The spectrometer mean emission angle was chosen to be 13.5°. The resolution can then be varied from 1 to 5 per cent with a corresponding transmission of 0.4 to 1.5 per cent.

Method for alignment of a short magnetic lens beta ray spectrometer by utilizing image rotation

A simple method for aligning short magnetic lens beta ray spectrometers is described.

Investigations on a Short Magnetic Lens Spectrometer

In the course of an attempt to find reversible relations between the parameters describing the trajectory of an electron in a short magnetic lens spectrometer, it was found that the magnetic lens can be surprisingly well represented by a thick converging type optical lens which satisfies Newton's laws for the conjugate planes and the tangent relation far outside the paraxial range where the lens power calculated by the paraxial method can be in error by as much as 50%. Expressions have been obtained for the focal length as a function of the object angle and momentum of the electron. Various other properties of the lens spectrometer have been investigated. In particular, the use of a continuous baffle system to improve the resolution and line-shape for an extended source has been studied by an easy and accurate method.

An Electron Pair Spectrometer of Lens Type for Hard Gamma-Radiation

A new type of pair spectrometer is described. The rotation of the image in a short magnetic lens is used to separate negatrons and positrons by putting the pair converter a little aside from the optical axis of the lens. It is then possible to obtain coincidence ``lines.'' The apparatus has been tried on the 2.62-Mev γ-ray of ThC″ and the 2.76-Mev γ-ray of Na24.

Theory, Design, and Applications of a Short Magnetic Lens Electron Spectrometer

A beta-ray spectrometer has been constructed utilizing the chromatic aberration of a ``thin'' magnetic lens. The lens is wound of 300 pounds of copper wire and does not utilize iron. Its focal length for transmitted electrons can be varied from 25 to 50 cm and the magnification from 0.5 to 2. Circular sources varying in diameter from 0.4 to 1.6 cm are used and the solid angle subtended at the source is varied between 0.025 and 0.1 steradian. The half-maximum width of the transmitted distribution is 0.017 to 0.06 of the momentum of the focused electrons. Larger solid angles or better resolution could probably be obtained. The focusing properties of the instrument are derived from the calculated field distribution of the lens by the method of Busch. The spectrometer has been applied to studies of radioactive disintegration schemes. Appropriate techniques are described for the measurement of discrete and continuous beta-ray spectra, of coincidences of focused electrons with other radiations, and of gamma-ray energies through secondary electron spectra. A special baffle system allows the separation of negatrons and positrons. The performance of the short lens spectrometer is compared with that of other types of beta-ray spectrometer and it is concluded that it is a particularly useful tool for the investigation of disintegration schemes because of its flexibility, the use of large circular sources, and the accessibility of source and counter which are located outside the magnetic field at a distance of 100 cm from each other.