Study of Pulsed Cathodoluminescence of Calcium, Barium, Lithium, and Magnesium Fluorides
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Russian Physics Journal, Vol. 63, No. 5, September, 2020 (Russian Original No. 5, May, 2020)
STUDY OF PULSED CATHODOLUMINESCENCE OF CALCIUM, BARIUM, LITHIUM, AND MAGNESIUM FLUORIDES M. V. Erofeev,1 E. Kh. Baksht,1 V. I. Oleshko,2 and V. F. Tarasenko1
UDC 535.376, 537.527
Studies of the spectral and kinetic characteristics of CaF2, BaF2–Ce, LiF, LiF–W and MgF2 crystal glow irradiated by the electron beam with energy of 350 keV have been carried out. It has been shown that the cathodoluminescence spectrum of CaF2 and BaF2–Ce consists of high-intensity exciton bands in the UV-region of the spectrum, the radiation time of which exceeds the duration of the electron beam current. Radiation of the LiF and LiF–W crystals also has exciton bands in the UV-region, but their transmittance decreased during the excitation pulse due to accumulation of radiative defects. It has been found, that the MgF2 crystal has the lowest cathodoluminescence intensity. This has allowed us to distinguish Cherenkov radiation the duration of which corresponds to the electron beam current duration in the wavelength range of 240–400 nm. Keywords: pulsed cathodoluminescence, electron beam, Cherenkov radiation.
INTRODUCTION Overall performance of modern accelerating complexes depends in many respects on the quality of diagnostics of high-energy beams of different particles the energy of which can reach several hundred or even thousand kiloelectron volts. Ionization cameras, scintillation spectrometers, and gauges are used to record these particles. In Tokamak-type installations, runaway electrons with different energies are generated upon discharge failure. They hinder plasma heating and can cause melting and evaporation of the walls of the working chamber [1]. Hence, measurement of the energy and the number of the runaway electrons is one of the important problems of prediction and control of the plasma state in Tokamak-type installations. There are various gauges and methods of measuring the energy of runaway electrons and their spatial distribution [2, 3]. One of the promising devices for detecting runaway electron beams are the optical systems using, according to [4, 5], Cherenkov radiation. Radiation detectors in these systems are diamond crystals the luminescence of which is transmitted through a lightguide to a photomultiplier tube (PMT) placed outside of the working chamber. According to L. Jakubowski et al. [4, 5], Cherenkov radiation is recorded by these detectors; however, no optical radiation spectra were presented in works of these authors. The radiation detector was calibrated only in [5], and the radiation spectrum was presented that did not correspond to the Cherenkov radiation spectrum in diamond. Studies of the luminescence of specimens made of natural and artificial diamonds irradiated by electron beams with energies of several ten to several hundred kiloelectron volts using standard spectrometers in the range of 200– 1000 nm showed that only pulsed cathodoluminescence (PCL) bands were recorded [6]. UV part of Cherenkov radiati
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