Radiation Spectrum of an Electron Cyclotron Maser

We consider generation of electromagnetic radiation at the electron cyclotron harmonics by energetic-electron beams having the mean momentum parallel, transverse, or oblique to the external magnetic field. This process is most efficient if the characteristic transverse momentum is sufficiently large. The radiation spectrum of the beam moving exactly along the magnetic field is closest to the equidistant one. The angle between the direction of the maximum emission and the magnetic field varies from 70^° for the field-aligned beam to 90^° for the beam whose characteristic momentum is transverse to the magnetic field. In fairly strong magnetic fields, i.e., for _Be >_pe, where _Be and _pe are the electron cyclotron and plasma frequencies, respectively, the radiation is maximum at low cyclotron harmonics and the second harmonic dominates. In the weaker fields (_Be < _pe), higher harmonics, up to fifth or sixth, are generated. Both wave modes are generated, but generation of the ordinary waves is far less efficient than that of the extraordinary waves under the same conditions.     

Performance of a slow positron beam using a hybrid lens design

The University of Hong Kong positron beam employs conventional magnetic field transport to the target, but has a special hybrid lens design around the positron moderator that allows the beam to be focused to millimeter spot sizes at the target. The good focusing capabilities of the beam are made possible by extracting work-function positrons from the moderator in a magnetic field free region using a conventional Soa lens thus minimizing beam canonical angular momentum. An Einzel lens is used to focus the positrons into the magnetic funnel at the end of transportation magnetic field while at the same time bringing up the beam energy to the intermediate value of 7.5 keV. The beam is E × B filtered at this intermediate energy. The final beam energy is obtained by floating the Soa-Einzel system, E × B filter and flight tube, and accelerating the positrons just before the target. External beam steering saddle coils fine tune the position, and the magnetic field around the target chamber is adjusted so as to keep one of the beam foci always on the target. The system is fully computer controlled. Variable energy-Doppler broadened annihilation radiation (VEDBAR) data for a GaN sample are shown which demonstrate the performance of the positron beam system.     

Polarization properties of boson radiation

The polarization properties of boson radiation in a magnetic field have been studied, and expressions obtained for the integral intensity of boson and fermion radiation in a magnetic field which are suitable for random energies. The investigation of boson radiation in an external field is of limited practical interest; however, from the methodological point of view it is very instructive and has already been investigated by several authors [1, 2, 4], Also of undoubted interest is the comparison of boson and fermion (electron) radiation and hence the explanation of the role of spin in radiation.In conclusion the author expresses his deep appreciation to Prof. I, M. Ternov for assistance with the work and discussion of the results.     

Positron states in KCL crystals before and after radiation exposure

The features of positron annihilation in KCl crystals before and after radiation exposure is investigated. A significant increase in the efficiency of the ortho-vapor process of positronium state conversion is detected. A model is proposed for taking part in the ortho-vapor conversion of conduction electrons drawn into the conduction band by a positron field that affords a qualitative interpretation of the results obtained and permits values of the electron concentration in a spur to be obtained.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 98–102, July, 1988.     

Ultrahigh magnetic field diagnostic with spectral profile calculation

We report the theoretical results on use of neon as a tracer element to measure the multi-megagauss magnetic field, which is induced in the ultrahigh intense laser-matter interactions. The shape of Zeeman splitting of spectral line for transition of He-like neon are calculated for high-intensity laser produced quasi one-components plasma with the consideration of the electron collision broadening, electron collision shift and magnetic field splitting. The results show that all of the Zeeman splitting spectrum can be identified under Rayleigh criterion for the plasma with the electron temperature from 10 to , the magnetic field from 10⁶ to and the electron density . With both the electron temperature and magnetic field increasing, the requirement for the resolution power of the spectrometer decreases. If a spectrometer with the resolution power of 1/1000 is used, the measurement of the quasistatic magnetic field by Zeeman splitting of spectral lines is applicable when quasistatic magnetic field is larger than some tens of megaGauss.     

Energy scale calibration of the KEDR tagging system

The KEDR detector tagging system is a symmetric focusing magnetic spectrometer of small-angle electrons born in the interaction region of the VEPP-4M collider. Using this system, which is designed for studying the two-photon processes, the scattered electrons and positrons energy is measured with a resolution of ΔE/E₀= 0.03–0.6% where E₀ is the beam energy. Two different methods are employed for calibrating the tagging system energy scale: the first one involves the electron/positron tagging by the energy of the singlebremsstrahlung photon measured in the BGO calorimeter, and the second one is based on the determination of the recoil electrons spectrum edge in the Compton backscattering of monochromatic laser radiation. The technical implementation and the present status of the calibration system are discussed in this paper.     

Investigation of the spectral characteristics of pulses of diffraction radiation

The physical phenomena which lead to distortions of the spectrum of diffraction radiation pulses are analyzed by means of theoretical estimates and experimental investigations. The experimental investigations were carried out for pulses of high-frequency oscillations with a duration of 0.15–10sec, excited in a diffraction radiation generator in the millimeter-wavelength range. The effect of steepness of the electron frequency retuning, the magnitude of the focusing magnetic field, and the pressure of the residual gases on the spectral characteristics of the instrument is established. The range of variation of the generator parameters is determined, where parasitic effects leading to distortions of the spectrum are expressed only slightly.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 21, No. 12, pp. 1853–1861, December, 1978.     

Characterization of diamond single crystals by means of double-crystal X-ray diffraction and positron annihilation

The crystallinity of synthesized and natural crystals of diamond was characterized by double-crystal X-ray diffraction and positron annihilation. The two-dimensional angular correlation of annihilation radiation and positron lifetime measurements revealed that in natural crystals positroniums are formed in a high fraction. The synthesized crystal Ib showed both an extremely small width for the diffraction and a positron lifetime spectrum with a single component of the lifetime of 115 ps. In contrast, the natural diamonds contain a long-lived component of lifetime longer than 2 ns. The diffusion length of positrons was also measured by a variable-energy positron beam. In the synthesized crystal IIa, a diffusion length of about 100.8 nm was observed.Paper presented at the 132nd WE-Heraeus-Seminar on Positron Studies of Semiconductor Defects, Halle, Germany, 29 August to 2 September 1994     

Possible schemes for cyclic acceleration of electrons without emission of radiation

The motion of an electron or positron with acceleration along a curvilinear trajectory is accompanied by the continuous radiation of electromagnetic energy. The motion of an electron in the central force field of the atomic nucleus is not so accompanied. Atomic systems exhibit only quantum radiation, a phenomenon which can also manifest itself in accelerators under certain conditions. The paper reports a study of physically possible hydrogenlike nonradiating cyclic accelerators. The cyclic acceleration of a large number of electrons or positrons can be accompanied by the appearance of conditions under which there is no radiation or the radiation cancels out by interference in the volume of the beam. Radiation quenching occurs when the accelerated electrons and their radiation are in thermodynamic equilibrium.Presented May 20, 1971 at seminar held by Moscow State University Physics Faculty (supervisor Professor D. D. Ivanenko) and on May 19, 1972 at meeting of Electron Accelerators section of Scientific Council of USSR Academy of Sciences on accelerators.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 10–15, October, 1973.     

Wave function of an electron in a magnetic field in the rotator approximation

The electron wave function is determined for the case in which only the orbital moment of the electron is quantized. It is shown that the radiation quantum corrections calculated on the basis of the resulting wave functions coincide, through squared terms in , with the corresponding corrections obtained from the exact wave functions for an electron in a homogeneous magnetic field.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 16–20, January, 1977.The author is pleased to acknowledge Professor I. M. Ternov for valuable assistance.     

Polarization and angular distribution of the radiation of electrons moving in a focusing magnetic field

The angular distribution of the linear-polarization components is found for the radiation of an electron moving in a nonuniform weak-focusing magnetic field. The distribution shape is studied as a function of the amplitudes of the axial and radial betatron oscillations. It is shown that the minimum intensity of the component of the radiation does not vanish, in contrast with the case of a uniform field.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 3, pp. 52–58, March, 1971.The authors thank A. A. Sokolov for suggesting the topic and for fruitful discussions.     

Intensity Effects in Scattering of Electromagnetic Waves by Electrons Moving in External Magnetic Field

In this paper we consider the emission processes of a relativistic electron moving in the field of a plane electromagnetic wave and in a homogeneous magnetic field. A detailed analysis of the most important characteristics of the radiation properties for arbitrary values of the magnetic field, compared with \documentclass{article}\pagestyle{empty}\begin{document}$ [H_0 = \frac{{m^2 c^3}}{{e\hbar}}]$\end{document} = 4.41.10¹³ gauss, is presented.     

Intense source of slow positrons from pulsed electron accelerators

A pulsed LINAC is used for pair production in a tantalum target of 2.5 radiation lengths in an energy range from 80 to 260 MeV. Several well-annealed tungsten vanes are placed immediately behind the target and thermalize a small fraction of the fast positrons. The slow positrons are extracted from the target region and magnetically guided over a distance of 17 m to the detector at the end of an S-shaped solenoid. Two Nal detectors with well-known detection efficiency are used to register the 511 keV annihilation-rays. To reduce pile-up effects 50 mm of Pb were placed in front of the detectors. At an average electron current of 1 A we could detect about 10⁷ slow positrons per second. The positron yield is proportional to the electron current, and shows an increase with the electron energy for our target. The positron energy distribution has a FWHM of 1.8 eV.     

PAMELA spectrum of electrons and positrons of cosmic rays in the energy range of 0.05–1.2 TeV

A proprietary method is used to process measurement data from a high-energy particle (protons, electrons, and positrons with Е ≥ 50 GeV) spectrometer in a near-Earth orbit. The data from three detector systems are used: a tracker in a constant magnetic field (TRK), a calorimeter (CAL), and a neutron detector (ND). A relatively simple and efficient way of isolating electrons and positrons from the total charged particle flux entering the PAMELA spectrometer is proposed. A technique for determining the energy of isolated primary particles and retrieving their energy spectra is described. The composite electron and positron spectrum (below, the total electron and positron flux is referred to simply as the electron flux) for energies up to 1.5 TeV is presented.     

Observable radiation zeroes in HERA interactions

Radiation zeroes were discovered over 10 years ago and heralded as a direct probe of gauge couplings and fractional quark charges. Observations of such zeroes have eluded proton-antiproton collider experiments so far. We here point out that radiation zeroes appear in electron-quark collisions and conclude that they should be observable at HERA in the subprocesseqeq. Choosing suitable cuts, we expect 660 (430) events/year in the electron (positron) channel of the neutral current single jet plus direct photon events at HERA, i.e. we expect 12 (4) events/bin/year in the electron (positron) channel over a large fraction of the range of cos (10 of the 30 bins we use).     

Features of Fundamental- and Subharmonics ECR Heating in a Magnetic Trap

We compare the efficiency of microwave heating of electrons in a dense plasma at the fundamental harmonics ( = eH/(mc)) and at the subharmonics ( = eH/(2mc)) of the electron gyrofrequency. In particular, recent experimental results showing a higher efficiency of microwave heating at the frequency equal to one half of the electron gyrofrequency are analyzed. Equations describing the nonlinear subharmonic electron cyclotron resonance (ECR) heating are derived for an arbitrary geometry of the microwave field. If the microwave field has the vacuum polarization, then the microwave power absorbed by electrons at the fundamental harmonic of the electron gyrofrequency in rarefied plasmas exceeds by many orders of magnitude the corresponding power absorbed by electrons in the case of nonlinear heating at one half of the electron gyrofrequency. However, it is shown that this difference in a dense plasma does not exceed one order of magnitude, which is explained by the effect of depression of the resonance component of the microwave field. In this case, the efficiency of the formation of high-energy electron population can be influenced not only by the energy-deposition rate but mainly by the stability condition of an electron in the magnetic trap. It is shown that a twofold decrease in the magnetic field, necessary to satisfy the ECR condition at one half of the electron gyrofrequency, leads to a dramatic shortening of the hot-electron lifetime in a magnetic trap and, in turn, to a dramatic decrease in the energy-deposition efficiency. We discuss the dependence of the electron heating on the effect of quasi-static enhancement of the microwave field near a target located in a magnetic trap for the generation of X-ray emission.     

Resotron: A Novel Tunable Millimeter and Submillimeter Wave Source of Radiation

The need for tunable radiation sources in the millimeter and submillimeter range for spectroscopic purposes is still a research area of great interest. The tunable radiation source, proposed in this paper, is a special free electron laser device with the prerequisite of low electron energy. The output power density in the millimeter (GHz)-range is of the order of MW/cm² and in the submillimeter (THz)-range of the order of kW/cm². The device consists of an electron source with electron optics, wiggler/microwiggler, and a longitudinal magnetic field. The wiggler for the THz-regime has a very short wiggler period of approximately 400 m and could be manufactured with laser micromachining techniques. The free electron laser operates in magnetoresonance and shows surprisingly stable electron orbits and therefore narrow output frequencies. Computational results of the temporal behavior of the output power done with a multi-frequency code are reported.     

Operation of a high-harmonic gyrofrequency multiplier

The operation of a sixth-harmonic gyrofrequency multiplier is described. The initial experimental results produced 3.5 kW of 17.23 GHz radiation from a 260 keV, 0.3 A, =v/v=4.8 axis-encircling electron beam in a near uniform magnetic field. The output cavity conversion efficiency was measured at 4.5% compared to the predicted value of 8% from a nonlinear simulation code. The design for a higher power, higher efficiency device utilizing magnetic tapering is also presented.     

Radiational self-polarization of electron-positron beams in an axially symmetric focusing electric field

Radiational self-polarization of an electron (positron) beam with spontaneous emission in an axially symmetric focusing electric field with a potential of the form (r)=Ur^µ is considered. The analysis is based on the solutions of the Dirac equations found in the approximation of small oscillations in the vicinity of the equilibrium radius of rotation. It is shown that the existence of self-polarization depends significantly on the structure of the field; in particular, the probability of electron transitions with spin reversal is zero when =–1.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 88–92, April, 1989.