Passage of a plasma burst through a magnetic mirror machine

A study has been made of the behavior of plasma bursts as they move along the axes of an Ogrenok magnetic mirror machine, The bnrsts were accelerated by a coaxial ptasma injector. For the parameters chosen, the main plasma current was injected in the form of two bursts with velocities of 10⁷ and 2·10⁵ cm/sec, In passing through the first magnetic mirror, both bursts were broken up into streams. This occurred to a larger extent in the burst with the lower velocity. The first burst passed through 380 cm of machine in a time of the order of 90 sec. The luminescence from the streams in the machine lasted 700 sec.Translated from Atomnaya Énergiya, Vol. 14, No. 4, pp. 354–358, April, 1963     

Some characteristics ofγ-ray scattering at the boundary of two media

The characteristics of -ray scattering (0.33 E 1,25 MeV) at the boundary between two media were experimentally investigated. It was established that the scattered radiation was produced mainly by a narrow beam of primary radiation. The effective scattering area was contained within a region with a radius r 10h (for h z). The contribution to the total energy from radiation scattered by the medium increased for angles of incidence of the primary narrow beam up to 85–88 °, and then decreased monotonically.An estimate was made of the effective dimensions of the area from which scattered quanta were emitted into the backward half-space when an isotropie source was located at the surface of the scatterer.The energy flux of the scattered radiation was measured with a gas counter which had a practically constant sensitivity for -rays of different energies.The authors are deeply grateful to Prof. O. I. Leipunskii and to A. S. Strelkov for assistance and for discussions of the results.     

Containment of plasma in a trap with combined magnetic field

The containing properties of an adiabatic trap with a magnetic field increasing in the longitudinal and radial directions are investigated. This field is obtained from a combination of the ordinary mirror field configuration (main field H0) and the field of a system of current-carrying conductors laid parallel to the axis of the trap (stabilizing field H). The conductors are placed uniformly in azimuth around the side walls. The trap is filled with plasma of density n10⁹–10¹⁰ cm^–3 and proton energy T_i5eV (T_e20 eV). The plasma lifetime is measured as a function of H. and the neutral gas pressure. From the results obtained, it is concluded that such combined fields ensure stable containment of the plasma, unbroken by magnetohydrodynamic instabilities [at any rate for = nI/(H²/8) 10^–4]. The stabilization of the instability is confirmed by analysis of the plasma oscillations for various values of H. The disintegration of the plasma is determined by the charge exchange of fast ions in the residual gas; the maximum containment time which can be achieved is 0.06 sec for p = 7.10^–9mmHg. A qualitative picture of the plasma density over the radius of the trap is obtained.Translated from Atomnaya Énergiya, Vol. 17, No. 5, pp. 366–375, November, 1964     

Immobilization of Radionuclides in Irradiated Reactor-Graphite Blocks

The immobilization of radionuclides in samples of GR-280 reactor graphite by the fixative atomik is described. A graphite block extracted from RBMK masonry after 17 years of operation is used for the investigations.The investigations showed that the strength of the fixative samples increases only with irradiation doses above 15000 Mrad. The radiation–chemical yield of gaseous products of radiolysis from samples of the fixative under irradiation in vacuum is 12·10^–10 cm³/(g·rad). , , and -emitting nuclides are leached from the samples of irradiated graphite; this process proceeds continually. When the irradiated graphite samples are permeated with the fixative atomik, no release of radionuclides is observed at 20°C for 2 yr.     

Resonance scattering of γ-rays in Mg24

Resonance scattering of -rays With energies E₁=1.38 Mev, corresponding to the transition to the ground state in Mg²⁴. have been observed in metallic magnesium. The energy given off by the -ray (E₁=1.38 Mev) in emission and collision with the nucleus, is compensated for by the energy obtained due to recoil associated with the emission of the preceding -ray with an energy E₂ = 2.76 Mev. Using a fast coincidence method and amplitude discrimination, coincidences were recorded between the -rays with energies E₁=1.38 Mev and E₂=2.76 Mev. Scattercrs of magnesium and aluminum were alternately placed in the path of the 1.38 Mev -rays. The source was radioactive Na²⁴ in a water solution of NaOH. At an angle of 120 ° between the -rays a strong attenuatlon of the 1.38 Mev -rays was observed; this is attributed to resonance scattering. When the angle between the -rays was varied by 5 °. the strong attenuation of the flux disappeared. The width of the level at 1.38 Mev in Mg²⁴ has been estimated at > 1.6· in^–4 Mev.     

γ-Ray spectra excited in inelastic scattering of fast neutrons on manganese,aluminum, iron,copper, tin,and antimony

The study of inelastic scattering of fast neutrons is an important problem of both theoretical and practical interest. From the theoretical point of view the importance of this work lies in the possibility of obtaining data concerning levels in stable nuclei. The practical value arises in connection with the important role played by inelastic scattering of neutrons in fast-neutron reactors as well as the fact that the extension of reactor theory to fast-neutron reactors requires data on the spectra of inelastically scattered neutrons [1, 2]. In this connection the necessity for developing a neutron spectrometer for fast neutrons and-spectroscopy for inelastic neutron scattering is obvious. In the last 5–7 years a great deal of work has been devoted to this problem.The present work reports on measurements of-ray spectra excited in inelastic scattering of 2.8 Mev neutrons by manganese, aluminum, iron, copper, tin and antimony. The measurements were carried out with a scintillation spectrometer consisting of an NaI(Tl) crystal, a FEU-1B photomultiplier and a 50-channel pulse-height analyzer with a magnetic-drum memory. The spectrometer resolution was 6.5–7% for-rays from Co⁶⁰.-Rays of the following energies (Mev) were found: in manganese 0.97, 1.41, 1.92, 2.3; in aluminum 0.84, 1.00, 1.80, 2.16; in iron 0.84, 1.25, 1.46, 1.70; in copper 0.63, 0.78. 0.96, 1.12, 1.38, 1.46, 1.72, 2.03; in tin 0.84, 1.16, 1.50, 1.80, 2.16; in antimony 1.04, 1.50, 1.84, 2.16.Abbreviated version of a paper appearing in the Ukrainian Journal of Physics.The authors wish to take this opportunity to thank L. M. Beliaev and G. F. Dorbrzkanskii of the Institute of Crystallography, Academy of Sciences, USSR for making the NaI(TI) crystal and for kndly allowing us to use it in carrying out the present work.     

On the classical thermal conductivity in a toroidal plasma

In toroidal equilibrium configurations the drift flow of heat causes a redistribution in plasma temperature along the magnetic surfaces. The resulting temperature gradient is equalized by an axial nonmagnetic heat flow, which leads to a certain effective flow of heat across the magnetic surfaces. This additional toroidat heat flow proves to be greater than the magnetic flow, which determines the heat loss from a plasma in a cylindrical geometry, The effective toroidal coefficient of thermal conductivity is calculated for smooth toroidal systems of Tokamak and stellarator types, the latter having a spatial figure-eight form. Expressions are also obtained for the distribution of the electric potential associated with the above-mentioned temperature redistribution.Translated from Atomnaya Énergiya, Vol. 19, No. 2, pp. 120–125, August, 1965     

D-T experiments on TFTR

Temperatures, densities and confinement of deuterium plasmas confined in tokamaks have been achieved within the last decade that are approaching those required for a D-T reactor. As a result, the unique phenomena present in a D-T reactor plasma (D-T plasma confinement, alpha confinement, alpha heating and possible alpha driven instabilities) can now be studied in the laboratory. Recent experiments on the Tokamak Fusion Test Reactor (TFTR) have been the first magnetic fusion experiments to study plasmas with reactor fuel concentrations of tritium. The injection of 20 MW of tritium and 14 MW of deuterium neutral beams into the TFTR produced a plasma with a T/D density ratio of 1 and yielded a maximum fusion power of 9.2 MW. The fusion power density in the core of the plasma was 1.8 MW m^–3 approximating that expected in a D-T fusion reactor. In other experiments TFTR has produced 6.4 MJ of fusion energy in one pulse satisfying the original 1976 goal of producing 1 to 10 MJ of fusion energy per pulse. A TFTR plasma with T/D density ratio of 1 was found to have 20% higher energy confinement time than a comparable D plasma, indicating a confinement scaling with average ion mass, A, of _E. The core ion temperature increased from 30 keV to 37 keV due to a 35% improvement of ion thermal conductivity. Using the electron thermal conductivity from a comparable deuterium plasma, about 50% of the electron temperature increase from 9 keV to 10.6 keV can be attributed to electron heating by the alpha particles. At fusion power levels of 7.5 MW, fluctuations at the Toroidal Alfvén Eigenmode frequency were observed by the fluctuation diagnostics. However, no additional alpha loss due to the fluctuations was observed. These D-T experiments will continue over a broader range of parameters and higher power levels.Work supported by U.S. Department of Energy Contract No. DE-AC02-76-CHO-3073.     

Angle-energy distribution ofγ radiation scattered in water and iron

In this paper we investigate the detailed characteristics of multiple scattering of rays, in particular the angle-energy distribution, a knowledge of which allows us to calculate the attenuation of radiation in complex geometries. Measurements have been made of the angle-energy distribution of rays from a Co⁶⁰ source in water and iron for a semiinfinite geometry and it has been established that these distributions have a maximum close to the energy corresponding to single scattering at the minimum angle. It is shown that the angular distributions are exponential and that the exponential factor is a linear function of the atomic number of the medium. The energy distributions are compared with calculations carried out by Goldstein and Wilkins [1].In conclusion the author wishes to thank I. I. Bondarenko and V. I. Kukhtevich and S. G. Tsypin for discussion of the present work; the author is also indebted to A. N. Voloshin and V. I. Popov for help in carrying out the experiments.     

Investigation of inelastic scattering of slow neutrons by polyethylene

Inelastic scattering of slow neutrons by polyethylene was studied in one of the horizontal channels of the VVR-M reactor at the Institute of Physics of the Academy of Sciences of the Ukainian SSR by the time of flight method. Energy spectra of neutrons scattered by polyethylene at 15°, 30°, 60°, 90° and 120° were measured for seven values of incident-neutron energy (15.4, 25.5, 49.4, 98,8, 136.1, 193.2, and 317 MeV). Doubly differential cross sections for neutron scattering by polyethylene were obtained, the scattering law S(, ) was found, and the frequency spectrum P() was generalized for polyethylene. Averaged characteristics for neutron scattering by polyethylene were computed (average energy release, logarithmic loss, etc.).Translated from Atomnaya Énergiya, Vol. 20, No. 1, pp. 30–35, January, 1966     

Absorption and outgassing of helium during He+ ion bombardment of niobium

Conclusions The capute and outgassin of helium during bombardment by He⁺ ions of energy up to 15 KeV of a niobium target witha temperature of 290–1800°K have been studdied. It has been shown that as the temperature during irradation, T_b, is increased the coefficient of gaseous emission, , increases, while the number of injected atoms, N₀, and the capture coefficient decrease. For temperature greater than 1500°K practically 100% of the bombarding atoms are released to the vacuum. As the dose is increased, and N₀ increase and falls. An increase in to unity indicates saturation of saturation of theniobium by helium. The irradiation dose at which this saturation sets in and its level decrease with the temperature T_b.As a result of an analysis of the outgassing spectra, it has been shown thatthe release of helium occurs in three stages, each of which is due to one of the following causes: diffusion of individual atoms dissolved in the lattice; relase of helium from gas bubbles located in the volume of the metal; release of gas due to bursting of the shells of surface blisters. The last process has a basic role in outgassing at large irradiation doses.Translated from Atomnaya Énergiya, Vol. 38, No. 3, pp. 152–155, March, 1975.     

Experiments on the acceleration and extraction of ions in a cyclotron with an azimuthally varying magnetic field and adjustable energy

Questions concerning the shaping and shimming of magnetic fields are discussed. Results of investigations of the ion acceleration process are presented. Results of experiments on extraction of the accelerated ion beam are reported. The construction of a deflecting system which fully compensates for the field dispersion effect is described. Ion energy adjustment was carried out for a magnetic field interval from 5 to 17 koe. The maximum deuteron energy in the extracted beam was 31.5 mev. The energy spread of the accelerated ions was ±1%.The experiments were carried out on the one and one-half meter cyclotron at the I. V. Kurchatov Order of Lenin Institute of Atomic Energy Academy of Sciences USSR [1].In conclusion the authors express deep gratitude to L. F. Kondrashev, N. Z. Kubyshkin and S. I. Prokof' ev for their great aid in the preparation of the experiments and also to all the service personnel of the cyclotron installation and to the machine shop workers.     

Initial high beta operation of the HBT-EP Tokamak

HBT-EP is a new research tokamak designed and built to investigate passive and active feedback techniques to control MHD instabilities. In particular, HBT-EP will be able to test techniques to control fast MHD instabilities occurring at high Troyon-normalized beta, _N Ba/I_p [Tm/MA], since it is equipped with a thick, close-fitting, and adjustable conducting shell. The major goals of the initial operation of HBT-EP have been the achievement of high beta operation (_N 3) using only ohmic heating and the observation of MHD instabilities. By using a unique fast startup technique, we have successfully achieved these goals. A variety of MHD phenomena were observed during the high beta operation of HBT-EP. At modest beta (_N 2), discharges have been maintained for more than 10 msec, and these discharges exhibit saturated resistive instabilities. When _N approaches 3, major disruptions occur preceded by oscillating, growing precursors. During start-up, one or more minor disruptions are usually observed. A 1-D transport code has been used to simulate the evolution of the current profile, and these early minor instabilities are predicted to be double tearing modes. The simulation also reproduces the observed high beta operation when saturated neo-Alcator energy confinement scaling is assumed.     

3D Wave Propagation and an Ultra–Low-Frequency Instability in Magnetopause

A model set of equations for the low-frequency electromagnetic perturbations in a magnetized nonuniform plasma is presented. A more convenient and systematic procedure is suggested to treat the fluid equations in order to deduce electrostatic and electromagnetic limits. A general dispersion relation is derived for the waves propagating in 3D under local approximation in nonuniform plasmas, which includes almost all the known modes of cold ion magnetized plasmas in the limit < _i (where _i is the ion cyclotron frequency). Both the limits 1 and O(1) have been discussed briefly. The shear Alfvén waves and electromagnetic ion acoustic waves near ultra low frequency (ULF) range are found unstable in the high plasma of magnetopause. The results are in complete agreement with the satellite observations.     

Helical magnetic configurations with minimum\bar B

A general consideration of magnetic configurations with helical symmetry and minimum is presented. An approximate analytic expression is obtained for the specific volume V'() in the neighborhood of the helical magnetic axis. Exact formulas for the specific volume V'() and the mean torsional angle of the lines of force i=2X'() are given in terms of single integrals. Graphs of V'() and X'() are plotted from numerical calculations of these integrals up to the separatix of the magnetic surfaces.Translated from Atomnaya Énergiya, Vol. 20, No. 5, pp. 396–401, May, 1966.     

Interaction of fast H1 + ions with metal surfaces in very high vacuum

The results of experiments on the interaction of fast hydrogen ions (H₁ ⁺) with metals forming weak chemical bonds (nickel, stainless steel) and metals forming strong chemical bonds (tantalum and titanium) with hydrogen are presented. The weighing method was used under very-high vacuum conditions to determine the sputtering coefficient of stainless steel bombarded by 35-keV H ₁ ⁺ ions and the penetration coefficient of H ₁ ⁺ ions entering the stainless steel (=9.10^–3, =0.5 for hydrogen concentrations greatly exceeding 10¹⁹ atoms/cm²). The variation of with the density of the hydrogen introduced and the temperature of the metals was determined by the pressure-variation method. The results indicate that metals of the titanium type are suitable for use in capturing fast hydrogen atoms in magnetic traps.Translated from Atomnaya Énergiya, Vol. 21, No. 5, pp. 339–345, November, 1966.     

Alternating-gradient focusing in linear accelerators

A linear theory for alternating-gradient (strong) focusing in linear ion accelerators is presented.Presented at the All-Union Conference on the Physics of High Energy Particles, May 18, 1956.     

Effect of single channels and slits on reactivity

The change in reactivity due to the change in transport cross section in an inclusion in the form of a cylinder or a plain layer is expressed as a perturbation of the neutron ftux at some distance from the inclusion, where the diffusion approximation holds. By using the results of flux calculations in the layer mediunh and in the cylinder, a relation may be found between the change in reactivity and the characteristics of the inclusion (such as transport cross section, volume, shape, where it is located, etc.). The effect of shape shows up in the coefficients B and B being different from unity. These same coefficients are what determine the average diffusion coefficients D and D, An interpolation formula is constructed for B based on the various limiting expressions.Translated from Atomnaya Énergiya, Vol. 14, No. 4, pp. 364–370, April, 1963.     

Constraints on very-high-β, edge-stabilized tandem-mirror reactors

There are several tandem-mirror schemes which propose a very high and edge stabilization for the center-cell plasma ( being the ratio of the plasma pressure to the vacuum magnetic-field pressure). While the exact criteria for the edge stabilization are uncertain, it is possible to analyze the option space in which a very-high- mirror reactor would operate. The primary physics constraints on such a reactor are the energy balance at ignition, the buildup of He⁴ ash and the hot-particle( ^hot ), and the need for adiabatic conservation of the hot-particle gyro-orbits in the axial field gradients at the center-cell ends. There are also engineering constraints on the allowable wall loading and plant size. In this paper, a wall-stabilized tandem-mirror reactor is analyzed and is found to be an attractive device requiring low center-cell vacuum fields (of the order of 2 to 3 tesla). A primary requirement is that the plasma edge have a thermal conductivity near classical values.     

An investigation of γ-emission associated with thermal neutron capture

A number of spectra of -rays from the (n, ) reaction brought about by irradiation by thermal neutrons were investigated with the use of a magnetic Compton spectrometer at the VVR reactor of AN SSSR. The conditions of the experiment are described, as well as the results of measurements made on the -spectra of tin and antimony.In conclusion, we wish to thank A. S. Volkov for constructing the electronic apparatus and providing for its stable operation; also, we thank the maintenance organization of VVR AN SSSR.