Table of contents

The energy of neutrons emitted tangential and perpendicular to the discharge axis of ZETA has been measured using a hydrogen-filled diffusion cloud chamber. Several different discharge conditions were studied.

The results are consistent with the conclusions of other workers that the neutron emission is due to a small number of high-energy deuterons. In addition, analysis of the shape of the neutron spectra suggests the possibility that the deuterons have a velocity which is predominantly perpendicular to the gas current axis and that they travel in a helix with energies up to 350 keV.

In this paper a Rogowski coil with a capacitive shieid is treated as a distributed circuit, so that the toroidally wound coil acts as a delay line. It is shown that, in general, the high-frequency response is limited by the transit time around this delay line, and for times greater than this transit time the individual circuit elements act as lumped impedances. However, if the flow of the current to be measured is such that it is symmetrical with respect to the toroidal coil (so that the voltage induced per unit length along the coil, when the current changes, is constant), the transient response becomes less than the transit time for a termination whose impedance is small compared with that of the toroidal coil. The best results may be obtained with an inductive termination whose impedance has the same phase angle as the impedance of the toroidal coil; and for this termination the output is proportional to the rate of change of current.

The layout and operating system of the synchrotron at the P. N. Lebedev Physics Institute of the U.S.S.R. Academy of Sciences are described. This machine accelerates electrons to a maximum energy of 680 MeV. The results obtained from a study of the more important characteristics of the accelerator are presented and a short account is given of the more effective experimental methods employed when starting up the accelerator.

An electron linear accelerator intended for use in neutron spectroscopy is described. The current in the pulse for electron energies 25-32 MeV and pulse durations of 0.6, 0.2 and 0.05 μsec is 160-500 mA. The pulse repetition frequency is 100 c/s or less. The neutrons are produced in a ²³⁸U target placed inside a water moderator. The spectrum of neutrons from this accelerator measured on a 109-m flight path at energy intervals from 4 eV to 30 keV is presented.

A procedure is described for making signal electrode design calculations for given particle bunch parameters and for a given amount of field-free space in the accelerator vacuum chamber. With this method it is possible to determine the sensitivity of such electrodes to changes of beam intensity and to displacements of the centre of gravity of the beam. A method is given of working out the design specification for the measuring equipment. The results of calculations carried out by this method agree well with experiment.

The diffusion of a decaying helium plasma has been studied by a v.h.f. method. The investigations were carried out at parameters for which the diffusion flux across the magnetic field was due to electron-ion collisions. The measured diffusion coefficients in magnetic fields of 700 to 800 Oe are in accordance with those derived on the basis of the classical theory of binary Coulomb collisions. In the range of magnetic fields from 1000 to 5000 Oe a considerable deviation from the theory is observed, the diffusion coefficient being proportional to 1/H. The asymptotic solution is found for the diffusion equation which describes a decaying fully ionized plasma in the case of axial symmetry.

The secondary field created by the moving bunches of particles in retarding structures is determined and the main properties of those features of electron linear accelerators which are sensitive to beam loading effects are analysed. A detailed discussion is given of the operation of a linear accelerator in the stationary and transitional regimes and also when it is loaded by short-duration pulses.