A. K. Berezin

The interaction of pulsed high-current beams with a plasma in a magnetic field

A study was made of the interaction of electron beams of currents up to 8.5 A and energies up to 15 keV with a plasma in a magnetic field the strength of which varied within the limits of 360-1320 oersted. The energy distribution of the electrons after the beam had passed through the plasma was investigated as a function of the beam current, the residual gas (air) pressure and the strength of the longitudinal magnetic field. The intensities of the transverse and longitudinal high-frequency fields established by the beam in the plasma were measured; they attained values of the order of 100 V/cm and 1-2 kV/cm respectively. This is an indication that great energy losses by a beam, arising on its passing through a plasma, are due to the excitation of high-frequency oscillations.

The interaction of modulated high-current pulsed electron beams with plasmas in a longitudinal magnetic field

The results of experimental investigations of the interaction of modulated high-current pulsed electron beams with a plasma in a magnetic field are presented. The plasma was created by the beam itself. It is shown that, under certain conditions, a modulated electron beam interacts with the plasma far more strongly than would an unmodulated beam. The longitudinal waves excited in the beam and in the plasma have a much greater electric field intensity with a modulated beam than with an unmodulated one (typically seven times greater). An explanation of the results obtained is put forward.

The interaction of strong electron beams with a plasma

The energy losses of an originally unmodulated electron beam during its passage through a plasma which is not in a magnetic field have been determined experimentally. With a current of 8 A, an energy of 26 keV and a plasma density of (-7 similar 9) × 1010 cm-3, these losses amount to 12 per cent of the energy of the electron beam. It is shown that these large energy losses are due to the coherent interaction of the beam with the plasma.

Interaction of intense electron beams with a plasma

In this work an experimental determination has been made of the energy losses of an initially unmodulated electron beam passing through a plasma (with no magnetic field). These losses amount to 12% of the beam energy for a beam current of 8 amp, a beam voltage of 26 kev and a plasma density of 7–9·1010 cm−3.It is shown that these high losses are due to the coherent interaction of the beam with the plasma.

High-frequency oscillations excited by the interaction of an electron beam with a plasma

Results are given of experiments on the detection and investigation of oscillations excited in a beam and in a plasma as a result of their mutual interaction. The experiments were carried out under conditions such that ω0 < ωH, where ω0 is the electron Langmuir frequency of the plasma and ωH is the electron cyclotron frequency. The conditions necessary for the excitation of waves in both the beam and plasma were determined, the frequency spectrum, phase velocities and spatial amplification factors for these waves were found, as well as the intensity of the electric field and the absolute values and spectral distribution of the power of the oscillations excited. The experimental values for the frequencies, amplification factors and phase velocities of the oscillations in the plasma were found to be in satisfactory agreement with the calculated data.

Interaction of modulated heavy-current electron-pulse beams with plasma in a longitudinal magnetic field

Results of experiments on the interaction of modulated heavy-current electron-pulse beams with plasma in a longitudinal magnetic field are presented. The plasma is formed by the beam itself. It is shown that under certain conditions the modulated electron beam interacts much more strongly with the plasma than an unmodulated beam. Longitudinal waves with a considerably greater electric field strength (some seven times) than in the absence of initial modulation are excited in the beam and the plasma. An explanation of the results is offered.

Focusing of relativistic electron bunches at the wake-field excitation in plasma

Analytical and numerical investigations of the trajectories of probing beam electrons in a two dimensional wake-field, generated in a plasma by a dense bunch of relativistic electrons with Gaussian longitudinal and transverse distributions of density have been carried out. Based on the calculations of probing beam deviations, the diagnostic instruments are developed for the parameters of experiments conducted at NSC KIPT. The diagnostic instruments include an electron gun generating a 10 keV electron beam with a current of 10 /spl mu/A and 2 mm in diameter, which passes through the chamber of interaction and falls on the collector of 10 mm diameter. The collector (screen) is placed in front of the first plate of a microchannel amplifier which consists of three microchannel plates (MCP) with sizes between 20 and 30 mm. The 3 kV voltage was applied to each plate. The total amplification of MCP amplifier is 10/sup 4/ to 10/sup 5/ depending on the number of particles incident on the first plate. As a result of probing beam deviations due to the excited wake-field, the electrons fall on the first plate of the amplifier and are registered by its anode located behind the third plate. The calculated probing beam deviations and the amplification attained with the MCP amplifier permit one to detect and investigate the electrical wake-fields excited by a sequence of relativistic bunches ( number of particles in a bunch is 2/spl middot/10/sup 9/, energy is 14 MeV) in a plasma of 10/sup 11/-10/sup 13/ cm/sup -3/ density. The intensity of the fields registered by this technique is no less than 2 kV/cm.

The interaction of high-current pulse beams with plasma in a magnetic field

We have studied the interaction of an electron beam with currents up to 8.5 A and energies up to 15 keV with a plasma in a magnetic field, the intensity of which varied between 36O and 1320 Oe. We studied the energy distribution of electrons after passage of the electron beam through the plasma as a function of the beam current, residual gas pressure (air), and the intensity of the longitudinal magnetic field. We measured the intensities of the transverse and longitudinal highfrequency fields excited by the beam in the plasma; these reach about 100 V/cm and 1–2 kV/cm respectively. This proves that the high energy losses of the beam due to its passage through the plasma are caused by excitation of high-frequency vibrations.