EXPERIMENTAL STUDY OF THE PROPAGATION AND FOCUSING OF AN INTENSE RELATIVISTIC ELECTRON BEAM (COLLECTIVE ION ACCELERATION, PULSED POWER, LIMITING CURRENTS)

The vacuum space-charge limited current for an intense relativistic electron beam (1.2 MV, 27 kA, 30 ns) as a function of applied axial magnetic field is determined experimentally under solenoidal focusing with immersed source in various evacuated drift-tubes, and compared with theory. A strong variation in the limiting current is observed as a function of applied magnetic field. Studies are performed using immersed and shielded source geometries and the results are compared with theory.; Focusing of the beam without the use of magnetic fields is also studied. The beam is injected into vacuum through a well localized cloud of hydrogen gas (0-100 mTorr). Hydrogen ions are accelerated out of the cloud by the space charge electric field of the beam. These ions neutralize the space charge of the electron beam. The electron beam and the resultant ion beam are observed to be focused allowing propagation in the vacuum region of the drift space. Currents well in excess of the vacuum space-charge limited current are observed to propagate up to 80 cm. Beam-front velocities, current magnitudes and radial distributions are studied. A simple model is developed to describe a possible electron ion-equilibrium and this is used to interpret the experimental results.