Observations of Collective Ion Acceleration by a Relativistic Electron Beam in a Magnetic Cusp

Abstract

We have observed ion pulses of ${10}^{13}$ protons by passing hollow relativistic electron beams through a magnetic cusp. Ion pulses are observed with drift-chamber fill pressures from 75 to 600 mTorr of ${\mathrm{H}}_{2}$. Magnetic fields of 0.8 kG suppress the mechanism responsible for acceleration without magnetic field. A different mechanism appears to turn on and peaks as the cusp threshold is approached. More than ${10}^{11}$ protons with energies greater than 2 MeV are observed.