<title>Electron-optic system of the multicharge ion source (MIS-I)</title>

Abstract

Results obtained in designing of the electron-optic system (EOS) of the multicharge ion source (MIS-1) are reported. This system forms an extended (~2 m) electron beam of power 1 MW. The length of the MIS-I ion trap with an electron beam density greater than 2x10<SUP>3</SUP> A/cm<SUP>2</SUP> in increased to 1.5 m. Recuperation of the electron beam energy is envisaged in the collector. The electron-optic system (EOS) of the source being designed consists of three basic sections. The first section includes an electron gun and electron-beam injection to the solenoid focusing field. The second section is the electron-beam drift region in the solenoid focusing field, where the working region of the ion source is created in a stationary magnetic field, i.e., an ion trap. The third section is electron-beam rejection to the collector with maximum possible recuperation to decrease the power scattered on the collector and also to decrease the energy consumed during EOS operation. In an electron-beam ion source (EBIS), the capacity of the electron trap should be equal to the number of electrons of an ionizing beam in its volume. The time for which the required ion-charge distribution is attained is proportional to the electron beam density <SUP>1</SUP>. IN using EBIS in modern accelerating heavy ion facilities <SUP>2</SUP>, it is necessary to ensure a capacity of ion traps no smaller than 10<SUP>12</SUP> at a electron beam density of 10<SUP>3</SUP> A/cm<SUP>2</SUP> in it. This problem can be solved most effectively by means of an EOS with double compression of the electron beam. That is, the electron beam is compressed electrostatically in an electron gun and at the second stage compression is ensured by an increasing focusing magnetic field. To do this, the magnetic field in the cathode - crossover region is distributed in such a way that the force lines of the magnetic field coincide with electron trajectories. The magnetic field increases behind the crossover and provides additional smooth compression of the electron beam with its laminar character preserved.