Influence of the space charge of an ion beam on the time-of-flight diagnostics of its composition

Abstract

The results of time-of-flight diagnostics of the composition of high-intensity pulsed ion beams are presented. The experiments were performed on a diode of focusing and flat geometry, in the mode of self-magnetic insulation of electrons (accelerating voltage 250–300 kV, pulse duration 120 ns, ion current density 20–300 A/cm2), and a focusing diode in an external magnetic insulation mode (300 kV, 80 ns, 100–200 A/cm2). A delay in the registration of protons by 40–50 ns (on the drift path 14–16 cm) was found in the absence of a delay in the registration of heavy ions. It has been shown that this delay can be related to the deceleration of light ions during the transport from the diode to a collimated Faraday cup. This effect of spatial compression of the ion beam in the direction of the drift increases its pulse power but complicates the time-of-flight diagnostics of its composition.

Diagnostics of Pulsed Beams of Electrons, Ions, and Atoms (Review)

“…The TOF diagnostics of pulsed ion beams that contain light (protons or deuterons) and heavy (С + or N + , Cu + , Fe + ) ions showed a delay in registering light ions by the Faraday cup in comparison with the calculated values [48]. The delay of protons with energies of 250-300 keV was 40-50 ns on a drift path of 14-16 cm.…”

“…At a low proton concentration, the ion-registration delay did not exceed the TOF diagnostic error. The delay in registering light ions is due to their deceleration by the space charge of the HPIB (which is negative due to an excess concentration of low-energy electrons) in the drift region from the diode to the CFC [48].…”