Transport of a high-intensity pulsed proton beam through a space-charge plasma lens

We have explored the transport of a high-intensity pulsed proton beam through a plasma focusing system with plasma formed in crossed electric and magnetic fields, i.e., a space-charge plasma lens. The excitation of relatively low-frequency, large amplitude anharmonic oscillations (from several hundred kHz to 1 MHz) in the transported ion beam current was detected, with a degree of beam current modulation up to ∼60%. The excitation of these oscillations is connected to the modulation of uncompensated electron space charge in the lens by the growth of plasma instabilities. The effect of focusing voltage, ion beam energy, and current on the development of beam oscillations, pulse shape, and frequency were investigated. We have found lens operating parameters that provide stable proton beam transport with minimal ion current oscillations.