Transverse distribution of beam current oscillations of a 14 GHz electron cyclotron resonance ion source

Abstract

The temporal stability of oxygen ion beams has been studied with the 14 GHz A-ECR at JYFL (University of Jyvaskyla, Department of Physics). A sector Faraday cup was employed to measure the distribution of the beam current oscillations across the beam profile. The spatial and temporal characteristics of two different oscillation "modes" often observed with the JYFL 14 GHz ECRIS are discussed. It was observed that the low frequency oscillations below 200 Hz are distributed almost uniformly. In the high frequency oscillation "mode," with frequencies >300 Hz at the core of the beam, carrying most of the current, oscillates with smaller amplitude than the peripheral parts of the beam. The results help to explain differences observed between the two oscillation modes in terms of the transport efficiency through the JYFL K-130 cyclotron. The dependence of the oscillation pattern on ion source parameters is a strong indication that the mechanisms driving the fluctuations are plasma effects.

Experimental investigation of plasma instabilities by Fourier analysis in an electron cyclotron resonance ion source

“…Plasma instabilities are studied experimentally in Q-machines and theoretically by various groups worldwide in the last six decades but there are few reports in the literature to study them in detail as per the multiple tuning parameters of the ECR ion sources by means of Fourier analysis of beam intensity. Recently, Tarvainen et al [3,4] reported an experimental observation of electron cyclotron instabilities in the minimum-B ECR plasma which led to ms scale oscillations in extracted beam currents. They monitored the microwave emission, bremsstrahlung radiation and extracted beam current oscillation which happen in the regime of ns, μs, and ms, respectively.…”