Upper hybrid resonance heating experiments by X-mode microwaves on electron cyclotron resonance ion source

Abstract

We have considered the accessibility condition of electromagnetic and electrostatic waves propagating in an electron cyclotron resonance (ECR) ion source (ECRIS) plasma and then investigated experimentally their correspondence relationships with production of multicharged ions. It has been clarified that there exists an efficient configuration of ECR zones for producing multicharged ion beams and has been suggested that a new resonance, i.e., upper hybrid resonance (UHR), must have occurred. We have been trying to perform advanced experiments with 4–6 GHz X-mode microwaves to the 2.45 GHz ECRIS plasma, and we have succeeded in enhancing the production of multicharged ions by launching X-mode microwaves of these bands. Furthermore, at the same time, we have observed sharp increases in electron energy distribution functions in the ECRIS plasma by means of probe methods. It has been concluded that the UHRs must have occurred when applying multiplex microwaves with their frequencies away from those frequencies for ECR in the ECRIS. In this paper, we will describe in brief the theoretical background and the results of these new experiments.

Cutoff limitation of left-hand polarization wave and candidates for further enhanced producing multicharged ions on ECRIS

“…Since it is difficult to distinguish the phenomenon of ECR and UHR with ordinary single frequency microwaves, we introduced microwaves for ECR and at the same time introduced high frequency microwaves far from that frequency in X-mode. As a result, we observed an increase in multicharged ion currents due to the UHR and simultaneously an increase on the high energy side of electron energy distribution function that supported it [10]. Furthermore, Dual ECR experiment was conducted and the yield of multicharged ions was successfully increased [11].…”

“…As a result, it was shown that the multicharged ion current is usually saturated with each single microwave power supply, but the increased multicharged ion currents can be obtained by simultaneous power supply [11]. Kato et al, the same group conducted an UHR experiment with X-mode pioneeringly on 2.45GHz ECRIS superimposed by using 4-6GHz microwaves [10].…”

Low Z gas mixing effects of Ar and Xe multicharged ions in electron cyclotron resonance ion source

“…We focus on the gas mixing effect [2] [3], which is known as an empirical method to increase multicharged ions in ECRIS's. In our previous studies, the increase of Ar multicharged ion yield has been confirmed by the upper hybrid resonance (UHR) [4] using 4-6 GHz Xmode microwaves, the dual ECR heating method [5] in which microwaves are fed from two antennas simultaneously. We are attempting to increase the multicharged ions using lower hybrid resonance (LHR) by introducing low frequency electromagnetic waves (radio frequency waves: RF waves).…”

Initial Experimental Results on Ion Cyclotron Resonance Heating Selectively Mixed Low Z Ions to Enhance Production Efficiency of Multicharged Ions on Electron Cyclotron Resonance Ion Source

“…In the highfrequency EM waves, one method is to induce resonance by mode conversion from EM waves with various cutoff densities, etc., to electrostatic waves with no cutoff densities. Results have already been obtained in upper hybrid resonance (UHR) experiments [7] independently supplying microwave powers from both upstream and downstream of the ECR zone [8]. On the other hand, in high-density regions, resonance phenomena using low-frequency EM waves (usually called Radio Frequency: RF) are known as lower hybrid resonance (LHR) and ion cyclotron resonance (ICR).…”