Microwave-accessibility conditions estimated by plasma parameters obtained experimentally on electron cyclotron resonance ion source

Abstract

We insert two probes in the upstream and the downstream regions with respect to the electron cyclotron resonance (ECR) zone which is formed at the center of mirror fields. We measure simultaneously plasma parameters in those regions by each of them under the same operating condition. We measure ion saturation currents Iis and electron energy distribution functions at two positions. We obtain measurement results that suggest the more efficient ECR on the side closer to the microwave-launchings than those on the other side. It is consistent with the accessibility condition of the right-hand polarization wave. We also compare the charge state distributions of Ar ion beams extracted in the case of launching microwaves from the coaxial semi-dipole antenna and those from the rod antenna. We observe the higher multicharged ion beam currents at the low microwave powers in the case of the rod antenna than those in the case of the coaxial semi-dipole antenna. We also confirm stable increasements of ion beam currents at considerably high microwave powers in the case of the coaxial semi-dipole antenna. Based on the experimental results, we propose a new microwave-launching method, “dual-ECR heating” and report its preferable preliminary experimental results in this paper.

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

“…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].…”

“…2.45GHz microwaves for ECR discharge are coaxially converted from the waveguide to the inside of the vacuum vessel via a three-dimensional circuit independently from two magnetron sources with a maximum power of 1.3kW through the waveguide coaxial conversion windows. One is a semi-dipole antenna at the tip of the inner conductor where the mirror magnetic field is at the maximum position after being reduced to a taper shape while keeping the aspect ratio of the inner and outer diameters constant in vacuum and then inserted along the mirror magnetic field from the upstream end side of the mirror at z = -418mm [11]. On the other hand, the microwave power is supplied from the Ti rod antenna from the side of the vacuum vessel on the downstream side near the extraction electrode.…”

“…It can be seen that the ECR resonance point can be reached without the propagation being hindered. After the ECR resonance point, the R-wave is a non-propagating region in the E region and propagation of a propagatable L or X wave is allowed [11]. After that, it was found that the route from any antenna reached the L-cutoff point, and that all modes reached the non-propagating G region.…”

“…group conducted an experiment based on the idea of Dual-ECR Heating, which simultaneously feeds microwaves from the strong magnetic field side on the upstream side and downstream side of the resonance point, which has not been performed in ECRIS in the past. 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).…”