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

Abstract

Based on experimentally obtained plasma parameters in an electron cyclotron resonance (ECR) ion source (ECRIS) and theoretical considerations, it is turned out the essential factor that is currently presumed to define the increase in multicharged ion current in ECRIS is not simply the density limit of ordinary wave and right-hand cutoffs, but is also higher density one of left-hand cutoff. There are two response guidelines that can be considered to make it possible to overcome limitations, except for the conventional simply increasing the frequency and the magnetic field strength. One is advanced high-frequency resonance, i.e., upper-hybrid resonance (UHR), which is conversion from electromagnetic to electrostatic wave essentially without cutoff. The others are due to the introduction of lower frequency waves than ECR’s one, which has no density limit in a more essential sense. The latter is the introduction of lower-hybrid resonance (LHR) or ion cyclotron resonance (ICR). We will describe experimentally obtained plasma parameters, and will discuss these candidate applications.

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

“…at the same frequency is about 2.5-3.5×10 17 m -3 in good agreement with the measurement results. [6]…”

“…The conventional solution to this problem is to increase the resonance frequency of microwaves with frequency tuning technique and increase the magnetic field strength as a means of increasing the cutoff density of electromagnetic (EM) wave propagation. [6] Therefore, from the viewpoint of heating by EM waves, there are two ways to break through the limit of multiply charged ion current. 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.…”

Initial Experimental Results of Producing Multicharged Ions Efficiently by Lower Hybrid Resonance Heating with Exciting Helicon Waves on Electron Cyclotron Resonance Ion Source

“…Accessibility conditions for EM wave propagation were investigated using the ne value obtained by probe measurements and their previously obtained z-direction distribution measurement results. [4] Regarding the conditions corresponding to CSD already shown in figure 3, figure 5 shows the ECR resonance point(black), O-cutoff(green), L-cutoff(blue), and LHR resonance point(brown). Each figure shows LHR regions for Ar +~4+ ions.…”

“…Current ECRIS has a density limit due to the left-hand cutoff density limitation, and it was suggested that this might cause a multicharged ion current limit basically. [4] Conventionally conducted solution for these problems is to increase microwave frequency and the magnetic field strength as a means of increasing the cutoff density.…”

“…[5] On the other hand, in the high-density region, resonance phenomena using low-frequency EM waves (usually called radio frequency (RF)) that do not have a similar cut-off density limit, such as lower hybrid resonance (LHR) and ion cyclotron resonance (ICR), are conceivable. [4] In this paper, we focus…”