Physics of Multiply Charged Oxygen in the Constance B Quadrupole Mirror

Abstract

Detailed experimental measurements of multiply-chargered ion densities, endloss currents,and temperatures have been made in a single cell quadrupole mirror. The purpose of these experiments is to determine the confinement physics of ions over a range of charge states in an ECR ion source. The parallel ion confinement times agree well with a theoretical model including Pastukhov and flow confinement for a potential dip of ϕi/Ti ~ 1. The ion endloss currents were found to be up to 50% hollow. Radial transport of ions'was found to be important in limiting the extraction of high charge state ions. In addition, by heating O4+ with ion cyclotron resonance heating we were able to increase its extracted current in the plasma center by 25%

Plasma diagnostic tools for ECR ion sources—What can we learn from these experiments for the next generation sources

“…18 In addition, the electrostatic confinement model is supported by experimental evidence 22 showing that the ion-ion collision frequency of high charge state ions exceeds their gyrofrequency, prohibiting magnetic ion confinement. The measured ion temperatures match well with those reported for a quadrupole mirror fusion device 39 and predicted theoretically for minimum-B ECRIS 40 but pose a problem for modeling of ECRIS charge breeders where low Ti of the buffer gas species has to be imposed to match with experimental observations. 41 The above ion temperatures 18 have been measured for discharges with only a single element being injected as neutral gas, whereas recent experiments 42 with gas mixing show that the temperature of high charge state argon ions can be reduced to 5-8 eV by mixing with oxygen.…”

Spectroscopic study of ion temperature in minimum-B ECRIS plasma

“…This is because the alleged electrostatic confinement of the ions in the potential dip favors losses of hot ions that have enough energy to overcome the potential barrier and form the extracted beam. Thus, it can be expected that the effective temperature of the beam is higher than the temperature of the ions in the plasma which has indeed been observed with the Constance-B device, where a similar technique was applied to study the energy distribution of ions escaping the confinement [14,15]. Furthermore, it needs to be emphasized that the connection between the temperature of the electrostatically confined ion population and the effective temperature of the extracted ion beam determined from the energy spread is not unambiguous.…”

“…In Ref. [14] the ion temperature of the Constance-B quadrupole mirror confinement device, which is essentially similar to a minimum-B ECRIS, has been measured with OES. A high resolution spectrometer was used to measure the Doppler broadening of oxygen emission lines in that work.…”

“…Approximately 20 eV ion temperatures were obtained without Ion Cyclotron Resonance Heating (ICRH) and 30-500 eV with the ICRH applied. It was also reported that the temperature of ions escaping from the Constance-B device is substantially higher than those probed by OES, the deviation increasing linearly with the (oxygen) charge state [14,15].…”

“…Effective ion temperatures have been measured in [13] indirectly from the extracted beam using a retarding field analyzer, reporting temperatures of 10-30 eV depending on the ion species and increasing with the charge state. In [14] the ion temperature of the Constance-B quadrupole mirror confinement device, which is essentially similar to a minimum-B ECRIS, has been measured with OES. A high resolution spectrometer was used to measure the Doppler broadening of oxygen emission lines in that work.…”