Spectroscopic study of ion temperature in minimum-B ECRIS plasma

Abstract

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

“…This qualitative model is convergent with the fact that high charge state ions have the longest confinement times 23,31 and temperatures. 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.…”

“…Langmuir-probes and optical emission spectroscopy (OES), which are applicable for high-density microwave discharges dominated by 1+ ions, are not suitable for the highly charged plasmas of minimum-B ECRIS either due to their invasive nature or the pressure broadening of ion emission lines being negligible in comparison with Doppler and instrumental broadening. 18 In the vacuum ultraviolet (VUV)-range, the measurement of the intensity ratios of singlet and triplet transitions of Be-like ions can yield information 21 of the cold electron population assuming that the excitation and de-excitation (spontaneous vs electron impact de-excitation of metastable states) are well-understood.…”

“…21 It is assumed that the capture of the injected 1+ ions occurs through ion-ion collisions whose frequency depends on Ti and, hence, the accuracy of the plasma density estimate could be improved by measuring Ti in the charge breeder plasma using OES to detect the Doppler broadening of the ion emission lines. 18 The estimated density being on the order of 10 11 cm −3 can be used to estimate the minimum ion confinement time using Fig. 2 together with the measured performance of the given charge breeder ECRIS producing fully stripped oxygen ions (or equivalent charge states of Cs).…”

“…Furthermore, it supports the experimentally observed ion temperatures of 5-28 eV derived from the Doppler broadening of ion emission lines. 18 Such high ion temperatures are presumably reached via energy exchange between the ions and the cold electron population as the ions can escape from the electrostatic confinement only if they have sufficient kinetic energy to overcome the ΔΦ potential barrier. This qualitative model is convergent with the fact that high charge state ions have the longest confinement times 23,31 and temperatures.…”

Semiempirical zero-dimensional approach for the estimation of beam features from plasma parameters in proton sources

“…According to the sensitivity of the instrumentation, OES allows one to evaluate the plasma emission lines that, analyzed with a proper collisional radiative model, enable achieving the electron density n e , the electron temperature T e of the cold electron population (0-100 eV) [8,9], the ion temperature T i [10], the neutral relative abundances, the rotovibrational molecular spectrum [11], and the concentration of highly charged ions in plasmas by acquiring the electromagnetic spectrum emitted by the plasma in the optical domain. Figure 1 shows a typical spectrum acquired in a MDIS ion source: Balmer lines and a Fulcher band are evidenced.…”