The effect of plasma instabilities on the background impurities in charge breeder ECRIS

Tarvainen, O.; Angot, J.; Izotov, I. V.; Skalyga, V. A.; Koivisto, H.; Thuillier, T.; Kalvas, Taneli; Toivanen, V.; Kronholm, Risto; Lamy, T.

doi:10.1063/1.5053348

Cited by 5 publications

(9 citation statements)

References 7 publications

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“…At LPSC, a value of 5.9 ms=q was measured for this charge state and element during recent experiments. The accumulation effect and the large discrepancies of the reported τ CB have motivated the authors to conduct charge breeding experiments in short pulse mode, as early proposed in [13]. Short 1þ pulses, in the order of 1 ms long, were injected into the CB buffer gas plasma at equilibrium, and Nþ responses were studied.…”

Section: Introductionmentioning

confidence: 99%

Charge breeding time investigations of electron cyclotron resonance charge breeders

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Tarvainen

Thuillier

et al. 2018

Phys. Rev. Accel. Beams

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To qualify electron cyclotron resonance charge breeders, the method that is traditionally used to evaluate the charge breeding time consists in generating a rising edge of the injected beam current and measuring the time in which the extracted multicharged ion beam reaches 90% of its final current. It is demonstrated in the present paper that charge breeding times can be more accurately measured by injecting short pulses of 1 þ ions and recording the time resolved responses of Nþ ions. This method is used to probe the effect of the 1 þ ion accumulation in the plasma known to disturb the buffer gas plasma equilibrium and is a step further in understanding the large discrepancies reported in charge breeding times. The experiments are conducted injecting a 85 Rb þ ion beam into the Laboratoire de Physique Subatomique et de Cosmologie (LPSC) charge breeder operated with helium as a buffer gas. The time needed for the extraction of 90% of the multicharged ions in short pulse mode is found slightly shorter (9%) than the charge breeding time measured with the traditional method. The charge breeding efficiency is identical with both methods. The pulse width and amplitude of the 1þ injection pulses have been varied to study their influence on the Nþ response and temporal parameters are proposed to qualify the time response. The short pulse method can be used to study the influence of the ion source tuning parameters on the charge breeding temporal characteristics. For example, it is shown here that an increase of the minimum magnetic field strength of the LPSC charge breeder in the range 0.432-0.444 T improves the multicharged ion confinement in the electron cyclotron resonance plasma, and so increases the charge breeding efficiency. The short pulse method is also used to estimate the charge breeding efficiencies of radioactive Rb isotopes taking into account their half-lives and charge states. The neutron-rich heavy isotopes have short half-lives, which makes the charge state distributions shift to lower charge states and the estimated charge breeding efficiencies of high charge states being close to three times less in comparison to the stable ions.

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Section: Introductionmentioning

confidence: 99%

Charge breeding time investigations of electron cyclotron resonance charge breeders

Angot

Tarvainen

Thuillier

et al. 2018

Phys. Rev. Accel. Beams

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“…scitation.org/journal/rsi biased disk current for these transients can be used as a diagnostic method to determine the presence of plasma instabilities, as has been reported by Isherwood et al 19 Furthermore, the disk can be used as a rudimentary Langmuir probe to quantify these instability-induced electron (and ion) losses, as has been demonstrated by Tarvainen et al 9 The instability-induced fast current transients can reach up to hundreds of milliamperes in a sub-μs time scales. The power supplies that are typically used with biased discs are not able to handle this kind of sudden current surges.…”

Section: Articlementioning

confidence: 82%

“…The electron and the ion transients carry approximately an equal amount of total charge, i.e., the areas of the negative and positive transient peaks are approximately the same. 9 The combined duration of the electron and ion transients is typically less than 10 μs, with the ion transient being the longer one due to the lower mobility of ions. During the instability-induced sequence, the measured transient currents can be 1-2 orders of magnitude higher than the steady state current of the biased disk.…”

Section: Articlementioning

confidence: 99%

“…34,37 (2) Estimations based on the results of the biased disk studies imply that the fraction of electrons expelled during each instability burst can be on the order of 10% of the total electron population. 9 (3) The instabilities cause electron losses across the whole range of the electron energy distribution (see, e.g., Refs. 9 and 41).…”

Section: Articlementioning

confidence: 99%

“…7) and the beam energy in μs-scale. 8,9 Such oscillations, restricting the parameter space available for optimization of the source performance, are often overlooked by the ion source operator attempting to single-mindedly maximize the average beam current with limited diagnostics. An illustrative example of the instability-induced periodic oscillations of the extracted beam current and the corresponding Fourier spectrum is shown in Fig.…”

Section: Introductionmentioning

confidence: 99%

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Diagnostic techniques of minimum-B ECR ion source plasma instabilities

Toivanen

Bhaskar

Izotov

et al. 2022

Review of Scientific Instruments

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Quasi-periodical kinetic instabilities in minimum-B confined plasma

et al. 2022

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We present the results of an experimental investigation of quasi-periodical kinetic instabilities exhibited by magnetically confined electron cyclotron resonance heated plasmas. The instabilities were detected by measuring plasma microwave emission, electron losses, and wall bremsstrahlung. The instabilities were found to be grouped into fast sequences of periodic plasma losses, separated by ∼100 µs between the bursts, followed by 1–10 ms quiescent periods before the next event. Increasing the plasma energy content by adjusting the plasma heating parameters, in particular the magnetic field strength, makes the instabilities more chaotic in the time domain. Statistical analysis reveals that the energy released in a single instability event depends on the magnetic field strength and microwave power but not on the neutral gas pressure. The effects of these ion source parameters on the instability characteristics are explained qualitatively by considering their influence on the electron energy distribution. A correlation is found between the energy dissipated in an instability event and the recovery time of the periodic bursts, i.e., a large amplitude instability leads to a long recovery time of the electron energy distribution.

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The effect of plasma instabilities on the background impurities in charge breeder ECRIS

Cited by 5 publications

References 7 publications

Charge breeding time investigations of electron cyclotron resonance charge breeders

Charge breeding time investigations of electron cyclotron resonance charge breeders

Diagnostic techniques of minimum-B ECR ion source plasma instabilities

Quasi-periodical kinetic instabilities in minimum-B confined plasma

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