Charge breeder electron cyclotron resonance ion sources (CB-ECRIS) are used as 1+ →n+ charge multiplication devices of post-accelerated radioactive ion beams. The charge breeding process involves thermalization of the injected 1+ ions with the plasma ions in ionion collisions, subsequent ionization by electron impact and extraction of the n+ ions. Charge breeding experiments of 85 Rb and 133 Cs ion beams with the 14.5 GHz PHOENIX CB-ECRIS operating with oxygen gas demonstrate the plasma diagnostics capabilities of the 1+ injection method. Two populations can be distinguished in the m/q-spectrum of the extracted ion beams, the low (1+ and 2+) charge states representing the uncaptured fraction of the incident 1+ ion beam and the high charge states that have been captured in ion-ion collisions and subsequently charge bred through electron impact ionization. Identification of the uncaptured fraction of the 1+ ions allows estimating the lower limit of ion-ion collision frequency of various charge states in the ECRIS plasma. The collision frequencies of highly charged ions (∼10 7 Hz) are shown to exceed their gyrofrequencies (∼10 6 Hz) at least by an order of magnitude, which implies that the dynamics of high charge state ions are dictated by magnetically confined electrons and ambipolar diffusion and only low charge state ions can be considered magnetized. Furthermore, it is concluded that the plasma density of the ECRIS charge breeder is most likely on the order of 10 11 cm −3 i.e. well below the critical density for 14.5 GHz microwaves.
Pinhole and CCD based quasi-optical X-ray imaging technique was applied to investigate the plasma of an Electron Cyclotron Resonance Ion Source. Spectrally integrated and energy resolved images were taken from an axial perspective. The comparison of integrated images taken of argon plasma highlights the structural changes affected by some ECRIS setting parameters, like strength of the axial magnetic confinement, RF frequency and microwave power. Photon counting analysis gives precise intensity distribution of the X-ray emitted by the argon plasma and by the plasma chamber walls. This advanced technique points out that the spatial positions of the electron losses are strongly determined by the kinetic energy of the electrons themselves to be lost and also shows evidences how strongly the plasma distribution is affected by slight changes in the RF frequency.
11] or electron cyclotron resonance ion sources (ECRIS) [12] to the charge breeding process. Both techniques were compared during FP6 [13] in view of the performances expected for EURISOL, and were found to be complementary: among the two, the ECRIS-based charge breeders (ECR-CB) are usually chosen for their high acceptance in terms of injected current and emittance, the reliability, the possibility to operate both in continuous and pulsed mode, and the high charge states produced. A drawback is the presence of contaminants in the extracted beam, that could possibly hide the peaks of the radioactive ions of interest: this effect can be limited by properly treating all the surfaces exposed to vacuum, and by implementing a spectrometer of adequate resolution downstream the charge breeder, as in the case of the SPES project, which will adopt this kind of device [14,15].
Experiments have recently demonstrated that kinetic instabilities occurring in magnetoplasma are huge limiting factors to the flux of highly charged ion beams extracted from ECR ion sources. Recently, it has been shown that the two-frequency-heating (TFH) mode has the proven potential to mitigate these instabilities. Since the fundamental physical mechanism of TFH is still unclear, a deeper experimental investigation is necessary. At ATOMKI-Debrecen, the effect on the kinetic instabilities of an argon plasma in a 'two-close-frequency heating' scheme has been explored for the first time by using a frequency gap smaller than 1 GHz (i.e. operating in the so-called twoclosed-frequency heating mode). A special multi-diagnostics setup has been designed and implemented. In this paper, we will show the data collected by a two-pin, plasma-chamber immersed antenna connected to an RF detector diode and/or to a spectrum analyzer for the detection of plasma radio-self-emission when varying the pumping frequency in single versus double frequency heating mode. Data have been collected simultaneously to the beam extraction and for different frequency gaps and relative power balances. The turbulent regime of the plasma has been tentatively described in a quantitative way, according to the properties of the plasma self-emitted RF spectrum. The measurements show that plasma self-emitted radiation emerges from the internal ECR region everytime (i.e. below the lower pumping frequency) but the almost total instability damping can be effective for some specific combinations of frequency-gap and power balance, thus eventually improving the plasma confinement. Keywords: electron cyclotron resonance ion source, plasma diagnostics, kinetic plasma instability 'scaling laws' [1]. More recently, this approach has become more difficult because of the technological limits. A deeper knowledge of plasma parameters (electron density, temperature and charge state distribution (CSD)) is thus fundamental: the characteristics of the extracted beam (in terms of current intensity and production of high charge states) are directly connected to plasma parameters and structure. Several experiments have, in fact, demonstrated that plasma instabilities limit the flux of highly charged ions extracted from ECR ion sources, causing beam ripple [2][3][4]. The
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