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
While the mechanism is still not fully clear, the beneficial effect (higher intensity of highly charged ions, stable plasma conditions) of the second microwave injected to the ECR plasma was observed in many laboratories, both with close and far frequencies. Due to the complexity of the phenomena (e.g. interaction of resonant zones, damped instabilities) complex diagnostic methods are demanded to understand its mechanism better and to fully exploit the potential hidden in it. It is a challenging task since complex diagnostics methods require the arsenal of diagnostic tools to be installed to a relatively small size plasma chamber. Effect of the injected second 13.6–14.6 GHz microwave to the 14.25 GHz basic plasma has been investigated by means of soft and (time-resolved) hard X-ray spectroscopy, by X-ray imaging and space-resolved spectroscopy and by probing the rf signals emitted by the plasma. Concerning the characterization of the X radiation, in order to separate the source and position of different X-ray photons special metallic materials for the main parts of the plasma chamber were chosen. A detailed description and explanation of the full experimental setup and the applied non-invasive diagnostics tools and its roles are presented in this paper.
In this paper, the Atomki Accelerator Centre (AAC, Debrecen, Hungary) incorporating several small-sized particle accelerators is reviewed. The energy range of our accelerators for proton beam is between 50 eV and 20 MeV. The technical and personnel organization of AAC is presented together with the rules of beamtime requests and usage. Three of our accelerators (Cyclotron, ECRIS, Tandetron) are described in detail with their technical descriptions and with the main application fields. As an example for highlights, a series of unique low-energy ion–sample irradiations and post-treatments are shown which, by our hopes and plans, form a bridge between physics and biology.
The research of magnetically confined plasmas with high energy content is nowadays an important branch of the plasma physics with several options considering the chosen technics. One of the ways is the detection of photons emitted by the plasma itself. A new experimental setup was built in the ECR Laboratory of Atomki (Debrecen, Hungary) to detect in 2D the dense EM-radiation emitted by the ECR-plasma. The main elements of the setup are: an ECR ion source (as plasma source, operating at 13.6-14.6 GHz RF pumping frequency) and a pinhole X-ray camera (operating in the 500 eV-20 keV energy domain). An innovative lead collimator system was designed and built between the plasma and the camera. As a result, it has been possible to acquire X-ray pictures up to 200 W total incident RF-power. This value represents the highest operative RF power for which X-ray imaging has been acquired in the field of ECR Ion Sources and ECR compact traps. A new treatment for the noise reduction was applied to study plasma morphology. The new setup gives opportunity not just to study energetic stable plasmas, but even plasma turbulences and instabilities. K: Ion sources (positive ions, negative ions, electron cyclotron resonance (ECR), electron beam (EBIS)); Plasma diagnostics -interferometry, spectroscopy and imaging * Corresponding author.
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