This article deals with ion confinement in small open-ended magnetic devices, the electron cyclotron resonance ion sources (ECRIS) that were developed for multicharged ion production. The ECRIS are basically ECR-heated plasma confinement machines with hot electrons and cold ions. The main parameters of the ion population in ECRIS plasmas are successively analyzed, temperature, collisions, losses, ionization, confinement times, charge state distribution equilibrium, followed by the analysis of the gas mixing effect, a specific technique to improve the performance as an ion source. A series of experiments is described for the systematic analysis of the phenomena related to gas mixing. It is shown that high charge state optimization by gas mixing relies on a compromise between three criteria, ion losses, mass effect, and ionization rates. The article stresses the role of some fundamental plasma parameters for the next generation of high charge state/high intensity ion sources.
For the needs of future heavy ion accelerators, electron cyclotron resonance ion sources (ECRISs) should be able to deliver higher intensities and higher charge states. The 1e mA level intensity has already been reached by room temperature ECRIS for medium charge states of light elements (O6+, Ar8+). However, such level of intensity for heavy elements (like Pb27+ for CERN/LHC and GSI) requires more powerful ECRIS with higher electron densities (up to 1013 cm−3). On the other hand, an optimized magnetic configuration system has to be used in order to obtain the suitable compromise between the electron confinement and the high flux ion losses. Before the design of the future “high intensity ECRIS,” experiments have been performed with the superconducting SERSE source both at 18 and 28 GHz. After an overview of major results recently obtained, some scaling laws will be presented. Our results show that much larger intensities and charges can be reached with ECRIS. Then, we will show how the next ECRIS generation will look like, based on the scaling laws derived in the above-mentioned experiments.
The hot electrons in the plasma of an electron-cyclotron-resonance ion source are investigated by three passive diagnostics: bremsstrahlung, electron cyclotron emission, and diamagnetism. For this type of plasma the feasibility of the second diagnostic is an innovative development, as is the simultaneous use of two independent plasma diagnostics for either steady-state or transient experiments. In the steady-state experiments the bremsstrahlung and the electron cyclotron emission are interpreted by comparing the experimental spectra with simulated spectra calculated for the first time from a non-Maxwellian electron distribution. The ‘‘perpendicular temperatures’’ obtained by the two diagnostics are in good agreement. In the transient experiments the electron cyclotron emission and the diamagnetic signals are recorded to study the electron density and the electron lifetime. All these experiments performed using the Minimafios ion source working at 18 GHz with oxygen gas demonstrate trends and saturation effects when the gas injection pressure and the radio-frequency power are varied.
Articles you may be interested inThe preliminary tests of the superconducting electron cyclotron resonance ion source DECRIS-SC2a) Rev. Sci. Instrum. 83, 02A334 (2012); 10.1063/1.3671746Performance and operation of advanced superconducting electron cyclotron resonance ion source SECRAL at 24 GHza) Rev. Sci. Instrum. 83, 02A320 (2012); 10.1063/1.3666913Design of a compact, permanent magnet electron cyclotron resonance ion source for proton and H 2 + beam productiona) Rev. Sci. Instrum. 81, 02A321 (2010); 10.1063/1.3267838 ARTEMIS-B: A room-temperature test electron cyclotron resonance ion source forThe SERSE source ͓P. Ludwig et al., Rev. Sci. Instrum. 69, 4082 ͑1998͒, and references therein͔ is a superconducting electron cyclotron resonance ͑ECR͒ ion source, operating at the Laboratori Nazionali del Sud in Catania since 1998; it is currently used as the main injector for the K-800 superconducting cyclotron. Its high magnetic field provides a high plasma confinement and large currents of highly charged ions, as compared to conventional sources. It can efficiently operate at the microwave frequency of 14 and 18 GHz ͓S. Gammino and G. Ciavola, Rev. Sci. Instrum. 71, 631 ͑2000͒; S. Gammino et al., ibid. 70, 3577 ͑1999͔͒ and has been used as a test bench for injection at 28 GHz. High-frequency operation is expected to create a higher plasma density, thus resulting in larger currents of multiply charged ions. In this article, we report the first operation of an ECR ion source at 28 GHz by using a gyrotron. The gyrotron itself and the waveguide line are described, along with the operational results ͑in xenon gas for the sake of simplicity͒. Given the limited amount of power ͑about 4 kW͒, which can be injected in the plasma chamber during dc-mode operation, the results are less outstanding than in the pulsed mode ͑up to 6.5 kW͒. However, in both cases the beam intensities are far better than the ones obtained by the other ECR ion sources operating at lower frequencies.
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