The possibility of increasing the electron cyclotron resonance (ECR) plasma electron density by secondary electron emission has already been pointed out and tested by different authors. In this work the effective secondary electron emission coefficient σeff under electron impact was measured and its evolution studied as a function of the primary electron beam energy and intensity of the target bias. The usual parameters of the ECR plasma such as the electron temperature, the plasma electric potential, and the ambipolar diffusion effects in the ECR plasma chamber have been considered during these measurements. With that end in view a research facility delivering electron beams with energies in the 0–15 keV range and intensities in the 1×10−11–2×10−5 A range was developed. The study of the effective secondary electron emission coefficient σeff was carried out on different targets made of graphite, of metals such as pure and technical Al, Ta, Ni, stainless steel, and of metal-dielectric structures Al–Al2O3. For some Al–Al2O3 structures high values of σeff strongly dependent upon the primary electron beam energy and intensity and upon the target negative bias have been obtained. Such a dependence was not observed for metals. The use of highly emissive metal-dielectric structures in the plasma chamber of an ECRIS should lead to a significant enhancement of the ECR plasma electron density and consequently of the production of highly charged ions.
Articles you may be interested inRole of a metal-dielectric structure for the high-charge-state-ion production in electron cyclotron resonance ion sources Rev. Sci. Instrum. 73, 4172 (2002); 10.1063/1.1519937Influence of the secondary electrons emitted by a cylindrical metal-dielectric structure on the Frankfurt 14 GHz electron cyclotron resonance ion source performances Rev. Sci. Instrum. 71, 918 (2000)
The output parameters of different types of vacuum (VAFEC) and gas filled (GAFEC) fission electric cells (FECs) have been measured during their irradiation in the nuclear reactor of the Central Institute of Physics in Bucharest, Romania, at different thermal neutron flux (ϕnth) values in the 108…1012 neutrons/cm2 s range. These measurements allowed us to estimate to what degree the FEC output parameters depend on the ϕnth variation and pointed out the differences in the operation of the VAFEC and GAFEC‐type devices. The main results for some of the tested FECs are presented.
Previous research allowed us to develop highly efficient electron emissive metal-dielectric (MD) structures, which are suitable to be used as sources of secondary electrons in electron cyclotron resonance ion sources (ECRIS). First tests have been performed replacing the stainless steel disk of the Frankfurt 14 GHz ECRIS by a MD structure. This method was recently extended by inserting a MD cylinder (150 mm long and 58 mm in diameter) into this source. The experiments were performed with pure argon as source gas and with gas mixing (argon+oxygen). In this contribution, the performance with MD cylinder is compared to that of the standard source (stainless steel plasma chamber) and to the case, where a cylinder of technical aluminum was installed. With the MD cylinder the yield of highly charged ions from the ECRIS are significantly enhanced. For Ar16+ ion current enhancement factors of up to 50 were obtained.
A 14.5 GHz ECR ion source is in an advanced stage of construction at the Institute of Atomic Physics of Bucharest, Romania. This ECR multicharge heavy ion source (RECRIS) is designed to be independently used in atomic physics research as well as an injector into the existing rf heavy ion postaccelerator of the Bucharest FN tandem accelerator. The general design and main characteristics of RECRIS are presented as well as the present status and the schedule of this project. A research program and facility was started in order to study physical ways to improve the ECR ion source performances.
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