High secondary electron emission for an enhanced electron density in election cyclotron resonance plasma

Abstract

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.

Study on monatomic fraction improvement with alumina layer on metal electrode in hydrogen plasma ion source

“…The effect of the alumina layer on the monatomic fraction in hydrogen plasma ion sources was reported previously, the authors report that increases in highly charged ions and the proton fraction in an alumina-covered ECR ion source might be generated by the increase in electron density and temperature due to the increased secondary electron emission and enhanced ion confinement. 3,4 Therefore, the values for the electron density of the aluminum and copper electrodes are measured with a Langmuir probe and compared to try to understand the increase in the monatomic fraction in hydrogen plasma ion sources. Figure 4 shows that the ion saturation currents with the aluminum electrode are higher than that of the copper electrode with an identical input power condition.…”

“…Recently, a helicon plasma ion source generated a high monatomic fraction of 94% even with a low RF power of 1.3 kW, and numerical simulations failed to explain its high monatomic fraction fully with its high plasma density and raised the existence of energetic electrons in the helicon plasmas as a possible reason. 1 On the other hand, chamber wall materials such as quartz were reported to increase the monatomic fraction by decreasing the recombination coefficient 2 or increasing the plasma density with a higher secondary electron emission coefficient and enhanced ion confinement with an alumina layered plasma boundary, 3,4 which was utilized in ECR (electron cyclotron resonance) ion sources not only as a wall material but also as a plasma electrode material. However, increases in the monatomic fraction in hydrogen plasmas with a dielectric chamber wall are not clearly understood whether they are due to the increase in the plasma density by a higher secondary emission coefficient and enhanced ion confinement, or due to a lower recombination coefficient of dielectric materials.…”

Effect of a metal–dielectric structure introduced in the plasma chamber of the Frankfurt 14 GHz electron cyclotron resonance ion source

“…First tests of the emissive qualities of these structures were performed in a specially designed electron-beam facility at NIPNE, Bucharest. 8,9 In this article are reported our first rea͒ Electronic mail: sdob@roifa.ifa.ro …”

Measurements of beam current density and proton fraction of a permanent-magnet microwave ion source

“…Steel by virtue of being the material of the front and back plates, aluminum as an alternative conducting material, which has been reported to build an oxide layer on its surface, 13 and alumina and boron nitride as dielectric materials that were reported to have a higher secondary electron yield [14][15][16] and a lower recombination probability 17 than metals. Increasing the number of secondary electrons and lowering the recombination rate leads to a higher degree of ionization.…”