Gasdynamic ECR source of multicharged ions based on a cusp magnetic trap

Abstract

One of the modern trends in the development of electron cyclotron resonance (ECR) sources of multicharged ions is enhancement of the power and frequency of microwave pumping. Therefore, gyrotrons-powerful sources of radiation in the millimetre wavelength range-are now used for the creation and heating of plasma. These generators of microwave radiation are capable of producing and confining plasma of very high density (10 13 cm −3 and higher), thus providing conditions for a substantial increase in the extracted ion beam current. Most ECR sources use for plasma confinement mirror magnetic traps with 'min B' configuration, which suppress MHD plasma instabilities. However, it is extremely difficult to construct such systems for pumping frequencies higher than 30 GHz because strong magnetic fields of complicated configuration are needed. All this makes the search for simpler axisymmetric MHD-stable systems for plasma confinement very topical.A cusp trap produced by two coils with opposite currents is the simplest MHD-stable magnetic trap. Magnetic lines at any point of plasma in such a trap have a curvature that suppresses MHD perturbation in the plasma. In the present work the possibility of creation of an effective ECR source of multicharged ions based on a cusp magnetic trap was investigated numerically and in experiments. The pioneer result is the realization of the quasi-gasdynamic regime of plasma confinement in the trap of the multicharged ion ECR source of multicharged ions with cusp configuration of the magnetic field. Experiments were made with a small cusp trap which was designed for plasma creation by 37.5 GHz gyrotron radiation under ECR conditions. The total current and ion charge state distribution in the extracted ion beam were studied. The results of experiments with the simplest kind of cusp trap have demonstrated good correspondence with theoretical calculations, and therefore the adequacy of the developed approach and the possibility to build more effective source on this basis. Two ways of possible evolution of ECR ion sources based on a cusp magnetic trap are proposed.

New progress of high current gasdynamic ion source (invited)

“…8,9 Significant increase of the plasma density leads to a change of the confinement mode. A so-called quasi-gasdynamic confinement 4,5 was realized in the presented experiments instead of the collision-less confinement, 10 which is typical for modern ECRISs. The transition from collisionless to quasi-gasdynamic confinement occurs when the plasma density is high enough for the scattering rate of electrons into the loss-cone to be higher than the maximum possible electron loss rate caused by the ion-sound flux through the magnetic mirrors.…”

“…[1][2][3][4][5] In this paper, the main results obtained some years ago are shown to demonstrate the typical source performance. In Fig.…”

“…4,5 Investigation results on multi-charged ions production under condition of powerful gyrotron plasma heating with 37.5 and 75 GHz are presented. It is shown that the described peculiarities of quasigasdynamic ECR discharge sustained by mm-waveband radiation, namely, short lifetime and high density, provide unprecedented ion current densities up to 800 emA/cm 2 .…”

“…[1][2][3][4][5] In the beginning, the work was devoted to development of a high frequency ECR source of multi-charged ions with outstanding parameters of plasma heating (37.5 GHz, 100 kW). According to Geller's scaling laws, 6 such increase in frequency and power in comparison to conventional electron cyclotron resonance ion source (ECRIS) was expected to boost the ion source performance and provide a significant progress in ECRIS development.…”

High yield neutron generator based on a high-current gasdynamic electron cyclotron resonance ion source

“…Here, the authors demonstrate neutron production using a high-current quasi-gasdynamic ECR ion source, which utilizes a powerful gyrotron radiation of mm-waveband for plasma creation and heating. [39][40][41] Such ion sources are capable to form ion beams with record current densities of 0021-8979/2015/118(9)/093301/7/$30.00…”