Confinement of multiply charged ions in an electron cyclotron resonance heated mirror plasma

Abstract

Multiply charged ions are studied in the Constance B quadrupole mirror experiment [Phys. Rev. Lett. 59, 1821 (1987)] in order to better understand the ion physics of electron cyclotron resonance (ECR) high charge-state ion sources. By measuring the ion densities and end loss fluxes, the parallel confinement times for the first five charge states of oxygen plasmas are determined. The parallel ion confinement times increase with charge state and peak on axis, both indications of an ion-confining potential dip created by the hot electrons. The radial profile of ion end loss is normally hollow, with the peak fluxes occurring at the edge of the ECR zone. An attempt is made to increase the end loss flux of a selected ion species by decreasing its parallel confinement time using minority ion cyclotron resonance heating (ICRH). In addition, an ion model is developed to predict the ion densities, end loss fluxes, and confinement times using the ion particle balance equations, the quasineutrality condition, and theoretical confinement time formulas. The model generally agrees with the experimental data to within experimental error.

Investigation of the density and temperature of electrons in a compact 2.45 GHz electron cyclotron resonance ion source plasma by x-ray measurements

“…In the literature one finds several studies in which electron temperatures and fractions of cold and hot electron populations are presented, but all of them are measured in ECR ion sources operated at frequencies higher than our 2.45 GHz. Alton and Smithe [17] use a 8 GHz ECRIS and measure T cold = 1 eV, T hot = 100 eV and p hot = 0.01, Girard et al [8] use 10-18 GHz with T hot = 80 keV and p hot = 0.1, Golubev et al [24] use 37.5 GHz with T cold = 300-400 eV, T hot = 7-10 keV and p hot = 4 × 10 −5 and Petty et al [25] use 10.5 GHz with T cold = 100 eV, T hot = 300 keV and p hot = 0.5, to name only a few. These examples show two things: first the span of electron temperatures is very broad and second the colder the temperature for the cold electron population the hotter the temperature for the energetic electrons, often together with a smaller fraction.…”

Experimental evidence on microwave induced electron losses from ECRIS plasma

“…1 Upon entering the loss cone, the electrons experience a force as a result of the gradient and curvature of the magnetic field and will leak out of the magnetic bottle as thoroughly discussed by Thuillier et al 11 From the analysis performed, it appears that the electron losses through the weakest mirrors occur faster in comparison to the characteristic time of the diffusion into the loss cone 11 i.e., the loss cone can be assumed to be empty. Contrary to the plasma electrons, high charge state ions are confined electrostatically 5,12 and their losses are due to electron losses i.e., ions follow the electrons owing to the ambipolar field. 13 The (electron) loss cone can be populated by a number of processes, as thoroughly discussed in the literature, 10,14 including Coulomb collisions, inelastic collisions, microwave induced pitch angle scattering, and non-linear effects.…”

“…Additionally, the warm and hot electrons are thought to play a crucial role in the build-up of an electrostatic potential which is suggested to regulate ion confinement via a small potential dip in the core of the plasma. This confinement scheme, extensively discussed by Petty et al, 5 enables ions to remain in the plasma for a sufficiently long time in order to reach the desired charge state through step-wise electron impact ionization. Some of the first theoretical studies on electron cyclotron resonance heating (ECRH) in magnetic mirror devices were published in the 1970s, 6 with the relativistic theory of ECRH developed later.…”

Rocket Propulsion Through Multiply-Charged Ions From a Mirror Plasma

“…The plasma parameters calculated by the physics model were benchmarked against data from the Constance B mirror experiment [3]. The model predicted the measured ion densities and parallel confinement times fairly well for He, Ne, and Ar.…”

“…[3] for a more detailed discussion), the electron densities, electron temperatures, and ion temperatures are treated as fixed inputs. [3] for a more detailed discussion), the electron densities, electron temperatures, and ion temperatures are treated as fixed inputs.…”