Bryan G. Peterson

Peak Coalescence, Spontaneous Loss of Coherence, and Quantification of the Relative Abundances of Two Species in the Plasma Regime: Particle-In-Cell Modeling of Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) is often limited by space-charge effects. Previously, particle-in-cell (PIC) simulations have been used to understand these effects on FTICR-MS signals. However, none have extended fully into the space-charge dominated (plasma) regime. We use a two-dimensional (2-D) electrostatic PIC code, which facilitates work at very high number densities at modest computational cost to study FTICR-MS in the plasma regime. In our simulation, we have observed peak coalescence and the rapid loss of signal coherence, two common experimental problems. This demonstrates that a 2-D model can simulate these effects. The 2-D code can handle a larger numbers of particles and finer spatial resolution than can currently be addressed by 3-D models. The PIC method naturally takes into account image charge and space charge effects in trapped-ion mass spectrometry. We found we can quantify the relative abundances of two closely spaced (such as 7Be+ and 7Li+) species in the plasma regime even when their peaks have coalesced. We find that the frequency of the coalesced peak shifts linearly according to the relative abundances of these species. Space charge also affects more widely spaced lines. Singly-ionized 7BeH and 7Li have two separate peaks in the plasma regime. Both the frequency and peak area vary nonlinearly with their relative abundances. Under some conditions, the signal exhibited a rapid loss of coherence. We found that this is due to a high order diocotron instability growing in the ion cloud.

Image Quality Of Figured Multilayered Optics

The reflectivity and resolution of a multilayer structure is strongly affected by the roughness at the interfaces between two successive layers and by the amount that the constituent materials will diffuse into one another at the interfaces. Performance is also affected by the variations in individual layer thicknesses and by inhomogeneities in the materials. These deviations from the ideal multilayer will also affect the quality of the image from a figured multilayer optical element. The theory used to model the effects of non-ideal multilayers on the image quality of figured optics will be discussed. The relationship between image quality and multilayer structure quality will be illustrated with several examples.

Finding the radial parallel temperature profile in a non-neutral plasma using equilibrium calculations on experimental data

In 1992, Eggleston et al. [D. L. Eggleston et al., Phys. Fluids B 4, 3432 (1992)] reported on a technique for measuring the radial temperature profile in a pure-electron plasma confined in a Malmberg-Penning trap by partially dumping the plasma onto a charge collector at the end of the trap. For short plasmas and short confining rings, the assumptions in their paper are violated and a more general calculation is needed. This paper presents a variation of the standard equilibrium calculation to find the temperature profile of a pure-electron plasma. Eggleston’s shortcut “evaporation” temperature method is found to require a correction factor that can be calculated using methods described in this paper. For typical conditions, the evaporation method overstates the actual temperature by a factor ranging from 1.1 to 1.5 or more, depending on the plasma’s total charge and temperature and the geometry of the trap.

An interchangeable-cathode vacuum arc plasma source

A simplified vacuum arc design [based on metal vapor vacuum arc (MeVVA) concepts] is employed as a plasma source for a study of a (7)Be non-neutral plasma. The design includes a mechanism for interchanging the cathode source. Testing of the plasma source showed that it is capable of producing on the order of 10(12) charges at confinable energies using a boron-carbide disk as the cathode target. The design is simplified from typical designs for lower energy and lower density applications by using only the trigger spark rather than the full vacuum arc in high current ion beam designs. The interchangeability of the cathode design gives the source the ability to replace only the source sample, simplifying use of radioactive materials in the plasma source. The sample can also be replaced with a completely different conductive material. The design can be easily modified for use in other plasma confinement or full MeVVA applications.

Design and fabrication of heat resistant multilayers

Many promising applications of multilayer x-ray optical elements subject them to intense radiation. This paper discusses the selection of optimal pairs of materials to resist heat damage and presents simulations of multilayer performance under extreme heat loadings.

Observation of and model for nonlinear mode conversion in a non-neutral plasma

The nonlinear interaction of the two lowest Trivelpiece–Gould modes in a non-neutral plasma has been observed. Because of coupling in the nonlinear terms of the continuity and momentum equations, the two modes can exchange energy and convert one to the other. This can be modeled using the cold fluid equations and the averaging method. Experimentally, this process always stops with the lower frequency mode dominating the final state. Numerical integration of the model suggests that this occurs because the higher frequency mode is more strongly damped than the lower frequency mode.

Interacting solitons in a nonneutral plasma

We have been continuing our study of solitons and nonlinear interactions in a pure electron plasma. The solitons are grown from large amplitude normal-mode oscillations. When grown in this way, it is convenient to divide the resulting wave into two parts: localized soliton-like structures and global normal-mode-like waves. These two parts interact weakly with each other and cause various interesting effects. When we launch two solitons by using the nz=2 mode, the normal mode part quickly converts to an nz=1 mode and causes one of the solitions to disappear. Later, when only one solition exists, the nz=1 mode is locked to it. Because the soliton speed is faster than the linear wave speed, this increases the frequency of the normal-mode part of the system. It appears that when the soliton amplitude drops below some critical value, the two parts of the system decouple and propagate separately.

Measured response of multilayers to damaging fluxes.

We have measured the response of WC/C multilayers to x-ray fluxes on the order of 200 MW/cm2 using laser-generated plasmas and found that these multilayers will maintain near peak reflectivity for at least 1 ns but are eventually destroyed. A description of the experiments and data analysis methods is given. Transmission electron micrographs of WC/C multilayers before and after irradiation show melting to be the dominant damage mechanism. The results of the experiments will be compared with simulations.

Laser Plasma Damage To Multilayer Mirrors

We have measured the response of W/C multilayers to x-ray fluxes on the order of 150 MW/cm2 using laser generated plasmas and found that these multilayers will maintain near peak reflectivity for at least 1 ns but are eventually destroyed. A description of the experiments and data analysis methods is given. The results of the experiments will be compared with hydrodynamic code simulations.

Study Of Multilayers Subjected To Intense Radiation

Many promising applications of multilayer x-ray optical elements subject them to intense radiation. In this paper we present simulations of multilayer performance under extreme heat loads and preliminary results of robust multilayer characterization experiments.