Erik L. Antonsen

Hormonal Contraception and HIV Disease Progression

The majority of the 15.4 million human immunodeficiency virus (HIV)-infected women worldwide are of child-bearing age and need access to contraception. Hormonal methods of contraception are safe, acceptable, and effective in preventing unwanted pregnancies. Many published studies have examined the impact of hormonal contraception on HIV disease acquisition and transmissibility. Far fewer have investigated the relationship between hormonal contraception and HIV disease progression. This review examines available data on this relationship from clinical, animal, and immunological studies. Several clinical studies suggest an overall effect but are not definitive, and the mechanisms behind HIV disease progression are unclear. Animal and immunological data suggest that immunomodulation by hormonal contraceptive methods may affect the immune response to HIV infection. Additional work is needed in this area to elucidate the possible relationship between hormonal methods for birth control and progression to acquired immunodeficiency syndrome in HIV-infected women.

Ion debris characterization from a z-pinch extreme ultraviolet light source

An XTREME Technologies XTS 13-35 extreme ultraviolet (EUV) light source creates a xenon z pinch that generates 13.5nm light. Due to the near x-ray nature of light at this wavelength, extremely smooth metal mirrors for photon collection must be employed. These are exposed to the source debris. Dissolution of the z-pinch gas column results in high-energy ion and neutral release throughout the chamber that can have adverse effects on mirror surfaces. The XTREME commercial EUV emission diagnostic chamber was designed to maximize diagnostic access to the light and particulate emissions from the z pinch. The principal investigation is characterization of the debris field and the erosive effects on optics present. Light emission from the z pinch is followed by ejection of multiply charged ions and fast neutral particles that make up an erosive flux to chamber surfaces. Attenuation of this erosive flux to optical surfaces is attempted by inclusion of a debris mitigation tool consisting of foil traps and neutral b...

Propellant Charring in Pulsed Plasma Thrusters

The Teflon ablation in a micro-pulsed plasma thruster is studied with the aim of understanding the charring phenomenon. Microscopic analysis of the charred areas shows that it contains mainly carbon. It is concluded that the carbon char is formed as a result of carbon flux returned from the plasma. A simplified model of the current layer near the Teflon surface is developed. The current density and the Teflon surface temperature have peaks near the electrodes that explain preferential ablation of these areas, such as was observed experimentally. Comparison of the temperature field and the ablation rate distribution with photographs of the Teflon surface shows that the area with minimum surface temperature and ablation rate corresponds to the charring area. This finding suggests that the charring may be related to a temperature effect.

Electromagnetic Effects in the Near-Field Plume Exhaust of a Micro-Pulsed-Plasma Thruster

A model is presented of the near-field plasma-plume of a pulsed plasma thruster (PPT). As a working example, a micro-PPT developed at the U.S. Air Force Research Laboratory is considered. This is a miniaturized design of the axisymmetric PPT with a thrust in the 10-µ N range that utilizes TeflonTM as a propellant. The plasma plume is simulated using a hybrid fluid‐particle-in-cell direct simulation Monte Carlo approach. The plasma plume model is combined with Teflon ablation and plasma generation models that provide boundary conditions for the plume. This approach provides a consistent description of the plasma flow from the surface into the near plume. The magnetic field diffusion into the plume region is also considered, and plasma acceleration by the electromagnetic mechanism is studied. Teflon ablation and plasma generation analyses show that the Teflon surface temperature and plasma parameters are strongly nonuniform in the radial direction. The plasma density near the propellant surface peaks at about 10 24 m −3 , whereas the electron temperature peaks at about 4 eV near the electrodes. The plume simulation shows that a region with high density is developed at a few millimeters from the thruster exit plane at the axis. This high-density region exists during the entire pulse, but the plasma density decreases from about 2 × × 10 22 m −3 at the beginning of the pulse down to 0.3 × × 10 22 m −3 at 5 µs. The velocity phase is centered at about 20 km/s in the axial direction. At later stages of the pulse, there are two ion populations with positive and negative radial velocity. Electron and neutral densities predicted by the plume model are compared with near-field measurements using a two-color interferometer, and good agreement is obtained.

Optimization Issues for a Micropulsed Plasma Thruster

Several issues related to the design of a micropulsed plasma thruster (µPPT) are considered. It is concluded that the choice of the optimal energy level for a given µPPT geometry is very important. If the discharge energy is small, propellant charring would limit the operational time of the thruster. It is found that the charring phenomenon is associated with nonuniformity (in the radial direction between the electrodes) in the propellant ablation rate. On the other hand, higher energy leads to discharge constriction on the positive electrode and causes azimuthal nonuniformity. Reasoning leading to such nonuniformity is considered, and general suggestions for optimal energy and thruster size selections are presented.

Lifetime measurements on collector optics from Xe and Sn extreme ultraviolet sources

Next generation lithography to fabricate smaller and faster chips will use extreme ultraviolet (EUV) light sources with emission at 13.5nm. A challenging problem in the development of this technology is the lifetime of collector optics. Mirror surfaces are subjected to harsh debris fluxes of plasma in the form of ions, neutrals, and other radiation, which can damage the surface and degrade reflectivity. This manuscript presents the measurement of debris ion fluxes and energies in absolute units from Xe and Sn EUV sources using a spherical sector ion energy analyzer. Experimentally measured erosion on Xe exposed samples is in good agreement with predicted erosion. This result allows prediction of erosion using measured ion fluxes in experiment. Collector optic lifetime is then calculated for Xe and Sn sources without debris mitigation. Lifetime is predicted as 6h for Xe EUV sources and 34h for Sn EUV sources. This result allows calculation of expected collector optic lifetimes, which can be an important to...

XCEED: XTREME commercial EUV exposure diagnostic experiment

The XCEED chamber was designed to allow diagnostic access to the conditions experienced by collecting optics for a discharge produced plasma (DPP) source. The chamber provides access for EUV photodiodes, sample exposure tests, Faraday cup measurements, and characterization of the ion debris field by a spherical sector energy analyzer (ESA). The Extreme Ultraviolet (EUV) light source creates a xenon z-pinch for the generation of 13.5 nm light. Typical EUV emission is characterized though a control photodiode. The chamber also allows characterization of optic samples at varying exposure times for normal and grazing incidence reflection angles during tests lasting up to 40 million pulses. The principal investigation is characterization of the debris field and the erosive effects on optics present. Light emission from the z-pinch is followed by ejection of multiply-charged ions which can significantly damage nearby mirror surfaces. Characterization of the ejecta is performed with an ESA that diagnoses fast ion species by energy-to-charge ratio using ion time of flight (ITOF) analysis. The ITOF-ESA is used to characterize both the energy and angular distribution of the debris field. In the current paper, the ESA is applied only to the ion debris emitted from the source. The effects of total particle flux on mirror samples are investigated through exposure testing. Samples are exposed to the source plasma and surface metrology is performed to analyze erosion and deposition effects on mirrors within the source chamber.

Effects of Postpulse Surface Temperature on Micropulsed Plasma Thruster Operation

High-speed mercury cadmium telluride photovoltaic detectors sensitive to infrared emission are used in a micropulsed plasma thruster (micro-PPT) to explore the surface-temperature profile throughout the discharge process for an ablative arc over Teflon. Real-time surface-temperature measurements are made after the current pulse ends in a micro-PPT to examine heating methods and ablation characteristics of the Teflon® propellant. Calibration is performed on heated Teflon, experimentally accounting for temperature-dependent variations in emissivity. Time-dependent measurements are taken of the fuel face and used to determine a surface-temperature profile after the arc. Photographs of the arc breakdown are taken with a gated, intensified camera capable of 5-ns shutter times allowing visual interpretation of the arc emission in terms of nonaxisymmetric arc spoking effects. The data are analyzed to calculate Teflon vapor pressure and expected impulse bit contribution of the neutral vapor liberated from the fuel face during the ablative cooling process. The cooling profile is also compared with predictions from a code that is under development. Finally, methods for using this sensing technique during the current pulse of the thruster are proposed and evaluated for future applications.

Herriott Cell augmentation of a quadrature heterodyne interferometer

A quadrature heterodyne interferometer is augmented with a Herriott Cell multipass reflector to increase instrument resolution, enable a separation of the phase shift due to neutral density from room vibrations, and optimize the diagnostic for small scale length measurements or for planar measurements. Analysis is used to illustrate retro-reflective planar measurement geometries attainable with the instrument and to show that phase front degradation and loss of scene beam intensity does not introduce a systematic measurement uncertainty. The diagnostic capability is demonstrated with measurements of the electron and neutral densities in the plasma exhaust from electric propulsion thrusters. Experimental data with up to 18 passes through plasma demonstrates that the instrument resolution to electron and neutral density increases almost linearly with number of passes, and that the Herriott Cell can be used to increase the signal of neutral density phase shifts relative to the noise of the phase shifts due t...

Fast surface temperature measurement of Teflon propellant-in-pulsed ablative discharges using HgCdTe photovoltaic cells

High-speed mercury cadmium telluride photovoltaic detectors, sensitive to infrared emission, are investigated as a means of measuring surface temperature on a microsecond time frame during pulsed ablative discharges with Teflon™ as the ablated material. Analysis is used to derive a governing equation for detector output voltage for materials with wavelength dependent emissivity. The detector output voltage is experimentally calibrated against thermocouples embedded in heated Teflon. Experimental calibration is performed with Teflon that has been exposed to ∼200 pulsed discharges and non-plasma-exposed Teflon and is compared to theoretical predictions to analyze emissivity differences. The diagnostic capability is evaluated with measurements of surface temperature from the Teflon propellant of electric micropulsed plasma thrusters. During the pulsed current discharge, there is insufficient information to claim that the surface temperature is accurately measured. However, immediately following the discharge...