During hypersonic flight, compressional and viscous heating of the air can form a plasma layer which encases the aircraft. If the boundary layer becomes turbulent, then the electron density fluctuations can effect a parasitic modulation in microwave signals transmitted through the plasma. We developed an approach for studying the interaction of microwave signals with a turbulent, hypersonic plasma layer. The approach affords a great deal of flexibility in both the plasma layer model and the antenna configuration. We then analyzed a situation in which microwaves, transmitted from a rectangular aperture antenna, propagate through a turbulent plasma layer to a distant receiver. We characterized the first-and second-order statistics of the computed parasitic modulation and quantified the depolarization of the signal. The amplitude fluctuations are lognormally distributed at low frequencies and Rice-distributed at high frequencies. Fluctuations in the copolarized phase and amplitude of the far-field signal are strongly anticorrelated. We used a multioutput Gaussian process (MOGP) to model these quantities. The efficacy of the MOGP model is demonstrated by recovering the time evolution of the copolarized phase given the copolarized amplitude and occasional measurements of the phase.

The theoretical approach developed here uses the phase difference as a function of time between a reference signal and the reflected plasma signal in order to estimate the plasma parameters for a nonlinear bi-Gaussian electron density distribution using a single propagation frequency A developed multilayer bi-Gaussian model is used to determine the reflected phase response as a function of time. A derivation from this information is used to estimate the real variable of the complex index of refraction across the plasma layers. This is used along with the time difference in order to estimate the plasma thickness. The approach assumes that the individual layer reflection coefficients are not known only the range of values. The reflection coefficient as a function of the complex index of refraction is used to define the imaginary variable of the complex index of refraction. It is defined in two ways. The first way is as a function of the real variable of the complex index of refraction and the real component of the reflection coefficient. With the estimate of the real variable of the complex index of refraction, the solution space for a layer is determined by the range of the real variable of the reflection coefficient. The second way is as a function of the real variable of the complex index of refraction and the imaginary component of the reflection coefficient. With the estimate of the real component of the reflection coefficient, the solution space for a layer is determined by the range of the imaginary variable of the reflection coefficient. The radial propagation frequency along with the solution space for the estimated complex index of refraction terms are used to estimate the plasma frequency and electron neutral momentum transfer collision frequency.

A nonmagnetized collisional plasma parameter estimator from two frequency signal interrogation attenuation is developed. The plasma parameters that are estimated are the plasma frequency, electron neutral momentum collision frequency, and the plasma thickness. The plasma frequency and electron neutral momentum collision frequency are considered uniform across the plasma thickness. The relative permittivity is defined, and the complex index of refraction is developed. Using this definition and applying the plasma frequency, electron neutral momentum collision frequency, the radial propagation frequency, and plasma thickness, an attenuation is determined for known cases. The development of the estimator is discussed. The estimator uses a performance index where the minimum difference between the plasma frequencies and electron neutral momentum collision frequencies is determined for the two signal interrogation frequencies under the constraint of the same plasma thickness. The estimator was developed in three stages which include iterative, sequential, and adaptive. The setups of the iterative, sequential, and adaptive approaches are discussed. The impact of the interrogation frequency and the estimator setup is investigated. The estimator in the three development stages is compared with known cases and the plasma parameter estimator performance is quantified.

This paper presents the application of a theoretically developed method that provides plasma parameter solution space information from measured RF attenuation that occurs during reentry. The purpose is to provide reentry plasma parameter information from the communication signal attenuation. The theoretical development centers around the attenuation and the complex index of refraction. The methodology uses an imaginary index of the refraction matching algorithm with a tolerance to find suitable solutions that satisfy the theory. The imaginary matching terms are then used to determine the real index of refraction resulting in the complex index of refraction. Then a filter is used to reject nonphysical solutions. Signal attenuation-based plasma parameter properties investigated include the complex index of refraction, plasma frequency, electron density, collision frequency, propagation constant, attenuation constant, phase constant, complex plasma conductivity, and electron mobility. RF plasma thickness attenuation is investigated and compared to the literature. Similar plasma thickness for a specific signal attenuation can have different plasma properties.

This paper presents the application of a theoretically developed method, which when applied to a pulsed irradiance signal can provide information about the underlying chemical kinetics and reaction dynamics. The theoretical development uses a combination of state-space, Laplace transform, least-square, and correlation techniques to determine chemical kinetic and reaction dynamic terms from a pulsed discharge. The waveform irradiance signals come from a space-based optical radiometer. Four pulsed radiometry irradiance waveforms are examined where the reaction order, rate constant, and reaction rates are investigated. The application of the theory and the commensurate results demonstrate that irradiance signals obtained under similar circumstances come from distinct pulsed discharge conditions.

Summary form only given. Atomic Clocks are quantum devices; when ions are used they also become plasma devices. This paper investigates the ions that can be produced from the gas available in a RF linear Paul quadrupole trap used for an Yb ion frequency standard. The gas issues in plasma science and engineering investigated include dimensionless stability parameters from Mathieu's equation considering the clock ion, buffer gas ion and background gas ions. With the buffer gas having the highest partial pressure, the potential for a DC gas discharge is discussed. The coupling parameter is determined along with the potential depth and ion charge density for the ions previously mentioned. From these parameters it is determined that in this case the plasma is characterized as a weakly coupled nonneutral cold ion plasma gas. Using electron impact ionization and expected partial pressures, the reaction rates for ion production are also determined in order to compare how the different ions would fill up the trap. Considering the plasma characterization, ion particle traces for the configuration are determined and a comparison of analytical stability and numerical simulation stability is presented. The paper concludes with a discussion on the implications of the results on plasma engineering design for micro ion atomic clocks.

: We are developing a highly miniaturized trapped ion clock to probe the 12.6 GHz hyperfine transition in the (sup 171)Yb+ ion. The clock development is being funded by the Integrated Micro Primary Atomic Clock Technology (IMPACT) program from DARPA, where the stated goals are to develop a clock that consumes 50 mW of power, has a size of 5 cubic cm, and has a long-term frequency stability of 10(exp -14) at 1 month. Trapped ion systems are an excellent candidate for such extreme miniaturization, because ions are well isolated from the environment independently of the size of the trap. Trapped ion clocks are characterized by quality factors, Q, in excess of 10(exp 12) and excellent long-term stability, and the Q will be minimally degraded upon miniaturization. To realize the clock in a small package will require the miniaturization of several technologies. One of the primary technologies will be the miniaturized ion trap and vacuum package. Linear RF Paul traps routinely have dimensions of a couple millimeters, but miniaturizing the vacuum package with an integral trap, Yb source, and pump will require a novel design. Integrating the miniature, low-power light sources for state detection at 369 nm and 935 nm and for photoionization at 399 nm will also be critical. The 369 nm laser will be a frequency-doubled vertical external cavity surface-emitting laser (VECSEL). A low-phasenoise local oscillator at 12.6 GHz will also be developed using a micro resonator based on exciting acoustic resonances in aluminum nitride. We will present our proposed approach to developing the micro ion frequency standard and relevant current results.

Anode thermal response is important in determining the operation of repetitively pulsed electron diodes and the systems using them. Thermal response determines desorption, cooling requirements, and power deposition. This article describes experimental results from an electron beam diode fitted with both solid aluminum and two types of carbon-carbon fiber anodes. The temperature response is modeled and is used in conjunction with experimental data to study the effect of adsorbates on the anode. Power to the anode is determined through the material properties and modeled temperature response. Thermal properties of the anode are considered with respect to electron stimulated desorption of adsorbates on the anode as an ion source, leading to plasma development and diode impedance collapse.