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Plasma photonic crystals (PPCs) are photonic crystals formed from plasma that allows them an electrically tunable structure and permittivity. PPCs are potential microwave bandgap components with frequency ranges theoretically limited only by the physical control of the plasma distribution. In practice, they are limited by the controllability of the plasma distribution. Traditional approaches have minimal control and range of PPC reconfigurability because the plasma distribution is fixed. In contrast, this work explores reconfiguring the PPC structure by treating individual columns as pixels within a larger PPC structure. While the location of each plasma column is fixed, individual columns are adjusted to change the macroscopic plasma distribution of the total PPC. This work shows for the first time that individual plasma column control can tune a PPC bandgap frequency by an order of magnitude, from 190–300 GHz to 26–37 GHz. The changes to the larger supercell structure emulate changes to PPC parameters such as the lattice constant, column radius, and permittivity. This enables a wider tunable frequency range for PPC bandgaps as well as improved manipulation over the range. The collision frequency imposes a lower limit on the variable frequency range. The results demonstrate an expanded frequency variability for PPCs that highlight their potential as a wideband tunable bandgap device when each column is individually controlled. [ABSTRACT FROM AUTHOR]

Experiments were conducted at the University of Illinois at Urbana Champaign Electric Propulsion Laboratory to study the ion-induced secondary charge emission from surfaces bombarded by an [Emim][BF4] electrospray plume. The surfaces were unpolished and had oxide and hydrocarbon layers typical of as-received materials used in electrospray experiments. The effect of changing the bias from −85 to +85 V on the target collecting current from the electrospray plume was measured. These data are used to calculate the yield of positive and negative charged species emission from the target due to bombarding cations and anions. The yields of positive charges per incident cation (γ c a t i o n +) , negative charges per incident cation (γ c a t i o n −) , positive charges per incident anion (γ a n i o n +) , and negative charges per incident anion (γ a n i o n −) are measured for eight different industrial materials commonly used in electrospray diagnostics or thruster and spacecraft construction. These yields range from 0 to 1.3 charges per incident ion over a range of emitter voltages from 1.5 to 2.9 kV and largely display linearly increasing trends with increasing emitter voltage. Over this emitter voltage range, γ c a t i o n + ranges from 0 to 0.55, γ c a t i o n − ranges from 0 to 0.75, γ a n i o n + ranges from 0 to 0.4, and γ a n i o n − ranges from 0.3 to 1.3. The data show for the first time positive and negative charges being emitted due to both cation and anion bombardment and suggest that secondary ions sputtered from the surface are important to the secondary charge emission behavior in electrospray plumes. [ABSTRACT FROM AUTHOR]

We present a 3D-particle-in-cell (PIC) approach to modeling electrospray plumes typical of those formed by externally wetted emitter devices. Numerical grid-resolution techniques suitable for capturing strong electric fields in the emitter region were explored, and grid refinement criteria were quantified. The molecular dynamics simulations of the EMIM − BF 4 ionic liquid system were modeled to determine the fragmentation mechanism in the presence of an electric field and dimer temperature as well as to provide fragmentation rates for the PIC simulations. An energy analysis of the molecular dynamics (MD) fragmentation demonstrated that the key mechanism for dimer fragmentation corresponds to a decrease in the Coulomb energy between the cation and anion in the system and that dimers of temperatures 300 and 600 K are extremely stable for electric fields smaller than 1.5 V/nm. Using probabilities of fragmentation consistent with the MD simulations, we implemented a dimer fragmentation model in our PIC simulations. The ion energy distribution functions obtained from the PIC simulations were used to predict retarding potential analysis (RPA) curves that were compared directly to measurements. The sensitivity of the RPA shape to the fragmentation probability was found to be significant. By comparing predicted and measured RPA curves for both negative and positive operation modes, and the fact that dimers do not fragment for electric fields less than 0.6 V/nm, we conclude that fragmentation of dimers occurs spontaneously due to their high thermal energies. [ABSTRACT FROM AUTHOR]

Erratum: "Ion-induced charge emission from unpolished surfaces bombarded by an [Emim][BF4] electrospray plume" [J. Appl. Phys. The authorship of this article should read: Matthew R. Klosterman, SP 1,a) sp Joshua L. Rovey, SP 1,a) sp Deborah A. Levin, SP 1 sp and Avinash Rao SP 1 sp SP 1 sp Aerospace Engineering, University of Illinois Urbana-Champaign, 104 S Wright Street, Urbana, Illinois 61801, USA REFERENCES 1 M. R. Klosterman, J. L. Rovey, and D. A. Levin, "Ion-induced charge emission from unpolished surfaces bombarded by an [Emim][BF4] electrospray plume", J. Appl. Phys. [Extracted from the article]

A retarding field energy analyzer (RFEA) designed specifically for high energy pulsed electron beam measurements is described in this work. By proper design of the entrance grid, attenuation grid, and beam collector, this RFEA is capable of determining the time-resolved energy distribution of high energy pulsed electron beams normally generated under "soft vacuum" environment. The performance of the RFEA is validated by multiple tests of the leakage current, attenuation coefficient, and response time. The test results show that the retarding potential in the RFEA can go up to the same voltage as the electron beam source, which is 20 kV for the maximum in this work. Additionally, an attenuation coefficient of 4.2 is obtained in the RFEA while the percent difference of the rise time of the electron beam pulse before and after attenuation is lower than 10%. When compared with a reference source, the percent difference of the RFEA response time is less than 10% for fall times greater than 35 ns. Finally, the test results of the 10 kV pseudospark-based pulsed electron beam currents collected under varying retarding potentials are presented in this paper. [ABSTRACT FROM AUTHOR]