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In this paper, we present the design and implementation methods of quarter-wavelength resonators accommodating Beltrami standing waves with parallel electric and magnetic (E‖H) fields. The resonator is bounded by the quarter-wavelength longitudinal electromagnetic conductor (LEMC), the circumferential electromagnetic conductor (CMEC), and the radial electromagnetic conductor (REMC). The LEMC, CEMC, and REMC boundaries are artificially implemented by the circumferentially aligned corrugation, concentrically aligned circular fins, and axisymmetrically aligned radial fins, respectively. The coupling control methods by introducing slots in the CEMC and REMC with the external TM01 and TE01 circular waveguides are presented. We design the quarter-wavelength resonators with the implemented LEMC, CEMC, and REMC boundaries with controlled external couplings and numerically demonstrate their E‖H properties, which confirms the validity of the proposed design method.

Microwave cavity experiments make a quantum leap in the search for the dark matter of the universe.

We theoretically investigate the coupling of a single electron in a planar Penning trap with a remote superconducting microwave (MW) cavity. Coupling frequencies around [Formula: see text] MHz can be reached with resonators with a loaded quality factor of [Formula: see text], allowing for the strong coupling regime. The electron and the cavity form a system of two coupled quantum harmonic oscillators. This is a hybrid and linear microwave quantum network. We show that the coherent interaction can be sustained over distances of a few mm up to several cm. Similar to classical linear MW circuits, the coherent quantum exchange of photons is ruled by the impedances of the electron and the cavity. As one concrete application, we discuss the entanglement of the cyclotron motions of two electrons located in two separate traps.

In recent experiments, cavity-mediated bright and dark magnon modes have been observed in cavities containing two separated ferromagnetic materials. Motivated by these results, we study the bright and dark magnon modes of an exchange-coupled ferromagnetic bilayer in which both cavity-mediated and direct interlayer exchange coupling are present. Our results show that the occurrence of a magnon dark mode in the absence of interlayer coupling requires equal frequencies for the two magnon modes. With direct magnon–magnon coupling, the magnon dark mode is determined by both magnon frequencies, as well as by the magnon–photon and direct magnon–magnon coupling strengths. Our results may be useful for future cavity magnonic experiments involving ferromagnetic bilayers.

We introduce a compact atomic clock based on laser-cooled atoms trapped inside a loop-gap microwave cavity. The cavity occupies a volume eight times smaller than conventional cylindrical cavities while maintaining a high quality factor in the presence of the ten apertures required for optical manipulation of cold atoms. The measured linewidth of the Ramsey spectrum, which is limited by the free fall distance of the atomic cloud in the cavity, was 19.6 Hz. The corresponding frequency instability was σy(τ) = 2.5 × 10−12 τ−1/2, which could be further improved by reducing the local oscillator noise. This work paves a way toward high-performance portable atomic clocks.

We investigate the coherent control of the transmission spectrum in a cavity magnetomechanical system consisting of microwave photon, magnon, and phonon modes, where the microwave cavity is driven by a strong pump field and a weak probe field, and the magnon is driven by a weak microwave source. Different from a single transparency window in the absence of the phonon–magnon interaction, two transparency windows and three absorption dips can be observed in the presence of the phonon–magnon interaction, which originates from the joint interaction of phonon–magnon and photon–magnon. In addition, two absorption dips located at both sides of the central absorption dip can be modulated asymmetrically into amplification and absorption by varying the magnetic field amplitude of the magnon driving field. Interestingly enough, the relative phase of applied fields could have profound effects on both the transmission spectrum and the group delay of the output field by choosing the appropriate magnetic field amplitude of the magnon driving field. The transmission group delay can be switched between positive to negative and vice versa by adjusting the relative phase between the applied fields. The present results illustrate the potential to utilize the relative phase for controlling the microwave signal in the cavity magnomechanical system, as well as guidance in the design of information transduction and quantum sensing.

Recent experiments demonstrated that the cyclotron cooling rate of an electron plasma in a Penning–Malmberg trap can be increased by placing the plasma in a cavity and adjusting the magnetic field to make the cyclotron motion resonant with a cavity mode. Here this physics is studied with a coupled oscillator model and analyzed both analytically and numerically. Plasma cooling performance is evaluated over a wide range of system parameters, including the number of electrons, the coupling to the local electric field, the magnetic field gradient, and the detuning between the cavity and cyclotron frequencies. Scaling the equations shows that the system is well-described by a few key dimensionless quantities.

We investigate theoretically the quantum dynamics and statistics of magnons in a cavity–magnon system, where the magnons in a single yttrium iron garnet (YIG) sphere are coupled to microwave cavity photons. Under the rotating wave approximation, the Hamiltonian of the system is solved analytically. By using the coherent magnon state representation, we show that the magnon Kerr nonlinearity, which originates in the magnetocrystalline anisotropy in the YIG sample, could yield a periodic sub-Poissonian distribution and quadrature squeezing effects in the magnons. The generation and manipulation of these nonclassical quantum statistical properties of the magnons can be controlled by scaling the size of the YIG sample.

Motivated by the recently discovered nonlinear dynamics of cavity–magnon polaritons (CMPs), bistable CMP behavior is investigated theoretically in the case of two yttrium iron garnet (YIG) spheres (YIG1 and YIG2) in a microwave cavity, which is induced by the magnon Kerr effect of YIG1 originating from the magnetocrystalline anisotropy. The bistability appears in the form of sharp CMP frequency switching. More importantly, when the driving field acts on YIG1 and drives the magnon dark mode, the nonlinear Kerr effect at high excitation plays an important role in creating frequency detuning between the two YIG spheres. This results in sharply vanishing destructive interference between two YIG spheres and simultaneously makes the invisible magnon dark mode visible. However, when the driving field acts on the cavity, the magnon dark mode remains dark and there is no bistability in the CMPs when the driving frequency is tuned to the magnon dark mode, this being because the excitation energy cannot be transferred from cavity to magnon. The present research provides a promising approach for information storage and processing in multimode systems under high excitation.

Microwave to optical transduction has received a great deal of interest from the cavity optomechanics community as a landmark application for electro-optomechanical systems. In this Letter, we demonstrate a novel transducer that combines high-frequency mechanical motion and a microwave cavity for the first time. The system consists of a 3D microwave cavity and a gallium arsenide optomechanical crystal, which has been placed in the microwave electric field maximum. This allows the microwave cavity to actuate the gigahertz-frequency mechanical breathing mode in the optomechanical crystal through the piezoelectric effect, which is then read out using a telecom optical mode. The gallium arsenide optomechanical crystal is a good candidate for low-noise microwave-to-telecom transduction, as it has been previously cooled to the mechanical ground state in a dilution refrigerator. Moreover, the 3D microwave cavity architecture can naturally be extended to couple to superconducting qubits and to create hybrid quantum systems.

Inspired by the new discovery that the nonlinear dynamics of the cavity magnon polaritons have been observed with a small yttrium iron garnet (YIG) sphere (which introduces a nonlinear Kerr effect) placed into a microwave cavity, we theoretically study the nonlinear behaviors of the magnon dark mode without the magnon Kerr effect by inserting two YIG spheres into a microwave cavity under the strong driving field. The resulting bistability features of the magnon dark mode are sensitive to the frequency detuning between two YIGs and the magnetic field. Especially, when two YIGs have a finite frequency detuning, the magnon dark mode at the cavity resonance frequency does not display bistability. Our research not only sheds light on the nonlinear effect of the magnon dark mode in a strong driving field but also provides a theoretical basis for the application in information storage and novel spintronics.

Plasma assisted combustion is a very active research field due to the potential of using the technology to improve combustion efficiency and decrease pollutant emission by stabilizing lean burning flames. It has been shown in a number of studies that a small amount of electrical energy can be deposited in the flame by applying microwaves, resulting in enhanced flame propagation and thus improved flame stabilization and delayed lean blow-out. However, the effects have not yet been properly quantified since there are significant experimental challenges related to the determination of both the laminar burning velocity and the electric field strength. In the present work, a novel setup is described, where a well-defined burner system is coupled to a microwave cavity. The burner is of heat flux type, where a flat laminar flame is stabilized on a perforated burner head. The advantage of this burner for the current use is that the method and related uncertainties are well studied and quantified, and the geometry is suitable for coupling with the microwave cavity. The setup, experimental procedure, and data analysis are described in detail in this article. Laminar burning velocity for a methane-air flame at ϕ = 0.7 is determined to certify that the burner works properly in the microwave cavity. The flame is then exposed to pulsed microwaves at 1 kHz with a pulse duration of 50 µs. The laminar burning velocity at these conditions is determined to be 18.4 cm/s, which is an increase by about 12% compared to the laminar burning velocity that is measured without microwave exposure. The setup shows potential for further investigations of lean flames subjected to various microwave pulse sequences. The data are of high quality with well-defined uncertainties and are therefore suitable to use for validation of chemical kinetics models.

Maxwell equations in free space are solved for a standing wave torus configuration under axisymmetry, which provides a mathematical support to the microwave cavity hypothesis of ball lightning. With a null Poynting vector with the outgoing part canceling the incoming part, this torus configuration satisfies the E → / / B → gauge of the Maxwell equations.

We report on a novel electron paramagnetic resonance (EPR) technique that merges electrically detected magnetic resonance (EDMR) with a conventional semiconductor wafer probing station. This union, which we refer to as wafer-level EDMR (WL- EDMR), allows EDMR measurements to be performed on an unaltered, fully processed semiconductor wafer. Our measurements replace the conventional EPR microwave cavity or resonator with a very small non-resonant near-field microwave probe. Bipolar amplification effect, spin dependent charge pumping, and spatially resolved EDMR are demonstrated on various planar 4H-silicon carbide metal-oxide-semiconductor field-effect transistor (4H-SiC MOSFET) structures. 4H-SiC is a wide bandgap semiconductor and the leading polytype for high-temperature and high-power MOSFET applications. These measurements are made via both “rapid scan” frequency-swept EDMR and “slow scan” frequency swept EDMR. The elimination of the resonance cavity and incorporation with a wafer probing station greatly simplifies the EDMR detection scheme and offers promise for widespread EDMR adoption in semiconductor reliability laboratories.

Electromagnetic fields (EMFs) are ubiquitous in the digital world we inhabit, with microwave and millimetre wave sources of non-ionizing radiation employed extensively in electronics and communications, e.g., in mobile phones and Wi-Fi. Indeed, the advent of 5G systems and the “internet of things” is likely to lead to massive densification of wireless networks. Whilst the thermal effects of EMFs on biological systems are well characterised, their putative non-thermal effects remain a controversial subject. Here, we use the bioluminescent marine bacterium, Vibrio fischeri, to monitor the effects of pulsed microwave electromagnetic fields, of nominal frequency 2.5 GHz, on light emission. Separated electric and magnetic field effects were investigated using a resonant microwave cavity, within which the maxima of each field are separated. For pulsed electric field exposure, the bacteria gave reproducible responses and recovery in light emission. At the lowest pulsed duty cycle (1.25%) and after short durations (100 ms) of exposure to the electric field at power levels of 4.5 W rms, we observed an initial stimulation of bioluminescence, whereas successive microwave pulses became inhibitory. Much of this behaviour is due to thermal effects, as the bacterial light output is very sensitive to the local temperature. Conversely, magnetic field exposure gave no measurable short-term responses even at the highest power levels of 32 W rms. Thus, we were able to detect, de-convolute, and evaluate independently the effects of separated electric and magnetic fields on exposure of a luminescent biological system to microwave irradiation.

A wide variety of applications of microwave cavities, such as measurement and control of superconducting qubits, magnonic resonators, and phase noise filters, would be well served by having a highly tunable microwave resonance. Often this tunability is desired in situ at low temperatures, where one can take advantage of superconducting cavities. To date, such cryogenic tuning while maintaining a high quality factor has been limited to $\sim500$ MHz. Here we demonstrate a three-dimensional superconducting microwave cavity that shares one wall with a pressurized volume of helium. Upon pressurization of the helium chamber the microwave cavity is deformed, which results in in situ tuning of its resonant frequency by more than 5 GHz, greater than 60% of the original 8 GHz resonant frequency. The quality factor of the cavity remains approximately constant at $\approx7\times 10^{3}$ over the entire range of tuning. As a demonstration of its usefulness, we implement a tunable cryogenic phase noise filter, which reduces the phase noise of our source by approximately 10 dB above 400 kHz.

We evaluate a quasi-spherical, copper, microwave cavity resonator for accurately measuring the relative dielectric permittivity er(p,T) of helium and argon. In a simple, crude approximation the cavity’s shape is a triaxial ellipsoid with axes of length a,1.001a and 1.005a, with a=5 cm. The unequal axes of the quasi-sphere separated each of the triply degenerate microwave resonance frequencies of a sphere (f11TM,f12TM,…,f11TE,f12TE,…) into three nonoverlapping, easily measured, frequencies. The frequency splittings are consistent with the cavity’s shape, as determined from dimensional measurements. We deduced er(p,T) of helium and of argon at 289 K and up to 7 MPa from the resonance frequencies flnσ, the resonance half-widths glnσ, and the compressibility of copper. Simultaneous measurements of er(p,T) with the quasi-spherical resonator and a cross capacitor agreed within 1×10−6 for helium, and for argon they differed by an average of only 1.4×10−6. This small difference is within the stated uncertainty of...

We describe instrumentation and measurement procedures for performing microwave measurements on small metallic samples at dilution refrigerator temperatures using the microwave cavity perturbation technique. The quality factor Q of the lead-plated cavity was of order of 105 at temperatures below the superconducting transition temperature of lead. Microwaves were coupled into and out of the resonator through two room-temperature positionable semirigid coaxial lines, each terminated in a small-loop antenna. We describe in detail the arrangement of the apparatus used to tune to, and lock onto, a cavity resonance and the strategy used to categorize various resonance modes. One of the main features of this microwave spectrometer is the application of the FM detection method to measure changes in both the frequency and the quality factor of the sample-loaded cavity. The procedures for converting these quantities to the real and imaginary components of the surface impedance are described. As an application of th...

Water bath calorimetry was used to demonstrate one more peculiar phenomenon associated with a certain class of mixed gas plasmas termed resonant transfer, or RT plasmas. Specifically, He/H2 (10%) (500 mTorr), Ar/H2 (10%) (500 mTorr), and H2O(g) (500 and 200 mTorr) plasmas generated with an Evenson microwave cavity consistently yielded on the order of 50% more heat than non RT plasma (controls) such as He, Kr, Kr/H2 (10%), under identical conditions of gas flow, pressure, and microwave operating conditions. The excess power density of RT plasmas was of the order 10 W / cm-3. In earlier studies with these same RT plasmas it was demonstrated that other unusual features were present including dramatic broadening of the hydrogen Balmer series lines, unique vacuum ultraviolet (VUV) lines, and in the case of water plasmas, population inversion of the hydrogen excited states. Both the current results and the earlier results are completely consistent with the existence of a hitherto unknown exothermic chemical reaction, such as that predicted by Mills, occurring in RT plasmas., 30 pages, 2 tables, 5 figures

We present results for the estimation of the effective surface conductivity of the walls of a multimode microwave cavity applicator, based on measurements of reflected power from the cavity. During microwave thermal processing, this conductivity is a critical issue because the walls of the microwave applicator can become contaminated with evaporated material or process by-products, resulting in significantly reduced surface reflectivity from that of the bare metal. Thus, the cavity walls may absorb an increased amount of microwave energy, compared to that expected based on reflectivity data for clean metallic walls. A method based on the expansion of the total microwave fields in eigenmodes of a cylindrical waveguide is used to find the power reflection coefficient from an overmoded cylindrical applicator cavity as a function of the wall conductivity. The results of this analysis are compared with power reflection measurements from an experimental multimode applicator cavity, in order to determine a reali...

A resonant microwave cavity operating in the TM010 mode was used to determine the microwave susceptibility of single walled carbon nanotubes (SWNT) that are blended in polymer matricies. The frequencies of the probe signal were 9.8, 11.4, and 35.93 GHz. Samples of 3%–19% blends of SWNT in polycarbonate were tested to determine the best blends for shielding of devices from microwaves at these frequencies. It appears that blends of 9%–11% are very effective in shielding the electric vector of electromagnetic waves. Both the electric vector and the magnetic vectors were probed by the process to determine the nature of coupling between the SWNTs and the applied fields. Some details are given about the apparatus design that enables computer collection and processing of the data to be achieved. An electronic differentiation technique was used to allow the second derivative of the cavity absorption profile to be displayed for precise measurement. Data are presented to show the relative microwave absorption for d...

Results of a hydrogen Balmer line-shape study on microwave-induced plasma discharges operated with pure hydrogen and with argon–hydrogen or helium–hydrogen mixtures are reported. Plasma is generated in a rectangular or coaxial microwave cavity in two separate experiments. In both cases, the emission profiles of the Balmer lines did not show excessive broadening as reported by Mills et al. [J. Appl. Phys. 92, 7008 (2002)].

A radio frequency characterization of a split-ringed, electro-optical modulator (EOM) is provided herein. This characterization is given in terms of electromagnetic simulation data, as obtained from a finite-difference, time-domain code, and a lumped element circuit model. The simulation data provides insight into the field structure within the cavity; the circuit model provides a simple, yet accurate set of design and analysis formulas that relate resonant frequency, voltage levels and power levels to the geometrical and material parameters of the cavity. To validate the claims made from the simulation data and circuit model, experimental data is also provided and a favorable comparison among all data sets is shown. It is concluded that the cavity under consideration can be made to resonate at low frequencies, without increasing the overall size of the cavity. Even though the price in doing so is a reduction in cavity Q and electro-optical crystal voltage, this split-ringed EOM is well suited to an efficient thermal management scheme. Guidance is given on how to optimize the cavity in terms of voltage, Q, power levels, and voltage levels.

Electrical conductivity can be conveniently measured by the enclosed microwave cavity perturbation technique. We have investigated the double-sphere model, in which the exact solutions of the full Maxwell’s equations can be calculated analytically. Focusing on the complex frequency shift Δω/ω0 as a function of the filling factor for conducting or the insulating sample, we argue that Waldron’s perturbation formula, which has been considered fundamental in the cavity perturbation technique, cannot be applied beyond the depolarization regime, even when |Δω/ω0|≪1. Based on the exact solutions for a spherical sample, we obtain approximating formulas that are sufficiently accurate for both the filling factor appearing in the actual measurements and the wide range of conductivity values. We found that the effects of the induced fields just outside the sample must be taken into consideration.

This article is concerned to a TE01n mode resonant cavity coupled through a hole located in the center of the end wall to a cylindrical waveguide (equal in diameter to hole) supporting the evanescent TE01 mode. When the evanescent guide contains a dielectric sample, propagation of the TE01 wave will be permitted in the dielectric filled part. The air filled part in front of the sample is used to adjust the coupling level; the air filled part of the sufficient length behind the sample is used to form a matched reactance termination, otherwise a metal block is inserted to form a short-circuit termination or a reactance termination. It is shown that while using these arrangements quite a large change in the resonant length (or resonant frequency) and Q factor of the cavity resonator will be obtained, when the sample possessed suitable electric thickness is inserted into the evanescent guide. Therefore, it should be capable of yielding accurate values of the complex permittivity for high dielectric constant m...

This article reports direct experimental evidence of the so-called "S curve" of temperature versus electrical field strength when materials with positive temperature dependence of dielectric loss are heated in a microwave resonant cavity applicator. A complete discussion of how the experimental results were achieved is presented. From the experimental results, we believe the S curve theory provides an incomplete explanation of thermal runaway in microwave heating. To understand microwave heating in a resonant cavity, cavity effects must be considered. To explain the experimental results, a theoretical model based on single-mode waveguide theory is developed. Finally, a method to control thermal runaway is described. (C) 2002 American Institute of Physics.

The radio frequency (rf) magnetic field in a microwave cavity ought to be uniform along a line sample in electron paramagnetic resonance (EPR) spectroscopy so that all portions respond uniformly. Mett, Froncisz, and Hyde discovered a way to achieve this objective [Rev. Sci. Instrum. 72, 4188 (2001)]. Their resonators consisted of three regions, a central section for the sample with dimensions at the cutoff condition, and two end sections that had the same cross section as the central section but were made electrically larger by filling them with a low-loss dielectric. The end sections were each one-quarter wavelength long. We have found that the dielectric in the end sections can be omitted and the dimensions made correspondingly larger. Effects of the resulting discontinuities in cavity cross sections perpendicular to the cavity axis have been analyzed using finite element high frequency structure simulator calculations. Closed form expressions for Q values and relative rf field values have been obtained. The length of the uniform field region is decreased somewhat by the discontinuities (∼1 cm at X band). This disadvantage is outweighed by the benefits of higher Q values and elimination of impurity EPR signals from the dielectric materials. End sections may be cylindrical or hemispherical for cylindrical modes and rectangular or hemicircular for rectangular modes.

Frequency tunability of 3D microwave cavities opens up numerous possibilities for their use in hybrid quantum systems and related technologies. For many applications it is desirable to tune the resonance at cryogenic temperatures without mechanical actuation. We show that a superconducting 3D microwave cavity can be tuned at the percent level by taking advantage of the dielectric properties of superfluid $^4$He at milliKelvin temperatures, without affecting its intrinsic quality factor -- reaching $3\times10^5$ in the present experiment., 3 pages, 3 figures, submitted version

The coupling of the electric and magnetic fields leads to a strong interplay in materials' permittivity and permeability. Here, we proposed a specially designed cavity, called the mu cavity. The mu cavity, consisting of a mushroom structure inside a cylindrical resonator, is exclusively sensitive to permeability, but not to permittivity. It decouples materials' electromagnetic properties and allows an accurate measurement of the permeability. With the help of an epsilon cavity, these two cavities jointly determine the complex permeability and permittivity of the materials at microwave frequencies. Homemade epoxy-based composite materials were prepared and tested. Measurement and manipulation of the permeability and permittivity of the epoxy composites will be shown. The results will be compared with the effective medium theories.

In this letter, an atom-based approach for measuring the microwave (MW) cavity response (including cavity frequency and Q-factor) is presented, which utilizes a MW magnetic field detection technique based on atomic Rabi resonances. We first identify the Rabi resonances on seven π transitions in Cs atoms and demonstrate their uses in continuously frequency-tunable field detectors. With the atom-based field detectors, we then indicate the possibility of reconstructing the MW cavity response by measuring the MW frequency-dependent Rabi frequency (i.e., MW field strength) inside the cavity. To demonstrate this approach, we measured the response curves of a 9.2-GHz cavity and a cavity resonating at 8.3 GHz and 9.7 GHz using π transitions and σ transitions, respectively. We compared the results measured by our approach with those measured by Vector Networker Analyzer and obtained good agreement. From such atom-based, SI-traceable measurements, the MW cavity response can be linked directly to the Rabi frequency,...

A partially plasma filled reconfigurable cylindrical cavity is proposed. Plasma offers an encouraging alternative to metal for a wide variety of microwave engineering applications. Implementation of a low-cost plasma element permits the resonant frequency to be changed electrically. The level of the resonant frequency shifts toward the empty-cavity resonant frequency and depends on certain parameters, such as the plasma diameter, relative permittivity and thickness of the plasma tube. In this article, we first introduce the partially plasma filled reconfigurable cylindrical cavity; then, the resonant frequency equation of the cavity is obtained by variational methods. Finally, we plot the resonant frequency versus different parameters of the cavity, which we compare with the results of the CST software. We show that the two results are compatible with each other.

The complex permittivity analysis of microwave dielectric loss spectroscopy has been revisited to deduce the intrinsic values of the mobility of charge carriers injected at the interface between an organic semiconductor and a gate insulator. A perturbation model with a simple parabolic function for frequency-dependent microwave resonance in the cavity enables us to experimentally determine the real and imaginary parts of the permittivity change caused by the injected charge carriers based on the Drude–Zener model, leading to the simultaneous assessment of the intrinsic charge-carrier mobility, the averaged trap depth/density, and the ratio of free-trapped charge carriers. The present frequency-dependent precise analysis of complex permittivity provides rapid and non-destructive screening of the total landscape of the charge-carrier transport at interfaces.

We demonstrate a hybrid device architecture where the charge states in a double quantum dot (DQD) formed in a Si/SiGe heterostructure are read out using an on-chip superconducting microwave cavity. A quality factor Q = 5,400 is achieved by selectively etching away regions of the quantum well and by reducing photon losses through low-pass filtering of the gate bias lines. Homodyne measurements of the cavity transmission reveal DQD charge stability diagrams and a charge-cavity coupling rate g_c/2pi = 23 MHz. These measurements indicate that electrons trapped in a Si DQD can be effectively coupled to microwave photons, potentially enabling coherent electron-photon interactions in silicon.

An intense ultraviolet and visible radiation source for various applications has been conceptualized, designed, and developed using a TE011 mode microwave cavity filled with plasma immersed in a magnetic field. The radiation intensity emitted from the source, as a function of the magnetic field intensity, approaches maximum at the electron cyclotron resonance. Light intensity increases with pressure inside the Hg+Ar lamp and the microwave power.

A novel experiment to investigate single-surface multipactor on a dielectric surface was developed and tested. The compact apparatus consists of a small brass microwave cavity in a high vacuum system. The cavity is ∼15 cm in length with an outer diameter of ∼10 cm. A pulsed variable frequency microwave source at ∼2.4 GHz, 2 kW peak excites the TE111 mode with a strong electric field parallel to a dielectric plate (∼0.2 cm thickness) that is inserted at midlength of the cavity. The microwave pulses are monitored by calibrated microwave diodes. An electron probe measures electron current and provides temporal measurements of the multipactor electron current with respect to the microwave pulses. Phosphor on the dielectric surface is used to detect multipactor electrons by photoemission. The motivation of this experiment is to test recent theoretical calculations of single-surface multipactor on a dielectric.

High-frequency dielectric properties of A5B4O15 (A=Ba, Sr, Mg, Zn, Ca; B=Nb, Ta) dielectric ceramics are studied by means of the microwave cavity technique, a combination of far-infrared reflection and transmission spectroscopy and time-resolved terahertz transmission spectroscopy. Microwave permittivity e′ and Q×f factor vary, depending on the chemical composition, between 11 and 51, and 2.4 and 88 THz, respectively. The temperature coefficient τf varies between −73 and 232 ppm/°C, and in two samples |τf| is less than 15 ppm/°C. It is shown that the microwave permittivity e′ of the ceramics studied is determined by the polar phonon contributions and that linear extrapolation of the submillimeter dielectric loss e″ down to the microwave region is in agreement with the microwave data of single phase samples. The relationship among phonon spectra, the crystal structure, and the unit cell volume is discussed.

An experimental study of the electromagnetic behavior of a pulsed high frequency resonant cavity, operating in its fundamental TE111 mode, is presented. Typical pulse characteristics are a pulse width of 10 μs, microwave frequency of 1 GHz, and microwave power of a few kW. The various parameters (characteristic time τ, coupling factor β, incident power Pi) that determine the temporal variation of the electrical characteristics (power entering in the cavity, electric field) during the pulse are defined. In particular, the influence of the coupling factor on the transition stage to a steady state is discussed for the cavity without plasma. The temporal behavior of the cavity in the presence of a gas (argon and hydrogen) is also studied. For pressures ranging from 0.5 to 100 Torr, the discharge breakdown parameters (time τb, electric field Eb) in hydrogen are deduced from the experiments (tb∼0.1–1 μs, Eb∼300–3000 V/cm). The conditions to reach a quasisteady state plasma are derived from the qualitative analy...

In this article, a new type of physics package with high signal to noise ratio for a rubidium atomic frequency standard is reported. To enhance the clock transition signal, a slotted tube microwave cavity with a field orientation factor of 0.93 and an absorption cell with the diameter of 30 mm were utilized in design of the cavity-cell assembly. Based on the spectral analysis of the three commonly used rubidium spectral lamps, the spectral lamp filled with Xe gas was chosen as the optical pumping source for its small line shape distortion. To suppress the shot noise of the signal, a band pass interference filter was used to filter out Xe spectral lines from the pumping light. A desk system of the rubidium frequency standard with the physics package was realized, and the short-term stability of the system was predicted and tested. The measured result is 2.4 × 10-13 τ-1/2 up to 100 s averaging time, in good agreement with the predicted one.

Contactless thermally stimulated lifetime measurements were performed on detector-grade Cd1−xZnxTe (x∼0.1) crystals using a pulsed laser microwave cavity perturbation method. The carrier lifetime decreased from approximately 30 μs at 110 K to 4 μs at 160 K, and then remained relatively constant from 160 to 300 K. The sudden drop in carrier lifetime within a particular temperature range is consistent with the thermal activation of a charge trap with a detrapping time longer than the carrier lifetime. The maximum trap activation temperature and the minimum detrapping time are estimated from the lifetime versus temperature curve to be approximately 160 K and 10−6 s, respectively.

A resonant cavity based microwave differential device has been developed as a sensor for the measurement of small quantities of water vapor in gases. The presence of a contaminant is assessed by induced variations in the relative permittivity due to a shift in the resonant frequency of the measuring resonator. The measured output signal is related to the difference in the reflection coefficients of the measuring resonator and the reference one. A simple modeling approach of the system shows the proportionality between the difference of the reflection coefficients of the cavities and the variation in the dielectric constant. The evaluation of the minimum detectable change in the permittivity is possible using the Clausius–Mossotti equation for a binary gas mixture at a given concentration and pressure. The detection threshold is then determined by taking into account the signal-to-noise ratio of the differential setup. The estimation of the limit of detection for some practical moisture contaminated gases ...

We report on microwave studies of Nd0.7Sr0.3MnO3 thin film losses in a shielded TE011 dielectric cavity. The cavity quality (Q) factor and resonant frequency are measured as a function of temperature with the dielectric cavity loaded with a thin film on a LaAlO3 substrate. A reference Q measurement is then made without the film enabling the extraction of the film-Q factor Qfilm. Here the temperature dependence of the Q factor is discussed in terms of resistive losses in the thin film. A numerical finite difference time domain code is then used to extract the microwave resistivity as a function of temperature from the measured Q factors. The numerical method involves the discretization of Maxwell’s equations on an axisymmetric space-time grid coupled to a discrete Fourier transform to determine the resonant frequency.

Methyl radicals are trapped in the solid Kr film by simultaneous condensation of gaseous Kr and the products of a gas discharge in CH4-doped Kr on a low-temperature (4.2K) substrate located at the center of the microwave cavity. The observed EPR spectrum is a superposition of broad-line and narrow-line series. At a low resonance microwave power, the latter series consists of four hyperfine components with nearly equal intensities and shows small axial anisotropy of both the g and A tensors. At a sufficiently high power the two central narrow lines split, so that the narrow-line series takes on the appearance recorded elsewhere for CH3 in Ar at higher temperatures above 12K. Simultaneously, the intensity of the two central broad lines increases dramatically, while the outer components become saturated. A possible explanation is discussed.

For the first time Stark experiments in a pulsed nozzle Fourier transform microwave spectrometer are successfully performed with the pulsed molecular beam parallel to the resonator axis, together with a new geometry for the Stark electrodes which prevents line broadening due to E-field inhomogeneity. The coaxially oriented beam-resonator arrangement, introduced in the 1990s, is known to provide a considerable improvement in resolution and sensitivity in comparison to the perpendicular geometry, but Stark effect experiments performed in a microwave cavity, using the conventional cubic electrode geometry with this arrangement, suffer from an inhomogeneous field distribution. This gives rise to broadened profiles of the Stark shifted lines and a persistent zero-field line. The linewidth achieved with our new configuration is now close to the typical value found in the absence of a Stark field: less than 10 kHz at 10 GHz half width at half height, which makes the system very suitable for yielding precise valu...

Major improvements have been made on the sensitive high pressure electron paramagnetic resonance (EPR) system developed previously in 1978 at this laboratory. These changes allow low temperature measurements and provide a more stable signal. The high pressure EPR cell is placed inside a vacuum chamber to provide thermal isolation, so that the system may be cooled by a closed cycle refrigerator to temperatures between 45 and 60 K, depending on the energy input to the modulation coil. The combination of high pressure and low temperature greatly expands the thermodynamic range over which EPR measurements can be made. An improved and effective method of forming a conductive surface to define the microwave cavity is presented. This method successfully avoids the deterioration of the sapphire’s polished surface which causes premature breaking of the sapphire high pressure anvil, and therefore significantly improves the reliability of the system at high pressure. Other modifications to the system, such as the mi...

A significant source of errors in quantitative electron paramagnetic resonance measurements is incorrect sample positioning in the microwave cavity. In this article a modification to our previously described sample alignment tool which allowed the precise and reproducible positioning of cylindrical samples along the vertical central axis of the rectangular cavity is described. These revisions allow cylindrical sample movement in the horizontal (y,z) plane which is perpendicular to the cavity x axis. Using this upgrade, the new sample setup procedure is now able to position samples precisely and reproducibly at arbitrary points in the intracavity space.

A new type of microwave instrument is developed for quick determination of the molecular orientation and dielectric anisotropy in sheet materials. Its cavity resonator differs from the conventional one in that the waveguide is separated by a narrow gap. Thus, it consists of a pair of rectangular waveguides, each partitioned by an iris plate. A given sheet is inserted into the gap, and can be rotated around the axis normal to its plane. The iris diameter and gap width are determined so as to meet the requirement that the transmitted microwave power and the Q value may not drop markedly after insertion of thick films into the gap. Polarized microwaves are irradiated perpendicularly to the sheet, and the transmitted wave intensity is measured at every 1° of rotation angle as the sheet is rotated at a speed of 6.0 s per turn. This operation quickly gives information related to the molecular orientation in the given sample. Dielectric measurements can be made at any rotation angles, allowing the angular depend...

An analytical expression and a perturbation formula for the cavity resonant frequency dependence of plasma are derived for the cylindrical TM010-microwave plasma cavity. A comparison between the exact and the approximate solution shows that the perturbation theory can be used accurately to analyze the perturbation effect on the cavity resonant frequency caused by microwave plasma in low pressure microwave excited gas lasers. A new method is proposed to prevent detuning of the cavity by the perturbation of the plasma and glass tube, so that a uniform and steady-state microwave plasma is successfully formed and a stable laser output power is also obtained. The electron density and the microwave dielectric constant of a tube shell can be measured by the perturbation approach.

A description is presented for two unconventional highly sensitive spectrometers operating in the decimeter‐wave region (90–450 MHz) and millimeter‐wave region (90–150 GHz), respectively. In both cases a resonant cavity is used as an absorption cell. Either design combines high sensitivity with high resolution and wide spectral range. The radio frequency spectrometer allows measuring of extremely low absorption quantity 3×10−12 cm−1 in combination with high spectral resolution of order 1 kHz with the radio frequency–microwave double resonance method. The gas cell is a coaxial cavity (Q≊103) with a diameter of 40 cm and length about a wavelength. The millimeter‐wave spectrometer utilizes an orotron oscillator as the tunable, coherent source of radiation from 90 to 150 GHz. A gas cell is placed into a high quality (Q≊104) Fabry–Perot resonator of the orotron, and the absorption signal is detected by variation of the orotron electron current in the collector circuit. The sensitivity limit of (2–5)×10−10 cm−1...

The ‘‘frequency squared scaling’’ law, relied upon to enhance the production of high charge state ions from electron cyclotron resonance (ECR) ion sources, indicates that low frequencies of operation may not be viable for production of high ion densities, and hence for the production of high charge state ions. The superconducting electron cyclotron resonance ion source (SCECR) at the National Superconducting Cyclotron Laboratory is a fully superconducting, hexapole stabilized tandem mirror ECR ion source with a multimode microwave cavity. When operated at its optimized high magnetic field (high‐B) mode at 6.4 GHz, the high charge state current output of the SCECR approaches all existing ECR ion sources, including higher requency ECR ion sources (ECRIS). In this study, the SCECR is operated at 2.45 GHz in its high‐B mode that is scaled down for that frequency of operation. Initial results with oxygen and argon ion production at 2.45 GHz are presented. It is demonstrated that the SCECR can produce a plasma ...