TE011 Cavity Research Articles

Wall-less microwave cavity for optical detection of magnetic resonance

This paper describes a versatile TE011 cavity for 35-GHz optical detection of magnetic resonance (ODMR) spectroscopy. The cavity provides not only wide optical access but also a high Q factor. A novel design, including externally adjustable coupling and fine frequency tuning, allows quick and simple changing of samples and provides a facility to apply uniaxial stress.

Cavity stabilised Gunn oscillator as RF source for ESR spectroscopy

The construction of a Gunn oscillator stabilised by means of a cylindrical TE011 cavity is described. The resulting oscillator has a mechanical tuning range of about 1 GHz around a centre frequency of 9.5 GHZ. A varicap diode inserted on the wall of the stabilising cavity provides a tuning range of 20 MHz. The results obtained by the use of this oscillator as RF source in a reflection cavity homodyne spectrometer are discussed. It is shown that this kind of oscillator can substitute for low noise klystrons without significant noise degradation in ESR spectrometers.

Linear theory of an electron cyclotron maser operating at the fundamental

The linear theory of an electron cyclotron maser (ECM) operating at the fundamental is developed. A set of analytic expressions, valid for all TE cavity modes, is derived for the starting current and frequency detuning using the Vlasov-Maxwell equations in the weakly relativistic limit. These results are applicable for an arbitrary electron velocity distribution as well as any longitudinal distribution of the RF field. It is shown that the starting current can be expressed in a simple form which contains the Fourier trans-form of the longitudinal field distribution. Analytic results are presented for specific longitudinal field variations, including uniform, sinusoidal, and Gaussian. It is found that the starting characteristics of an ECM are strongly influenced by the axial dependence of the RF field, but weakly affected by the velocity spread of the electron beam. The problem of multimode oscillation is treated in the linear theory by using a Slater expansion of the cavity field. The complete formulation for mode competition based on this expansion is presented and preliminary results are derived. This comprehensive analysis of ECM linear theory should be useful as a diagnostic of ECM performance and should facilitate comparison between theory and experiment.

Effect of sample quantity on the results of ferromagnetic resonance studies of lunar samples

Quantitative ferromagnetic resonance (FMR) measurements at 9.5 and 35 GHz were made on lunar fines in order to determine the amount of single domain Fe0 and to ascertain the effect of sample quantity on the results of these experiments. Samples containing more than 10 μg of Fe0 in an X‐band TE104 cavity, or more than 0.11 μg in a Kα‐band TE011 cavity can cause errors greater than 1% in the quantitative determination of Fe0, as well as cause anomalous broadening of the FMR line. Theoretical calculations were derived to show this effect which results from a nonlinear response of the FMR experiment with the sample quantity. Using samples of nominal weights, the amount of Fe0 determined at 35 GHz was 1.2–1.8 times greater than at 9.5 GHz, while the linewidths increased by a factor of 1.2. As the particle size increases, the ratio of Fe0 determined at 35 GHz to that determined at 9.5 GHz increases, suggesting that the additional iron is due to larger spheroidal particles which change from multidomain to single domain at the larger fields.

High pressure low temperature ENDOR/EPR cavity

We discuss an X-band TE011 cavity and bomb for use in performing ENDOR (electron nuclear double resonance) and EPR at 2 K and pressures to 5 kilobar, with gaseous and solid helium as pressure conducting media.

A Gas-Phase EPR Cavity

The design of an X-band cylindrical TE011 cavity resonator with a 25 mm diam axial access hole for gas-phase EPR studies is described. The empty cavity is tunable over a frequency range of at least 8.0–10.0 GHz and critical coupling is attained over this range with a novel variable coupling device.

A new method of electropolishing niobium

By a new method of electropolishing niobium we have obtained very smooth surfaces. In electropolished TE 011-cavities with an anodic oxide film a Q-value of 3 × 10 10 and a critical magnetic field of 80 mT were obtained in the X-band without any heat-treatment.

Superconducting Niobium S-Band Cavities

Recent studies of long-pulse separated beams indicate the need for the development of superconducting rf separators for counter experiments. To achieve this goal we investigated microwave resonators at S-band frequencies manufactured by the three following methods: 1) machining from solid electron-beam-melted niobium, 2) electroforming in molten fused salts by the Linde Company, 3) machining hydroformed cups of commercial grade niobium. Machined parts were electron-beam welded to form microwave cavities. All cavities were heat treated in either the Oak Ridge, Stanford or SLAC high-vacuum, high-temperature furnaces and chemically polished. We investigated and compared both surface resistance and peak rf magnetic field of the above cavities after every step. We measured an improvement factor of ~ 106 at B? = 330 G in a TE011 cavity. The highest rf magnetic field achieved was 464 G in the TM010 mode which corresponds to E of ~17 MV/m. In addition, we were looking for peaks in the microwave absorbtion caused by rf magnetic field induced surface states similar to those reported by various researchers on highly polished crystals in low dc magnetic fields. No such anomalies were found.

On cavity modes for determination of plasma electron distribution †

A theoretical investigation has been made on the choice of various TM and TE cavity modes and their combinations in the perturbation method of determination of radial electron density distribution in a plasma column. The modes at S and X bands have been chosen from consideration of electric field configuration, cavity design, calculated frequency shifts for different axial electron densities and the ratios of such shifts corresponding to a pair of modes for rectangular, killian, parabolic and trapezoidal types of distribution. Further, it has been suggested that the additional cavity modes may provide more data for electron density distribution by the perturbation methods due to Hess (1964) and Burkley and Sexton (1968).

Investigation of Superconducting Niobium Cavities at S-Band

This paper describes the investigation of superconducting Nb cavities at S-band frequencies. The TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">011</sub> and TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">011</sub> cavities were machined by Varian Associates from solid billets of electron-beam-melted niobium and chemically polished to remove all work-damaged material. At low power levels, the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">011</sub> cavity had a measured Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> (4.2°K) 324 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> and a residual Qres ≈ 6.97 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> , whereas the TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">011</sub> cavity had a Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> (4.2°K) ≈ 89 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> and a residual <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</sup> res ≃ 425 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> . These results correspond to a surface resistance of R(4.2°K)/f <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 0.29 μΩ/GHz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . High level measurements were limited at a critical RF field H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ac</sup> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> = 15.5 G in the TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">011</sub> mode and H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ac</sup> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> = 290 G in the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">011</sub> mode.

Threshold Microwave-Field Amplitude for the Unstable Growth of Spin Waves under Oblique Pumping

The threshold microwave-field amplitude hcrit required for the unstable growth of spin waves has been investigated for oblique pumping with a linearly polarized microwave field applied at an arbitrary angle with respect to the static magnetic field. The experiment was performed on YIG (1% Dy) spheres at 9.2 GHz, using a rectangular TE102 cavity and a pulsed magnetron source. Data were obtained at static external fields of 400, 600, 1100, and 1500 Oe. In general, hcrit increases with the pump angle. Theoretical expressions for the oblique pumping hcrit have been derived for ferromagnetic insulators of ellipsoidal shape and with axial symmetry about the direction of the static magnetic field sufficient to saturate the sample. The threshold field is determined by maximizing 1/h=cosψ/h∥±sinψ/h⊥ with respect to the angle between the internal field and the spin-wave propagation direction. Here, h∥ and h⊥ are the parallel and perpendicular pump threshold fields of Schlömann and Suhl. For external fields sufficient to magnetize the spherical samples to saturation, the theoretical predictions are in good agreement with the experimental data. For small fields, the agreement is poor. However, fair agreement is obtained by assuming a transverse demagnetizing factor Nt greater than the value of ⅓, which is appropriate for saturated spherical samples. The value of Nt for the best theoretical fit depends on the way in which the sample is demagnetized. This result indicates that for samples not magnetized to saturation, the magnetic structure consists of elongated domains, and that the oblique-pumping data can be explained from the theory for saturated systems, assuming demagnetizing factors appropriate to the domain structure.

Measurement of the Surface Resistance of Superconducting Lead at 2.868 GHz

The surface resistance of superconducting lead at 2.868 GHz was determined from a measurement of the unloaded Q of a TE011 cavity. The results were compared to the analytical expression for the surface impedance of pure superconductors in the Pippard limit, which was worked out by Abrikosov et al. Adequate agreement was found by writing the reduced surface resistance in the form of r=A rAGK+r0, with r0 being a residual resistance and A a constant. The best fit was obtained for A = 3.0, r0=2.2×10−5 and the gap parameter Δ(0)=1.97kBTc.

Quantitative ESR Measurements of Gas-Phase H and OH Concentrations in the H–NO2 Reaction

An application of the intensity relations derived previously for determining absolute concentrations of H atoms and OH radicals in the gas phase by ESR spectroscopy is described. Magnetic-dipole transitions in O2 and electric-dipole transitions in NO are used as calibration standards for determining H and OH, respectively. The construction of a cylindrical TE011 cavity suitable for observing both types of transitions in a fast flow system is described. Results of measurements of H and OH concentrations during the ``titration'' reaction H+NO2→NO+OH are presented. The internal consistency of the theoretical OH intensity relations is demonstrated by experimental measurements on J=32 and J=52 OH lines. At reaction times of a few milliseconds, the H titration curve is shown to have an initial linear portion which extrapolates to an NO2/H ratio of unity. It then becomes curved as expected by the generation of an additional H from OH+OH→ lim k2H2O+O and OH+O→O2+H.The OH titration curves yield k2=1.2±0.3×1012 cm3 mole−1·sec−1 at 300°K in good agreement with the only other reported value. Finally, some qualitative observations on a striking generation of free electrons associated with the main H–NO2 reaction are noted.

Method of Obtaining Pressure and Temperature Insensitive Microwave Cavity Resonators

This paper describes a method of fabricating cavity resonators having very low temperature frequency dependence and also describes a means of building pressure insensitive cavity resonators. Simple schemes of compensation using invar walls with steel or brass end plates for TE011 cavity resonators are found to be unsatisfactory due to hysteresis type effects. With the arrangement described fixed frequency resonators are obtained having stable temperature-frequency coefficients less than ±0.2 ppm/°C and pressure-frequency characteristics of less than 0.003 ppm/mbar.