Wave Maser Research Articles

Contribution to the use of superconducting shields for magnetic field shaping

The low-field diamagnetism of superconductors has often been used to design quasi-ideal magnetic circuits, especially for traveling wave maser (TWM) magnets. An analogical approach to the calculation of the efficiency of such nonideal cylindrical superconducting shields is presented. In most cases, the problem reduces to a 2-dimensional Laplace equation with given boundary conditions. The logarithmic complex potential \log (Bx - iBy) has been used to obtain the field homogeneity and disorientation. Partially penetrated shields may be replaced by perfect equivalent ones. The analog measurements on conducting paper permit quick iterations of the solution. Various field component measurements have been done on TWM magnets using bismuth thin film Hall probes and found to be in good agreement with the analog measurements.

Superconducting magnet for an 8 mm travelling wave maser

A design which eliminates the superconducting magnetic insulator shields required to obtain the field uniformity necessary for the operation of travelling wave solid masers is described. This type of construction, previously in the U.S.A. at fields upt to 4 kOe, has been extended for use at a field of 10·2 kOe.

Performance of a Traveling Wave Maser for Monopulse Radars

This paper presents the results of theoretical and experimental work on the performance of a traveling wave maser for monopulse radar applications. Saturation, recovery, duplexing, and gain and phase stability are discussed.

Low-level microwave mixing in ruby

Microwave mixing in paramagnetic crystal using traveling wave maser with ruby as mixer element, noting frequency conversion

Superconducting magnet for variable bandwidth traveling wave masers

In order to amplify microwave signals with optimum gain, the ruby crystal of a 4-Gc/s traveling wave maser requires a 3300-G magnetic field uniform to 0.1 percent. By properly varying the magnetic field along the length of the ruby crystal, the bandwidth of the maser amplifier can be increased at the expense of gain. A compact superconducting magnet is described, which provides the required magnetic field. The field is obtained from a short solenoid, which is made to appear infinitely long through the use of a low reluctance enclosure. A portion of the resulting uniform field can be modified by a superconducting trimmer coil imbedded in the low reluctance enclosure. This coil produces an adjustable stepped magnetic field which allows for varying maser bandwidth. Alternatively, it can be used to operate two independent masers in a single magnetic structure. A high degree of reliability is attained. Problems of flux jumping have been avoided by a design in which the diamagnetic (magnetic insulating) properties of superconducting materials play a minor role.

Wide bandwidth traveling wave maser employing magnetic stagger tuning

This paper presents experimental work which shows that magnetic stagger tuning provides an efficient means for trading excess gain for bandwidth in traveling wave masers. A high gain traveling wave maser (20 dB/in. at 4·2°K) has been developed at 4000 mc and operated with a transverse field superconducting magnet as a wide-band amplifier system. The maser, which employs meander-line slowing and iron-doped rutile as the active material is operated with various sections of the paramagnetic crystal resonating at different frequencies. This is made possible by placing the maser in a superconducting magnet which generates a field profile that can be varied in steps along its length of the maser. A 4·0 in. iron-doped rutile crystal, which produces 78 dB peak electronic gain over a 12 mc instantaneous band, can be made to yield 33 dB of gain and 66 mc of bandwidth by stagger tuning. In addition to presenting experimental data which is in good agreement with the simple theory of magnetic stagger tuning, this paper describes for the first time the performance of a traveling wave maser which is magnetically stagger-tuned in a small compact superconducting magnet. This work is significant from a system standpoint since an electronically, variable gain-bandwidth microwave amplifier has been developed. Furthermore, both these devices can be operated in a closed-cycle helium refrigerator.

Measurement of the Flux Density of CAS A at 4080 Mc/sec.

view Abstract Citations (1) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Measurement of the Flux Density of CAS A at 4080 Mc/sec. Wilson, R. W. ; Penzias, A. A. ; Hogg, D. C. Abstract The 20- ft-aperture horn reflector at the Crawford Hill Laboratory,, Holmdel, New Jersey, has been used to measure the flux density of Cas A at 4080 Mc/sec. Some forty drift curve observations, each approximately forty minutes in duration, were made on five nights in September and October of 1964. An argon noise tube was used for comparison in each observation. The night to night variation in the results was less than *0.3%. The equivalent effective temperature ~ontributed by the noise tube was measured by four different calibration methods in order to avoid possible systematic errors associated with any single method. The methods employed were: a comparison between the effective temperature of a room temperature resistor and a helium cooled waveguide termination; the direct connection of the noise tube through precision attenuators; the increment in effective temperature produced by a variable attenuator mounted in front of a helium cooled termination; and the increment produced by warming a room temperature termination. The resulting probable error in the calibration is approximately 0.5 %. The radiometer employs a travelling wave maser and a low-loss comparison switch. The system temperature is 190K for zenith orientation. The system gain was found to change less than 1 % per hour during a forty minute observation period, and was thus sufficiently stable to permit all observations to be made with the radiometer operating in an unswitched mode. The gain of the horn-reflector antenna used was obtained by comparison with that of a small standard horn mounted beside its aperture, while the whole assembly was pointed at a helicopter-borne source. The gain of the standard horn was subsequently measured in the laboratory. From these measurements we were able to obtain the gain of the antenna with probable error of approximately 2%. Combining the results obtained above and making a correction for atmospheric absorption based on our measured value of the sky temperature at this frequency (2.30K) we arrive at a flux density of 1.09 X 1()~23 Wm-2 (c/sec)-1 with a total probable error of 2%. Publication: The Astronomical Journal Pub Date: 1965 DOI: 10.1086/109590 Bibcode: 1965AJ.....70R.150W full text sources ADS |

Microwave Solid State Masers

This is a postgraduate book, partly for electronics engineers, who would find a good deal of the material difficult, because it is a comprehensive account of the subject which demands a good deal of familiarity with quantum mechanics. The contents include chapters on internal structure and energy levels of atoms, the magnetic properties of atoms, energy levels of paramagnetic maser materials, paramagnetic resonance and the dynamics of spin systems, the three level solid state maser and travelling wave maser.

Direct observation of difference frequency signal in a traveling–wave maser

Direct observation of difference frequency signal in a traveling–wave maser

Accurate Low Magnetic Field Measurements on Superconducting Coils

Sensitive Hall effect probes, which are now commercially available, have been used to measure the magnetic fields generated by superconducting coils. The sensitivity has been measured to be 0.080 V/kG-A at 4.2°K. Field resolution at IH=100 mA using a Keithley 149 millimicrovoltmeter is 12.5 mG. The probe calibration is linear from 0–6 kG which is the range of interest for several experiments which are described. Probe performance is demonstrated by measurements of the residual field of a NbZr solenoid, the magnetization of vapor-deposited Nb3Sn cylinders, and the uniformity of a superconducting magnet for a traveling wave maser.

Superconducting magnet for a traveling wave maser

A superconducting magnet has been developed to supply the magnetic field necessary to operate a 4 Gc traveling wave ruby maser. The field required by the maser is about 3000 oersteds uniform throughout the volume of the ruby to one part in a thousand. The field is directed across a gap of about 0.8 inches whose cross section is 5 inches by 0.5 inches. A close approach to the ideal magnetic circuit has been achieved by placing superconducting shields adjacent to the pole pieces. Circulating currents are set up in the shields which prevent the existence of leakage and fringing flux. Since there is no loss mechanism in the shields, the currents persist and the air-gap field remains everywhere uniform. With the absence of leakage and fringing flux, the size and weight of the magnetic circuit is considerably reduced. Superconducting coils allow the use of a persistent current to generate the field. A heater element encased in a glass sleeve is used to initiate the persistent current. The switching procedure is simple and involves no moving parts in the cryostat.

A study of the sources of noise in centimeter wave antennas

This paper deals with a theoretical and experimental investigation of antenna noise which at present limits the sensitivity of centimeter wave receivers. Of importance are the inherent characteristics of the receiving antenna, primarily its radiation pattern and resistive losses. Since paraboliods are the most commonly used microwave antennas, some of their undesirable noise characteristics are evaluated and measurements of these are discussed. Absorption by the oxygen and water vapor in the earth's atmosphere is one of the important sources of noise; its dependencce on frequency and meteorological is described in detail. Results of sky noise measurements at centimeter wavelengths using a receiver comprised of a horn-reflector type antenna and a traveling wave maser having a total effective noise temperature of about 20°K are discussed. Special attention is given to the thermal noise produced by rain and clouds since this gives rise to a varying noise level which must be taken into account in the design of a reliable radar or space communication system.

The maser and its application to satellite communication systems

The principles of operation of the maser are reviewed with emphasis on its ability to give low-noise amplification. The properties of the comb structure travelling wave maser are discussed and related to the microwave “space window”, with special reference to an S-band amplifier which has been constructed. The performance of a receiver, incorporating a maser or a parametric amplifier, is analysed as a function of aerial noise temperature. The basic elements of a maser installation are described with particular regard to the problems of attaching it to an ultrasensitive receiver incorporating a fully steerable, highly directive low-noise aerial. Some consideration of possible cost is included.

Resonators for Millimeter and Submillimeter Wavelengths

Further considerations on the mm-wave Fabry-Perot interferometer are presented. Computed Q values for parallel metal plate resonators indicate that at spacings around 2.5 cm, values ranging from 60,000 at 3 mm, to 300,000 at 0.1 mm wavelengths are possible. The plates must, however, be quite flat. These results are important for many investigations, and in particular for mm and sub-mm wave maser research. For the aperture per wavelength ratios possible here, diffraction effects should be small. Consideration is given to using curved reflectors or focused radiation in applications where the fields must be concentrated. For this purpose, re-entrant conical spherical resonators are treated in detail, as regards operation in the TEM mode at high orders of interference. Expressions for the Q and shunt impedance are given, and high values are possible at mm and sub-mm wavelengths. Quasi-optical methods of coupling into and out of such a resonator are proposed, and the higher modes possible in such a resonator are considered. Results indicate that it could have application to the mm-wave generation problem, and that it represents a good resonant cavity for solid state research at mm and sub-mm wavelengths, and for maser applications in particular.

Cross Relaxation and Concentration Effects in Ruby

Cross relaxation effects in ruby maser crystals are treated by introduction of a cross relaxation probability in the rate equations. Detailed solutions have been obtained for several specific processes and compared to recent experiments. It is shown that cross relaxation can improve maser performance even in the absence of impurity doping. Pulse experiments at 0.06 and 0.14% chromium ion concentrations in a ruby traveling wave maser are interpreted in terms of a five-spin process in addition to a four-spin process.

Cross Relaxation Studies in Diamond

A microwave double resonance experiment performed on the paramagnetic nitrogen centers in diamond shows that in this system cross relaxation occurs via a four spin flip mechanism which exactly conserves Zeeman energy. In this process, which was first postulated by Bloembergen and co-workers in their paper on cross relaxation, two spins of the center line make a downward transition while a spin belonging to each satellite makes an upward transition. Simple rate considerations for this process indicate that if a saturating microwave field is suddenly applied to one of the three lines of the nitrogen spectrum, a weak probing microwave signal at either of the two other lines should register a definite change in absorption in a time ${T}_{21}$. Specifically, if ${T}_{21}$ is much less than other relaxation times of the system, then setting the pump upon the center line should force the absorption at either satellite to drop to zero. Setting the pump at the position of one of the satellites, on the other hand, should reduce the center line absorption to $\frac{3}{5}$ its thermal equilibrium value but should increase the absorption measured at the other satellite by the factor $\frac{6}{5}$. This behavior was precisely observed at 1.6\ifmmode^\circ\else\textdegree\fi{}K, using a bi-modal cavity.By resolving the rate at which a satellite decays to zero when the pump is set on the center line, ${T}_{21}$ is measured for all five satellites in the three principal orientations: ${H}_{0}\ensuremath{\parallel}[100]$, ${H}_{0}\ensuremath{\parallel}[110]$, and ${H}_{0}\ensuremath{\parallel}[111]$. The measured anisotropy is discussed.It is shown that the four spin flip transition may be used in special cases to establish continuous wave maser operation by inverting the population of one of the satellite lines. Steady state inversion of one of the nitrogen satellites is incidentally observed in a number of diamonds.

Three-Level Solid State Maser

The maximum values of the real and imaginary components of the paramagnetic susceptibility of a three-level solid state maser are calculated. For the case of K3Co(CN)6 paramagnetic salt with 0.5% Cr, the values χmax′=2.5×10−4 and χmax″=5×10−4 are obtained. General expressions for the gain and band width of a traveling wave maser are given. An analogy is brought up between the quality factor Q per unit length of wave guide in the traveling wave maser and the Q in the cavity maser.