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Cryogenic Magnetometer Development https://ntrs.nasa.gov/search.jsp?R=19680017231 2020-03-12T10:50:22+00:00Z NASA CONTRA REPORT .- CRYOGENIC MAGNETOMETER -x. DEVELOPMENT by WeS. Goree, R. S. Deauer, Jy., V. W. Hestermmz, and T. W. Rarbee, Jr. 1 .I/>. c .. Prepared by STANFORD RESEARCH INSTITUTE Mcnlo Park, Calif. for Anzes Research Center NATIONALAERONAUTICS AND SPACE ADMINISTRATION WASHINGTON,D. C. JUNE 1968 g# .. - TECH LIBRARY KAFB, NY 006038b F_ NASA CR- 10'73 /' CRYOGENIC MAGNETOMETER DEVELOPMENT .. - BY w. s. Goree, B. S. Deaver, Jr., V. W. Hesterman, ' and T-.-W; Barbee, Jr. Distribution of this report is provided in the interest of informationexchange. Responsibility for the contents resides in the author or organization that prepared it. Prepared under Contract No. NAS 2-2088 by Y" STANFORD RESELUCH INST- Menlo 'Park, Calif. for Ames Research Center NATIONAL AERONAUTICS AND SPACE ADMINISTRATION For sale by the Clearinghouse for Federal Scientific and Technical Information Springfield,Virginia 22151 - CFSTI price $3.00 ". " \ ABSTRACT A low field euperconducting shield has been developedand used to provide otable magnetic fieldsof lees than lod G, maintained stable for ao long as 6 days, The shield is a superconducting cylinder 91.5 cm long by 16.5 cm ID, The measured attenuation of externally applied axial field changes is a factor of 31 per shield radius. The Meissner-effect and zero resistance propertyof superconductors has been used inthe development of a magnetometer for measuring the ab- solute value of magnetic fields, This device has been usedto measure fields as small as 2 x 10" G. A magnetometer utilizing the unique zero resistanceand quantized flux properties of superconductors has been developedand used to measure magnetic field changes as small as 5 x lo4 G. The dc Josephson tunneling effect has been usedto construct (1) magnetometers with field sensitivity as goodas lo4 G, (2) magnetic grad- iometers with which field gradients oflo4 G cm have beenmeasured, (3) linear displacement detectors with which displacementsof less than 1500 8 have been measured, and (4) a system for measuring static magnetic susceptibility, which was usedto study the time dependenceof the Meissner effect in hollow tin cylinders. iii FOREWORD This is thefinal report on Contract NAS 2-2088 betweenStanford ResearchInstitute and the NASA-Ames ResearchCenter (SRI Project PHU- 5093).The research period covered 32 months,from 1 July1964 to 7 March 1967. Theprincipal investigator was Bascom S. Deaver , Jr. until Septem- ber 1965. William S. Goreethen was appointedprincipal investigator for theremaining 18 months of theproject. Other participants in the research program were T. W. Barbee, Jr., H. J. Bradley,F. Chilton, V. W. Hesterman, and J. Swedlund. V CONTENTS I INTRODUCTION AND SUMMARY 1 I1 UNIQUE PROPERTIESOF SUPERCONDUCTORS 3 A. Zero Resistance 3 B. Meissner Effect 3 C. Fluxoid Quantization 4 D. Supercurrent Tunneling 5 I11 SUPERCONDUCTING MAGNETICSHIELD 8 IV THERMALLY-FLUSHED JXAD SUPERCONDUCTING SHIELD 1.3 v MEISSNER-EFFECT MAGNETOMETER 16 A.Construction 18 B. Experiments and Results 19 VI QUANTIZED-FLUX MAGNETOMETER 28 VI I OPTICAL HEATING EXPERIMENTS WITH A QUANTIZED-FLUX MODULATOR32 VI1 I APPLICATIONS OF THE dc JOSEPHSON EFFECT 35 IX CONCLUSIONS AND RECOMMENDATIONS 42 A. Magnetic Shield 42 B. Meissner-Effect and Quantized-Flux Magnetometers 42 C. Josephson Junction Devices 46 AppendixA - MAGNETOMETER CIRCUIT ANALYSIS 47 Appendix B - CALCULATIONS OF SKIN DEPTH AND THERMAL RELAXATION FOR SUPERCONDUCTINGTIME FORMODULATORS 58 References 61 vii ILLUSTRATIONS 1 Idealized Critical Tunneling Current versus Magnetic Field for a Double Josephson Junction Interferometer 7 2 Superconducting Magnetic Shield Assembly 9 3 Attenuation of Axial Magnetic Fieldby Superconducting Field 12 4 Thermally-Flushed Superconducting Shield 14 5 Basic Superconducting Magnetometer Circuit 16 6 Meissner-Eff'ect Modulator Construction 18 7 Fixture for Casting Mcissner-Effect Modulators 20 a Noise in Output from Meissner-Effect Magnetometer Mounted in Liquid Helium Bath 22 9 Noise in Output from Meissner-Effect Magnetometer Mounted in Helium Exchange Gas 22 10 Meissner-Effect Modulator Mounted in the 16.5-cm-Diameter Superconducting Shield 24 11 Magnetometer Sensitivity versus Transverse Magnetic Field 25 12 Modulation Efficiency versus Operating Frequencyfor a Meissner-Effect Modulator 26 13 Output Signal from Meissner-Effect Magnetometerfor Square- Wave Heating 27 14 Response of Superconducting Circuit 29 15 Quantized-Flux Magnetometer Circuit 30 16 Quantized-Flux Magnetometer Response 31 17 Optical Modulation Apparatusfor a Quantized-Flux Modulator 33 18 Construction of a Slug Type Josephson Junction 36 19 Josephson Junction Magnetometer 37 20 Josephson Junction Magnetic Gradiometer 38 21 Josephson Junction Displacement Indicator 39 22 Superconducting Transition of a Meissner Modulator 41 viii ILLUSTRATIONS 23 Proposed Design for a SuperconductingMagnetic Shield 43 24 Cooling of the Melssner-Effect Magnetometer from the Inside Out 45 A-l Equivalent Circuit of the Modulated Inductance Superconducting Magnetometer 48 A-2 Reduction of EquivalentCircuit for Analysis 48 A-3 Transformer Primary Inductance versus Coupling Cocfficient for Maximum Output 54 ix I INTRODUCTION AND SUMMARY The general objectiveof the researchprogram described in this report was to investigate the application of unique the properties of superconductors to instruments. The program had three specific objec- tives: (1) the construction of a superconducting magnetic shield with room temperature access. and the useof this shield for long term stabil- ity tests of theAmes flux gate magnetometer, (2) the investigation of the use of superconducting Meissner-effect circuitsas absolute reading magnetometers for measuring magnetic fields as low as G, (3) the investigation of the use of superconducting quantized-flux circuits to measure magnetic fields or field changes as small as G. These objectives were met as follows: 1. A cylindrical superconducting shieldwas constructed that was 16.5 cm ID by 91.5 cm long with an 8-em-diameter room temperature access coaxial with the shield. Magnetic fields transverseand parallel to the shield axis could be reduced to less than G at the center of the shield and maintained stable as long as the shield was superconducting. The longest test ofthe shield lasted about six days.During this experi- ment,twoAmes flux gatewere tested for long term stability. 2. The linear field-versus-output voltage of Meissner-type modula- tors was used asan absolute magnetometer with sensitivitiesas good as 2 x G. Studies were made of the signal-to-noise ratio as a function of applied magnetic field parallel and perpendicular to the modulator axis; operating frequency; ambient temperature at the modulator; and thermal environment, i.e., the effect of dif’ferentthermal contact between the modulator and the liquidhelium bath. 3. Numerous quantized-flux circuits were constructed and tested. The best of these was usedto detect magnetic field changes assmall as 5 x G. This work was reported in detail in Midterm Report - October 1965 and in a published paper.4 We also studied Josephson tunneling junctions of the type described by Clarke,’ and constructed magnetometersand magnetic gradiometers using the direct current characteristics of thesedevices. A cylindrical cavity was built to study the alternating current characteristicsof the Clarke- type Josephson junction, although time did not permit completionof this stud y . *References are listed at the end of this report. 1 Progress on this research contract was reportedin informal reports to WSA-Ames: 0 August 23, 1965: an interim report covering the long term stability test of two NASA-Ames flux gate magnetometers.6 0 October 1965: a smary of progress madeduring the first lk months of the contractperi~d.~ This report is very detailed and may be considered to supersedeall previous reports except the August 1965 interim report discussedabove. Further results of research performed under this contract were reported in a paper published in The Review of Scientific Instruments.* This paper describesall of the work performed on the rotating supercon- ducting shield and thequantized-flux magnetometers except for the optical heating experiments, which are presentedin Section VI1 of this report. The research effort duringthe last 14 months of the contract has been devoted primarilyto the study of Meissner-effect magnetometers. However, other very interesting programs have received significantatten- tion. The research program during this14-month period can be categorized as fol.lows: 1. Meissner-effect magnetometer. 2. Optical heating experiments with a quantized-flux modulator. 3. Josephson junctions, Clarke slug type. 4. Thermally-flushed lead superconducting shield. These four topics, plus the magnetic shield and quantized-fluxthe magnetometer, are discussed in separate sections of this report. A des- cription of the Meissner-effect magnetometer and our applications theof dc Josephson effectis given also in Reference 8. The next section of this report presents the unique propertiesof superconductors that are applicableto this research program. The order of presentation in the following sections(I11 through VIII) is the chron- ological order ofthe discovery of the property most directly relatedto the application. Thus we describe the superconducting magnetic shields in Sections I11 and IV (zero resistance- 1911), the Meissner magnetometer in Section V (Meissner effect- 1933),
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