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This is the first of five connected papers detailing progress on the Gravity Probe B (GP-B) Relativity Mission. GP-B, launched 20 April 2004, is a landmark physics experiment in space to test two fundamental predictions of Einstein’s general relativity theory, the geodetic and frame-dragging effects, by means of cryogenic gyroscopes in Earth orbit. Data collection began 28 August 2004 and science operations were completed 29 September 2005. The data analysis has proven deeper than expected as a result of two mutually reinforcing complications in gyroscope performance: (1) a changing polhode path affecting the calibration of the gyroscope scale factor C g against the aberration of starlight and (2) two larger than expected manifestations of a Newtonian gyro torque due to patch potentials on the rotor and housing. In earlier papers, we reported two methods, ‘geometric’ and ‘algebraic’, for identifying and removing the first Newtonian effect (‘misalignment torque’), and also a preliminary method of treating the second (‘roll-polhode resonance torque’). Central to the progress in both torque modeling and C g determination has been an extended effort on “Trapped Flux Mapping” commenced in November 2006. A turning point came in August 2008 when it became possible to include a detailed history of the resonance torques into the computation. The East-West (frame-dragging) effect is now plainly visible in the processed data. The current statistical uncertainty from an analysis of 155 days of data is 5.4 marc-s/yr (∼14% of the predicted effect), though it must be emphasized that this is a preliminary result requiring rigorous investigation of systematics by methods discussed in the accompanying paper by Muhlfelder et al. A covariance analysis incorporating models of the patch effect torques indicates that a 3–5% determination of frame-dragging is possible with more complete, computationally intensive data analysis.

The Gravity Probe B experiment was developed to test two predictions of General Relativity; the Geodetic and the frame-dragging precessions of a mechanical gyroscope due to the gravitational field of the Earth. This space-based, cryogenic experiment was carried into orbit on 20 April 2004 atop a Boeing Delta II rocket. On-orbit operations consisted of 4.3 months of experiment setup, 11.6 months of science data collection, and 1.4 months of post-science calibrations. Analysis of the science data is now in progress, scheduled to complete in 2007.

We describe two space based gravitational physics experiments, the Gravity Probe B Relativity Mission (GPB) and the Satellite Test of the Equivalence Principle (STEP). GP-B will perform precision tests of two independent predictions of general relativity, the geodetic effect and frame dragging. STEP will provide a precision test of a foundation of general relativity, the Equivalence Principle.

Most of the Flight Payload hardware for the Gravity Probe B Relativity Mission is currently being manufactured. The design, fabrication, and integration of this hardware has already been subjected to an extensive program of full scale prototyping and testing in order to provide maximum assurance that the payload will meet all requirements. Full scale prototyping is considered to be a crucial aspect of the payload development because of the complexity of the payload, the stringency of its requirements, and the necessity for integration of a warm cryostat probe into a dewar maintained at liquid helium temperature. This latter requirement is derived from the fact that the dewar contains a superconducting ultralow magnetic field shield which provides an ambient magnetic field environment for the probe of

Gravity Probe B is an experiment to measure the geodetic and frame-dragging precessions, relative to the “fixed” “stars”, of a gyroscope placed in a 650 km altitude polar orbit about the earth. For Einstein's general relativity, the precessions are calculated to be 6.6 arcsec/yr for the geodetic precession and 0.042 arcsec/yr for the frame-dragging precession. The goal of the experiment is to measure these precessions to better than 0.01% and 1%, respectively. This paper gives an overview of the experiment and a discussion of the flight hardware development and its status. This paper also includes an estimate of the geodetic and frame-dragging errors expected for the experiment.

We report on progress in the development of free-falling moving test-masses for LISA and for the related technology demonstration mission. We present simple formulae to evaluate the performance of the device as a function of the various design parameters, and we compare them with preliminary experimental results from a test prototype we are developing. Quantitative agreement is found. Finally, we present a control law, along with a performance simulation, for low-frequency electrostatic suspension of the test-mass with minimal perturbation of the motion within the measuring frequency band.

The most demanding goal of the Gravity Probe B Relativity Mission (GP-B) is the measurement of the parametrized post-Newtonian parameter γ to one part in 105. This goal requires a total experimental accuracy of ≤ 0.044 marcsec/yr. Analysis of and results from 100,000 hours of gyroscope operation on the ground show that the residual Newtonian drift will be < 0.17 marcsec/yr for a supported gyroscope in 10−9 m/s2, and < 0.020 marcsec/yr for an unsupported gyroscope in a fully inertial orbit. The expected error due to gyroscope drift is thus consistent with the measurement goal. The main gyroscope disturbance caused by cosmic radiation is charging of the rotor. A force modulation technique allows measurement of the charge of the gyroscope rotor to about 5 pC, while bipolar charge control to 10 pC is achieved using electrons generated by UV photoemission.

Superconducting Cavity Stabilized Oscillators, SCSO, have produced the most stable clocks to date, achieving an Allen variance of 3×10−16 for integration times between 102 and 103 seconds. Cavity frequency variations are mainly caused by acceleration effects due to gravity and vibrations, temperature variations, and fluctuations in the energy stored in the cavity. We describe the status of a project aimed at building an improved cavity system suitable for use on the International Space Station, ISS. Primary experimental applications include the measurement, in conjunction with other types of clocks, of the dependence of fundamental constants on the gravitational potential, gravitational redshift measurements, and the measurement of the anisotropy of the velocity of light. A major secondary application is as a flywheel for the atomic clocks co-located on the ISS.

The NASA/Stanford Relativity Mission Gravity Probe B (GP-B) experiment will provide two extremely precise tests of General Relativity based on observations of electrically suspended gyroscopes in a satellite in a 650 km circular polar orbit around the Earth. The project is now nearing completion. Final assembly of the instrument will take place later this year and launch is scheduled for October 2000. GP-B will provide a very accurate measurement of the frame-dragging effect, with its subtle connections to gravitomagnetism and Mach's principle. In addition to measuring frame dragging to 0.3%, it will measure the geodetic effect to approximately 1 part in 105. GP-B is a controlled physics experiment where error terms such as the Newtonian drifts of gyroscopes are reduced to negligible values, and where the apparatus is under the experimenters' control.

The Gravity Probe B relativity mission experiment is designed to measure the frame dragging and geodetic relativistic precessions in a 650 km polar orbit. We describe some of the advanced experimental techniques used to achieve the required gyroscope accuracy of between 0.05 and . The subjects discussed are: (i) the development of high-precision gyroscopes with drift rates of less than , (ii) a low-temperature bake-out procedure resulting in a helium pressure of less than at 2.5 K, (iii) a read-out system using DC SQUID magnetometers with a noise figure of at 5 mHz and (iv) AC and DC magnetic shielding techniques which produce an AC attenuation factor in excess of and a residual DC field of less than .

Single-component and multilayer films of TiC, Ti and Cu have been produced by sputtering on fused quartz substrates and have been investigated for suitability as electrodes for the electrostatically suspended gyroscopes of Gravity Probe B. The main requirements for these films are low electron field emission in fields of 3 x 10 7 V m −1 , low film stress, and good thermal and electrical conductivity in the temperature range 2 K–400 K. The films have been studied using X-ray diffraction, scanning electron microscopy (SEM), Auger electron spectroscopy, Rutherford backscattering spectrometry, and four-point resistivity techniques. SEM measurements indicate that the TiC films have very smooth surfaces and that multilayer films of TiC, Ti and Cu have reduced roughness as compared with the Ti-Cu multilayer films. Seven-layer 2.5 μm thick Ti-Cu films have been successfully used in the Gravity Probe B gyroscopes, meeting all requirements. Multilayer films of TiC Ti and Cu are at present being tested with the expectation that they will further improve gyroscope performance.

Magnetic hysteresis loops were measured on thin Nb superconducting disks using a SQUID-based technique; field-dependent critical currents have been observed in thin superconducting disks at low magnetic flux trapping densities (⩽ 4 G). Such phenomena were found to exist over a wide range of temperatures below the transition temperature. The observed field-dependent critical current densities are attributed to long-range interactions between trapped vortices in a superconducting film whose thickness is much less than or comparable to the penetration depth. In the framework of Kim's critical state model, we developed a numerical method to calculate the field-dependent critical currents by fitting the measured magnetic hysteresis loops. Our experimental data were adequately explained by Kim's critical state model. Shielding currents and magnetic field patterns in thin superconducting disks were calculated.

The Gravity Probe B spacecraft was launched on 20 April 2004 to measure the geodetic and frame-dragging effects predicted by the theory of general relativity. A cryogenic optical telescope was used to establish the inertial reference frame for the measurements by tracking a reference or guide star. The motion of this star was independently checked by reference to background galaxies. With the mission now over, we describe the design, construction and evaluation of the optical and electrical performance of the telescope, comparing ground and flight results. We find that the pointing noise was sufficiently low to meet the mission requirements and in fair agreement with extrapolations from ground tests. Due to slight defocusing, the linear range of the telescope output was significantly wider than expected.

The Gravity Probe B (GP-B) gyroscope, a unique cryogenically operated mechanical sensor, was used on-orbit to independently test two predictions of general relativity (GR). Here, we describe the development and performance of the GP-B gyroscope, its geometry and fabrication, spin-up and vacuum approach, magnetic considerations, and static charge management. The history of electrically suspended gyroscopes puts the current work in context. Fabrication and ground testing of the GP-B gyroscope are detailed, followed by a review of on-orbit initialization, calibration, operation, and performance. We find that the performance was degraded relative to the mission goals, but was still sufficient to provide excellent new tests of GR. The degradation is partially due to the existence of gyroscope torques due to an unanticipated interaction between patch potentials on the rotor and the housing. We discuss these patch potentials and describe the effect of related torques on gyro drift. It was essential to include models for the effects due to the patch potentials in the complete data analysis model to yield determinations of the two GR effects.

The Gravity Probe B mission provided two new quantitative tests of Einstein's theory of gravity, general relativity (GR), by cryogenic gyroscopes in Earth's orbit. Data from four gyroscopes gave a geodetic drift-rate of −6601.8 ± 18.3 marc-s yr−1 and a frame-dragging of −37.2 ± 7.2 marc-s yr−1, to be compared with GR predictions of −6606.1 and −39.2 marc-s yr−1 (1 marc-s = 4.848 × 10−9 radians). The present paper introduces the science, engineering, data analysis, and heritage of Gravity Probe B, detailed in the accompanying 20 CQG papers.

Gravity Probe B (GP-B) was a cryogenic, space-based experiment testing the geodetic and frame-dragging predictions of Einstein's theory of general relativity (GR) by means of gyroscopes in Earth orbit. This first of three data analysis papers reviews the GR predictions and details the models that provide the framework for the relativity analysis. In the second paper we describe the flight data and their preprocessing. The third paper covers the algorithms and software tools that fit the preprocessed flight data to the models to give the experimental results published in Everitt et al (2011 Phys. Rev. Lett. 106 221101–4).

Spherical gyroscope rotors for a fundamental experiment to test two predictions of General Relativity Theory, geodetic precession and frame dragging, were manufactured out of fused quartz and single-crystal silicon. These rotors required a mass unbalance and asphericity of less than 25 nm (1 μin), a fractional difference in the moments of inertia of less than 10−5, and a diameter within 0.5 μm (20 μin) of a standard sphere with a diameter of 37.996 mm (1.4959 in). We describe the manufacturing process and the associated metrology.

The results of the Gravity Probe B relativity science mission published in Everitt et al (2011 Phys. Rev. Lett. 106 221101) required a rather sophisticated analysis of experimental data due to several unexpected complications discovered on-orbit. We give a detailed description of the Gravity Probe B data reduction. In the first paper (Silbergleit et al Class. Quantum Grav. 22 224018) we derived the measurement models, i.e., mathematical expressions for all the signals to analyze. In the third paper (Conklin et al Class. Quantum Grav. 22 224020) we explain the estimation algorithms and their program implementation, and discuss the experiment results obtained through data reduction. This paper deals with the science data preparation for the main analysis yielding the relativistic drift estimates.

Gravity Probe B, launched 20 April 2004, is a space experiment testing two fundamental predictions of Einstein's theory of general relativity (GR), the geodetic and frame-dragging effects, by means of cryogenic gyroscopes in Earth orbit. Data collection started 28 August 2004 and ended 14 August 2005. Analysis of the data from all four gyroscopes results in a geodetic drift rate of $\ensuremath{-}6601.8\ifmmode\pm\else\textpm\fi{}18.3\text{ }\text{ }\mathrm{mas}/\mathrm{yr}$ and a frame-dragging drift rate of $\ensuremath{-}37.2\ifmmode\pm\else\textpm\fi{}7.2\text{ }\text{ }\mathrm{mas}/\mathrm{yr}$, to be compared with the GR predictions of $\ensuremath{-}6606.1\text{ }\text{ }\mathrm{mas}/\mathrm{yr}$ and $\ensuremath{-}39.2\text{ }\text{ }\mathrm{mas}/\mathrm{yr}$, respectively (``mas'' is milliarcsecond; $1\text{ }\text{ }\mathrm{mas}=4.848\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\text{ }\text{ }\mathrm{rad}$).

Following the procedure of Mikheenko and Kuzovlev, we present analytical solutions of field and current patterns in thin film disk-shaped type-II superconductors in perpendicular time-varying periodic external magnetic fields. We also calculate the magnetic moment and effective susceptibility. The analysis is carried out within the framework of the critical state model assuming a constant critical current. Our results are compared to that of Mikheenko and Kuzovlev; and we discuss the discrepancies.

Multilayer Ti-Cu films with three, five, and seven individual layers have been prepared by sputtering on fused quartz substrates. The multilayer films have been studied by electron field emission, X-ray diffraction, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy. Trilayer Ti-Cu-Ti electrode films exhibit reduced electron field emission. Ti-Cu-Ti trilayer films have been applied to the Gravity Probe B gyroscope housings. The thin films have been deposited by sputtering onto the fused quartz housings to form suspension electrodes and lands. The gyroscopes have been successfully spun to 170 Hz.

The contribution of the Mattis-Bardeen theory to the understanding of the surface impedance of superconductors and normal conductors is reviewed. The early theoretical and experimental studies of the surface impedance of conductors are sketched to provide the context in which the Mattis-Bardeen theory and, independently, the Abrikosov-Gor'kov-Khalatnikov theory were developed. The Mattis-Bardeen theory is described along with the methods for numerical calculation of the surface impedance from their expression for the current density. Extensions to include the effects of anisotropy and strong coupling are briefly discussed. Theory is compared with representative measurements of the surface impedance, demonstrating excellent agreement in absolute magnitude and in the dependences on frequency, temperature, and material parameters.

NASA’s Gravity Probe B Mission is a test of two predictions of Einstein’s General Theory of Relativity based on observations on very precise cryogenic gyroscopes in a satellite in a 650 km polar orbit about the Earth. Construction and the first round of testing of the flight payload was completed in December 1999. Of the 32 planned qualification tests 28 were passed with complete success, meeting or in several instances surpassing the program requirements. However, one test very unexpectedly revealed a problem in the thermal performance of the Dewar/Probe system which has required a significant redesigin and rework, now successfully completed. Gravity Probe B is scheduled for launch on April 1, 2002. This article reviews from the physicist's viewpoint the experience of living through a space flight program.

The Gravity Probe B spacecraft was launched on April 20, 2004 to measure the geodetic and frame dragging effects predicted by the theory of general relativity. A cryogenic optical telescope is used to establish the inertial reference frame for the measurements by star tracking. With a year of flight data collected, we describe the initial evaluation of the optical performance of the telescope. We find that the pointing noise is sufficiently low to support the mission and in reasonable agreement with extrapolations from ground tests. Our results show that appropriately designed precision optics can be operated over the temperature range from 300 to 3.5 K with little degradation.

Gravity Probe-B (GP-B) is a space mission that was launched in April 2004 that is intended to measure the prediction by General Relativity Theory that a rotating gravitational field, namely the Earth's, "drags" the space-time continuum by a definite amount. GP-B utilizes a telescope with silicon photodiode detectors. Light from a distant reference frame, namely, a star designated as IM Peg, is used to reference the orbital motion of the spacecraft about the Earth and Sun to within 200 milliarcseconds at a frequency of 10 Hz. Fine angular control of the spacecraft orientation uses the signals from the telescope detectors during the 55 minute portion of the orbit during which the star is visible. The performance of the detectors and the control system's resultant pointing are discussed.

The Gravity Probe B Relativity Mission uses a fused-quartz optical star tracking telescope as the sensor for the control system which points the spacecraft towards its guide star. The telescope is cooled to

The International Space Station provides an ideal platform for high precision frequency measurements, both as applied to scientific experiments and as regards basic time metrology. Consequently, a variety of clocks are being developed for flight on the Space Station, a majority of which are atomic clocks with very good stability for time periods in excess of 1,000 seconds. We plan to significantly augment the scope and capability of the ensemble of space clocks by adding to it SUperconducting Microwave Oscillator, SUMO. SUMO is a space version of the superconducting cavity stabilized oscillator, SCSO; the most precise clock developed to date for the interval range of around 100seconds. Short descriptions are given of the SUMO project and the SCSO technology and the principal disturbances causing frequency fluctuations are outlined. The planned improvements to the SCSO and preliminary results of the development work for SUMO are also highlighted.

We have characterized the stress and its effects on surface morphology for multi-layer thin films of about 3μm total thickness, consisting of three or seven layers of Ti and Cu. These films constitute the electrostatic suspension electrodes for the gyroscope housings of the Relativity Mission Gravity Probe B. Full understanding of surface morphology is critical for meeting the complex requirements of this application.The residual stresses have been measured using a laser curvature technique, while the surface morphology was studied by scanning electron microscopy (SEM). We find that the surface morphology depends strongly on the stress, which evolves with the Ti-Cu multi-layer period. Average stress and the resulting surface roughness decrease for thinner Cu layers (increased total number of layers). Seven layer Ti-Cu films with low stress and very smooth surface have been successfully used for the electrodes of the gyroscope housings.

The principal reason for employing a superconducting linear electron accelerator is to increase the duty cycle from 10-3 to 10-4 of typical high-energy gradient, roomtemperature accelerators to unity without reduction of the energy gradient. The duty cycle is the fraction of the time that the electron beam is accelerated and is an important factor in the design of many nuclear experiments. The increased duty cycle is possible because the power loss in a superconducting accelerator structure is extremely small. Secondary reasons for employing such an accelerator, which follow from the unity duty cycle, are increased energy resolution and increased accelerated electron current.

Gravity probe B (GP-B) was designed to measure the geodetic and frame dragging precessions of gyroscopes in the near field of the Earth using a drag-free satellite in a 642 km polar orbit. Four electrostatically suspended cryogenic gyroscopes were designed to measure the precession of the local inertial frame of reference with a disturbance drift of about 0.1 marc sec/yr-0.2 marc sec/yr. A number of unexpected gyro disturbance effects were observed during the mission: spin-speed and polhode damping, misalignment and roll-polhode resonance torques, forces acting on the gyroscopes, and anomalies in the measurement of the gyro potentials. We show that all these effects except possibly polhode damping can be accounted for by electrostatic patch potentials on both the gyro rotors and the gyro housing suspension and ground-plane electrodes. We express the rotor and housing patch potentials as expansions in spherical harmonics Y(l,m)(θ,φ). Our analysis demonstrates that these disturbance effects are approximated by a power spectrum for the coefficients of the spherical harmonics of the form V(0)(2)/l(r) with V(0) ≈ 100 mV and r ≈ 1.7.

We have fabricated and tested two types of SQUIDs. The first, a low inductance stripline device, was characterized using a commercial dc SQUID as a following amplifier. The second type was well coupled to a 0.16µH input coil and was characterized and flux-locked using an ultralow noise room temperature preamplifier. We present device characterization and noise data for both types of devices.

The relativity mission, also known as gravity probe B (GP-B), uses high-precision electrostatically suspended cryogenic gyroscopes for measuring the relativistic precessions of the frame of reference in a 650 km polar orbit. A 2 K environment is used to ensure the thermal stability and to implement the readout technique based on the magnetic dipole moment generated by a rotating superconductor. Analysis and results from more than 100 000 h of gyroscope operation show that the residual Newtonian drift is less than 0.17 marcsec/yr for a supported gyroscope in 10 −9 m/s 2 , and less than 0.020 marcsec/yr for a gyroscope in a fully inertial orbit.

Gravity Probe B (GP-B) is a landmark physics experiment in space designed to yield precise tests of two fundamental predictions of Einstein's theory of general relativity, the geodetic and frame-dragging effects, by means of cryogenic gyroscopes in Earth orbit. Launched on 20 April 2004, data collection began on 28 August 2004 and science operations were completed on 29 September 2005 upon liquid helium depletion. During the course of the experiment, two unexpected and mutually-reinforcing complications were discovered: (1) larger than expected 'misalignment' torques on the gyroscopes producing classical drifts larger than the relativity effects under study and (2) a damped polhode oscillation that complicated the calibration of the instrument's scale factor against the aberration of starlight. Steady progress through 2006 and 2007 established the methods for treating both problems; in particular, an extended effort from January 2007 on 'trapped flux mapping' led in August 2007 to a dramatic breakthrough, resulting in a factor of ~20 reduction in data scatter. This paper reports results up to November 2007. Detailed investigation of a central 85-day segment of the data has yielded robust measurements of both relativity effects. Expansion to the complete science data set, along with anticipated improvements in modeling and in the treatment of systematic errors may be expected to yield a 3–6% determination of the frame-dragging effect.

Techniques based on superconductivity are crucial in providing the means of achieving the high accuracy and low noise required by experimental tests of gravitational theories. We discuss applications of superconductivity to two space-based experiments: the Gravity Probe B Relativity Mission (GP-B), and the Satellite Test of the Equivalence Principle (STEP). Superconducting shields attenuate the dc magnetic field to less than 10−11 T and provide an ac shielding factor in excess of 1012. The readout of the GP-B gyroscopes is based on the London magnetic dipole generated by a rotating superconductor and detected with state-of-the-art dc SQUIDs, which are also used in STEP.

We report measurements of flux distributions on superconducting spherical shells in an ambient magnetic field of 0.2±0.1 μG. The aim of these experiments is to minimize the number of flux lines trapped in the superconducting shells, an important requirement for the Gravity Probe B gyroscopes.

We propose to perform a null-gravitational redshift experiment by comparing a mechanical gyroscope clock with atomic clocks. The Gravity-Probe-B Relativity Gyroscope Experiment provides the opportunity for this co-experiment. The goal is to measure the effect to an accuracy of 0.01% of the gravitational redshift due to the eccentricity of the orbit of the earth about the sun. This corresponds to an integrated frequency measurement over one year of Av/v=3∗10−14. A major disturbance torque on the gyroscope is due to fluctuations in the molecular drag of the residual gas caused by temperature variations. We propose to use a low temperature bake-out technique in order to achieve the required vacuum of 10−17torr.

A test of the Einstein equivalence principle (EEP) was performed by carrying out a 'null' gravitational red-shift experiment. The experiment compared the rates of a pair of hydrogen maser clocks with those of a set of three superconducting-cavity stabilized oscillator clocks as a function of the solar gravitational potential. If EEP were not valid, the relative rates could vary with potential. During the experiment, the solar potential in the laboratory varied approximately linearly at 3 parts in 10 to the 12th per day because of the earth's orbital motion, and diurnally with an amplitude of 3 parts in 10 to the 13th because of the earth's rotation. An upper limit on the relative frequency variation of 1.7 parts in 100 of the external potential was set. The accuracy was limited by the frequency stability of the clocks and by unmodeled environmental effects. The result is consistent with the EEP at the 2 percent level. The experiment can also be viewed as setting a limit on a possible spatial variation of the fine-structure constant.

The Gravity-Probe-B relativity gyroscope experiment (GP-B) will measure the geodetic and frame-dragging precession rates of gyroscopes in a 650 km high polar orbit about the earth. The goal is to measure these two effects, which are predicted by Einstein's General Theory of Relativity, to 0.01 percent (geodetic) and 1 percent (frame-dragging). This paper presents the development progress for full-size prototype flight hardware including the gyroscopes, gyro readout and magnetic shielding system, and an integrated ground test instrument.

Measurements of the x radiation and the electron loading in a niobium cavity resonant in the TM010 mode at 1208 MHz have been made in order to study enhanced electron field emission in superconducting cavities. Measurements have also been made of the low‐temperature dc electron field emission from bismuth, niobium, copper, and tungsten utilizing a configuration which approximates the point‐to‐plane geometry. In the rf cavity measurements, it is found that the x‐radiation count rate data follow a modified Fowler‐Nordheim equation, which takes into account the time‐dependent rf fields, the electron dynamics in the rf fields, the emission of secondary electrons, and the production and absorption of x radiation. Further, it is found that the x radiation from the cavity can be reduced by a factor of 104−106 by helium‐ion sputter processing at low temperature. From x‐radiation data and electron loading data interpreted with the modified Fowler‐Nordheim equation, it has been shown that, after helium‐ion sputter ...

The fabrication, processing, and measurement of two S-band niobium prototype electron accelerator structures are discussed. Maximum surface magnetic fields were typically between 250 and 550 Oe, corresponding to average energy gradients between 4.6 and 6.5 MeV/m, with Q0 values typically greater than 5 × 109. The structures which were electropolished gave more reproducible results than those which were chemically polished.

The unloaded Q's of pure Nb cavities in the TE011 mode at 11.2 GHz and in the TM010 mode at 8.4 GHz were measured between 1.2° and 4.2°K to determine whether the residual surface losses in Nb could be made sufficiently low to make it a useful material for practical microwave devices. Three forms of reactor grade Nb were evaluated: recrystallized fully wrought, arc melted, and electron‐beam melted. Each of these materials was subjected to additional metallurgical processing including high‐temperature vacuum firing and polishing to determine their effects on surface losses. In the TE011 mode, a residual Q of 3.8×1010 was achieved. Also in the TE011 mode, the unloaded Q was observed to be essentially a constant up to the ac critical magnetic field Hcae, where it abruptly decreased by a factor of 100 or more. An Hcae as large as 436 Oe was observed for unstrained Nb. In the TM010 mode, which has electric fields terminating on the surface of the Nb, a residual Q of 2×109 was achieved, the limitation on the max...

The object of this paper is to identify the many low temperature aspects of a cryogenic accelerator and to indicate how these are related to the operating characteristics which might ultimately be achieved.

A computer program which simulates the multiplications of electrons in cavities using Monte Carlo techniques has been developed. This electron multiplication program has provided an understanding of the x-ray energy spectrum produced by cavities and of x-ray photographs taken of cavities at high fields. Also, this simulation has predicted two new effects: (1) an electron avalanche multiplication effect which is non-resonant in nature (as opposed to the well known resonant electron multi-pactoring), and (2) electrons produced in this way tend to form a low energy (on the order of 10 eV) electron cloud near the cavity major diameter.

Electron multipacting in a 2.8‐GHz TM010‐mode anodized niobium test cavity at 1.4 K has been studied experimentally. An electron multipactor simulation computer program, which we developed, successfully calculates the multipactor field levels and multipactor location observed experimentally and also provides additional details of the multipactor phenomena. With the multipactor simulation program, a sharp‐cornered TM010‐mode cavity has been designed in which multipacting is greatly reduced. A subsequent experiment on such a sharp‐cornered anodized niobium cavity has shown that electron multipacting is in fact eliminated for this cavity up through the highest field achieved. This work has shown that, with a simple modification in geometry, multipacting can probably be eliminated in the superconducting structure for the Stanford electron accelerator.

The design, manufacture, and performance of several 6‐m‐long 1300‐MHz superconducting niobium accelerator structures, which are part of the Stanford superconducting accelerator, are briefly described. In these standing‐wave accelerator structures, we have achieved cw energy gradients as high as 3.8 MeV/m and unloaded Q's as high as 6.9×109 measured at 3.0 MeV/m and 1.9 K. In addition, electron‐beam currents up to 5000 μA have been accelerated through the structure without exciting beam‐breakup modes.