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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.

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 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...

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.

Several superconducting TM010 mode Nb cavities at 8.6 GHz with high measured unloaded Q's and fields were made using commercial reactor‐grade Nb, practical fabrication techniques, and practical processing techniques. The cavities were fabricated by machining the cavities in two parts from a solid billet of Nb and then joining the two parts with electron‐beam welding. The cavities were processed primarily by using ultra‐high‐vacuum firing (1750–2100 °C) and chemical polishing. Unloaded Q's as high as 1011 were measured at low field levels, and surface fields as high as 1080 Oe and 70 MV/m were obtained with unloaded Q's on the order of 1010.

A superconducting Nb TM010 mode cavity at 8.5 GHz machined from a single piece of reactor‐grade electron‐beam‐melted Nb to avoid joints had an unloaded Q (Q0) of 2 × 1010. After some degradation in the Q0, which took place as the microwave fields were increased, a high Q0 of 1 × 109 was obtained at a peak electric field on the cavity surface of 27 MV/m. These results were obtained by using ultrahigh‐vacuum firing and chemical polishing of the Nb cavity, and ultrahigh vacuum within the cavity during measurement. The high Q0 at high electric field demonstrates the usefulness of superconducting Nb cavities for devices such as linear particle accelerators and rf separators.