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This paper discusses flux jumps, using solid-state physics. The forces on the outermost leptons due to the current flowing through the metal are small compared with the forces in the interatomic environment. The processing of NbTi used in superconducting cables creates defects that pin magnetic flux lines. If one of these pinning sites lets its flux line go, it starts a positive feedback event known as ''flux jump''. The heat generated can be conducted away before the material goes normal if the superconductor has large enough surface area, hence the multifilamentary composite wires. (DLC)

Previous measurements1 of the positive ion mobility in liquid 3He below 1°K indicated the existence of a minimum with temperature; however, scatter and a hysteresis phenomena prevented a clear conclusion. A better measurement of this mobility is relevant as it should provide information on the structure of the positive ion in liquid He, a structure that is now under closer examination. Recent measurements by Johnson and Glaberson2 revealed the effect of various impurity ions on the mobility of these structures. According to the classical snowball model of Atkins,3 the minimum with temperature mentioned above is expected near 0.3°K as a consequence of the well-known minimum in the melting curve of 3He. In this work we suggest that the shape of the mobility minimum is related to the layered model proposed by Johnson and Glaberson.2

The design and performance of a prototype detector with two 60 cm diameter superconducting loops is presented. During one month of data-taking, no candidate events are observed and an upper limit on the flux of cosmic ray magnetic monopoles Fm ≲ 6.9 × 10−11 cm−2 s−1 sr−1 is set. This exposure corresponds to 21 times the original exposure of Cabrera.1 The detector demonstrates the possibility of large, high-ambient-field inductive detectors.

Heat leak measurements of superconducting magnet suspension systems, and multi-layer insulation (MLI) systems are important for the optimum design of magnet cryostats. For this purpose, a versatile cryogenic test facility was developed having a functional end in which test components of differing geometrical configurations could be installed and evaluated.

This paper describes the system used to acquire cryogenic data for the testing of SSC magnets at the Fermilab Magnet Test Facility. An array of pressure transducers, resistance thermometers, vapor pressure thermometers, and signal conditioning circuits are used Readings with time resolution appropriate for quench recording are obtained with a waveform digitizer and steady-state measurements are obtained with higher accuracy using a digital voltmeter. The waveform digitizer is clocked at a 400 Hz sampling rate and these readings are stored in local ring buffers. The system is modular and can be expanded to add more channels. The software for the acquisition, control, logging, and display of cryogenic data consist of two programs which run as separate tasks. These programs (as well as a third program which acquires quench and magnetic data) communicate and pass data using shared global resources. The acquired data are available for analysis via a nationwide DECnetα network.

We present the design and performance of a superconducting induction magnetic-monopole detector with 1.1-m-diameter gradiometer loops. The detector demonstrates that gradiometers can be overlapped with no mutual inductance to yield high redundancy without increasing shield volume. One of two detector units was sensitive to the passage of monopoles through two overlapped gradiometers with 98% coincidence efficiency for 161 hours. The unit has a coincident sensitive area averaged over 4\ensuremath{\pi} sr of 4400 ${\mathrm{cm}}^{2}$. No candidate events were observed, setting an upper limit on the flux of cosmic-ray magnetic monopoles of f\ensuremath{\lesssim}7.1\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}11}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ ${\mathrm{sr}}^{\mathrm{\ensuremath{-}}1}$ ${\mathrm{sec}}^{\mathrm{\ensuremath{-}}1}$ (90% C.L.). The detector was operated in ambient magnetic fields of \ensuremath{\sim}5--125 mG.

Correction of the magnetization sextupole and decapole fields with strips of superconductor placed just inside the coil winding is discussed. Calculations have been carried out for such a scheme, and tests have been conducted on a 4 cm aperture magnet. The calculated sextupole correction at the injection excitation of 330 A, 5% of full field, was expected to be 77% effective, while the measured correction is 83%, thus suggesting the scheme may be useful for future accelerators such as SSC and LHC.

Eight 5-cm-aperture, 15-m-long dipole magnet prototypes have been produced and cold-tested at Brookhaven National Laboratory (BNL) and Fermi National Accelerator Laboratory (FNAL) under contract with the Superconducting Super Collider Laboratory (SSCL). These magnets are the last phase of an R&D program aimed at demonstrating the feasibility of the 5-cm-aperture designs developed by BNL and FNAL. They are also used as vehicles to transfer technology from the National Laboratories to the collider dipole magnet contractors. The BNL magnets, which rely on an horizontally-split yoke, and the FNAL magnets, which rely on a vertically-split yoke, perform according to their somewhat different mechanical designs and have equally successful quench performance.

This paper reports results of field quality measurements of the initial 15 m-long, 50 mm-aperture SSC Collider dipoles tested at Brookhaven National Laboratory and Fermi National Laboratory. These data include multipole coefficients and the dipole angle at room temperature and 4.35 K, 4.35 K integral field measurements, and time-dependent effects. Systematic uncertainties are also discussed.

Overlap of betatron tune frequencies with the power supply noise spectrum can cause transverse beam emittance growth in a storage ring. This effect has been studied for tunes near the integer, where the betatron frequency is low. By injecting noise onto the main power supply bus, it was determined that common mode noise was the dominant source of emittance growth. A noise suppression feedback loop was used to reduce the noise and the emittance growth. These experiments are described, as are investigations of the common mode propagation along with the Tevatron bus and measurements of the fields generated by common mode excitation of isolated Tevatron magnets. >

Magnet Design B for the Superconducting Super Collider (SSC) consists of a 5 cm diameter collared coil assembly 12 m long with concentric aluminum thermal shields at 10 K and 80 K, a G-10 post type support system and a minimal iron vacuum vessel located at a large radius from the coil. In order to determine the behavior of such a magnet under both direct current and quenching conditions, a 6 m model was built using Tevatron tooling to produce a 7.6 cm diameter coil. The dc operation demonstrated that the post type suspension has acceptable rigidity. Distortions in the aluminum thermal shield during quench resulted from stresses in the material below the yield values. Temperature increases in the thermal shield due to eddy currents were larger than those calculated using simple assumptions, demonstrating the value of using a model to verify eddy current behavior in complex situations.

A 40-mm-aperture, 17-m-long Superconducting Super Collider (SSC) model dipole was assembled at Brookhaven National Laboratory (BNL) and tested initially at Fermi National Accelerator Lab (FNAL) and later at BNL. At BNL an extended cycle test was devised to examine the magnet’s performance through numerous cold tests and thermal cycles. This paper discusses the magnet’s mechanical and quench performance and magnet field measurements during the tests.

Results are presented from tests of the first full length prototype SSC dipole magnet. The cryogenic behavior of the magnet during a slow cooldown to 4.5K and a slow warmup to room temperature has been measured. Magnetic field quality was measured at currents up to 2000 A. Averaged over the body field all harmonics with the exception of b 2 and b 8 are at or within the tolerances specified by the SSC Central Design Group. (The values of b 2 and b 8 result from known design and construction defects which will be corrected in later magnets.) Using an NMR probe the average body field strength is measured to be 10.283 G/A with point to point variations on the order of one part in 1000. Data are presented on quench behavior of the magnet up to 3500 A (approximately 55% of full field) including longitudinal and transverse velocities for the first 250 msec of the quench.

New ideas are being developed to cool muon beams for colliders, neutrino factories, and muon experiments. Analytical and simulation studies have confirmed that a six-dimensional (6D) cooling channel based on helical magnets surrounding RF cavities filled with dense hydrogen gas can be used to achieve very small emittances. This helical cooling channel (HCC) has solenoidal, helical dipole, and helical quadrupole magnetic fields to generate emittance exchange and achieve 6D emittance reduction of over 3 orders of magnitude in a 100 m segment. Three such sequential HCC segments, where the RF frequencies are increased and transverse dimensions reduced as the beams become cooler, implies a 6D emittance reduction of almost six orders of magnitude. Two new post-cooling ideas then can be employed to reduce transverse emittances to one or two mm-mr, which allows high luminosity with fewer muons than previously imagined. We describe the new post-cooling ideas as well as a new precooling idea based on a HCC with z -dependent fields that can be used as an exceptional 6D cooling demonstration experiment.

''Spool Piece'' is the name given to the modular component of the Energy Saver which contains the correction magnets and several other devices required by the superconductive and cryogenic nature of this synchrotron. Approximately 230 spool pieces will be built to go along with 774 dipoles and 224 quadrupoles. To this date four have been built and the plans for a production rate of five per week are being implemented. 5 refs.

We have determined the thermal expansion of liquid 4He from 0.1 to 0.7 K by comparing the temperature dependence of the constant-density and the constant-pressure sound velocities. The agreement with the theoretical phonon contribution is very good.

Construction of a thermal feedthrough which is useful at ultralow temperatures and high magnetic fields is described. The thermal link consists of several thousand small diameter copper wires which are capable of making good thermal contact to liquid helium while minimizing the effects of eddy current heating.

The negative-ion mobility in liquid $^{3}\mathrm{He}$ has been determined in the range 17-300 mK. The pressure dependence of the mobility up to 2 atm was also studied.

In order to seal off an experimental cell containing liquid He at temperatures down to 20 mK and at pressures up to 25 atm we have developed a valve that is actuated hydraulically by liquid He and which seals repeatedly with a leak rate of less than 10−10 cm3/sec of liquid He II.

The simultaneous existence of two different ring velocities observed in dilute 3 He- 4 He solutions below 45 mK can be interpreted as evidence for the existence of rings with different quanta of circulation or a resonance in the ring- 3 He scattering cross section.