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The article presents the results of the study the ability of four not studied strains of enterococci (E. durans, SB6, E. faecium SB12, E. durans SB18, E. durans SB20), which were isolated from the Carpathian brynza, to reduce the acidity of medium of cultivation, the rate of biomass accumulation and the ability to exhibit antagonistic properties to the opportunistic microflora. Lactic acid and minor compounds are producing in a result of lactose fermentation, which form the specific taste and aroma properties of the product. The activity of acid formation has crucial because it directly connected with the coagulation of proteins and the prevention of the growing of extraneous microflora. Therefore, the rate of acidity increasing of the medium is one of the most important characteristics in selection of strains of lactic acid bacteria for the manufacture of dairy products. High growth rate, resistance to the contamination of extraneous microflora and preservation of their properties in the finished product are the technological properties of the strains. The inhibition of the growth of pathogenic cultures of microorganisms is the main probiotic functions of beneficial bacteria namely antagonistic activity. It was found, that the strain E. durans SB20 manifested the highest ability to increase the acidity of the medium under the cultivation for 24 hours at 37 °C as it reduced the pH on 30.3 %, and the strain E. durans SB18 increased the acidity on 29.9 %. Under 48 hours strains E. durans SB20 and SB18 increased the acidity on 31.1 and 30.5 % (P< 0.001) respectively compared with the control. The growth rate of stains E. durans SB20 and E. durans SB18 were in 18,0 and 17,6 times higher than in control under the cultivation for 24 hours at 37 °C, the optical density were in 18.3 and 18.2 times higher respectively than in the control sample under the cultivation for 48 hours at the same temperature. Furthermore, strains of enterococci showed antagonistic properties against conditionally pathogenic cultures of microorganisms on 24 and 48 hour of cultivation. In addition, it was found that with an increasing temperature of the antagonistic activity of the strains cultivation increased. Obviously, it was connected that more biologically active substances and microbial secondary metabolites are formed under the longer cultivation and higher temperatures. In particular on 48 hours at 37 °C almost of all the tested strains showed moderate antagonistic activity against E. coli, S. enteritidis, E. aerogenes, P. mirabilis and P. aeruginosa. However, all four strains didn`t have antagonistic activity against the test-strain S. aureus.

Microscopic images of the surfaces of metallic electrodes used in high-pressure gas-filled 805 MHz RF cavity experiments1 have been used to investigate the mechanism of RF breakdown.2 The images show evidence for melting and boiling in small regions of ~10 micron diameter on tungsten, molybdenum, and beryllium electrode surfaces. In these experiments, the dense hydrogen gas in the cavity prevents electrons or ions from being accelerated to high enough energy to participate in the breakdown process so that the only important variables are the fields and the metallic surfaces. The distributions of breakdown remnants on the electrode surfaces are compared to the maximum surface gradient E predicted by an ANSYS model of the cavity. The local surface density of spark remnants, proportional to the probability of breakdown, shows a strong exponential dependence on the maximum gradient, which is reminiscent of Fowler-Nordheim behavior of electron emission from a cold cathode. New simulation results have shown good agreement with the breakdown behavior of the hydrogen gas in the Paschen region and have suggested improved behavior with the addition of trace dopants such as SF 6.3 Present efforts are to extend the computer model to include electrode breakdown phenomena and to use scanning tunneling microscopy to search for work function differences between the conditioned and unconditioned parts of the electrodes.

An 800 MHz RF test cell filled with high pressure gaseous hydrogen was used to study RF breakdown phenomena in hydrogen and helium gases as a function of pressure and temperature. The maximum achieved RF surface gradient was 80 MV/m at 1.83 MPa and 77 K, where the breakdown of the molybdenum electrodes of the test cell limited the study of the linear dependence of the breakdown voltage on gas density known as Paschen's Law. The test cell conditioning was also much faster in gas than in vacuum cavities. The high gradient and fast conditioning are encouraging results for the use of high-pressure RF cavities for ionization cooling of muon beams for muon colliders, neutrino factories, and intense sources.

Eighteen 5-cm-aperture, 15-m-long Superconducting Super Collider (SSC) dipole magnet prototypes have been produced and cold tested. On each prototype, the dependence of harmonic field coefficients on magnetic current was measured as part of a study of the magnetic field quality. For most of the magnets, the observed behavior conforms to what can be expected from the effects of persistent magnetization currents and iron yoke saturation. A few prototypes, however, exhibited anomalies during current ramp at 4 A/s which can be attributed to large cable eddy currents. >

Tests have recently been performed at Fermilab in order to measure the energy losses due to eddy currents and iron and superconductor magnetization. These measurements were performed on six 1.5-m-long model magnets and eight 15-m-long full-scale collider dipole magnets. AC losses were measured as a function of ramp rate using sawtooth ramps from 500 to 5000 A for both types of magnets, while bipolar studies were additionally performed on some of the short magnets. The measured magnet voltage and current for a complete cycle were digitally integrated to yield the energy loss per cycle. Measurement reproducibility was typically 5%, with good agreement between long magnet measurements and extrapolations from short magnet measurement results. Magnetization loss measurements among similar magnet types agree to within experimental error, while eddy current losses correlate strongly with the observed dependence of quench current on ramp rate. >

The authors summarize the mechanical performance of the most recent 5-cm-aperture, 15-m-long SSC dipole magnet prototypes. The magnets were produced at Brookhaven National Laboratory (BNL) and Fermi National Accelerator Laboratory (FNAL) under contract with the Superconducting Super Collider Laboratory (SSCL). The BNL magnets rely on a horizontally split yoke with collared ends, while the FNAL magnets rely on a vertically split yoke with collet-style end clamps. Magnets of both designs are equipped with strain gauges enabling measurement of the azimuthal pressures exerted by the coils against the collar poles as well as the axial forces transmitted from the coil ends to the end plates. A comparison of the mechanical behaviors measured by the strain gauges is presented. How the behavior of the 5-cm-aperture magnets compares to that of the 4-cm-aperture prototypes is also discussed. >

The quench performance and ramp rate sensitivity of 18 5-cm-aperture, 15-m-long Superconducting Super Collider (SSC) dipole magnet prototypes are discussed. All the magnets appear to reach a quench plateau near their extrapolated short sample current limit and well in excess of the operating current with very little training. Most of the magnets, however, exhibit a dramatic degradation of their quench current as a function of ramp rate, which, for the most part, can be attributed to large cable eddy currents. >

Several 40-mm-aperture, 17-m-long dipoles have been built by Fermilab as developmental prototypes for the Superconducting Super Collider (SSC). These magnets have an external inner-outer coil splice design, a collet style end clamp assembly, a new, analytically designed minimum stress coil end design, and a new insulation system which does not employ shims or 'shoes'. In addition, the magnets were built using production-style tooling. The magnets were tested at the Fermilab Magnet Testing Facility. Quench testing and mechanical measurement results are presented and analyzed with emphasis on the new design and fabrication features of these magnets. The performance of these magnets was very good from a quench and mechanical behavior standpoint. The magnets did not exhibit excessive training behavior and only one training quench was below the nominal operating current. The coil prestress remained positive to >7 T in both magnets and most of the quenches originated in the high field region of the pole turn. >

Magnetic field measurements have been made on twelve 17-m-long, 40-mm-aperture R&D superconducting dipoles. Data on dipole field strength, multipole coefficients, and alignment have been obtained. The data indicate that the magnets as built are generally within the expectations for this design. >

Eleven 17-m-long, 40-mm-aperture SSC (Superconducting Super Collider) R&D superconducting collider dipole magnets, built at BNL (Brookhaven National Laboratory), have been extensively tested at BNL and Fermilab during 1990-1. Quench performance of these magnets and details of their mechanical behavior are presented. Although the quench performance of the most recent magnets shows slightly more quenches than expected, there is now a better understanding of the mechanical behavior of these magnets. The baseline design leads to reasonable quench performance. The quench performance of the DC series magnets seems to indicate a strong sensitivity to change in design parameters, key among them being the collar-yoke interference and the coil end loading. >

The ability of high temperature superconducting (HTS) conductor to carry high currents at low temperatures makes feasible the development of very high field magnets for uses in accelerators and beam-lines. A specific application of a very high field solenoid is to provide a very small beta region for the final cooling stages for a muon collider. Since ionization cooling in a solenoid acts simultaneously on both transverse planes, any improvement in maximum field has a quadratic consequence in the reduction of the 6-dimensional (6D) beam emittance. This paper describes a conceptual design of a 45 Tesla solenoid based on Bi-2223 HTS tape, where the magnet will be operated at 4.2 K to take advantage of the high current carrying capacity at that temperature. In this design, an outer Nb3Sn shell surrounds the HTS solenoid. This paper describes the technical issues associated with building this magnet. In particular it addresses how to mitigate the large Lorentz stresses associated with the high field magnet and how to design the magnet to reduce the compressive end forces. Also this paper discusses the important issue of how to protect this magnet if a quench should occur.

Most ionization cooling schemes now under consideration are based on using many large flasks of liquid hydrogen energy absorber. One important example is the proposed Muon Ionization Cooling Experiment (MICE), which has recently been approved to run at the Rutherford Appleton Laboratory (RAL). In the work reported here, a potential muon cooling demonstration experiment based on a continuous liquid energy absorber in a helical cooling channel (HCC) is discussed. The original HCC used a gaseous energy absorber for the engineering advantage of combining the energy absorption and RF energy regeneration in hydrogen-filled RF cavities. In the Muon And Neutrino eXperiment (MANX) that is proposed here, a liquid-filled HCC is used without RF energy regeneration to achieve the largest possible cooling rate in six dimensions. In this case, the magnetic fields of the HCC must diminish as the muons lose momentum as they pass through the liquid energy absorber. The length of the MANX device is determined by the maximum momentum of the muon test beam and the maximum practical field that can be sustained at the magnet coils. We have studied a 3 meter-long HCC example that could be inserted between the MICE spectrometers at RAL.

Ionization cooling, a method for shrinking the size of a muon beam, requires a low Z energy absorber, high-field magnets, and high gradient RF. We have studied the use of hydrogen systems to provide ionization energy loss for muon beam cooling, breakdown suppression for pressurized high-gradient RF cavities, and refrigeration for superconducting magnets and cold RF cavities. We report progress on the designs of cryostat and refrigeration systems for different sections of muon cooling channels to achieve safe and robust means to enable exceptionally bright muon beams. We find that engineering designs can be greatly simplified if high temperature superconductor can be used that has the capability to carry adequate current in fields above 10 T for temperatures above 33 K for the use of integrated pressurized RF cavities, or for temperatures above 16 K for designs where the RF and cooling sections are sequential.

A study of RF breakdown of metals in gases has begun as part of a program to develop RF cavities filled with dense hydrogen gas to be used for muon ionization cooling. A pressurized 805 MHz test cell is being used at Fermilab to compare the conditioning and breakdown behavior of copper, molybdenum, chromium, and beryllium electrodes as functions of hydrogen and helium gas densities. These results will be compared to the predicted or known RF breakdown behavior of these metals in vacuum.

Ionization cooling, a method for shrinking the size of a muon beam, requires a low Z energy absorber, high field magnets, and high gradient radio frequency cavities. The use of high temperature superconductors (HTS) for the high field superconducting magnets is being considered to realize a helical muon cooling channel using hydrogen refrigeration. A test stand was set up at Fermilab to perform critical current (Ic) measurements of HTS wires under externally applied perpendicular and parallel fields at various temperatures. A description of the test setup and results on (Bi,Pb)2Sr2Ca2Cu3Ox (BSCCO‐2223) tapes and Bi2Sr2CaCu2O8 (BSCCO‐2212) round wires are presented. Finally, the engineering critical current density, JE, of HTS and Nb3Sn were compared in the application’s field and temperature range of interest.

Muons, despite their short lifetime, have an advantage in that they can be accelerated through matter without suffering appreciable scattering as do strongly interacting protons or electromagnetic showering as do less massive electrons. Thus RF cavities filled with dense gas to suppress electrical breakdown can provide high gradients for relatively short muon ionization-cooling channels for Neutrino Factories and Muon Colliders. Hydrogen gas, with large dE/dx, radiation length, and heat capacity, also acts as the perfect energy absorber having several engineering advantages. The progress of a DOE STTR grant project to develop high-pressure high-gradient RF cavities is described. First measurements of RF breakdown curves are reported, where stable operation was achieved with surface gradients of 50 MV/m for hydrogen and 28 MV/m for helium.

Four full-scale SSC (Superconducting Super Collider) development dipole magnets have been tested for mechanical and quench behavior. Two are of a design similar to that of previous magnets but contain a number of improvements, including more uniform coil size, higher prestress, and a redesigned inner-outer coil splice. One exceeds the SSC operating current on the second quench, but the other appears to be limited by damaged superconductor to a lower current. The other two magnets are of alternate designs. One trains erratically and fails to reach a plateau, and the other reaches a plateau after four quenches. >

The time behavior of the sextupole component of the Tevatron superconducting dipoles under ramping conditions was studied. Large time-dependent sextupole corrections are necessary to maintain constant chromaticities in the Tevatron. The authors discuss the implementation and results of these corrections in terms of emittance growth and intensity loss during the Tevatron ramp. >

Ionization cooling, a method for shrinking the size of a particle beam, is an essential technique for future particle accelerators that use muons. In this technique, muons lose energy in all three directions by passing through an absorber while only the longitudinal energy is regenerated by RF cavities. Thus the beam phase space area decreases down to the limit of multiple scattering in the energy absorber. Hydrogen is the material of choice for ionization cooling because of its long radiation length relative to its energy loss. In the application discussed here, dense gaseous hydrogen also suppresses RF breakdown by virtue of the Paschen effect, thereby allowing higher accelerating gradients and a shorter and less‐expensive cooling channel. As described in this paper, a channel of RF cavities pressurized with about 3 tons of cold hydrogen gas could provide transverse muon cooling for a Muon Collider or Neutrino Factory. The present status of this research effort and several issues related to the use of hydrogen in this application are described.

In order to increase the usable accelerating gradient in Superconducting TESLA cavities, the field emission threshold barrier must be raised. As has been previously demonstrated on S-Band cavities, a way to accomplish this is with the use of high peak power RF processing. A transmitter with a peak power of 2 MWatt and 300 /spl mu/sec pulse length has been assembled and has been used to process TESLA cavities. Several five cell TESLA cavities at 1.3 GHz have been manufactured for this purpose. This transmitter and the cavities will be described and the results of the tests will be presented. >

A research and development program is underway to construct superconducting cavities to be used for radiofrequency separation of a kaon beam at Fermilab. The design calls for installation of twelve 13-cell cavities operating in the 3.9 GHz transverse mode with a deflection gradient of 5 MV/m. We present the mechanical, cryogenic and vacuum design of the cavity, cryomodule, rf power coupler, cold tuner and supporting hardware. The electromagnetic design of the cavity is presented in a companion paper by Wanzenberg and McAshan (2001). The warm tuning system (for field flatness) and the vertical test system will be presented along with test results of bench measurements and cold tests on single-cell and five-cell prototypes.

The facility at Fermilab was used to develop, fabricate, and commission an RF gun for the TeSLA Test Facility Linac. A time dependence is observed in the photo-emission and field emission from the photo-injector at Fermilab. The focussing solenoids can be adjusted to cause the QE and dark current to increase or decrease with time. The observed variation is in excess of a factor of 5 in the QE and a factor of 10 in the dark current, with time constants measured in hours. The evidence suggests that the source of the time-dependent behaviour is the Cs/sub 2/Te cathode.

Measurements of the magnetic field angle along the length of collider dipole magnets are discussed. These superconducting magnets were built at Fermilab for the Superconducting Super Collider (SSC) by Fermilab and General Dynamics personnel. These measurements were made at four stages in the assembly and test sequence. The data show that changes can occur both during installation in the cryostat and as a result of cold testing. Most of the changes during installation are correlated with the welding of the tie bar restraints, but the changes observed as a result of the cold testing can be attributed to changes in the magnetization of the iron laminations. >

The conceptional design of the proposed linear electron-positron collider TESLA is based on 9-cell 1.3 GHz superconducting niobium cavities with an accelerating gradient of ${E}_{\mathrm{acc}}\ensuremath{\ge}25\mathrm{MV}/\mathrm{m}$ at a quality factor ${Q}_{0}\ensuremath{\ge}5\ifmmode\times\else\texttimes\fi{}{10}^{9}$. The design goal for the cavities of the TESLA Test Facility (TTF) linac was set to the more moderate value of ${E}_{\mathrm{acc}}\ensuremath{\ge}15\mathrm{MV}/\mathrm{m}$. In a first series of 27 industrially produced TTF cavities the average gradient at ${Q}_{0}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}5\ifmmode\times\else\texttimes\fi{}{10}^{9}$ was measured to be $20.1\ifmmode\pm\else\textpm\fi{}6.2\mathrm{MV}/\mathrm{m}$, excluding a few cavities suffering from serious fabrication or material defects. In the second production of 24 TTF cavities, additional quality control measures were introduced, in particular, an eddy-current scan to eliminate niobium sheets with foreign material inclusions and stringent prescriptions for carrying out the electron-beam welds. The average gradient of these cavities at ${Q}_{0}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}5\ifmmode\times\else\texttimes\fi{}{10}^{9}$ amounts to $25.0\ifmmode\pm\else\textpm\fi{}3.2\mathrm{MV}/\mathrm{m}$ with the exception of one cavity suffering from a weld defect. Hence only a moderate improvement in production and preparation techniques will be needed to meet the ambitious TESLA goal with an adequate safety margin. In this paper we present a detailed description of the design, fabrication, and preparation of the TESLA Test Facility cavities and their associated components and report on cavity performance in test cryostats and with electron beam in the TTF linac. The ongoing research and development towards higher gradients is briefly addressed.

The construction and performance of an electric current meter that operates in liquid He and mechanically splits apart to permit replacement of the current carrying conductor are described. It permits the measurement of currents induced in a loop of superconducting cable and expeditious exchange of such loops. It is a key component for a short sample cable testing facility that requires no high-current power supplies or high-current leads. Its superconducting pickup circuit involves a nonmagnetic core toroidal split-coil that surrounds the conductor and a solenoid whose field is sensed by a Hall probe. This toroidal split-coil is potted inside another compensating toroidal split-coil. Currents of up to 10 kA can be measured with a precision of 150 mA.

An electron photo-injector facility has been constructed at Fermilab for the purpose of providing a 14-18 MeV electron beam with high charge per bunch (8 nC), short bunch length (1 mm RMS), and small transverse emittance. The facility was used to commission a second-generation photo-cathode RF gun for the TESLA Test Facility (TTF) Linac at DESY; in the future, the Fermilab electron beam will be used for R and D in bunch length compression, beam diagnostics, and new acceleration techniques. Acceleration beyond 4 MeV is provided by a 9-cell superconducting cavity. The cavity also provides a longitudinal position-momentum correlation for subsequent bunch length compression. We report on the RF tests and a first beam test of this cavity.

An RF photo-injector was installed at Fermilab between January and June 97. The photo-injector produced its first beam on 4 June 97. This report provides a brief description of the accelerator and a summary of the experiments carried out through December '97.

A collaboration has been formed between FNAL, UCLA, LNFN Milano, the University of Rochester, and DESY to develop the technology of an RF photoinjector, followed by a superconducting cavity, to produce high bunch charge (8 nC) with low normalized emittance (

The electrical resistance of superconducting cable splices is known to be in the 10{sup -9} {Omega} range which to be measured conventionally would require the use of a micro voltmeter with a power supply capable of generating kilo Amperes plus a liquid helium cryostat with large power leads. Here we present a system for carrying on such measurements that requires besides the microvoltmeter a power supply capable of generating only up to 35 {Alpha} and a 152 mm diameter neck helium dewar using less than 25 liters per day after initial cool down. In this paper we describe the apparatus and present the data taken with it in its first use which for data acquisition used just a chart recorder. The method is based in making the splice in a loop of cable, inducing a current in it and measuring its decay time constant. Generating high currents in superconductors by induction is not a new technique but the use of the decay constant of currents generated this way for the determination of minute electrical resistance seems novel to the author. Unexpected details in the results will be discussed.

Similar to the power leads of accelerator superconducting magnets, the power couplers of accelerator superconducting cavities are components that link room temperature to superfluid helium temperature for the purpose of energy transfer. Instead of conducting kiloamperes of current they guide megawatts of RF power between those two temperatures. In this paper we describe a cryostat designed for testing the performance of these components and measuring their heat loads. A special feature of this cryostat is its minimum liquid inventory that considerably simplifies safety related requirements. This cryostat is part of a Fermilab facility contributing to the international collaboration working on TESLA (TeV Electron Superconducting Linear Accelerator). This facility is now operational and we will be presenting specifications as well as performance data on the cryostat as well as the first pair of power couplers tested with it.

A facility for coating RF power components with thin films of Ti and/or TiN has been in operation for some time at Fermilab supporting the Accelerator Division RF development work and the TESLA program. It has been experimentally verified that such coatings improve the performance of these components as far as withstanding higher electric fields. This is attributed to a reduction in the secondary electron emission coefficient of the surfaces when coated with a thin film containing titanium. The purpose of this Technical Memorandum is to describe the facility and the procedure used.

During 1992 at Fermilab, a series of nine 50-mm-aperture, 15-m-long, SSC superconducting dipole magnets, designed jointly by Fermilab, Brookhaven National Laboratory, and the SSC Laboratory, have been built and successfully cold tested. Seven of these dipole magnets, designated for the Accelerator System String Test (ASST) carried out at SSCL in Dallas, were assembled at Fermilab by General Dynamics personnel, and have achieved the nominal operating current level without significant training.1,2 In addition, a series of four R&D magnets (DCA320 323) were manufactured at Fermilab to test an alternative insulation schemes. In this paper we present the quench performance of these four R&D magnets, which were cold tested at the Fermilab Magnet Test Facility at nominal temperatures of 4.35 K, 3.85 K, and 3.50 K. An extended characterization test was performed on one of these magnets (DCA322). During this test the magnet was successfully cooled down to superfluid He temperature (1.8 K) and reached a field B ≥ 9.5 T.

At several stages in the production of the SSC collider dipole magnets and their final installation (as well as for beam orbit calculations) the magnetic field angle needs to be known. A simple device using a permanent magnet which aligns itself with the magnetic field (the Vertical Field Angle Probe, FAP) had been developed at FNAL to survey the direction of the magnetic dipole field with respect to the vertical (as determined by gravity) along the magnet axis.1 The determination of the dipole field angle was part of the field quality characterization of a series of thirteen full-length 50mm-aperture SSC Collider Dipole Magnet Prototypes (DCA311-DCA323) which were built for R&D purposes at FNAL (for design specification).5,6

Experiences are reported of welding niobium to stainless steel for the TESLA accelerator superconducting cavities.

Thirteen 16 m long, 50 mm aperture SSC dipole magnets, designed jointly by Fermilab, Brookhaven National Laboratory, Lawrence Berkeley Laboratory and the SSC Laboratory, have been built at Fermilab. The first nine magnets have been fully tested to date. The allowed harmonics are systematically shifted from zero by amounts larger than the specification. The unallowed harmonics, with the exception of the skew sextupole, are consistent with zero. The magnet-to-magnet RMS variation of all harmonics is much smaller than the specification.

In the fabrication of both 40 and 50 mm collider dipole superconducting magnets, surveys of the direction of the magnetic field along their length have been taken. This data besides being used for certifying compliance with the specifications for the finished magnet, yields interesting information on the straightness and rigidity of the coil placement between some stages in their manufacture and testing. A discussion on the measuring equipment and procedures is given. All of the 40 mm magnets that were built or cryostat at Fermilab have at least one of these surveys, and a summary of the data on them is presented. Most of the 50 mm magnets built and cold tested at Fermilab have been surveyed before and after insertion in the cryostat and before and after being cold tested. A summary of this data is also presented.

This note is about calculations aimed at quantifying adequate pumping speeds of evacuation of normally humid clean-room air from typical Superconducting Radiofrequency (SRF) cavities. The subject is of high relevance to the semiconductor industry, where the yield of VLSI (Very Large Scale Integration) chip production is affected by micron size particles which may cause fatal defects to their micron and sub-micron features. The recent availability of particle counters capable of operating in vacuum has stimulated measurements at reduced pressures in this subject.

This paper presents preliminary results of magnetic field measurements made on a series of 50 mm aperture 15 m long SSC collider dipole magnets designed and manufactured at Fermi National Accelerator Laboratory (Fermilab) for use in the Superconducting Super Collider Laboratory (SSCL) Accelerator System String Test. The magnets were assembled by Fermilab and General Dynamics personnel, and were tested at the Magnet Test Facility (MTF) at Fermilab. Measurements of the dipole field angle, dipole field strength, and field shape parameters at various stages in magnet construction and testing are described.

In this paper we present results of quench testing of full length SSC dipole magnets at Fermilab. The data are from the first six of a series of thirteen 15 m long, 50 mm aperture SSC dipole magnets which are being built and tested at Fermilab. These magnets were designed jointly by Fermilab, Brookhaven Laboratory, Lawrence Berkeley Laboratory and the SSC Laboratory. Among the major goals for this series of magnets are to transfer magnet production technology to the lead vendor for the Collider Dipole Magnet, the General Dynamics Corporation, and to demonstrate industrial production by the vendor. The first magnet in the series, DCA311, was built by Fermilab technicians to establish assembly procedures. The second magnet, DCA312, was the “technology transfer magnet and was built jointly by Fermilab and General Dynamics technicians. The next seven, DCA313-319 are being built by General Dynamics personnel using Fermilab facilities and procedures. However, Fermilab personnel still operate the major tooling, provide the welders, perform assembly of items that would not be part of production magnets (e.g. voltage taps), and oversee the QA program. Five of these 7 GD-built magnets will be used in the Accelerator Systems String Test (ASST) to be carried out in Dallas later this year. The last four magnets, DCA320-323, are being built by Fermilab alone.”

A series of full-scale demonstration SSC collider dipole magnets were built for the ASST (Accelerator System String Test). These magnets, DCA311 through DCA319, have 50 mm aperture and 15 m magnetic length with 6.6 Tesla uniform field. For the support structure of the W6733B cross section[1], the Fermilab design uses a vertical split[2] in the yoke. The end sections of the magnet have solid spacers and are supported by collet clamps[3]. The splices between inner and outer coils are made in preforms which lie outside of the high field region. The magnets were produced in pipeline fashion with no intentional major changes between magnets. As a part of the technology transfer program, the last 7 magnets were built by General Dynamics personnel using the magnet construction facilities of Fermilab, while the first two magnets were built entirely by Fermilab personnel.

During the last two years, nine 4‐cm aperture, 17‐m‐long dipole magnet prototypes were produced by Brookhaven National Laboratory (BNL) under contact with the Superconducting Super Collider (SSC) Laboratory. These prototypes are the last phase of a half‐decade‐long R&D program, carried out in collaboration with Fermi National Accelerator Laboratory and Lawrence Berkeley Laboratory, and aimed at demonstrating the feasibility of the SSC main‐ring dipole magnets. They also lay the groundwork for the 5‐cm‐aperture dipole magnet program now underway. After reviewing the design features of the BNL 4‐cm‐aperture, 17‐m‐long dipole magnets, we describe in detail the various steps of their fabrication. For each step, we discuss the paramaters that need to be mastered, and we compare the values that were achieved for the nine most recent prototypes. The data appear coherent and reproducible, demonstrating that the assembly process is under control. We then analyze the mechanical behavior of these magnets during cooldown and excitation, and we attempt to relate this behavior to the magnet features. The data reveal that the mechanical behavior is sensitive to the collar‐yoke interference and that the magnets exhibit somewhat erratic changes in coil end‐loading during cooldown.

Over the last year, several 4-cm-aperture, 17-m-long dipole magnet prototypes were built by Brookhaven National Laboratory (BNL) under contract with the Superconducting Super Collider (SSC) Laboratory. These prototypes are the last phase of a half-decade-long R & D program, carried out in collaboration with Fermi National Accelerator Laboratory and Lawrence Berkeley Laboratory, and aimed at demonstrating the feasibility of the SSC main ring magnets. They also lay the ground for the 5-cm aperture dipole magnet program to be started soon. After reviewing the design features of the BNL 4-cm-aperture, 17-m-long dipole magnets, we describe in detail the various steps of their fabrication. For each step, we discuss the parameters that need to be mastered, and we compare the values that were achieved for the five most recent prototypes. The data appear coherent and reproducible, demonstrating that the assembly process is under control.

The construction and performance of an electric current meter that operates in liquid He and mechanically splits apart to permit replacement of the current carrying conductor is described. It permits the measurement of currents induced in a loop of superconducting cable and expeditious exchange of such loops. It is a key component for a short sample cable testing facility that requires no high current power supplies nor high current leads. Its superconducting pickup circuit involves a non-magnetic core toroidal split-coil that surrounds the conductor and a solenoid whose field is sensed by a Hall probe. This toroidal split-coil is potted inside another compensating toroidal split-coil. The C shaped half toroids can be separated and brought precisely together from outside the cryostat. The Hall probe is energized and sensed by a lock-in amplifier whose output drives a bipolar power supply which feeds the compensating coil. The output is the voltage across a resistor in this feedback circuit. Currents of up to 10 kA can be measured with a precision of 150 mA. 3 refs., 4 figs.

Several 17-meter-long SSC R&D dipole magnets, instrumented with numerous voltage taps on the inner quarter coils, have been tested. These magnets, protected with quench heaters, differed in mechanical details as well as in the cables used for the winding. The voltage taps enabled us to measure longitudinal and azimuthal quench propagation velocities. Summary plots of these velocities are presented showing that, even though the Fourier conduction model doesn’t apply, the mechanism of the quench is reproducible from magnet to magnet. Correlations are established between the velocities and the fraction of short sample. After showing that for currents higher than 5000 A the magnet is self-protected, we investigate the relation between the number of MIITs and the quench characteristics.

A method suitable for measuring the thermal conductivity of good thermal conductors at low temperatures was implemented. It successfully served its purpose: to detect the effect of doping with manganese the interfilament part of the copper matrix of the superconducting wire used in the magnets of the Superconducting Super Collider. It uses two heaters and one thermometer per sample reducing the accuracy requirement on the thermometers, automatically compensating for zero offsets and reducing the number of critical thermal contacts. Commercially available strain gauges are used as heaters.

The procedure for installing Superconducting Super Collider dipoles in their respective cryostats involves aligning the average direction of their field with the vertical to an accuracy of 0.5 mrad. The equipment developed for carrying out these measurements is described and the measurements performed on the first few prototype magnets are presented. The field angle as a function of position in these 16.6-m long magnets is a characteristic of the individual magnet with possible feedback information to its manufacturing procedure. A comparison of this vertical alignment characteristic with a magnetic-field intensity (using magnetic resonance imaging) characteristic for one of the prototypes is also presented. >

The experimental study leading to the determination of the sensitivity needed for protecting the Fermilab Doubler from damage during quenches is presented. The quench voltage thresholds involved were obtained from measurements made on Doubler cable of resistance × temperature and voltage × time during quenches under several currents and from data collected during operation of the Doubler Quench Protection System as implemented in the B-12 string of 20 magnets. At 4kA, a quench voltage threshold in excess of 5.0V will limit the peak Doubler cable temperature to 452K for quenches originating in the magnet coils whereas a threshold of 0.5V is required for quenches originating outside of coils.

During the last few months, several full size prototype dipole magnets for the Fermilab Energy Doubler were successfully tested. This was the result of several concurrent programs in conductor development as well as magnet construction, production, and testing. The present magnets have achieved their design goal. Progress to this point has solved many pitfalls. A description is given of the present technology as well as some of the decisions that led to the present design.