Superconducting Super Collider Research Articles

Geostatistical Analysis of Fault and Joint Measurements in Austin Chalk, Superconducting Super Collider Site, Texas: ABSTRACT

Faults and joints are conduits for ground-water flow and targets for horizontal drilling in the petroleum industry. Spacing and size distribution are rarely predicted accurately by current structural models or documented adequately by conventional borehole or outcrop samples. Tunnel excavations present opportunities to measure fracture attributes in continuous subsurface exposures. These fracture measurements ran be used to improve structural models, guide interpretation of conventional borehole and outcrop data, and geostatistically quantify spatial and spacing characteristics for comparison to outcrop data or for generating distributions of fracture for numerical flow and transport modeling. Structure maps of over 9 mi of nearly continuous tunnel excavations in Austin Chalk at the Superconducting Super Collider (SSC) site in Ellis County, Texas, provide a unique database of fault and joint populations for geostatistical analysis. Observationally, small faults (<10 ft. throw) occur in clusters or swarms that have as many as 24 faults, fault swarms are as much as 2,000 ft. wide and appear to be on average 1,000 ft. apart, and joints are in swarms spaced 500 to more than 2l,000 ft. apart. Semi-variograms show varying degrees of spatial correlation. These variograms have structured sills that correlate directly to highs and lows in fracture frequencymore » observed in the tunnel. Semi-variograms generated with respect to fracture spacing and number also have structured sills, but tend to not show any near-field correlation. The distribution of fault spacing can be described with a negative exponential, which suggests a random distribution. However, there is clearly some structure and clustering in the spacing data as shown by running average and variograms, which implies that a number of different methods should be utilized to characterize fracture spacing.« less

Eddy currents in superconducting Rutherford cables

Eddy currents induced in magnet cables have long been recognized as contributing to the quench performance of superconducting accelerator magnets, and are thought to be a major contributor to degraded performance in the superconducting super collider (SSC) dipole magnets. There are several major paths which these currents might follow, however, and each path has an effect. We have experimentally isolated these several contributions and estimated their relative importance. The experimental observations support the recent theoretical predictions of Carr and Kovachev. The well known ‘crossover resistance’ is the most important component. In samples with very low crossover resistance, a quench was observed in the absence of transport current. A long time constant of the order of several seconds was observed for the build-up of eddy currents on cable samples which had very low crossover resistances and were only slightly longer than two twist-pitch lengths.

RF control at SSCL — an object oriented design approach

The Superconducting Super Collider (SSC) in Texas, the construction of which was stopped in 1994, would have represented a major challenge in accelerator research and development. This paper addresses the issues encountered in the parallel design and construction of the control systems for the RF equipment for the five accelerators comprising the SSC. An extensive analysis of the components of the RF control systems has been undertaken, based upon the Schlaer-Mellor object-oriented analysis and design (OOA/OOD) methodology. The RF subsystem components such as amplifiers, tubes, power supplies, PID loops, etc. were analyzed to produce OOA information, behavior and process models. Using these models, OOD was iteratively applied to develop a generic RF control system design. This paper describes the results of this analysis and the development of ‘bridges’ between the analysis objects, and the EPICS-based software and underlying VME-based hardware architectures. The application of this approach to several of the SSCL RF control systems is discussed.

Abandoned SSC Site can provide underground facility for geoscience research

By the time Congress terminated the Superconducting Super Collider (SSC) project in October 1993, the Department of Energy and the state of Texas had sunk $2 billion into the project. Now closure and remediation of the disturbed surface and subsurface lands are underway with a budget of $22 million, according to a recent agreement between the DOE and Texas. Rather than chalking up the creation of the large, expensive hole in the ground to failure, however, some are hailing the site as an excellent test‐bed for geoenvironmental and geotechnical research (Figure 1). They hope to use the site's tunnel, exploratory shaft, and test wells to identify new and improved methods for investigating subsurface fluid flow and transport processes, to characterize physical properties of weak and fractured rock through geophysics and geomechanical testing, and to test model predictions through large‐scale experiments conducted underground.

Interstrand resistance of SSC magnets

In situ interstrand resistance measurements were conducted on selected sections of the inner coil of a full size (15 m) and a short (1 m) model Superconducting Super Collider (SSC) magnet. A mathematical model for evaluating single contact resistance between two strands was developed. Using this model analyses of adjacent and non-adjacent strand contacts were performed. The interstrand resistance distribution throughout the coil was found to correlate with the quench location data as well as with the multipole decay characteristics of the magnet. An anisotropic continuum based model for evaluation of cable eddy current losses was developed and results were compared with the experimental data.

Electromagnetic analyses of the GEM detector magnet system for SSC

The magnet system for the Superconducting Super Collider (SSC) Gamma, Electrons and Muons (GEM) detector consists of a single layer, superconducting, split solenoid and two iron forward field shapers (FFS). In addition, major structural components, such as the central detector and FFS support structures and the vacuum vessels, are to be built with magnetic steel. This paper presents the nonlinear, two and three-dimensional electromagnetic analyses which are performed in support of the overall design effort. A detailed axisymmetric, finite element ANSYS model is used to determine the magnetic field distribution in the region of the detector, and the electromagnetic forces acting on the coil and various magnetic steel elements. A 3-D model is developed to capture the magnetic field perturbations produced by asymmetric, magnetic structural elements. The model produces 3-D field maps of the detector volume to evaluate the effects of these asymmetries on the detector resolution. Another 3-D model is used to determine the distribution of magnetic steel plates required to shield the nearby Electronic Rack Room from the coil's fringe field.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Cold beam tube photodesorption and related experiments for the Superconducting Super Collider Laboratory 20 TeV proton collider

The next generation of proton colliders that has been contemplated—the Superconducting Super Collider (SSC) in the U.S. and the Large Hadron Collider (LHC) at CERN—will be the first to encounter significant intensities of synchrotron radiation within the cold bore tube of superconducting magnets. Aside from removal of the synchrotron radiation heat load, the main problem encountered is how to deal with the magnitudes of photodesorbed gases. Choosing the beam tube to coincide with the cryosorbing magnet bore tube has the advantages of simplicity and, in principle, of providing very high pumping speed. Tightly bound H, C, and O in the near-surface layer (∼100 Å) are converted by photodesorption to a steadily increasing surface density of physisorbed molecules. However, the effective pumping by the bore tube is greatly reduced by the photodesorption of relatively weakly bound physisorbed molecules. In addition, the saturation vapor density of H2 at the ∼4.2 K temperature of the SSC cryostats exceeds, by a factor of fifty, the upper bound allowed by the nuclear scattering deposition of energy in the magnet cryostats. Consequently, accumulation of a monolayer of physisorbed H2 must be avoided even locally. An alternative approach is to install a coaxial perforated tube or liner inside the magnet bore tube which allows the photodesorbed gases to be pumped out of the view of the synchrotron radiation photons. The purpose of the work described in this paper is to develop a methodology that will allow prediction of the SSC beam tube vacuum for simple, 4.2 K beam tubes and for distributed pump or liner configurations—and to provide the technical data required for choosing among the alternative possibilities. The first photodesorption experiments have been completed on the VEPP2M storage ring at the Budker Institute of Nuclear Physics (BINP). Additional photodesorption experiments are underway at BINP and are being planned for a beamline at the UV ring of the Brookhaven National Laboratory National Synchrotron Light Source (BNL NSLS). Related experiments at BNL measuring molecular sticking coefficients and at the State University of New York-Albany (SUNY-Albany) measuring the depth profile of hydrogen on beam tube surfaces are also beginning to yield data. New ideas for directly measuring molecular density inside a cryosorbing beam tube are under development—neutralization of H− and H+ beams at BINP and positron annihilation at BNL. A status report of these activities is given in this paper.

Superconducting super collider (SSC) collider dipole magnet (CDM) cold test stand integration and performance

Integration of the General Dynamics specified CDM cold test stand, including 10k ampere DC power supplies, high and low speed data acquisition systems, cryogenic facility, cryogenic distribution and end cans, coil protection system, vacuum leak test equipment and test stand controller is discussed. This paper addresses the lessons learned from the integration of these various equipment items. A description of systems is presented. Definition of the hardware and software systems and the interface to the CDM is included. >

Magnetic design and analysis of the SSC High Energy Booster dipole magnets

This paper presents key magnetic design considerations and analyses performed on the Superconducting Super Collider (SSC) High Energy Booster dipole magnets (HDM). The design considerations include: optimization of the cell cross section to establish low magnetic field harmonic content and specified field strength throughout a wide range of cable azimuthal sizes; effects of wedge geometry and cable stacking procedures on the field harmonics; and effects of yoke geometry and material variations on the central field strength and harmonics of the magnet.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Production techniques for the Superconducting Super Collider Low Energy Booster quadrupole magnet

The manufacturing techniques used for a prototype quadrupole magnet, developed at Lawrence Berkeley Laboratory (LBL) for the Superconducting Super Collider (SSC) Low Energy Booster (LEB), are described. The SSC LEB Ring employs 96 dipoles and 90 quadrupoles connected in series to form the magnetic lattice, requiring the use of a 21.9 mm/spl times/23.0 mm hollow conductor for the quadrupoles. Due to the large conductor size and small bend radii required, development of special fixtures was necessary. A unique coil-forming method with close attention paid to tooling design and special assembly procedures was required to manufacture this prototype to stringent specifications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Fabrication of a prototype dipole for and the SSC Low Energy Booster

The Low Energy Booster of the Superconducting Super Collider (SSC) will be a synchrotron containing 96 dipoles operating between 0.13 T and 1.35 T at 10 Hz. Each dipole's 1.885 m-long core is made from /spl sim/2900 steel laminations (lams), each 52/spl times/66 cm and 0.835 mm thick. A need to minimize power supply costs and stringent field specifications led to a straight core with very tight mechanical tolerances of the order of 0.05 mm. To satisfy these tolerances, we decided to stack the core in a vertical position; i.e., with the laminations laid horizontally. We designed and built an unusual vertical stacking fixture that pivots into a horizontal position after all the laminations have been stacked and compressed and four support angles welded onto the laminations. The stacking fixture, our experience using it, and conclusions as to the merits of stacking such a long core vertically will be described. The methods of insulating and potting the pancake coils and their installation into the unsplittable core is also described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Harmonics suppression of fields arising from vacuum chamber eddy currents with application to SSC Low-Energy-Booster magnets

An expression for eddy currents induced in a thin-walled conductor due to a time-dependent electromagnet field excitation is formulated, allowing subsequent analytical development of a closed form expression predicting field harmonics in ac iron-core multipole electromagnets arising from eddy currents in the vacuum chamber. A passive technique for harmonics suppression is presented with specific application to the design of the Superconducting Super Collider (SSC) Low-Energy-Booster (LEB) Magnets.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Influence of azimuthal coil size variations on magnetic field harmonics of superconducting particle accelerator magnets

The superconducting super collider (SSC) would have required dipole and quadrupole magnets with a very high field quality. The field quality is determined mainly by the dimensions of the magnet coils and their positions with respect to the iron yoke. It is thus very sensitive to manufacturing errors. A model is here developed to estimate the field distortions in a dipole magnet due to azimuthal coil size variations. This model is applied to the data collected during the fabrication and testing of a series of 5 cm aperture, 15 m long SSC dipole magnet prototypes. A clear correlation is observed between the predicted field distortions from the azimuthal coil sizes and the measured skew quadrupole and skew sextupole coefficients.

Simulation studies of a scintillating fiber tracker for the SDC detector

Six design options for a scintillating fiber inner tracker for the SDC detector operating at the Superconducting Super Collider (SSC) are simulated. Concentric cylindrical configurations of axial fiber superlayers, ranging from four to six in number, are considered. Tracks from events generated by Pythia 4.8 at rates up to ten times design luminosity are swum through the tracker. Algorithms for reconstructing tracks of physics interest with p T > 10 GeV/ c among a background of low p T tracks are described. The optimum configuration found permits level 1 triggering up to η = 2.3 at ten times design luminosity. Inclusion of additional stereo fibers in this configuration permits level 2 stereo reconstruction up to eight times design luminosity.

Performance of the Superconducting Super Collider H−rf volume ion source and Linac injector

The Superconducting Super Collider (SSC) ion source is required to provide a 30 mA H− beam at 35 keV with a normalized rms emittance (εn-rms) of less than 0.18 π mm mrad. An rf-driven volume source was chosen for the commissioning of the SSC linear accelerator (Linac). The divergent ion source output beam is matched into the radio frequency quadrupole accelerator (RFQ) by an electrostatic low-energy beam transport (LEBT). The SSC Linac injector (consisting of ion source, LEBT, and RFQ) is required to provide 25 mA of H− beam (pulse width of 9.6–35 μs at 10 Hz repetition rate) at 2.5 MeV with transverse normalized rms emittance (εt-n-rms) of less than 0.2 π mm mrad and longitudinal normalized rms emittance (εl) of less than 0.82×10−6 eV s. The performance of our rf volume source and initial experimental results from the SSC injector are discussed.

Congress Challenges Shut-Down Plans for Superconducting Super Collider

If the hearing held earlier this month by the House Subcommittee on Science is any indication, the arguments about the government's largest failed research project--the Superconducting Super Collider (SSC)--are going to go on, and on. Many members of Congress are determined to get the government out as quickly as possible, spending as little as it has to. The Department of Energy is trying to find some way to save face and maximize the investment it made in the SSC without running afoul of an angry Congress. The state of Texas is trying to get what it can out of this soured deal by getting some reimbursement for funds spent, or a new government facility, or some other use of the property in the near future while trying to accommodate the arcane provisions of DOE's termination plan. It is clear that arguments over the government's largest failed research project are going to continue. They may be longer lived than the project itself.

SSC termination will be lengthy and expensive

Closing down the huge Superconducting Super Collider (SSC) is going to take a lot of time and money. Congress gave the Department of Energy $640 million to begin the shutdown in fiscal 1994, and DOE is asking for another $180 million next year. In the meantime, Energy Secretary Hazel R. O'Leary has come up with a termination plan for the project that will guide the department's activities. Much of the expense associated with terminating the SSC project involves closing out the many contracts the department has for building and supplying the site. Other major parts of the termination will be the environmental restoration and asset closeout, and the benefits provided for the SSCs employees. Two things still unresolved are the settlement DOE must make with Texas for the state's investment in the project and deciding what will be done with the facilities already there. Congress voted last year to close down the project as of ...

The SDC silicon tracking system

The silicon tracking system is a critical element of the tracking system of the Solenoidal Detector Collaboration's (SDC) experiment to meet the physics requirements at the Superconducting Super Collider (SSC). It will provide full-pattern recognition, vertexing, and stand-alone momentum measurement capabilities complementing the outer tracker. The key component of the system is a double-sided silicon microstrip sensor (DSSS) with fast-readout front-end electronics. The SDC DSSS design addresses problems associated with radiation damage on the surface and in the bulk of the silicon microstrip sensors. The SDC silicon tracking system, being the largest semiconductor tracking detector ever planned, requires a state-of-the-art design of the electromechanical system in order to minimize the dead regions, minimize the radiation length, cool and operate the system at 0°C, and have the mechanical precision necessary to match the spatial resolution of the microstrip sensors. The silicon ladders, shells, space frames, and butane evaporative cooling system are achieving the requirements imposed by the goals of the SDC experiment.

Optimization of magnet end-winding geometry

A simple, almost entirely analytic, method for the optimization of stress-reduced magnet-end winding paths for ribbon-like superconducting cable is presented. This technique is based on characterization of these paths as developable surfaces, i.e., surfaces whose intrinsic geometry is flat. The method is applicable to winding mandrels of arbitrary geometry. Computational searches for optimal winding paths are easily implemented via the technique. Its application to the end configuration of cylindrical Superconducting Super-Collider (SSC)-type magnets is discussed. The method may be useful for other engineering problems involving the placement of thin sheets of material. >

A proposed SSC damper system

A transverse beam damper system for providing stability against ground motion, resistive wall instabilities, and other effects in the Superconducting Super Collider (SSC) is outlined. Use of two monitors, as in existing designs, provides phase insensitivity. The novel feature is the use of two kickers, which permits almost exact orbit compensation within one turn. Bunch-by-bunch stabilization requires fast computation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>