121304002
A variational renormalization group approach to two coupled Ising systems
Using the variational block-spin approximation of Kadanoff (1975) a renormalization group recursion relation suitable for two-layered Ising systems is constructed. The critical behaviour of the Ashkin-Teller model is described in some detail.
9607753
Anomalous creation of branes
In certain circumstances when two branes pass through each other a third brane is produced stretching between them. We explain this phenomenon by the use of chains of dualities and the inflow of charge that is required for the absence of chiral gauge anomalies when pairs of D-branes intersect.
121755839
PHASE CONTOURS AND BOOTSTRAPS. I.
121062482
N=4 Yang-Mills and N=8 Supergravity as Limits of String Theories
The formulation of supersymmetric string theories in ten dimensions is generalized to incorporate compactified dimensions. Expressions for the one-loop four-particle S -matrix elements of N = 4 Yang-Mills and N = 8 supergravity in four dimensions are obtained by studying the string-theory loop amplitudes in the limit that the radii of the compactified dimensions and the Regge slope parameter simultaneously approach zero. If certain patterns that emerge should persist in the higher orders of perturbation theory, then N = 4 Yang-Mills in four dimensions would be ultraviolet finite to all orders, whereas N = 8 supergravity in four dimensions would have ultraviolet divergences starting at three loops.
120539667
Anomaly cancellations in supersymmetric D = 10 gauge theory and superstring theory☆
Abstract Supersymmetric ten-dimensional Yang-Mills theory coupled to N = 1, D = 10 supergravity has gauge and gravitational anomalies that can be partially cancelled by the addition of suitable local interactions. The remaining pieces of all the anomalies cancel if the gauge group is SO(32) or E 8 × E 8 . These cancellations are automatically incorporated in the type I superstring theory based on SO(32). A superstring theory for E 8 × E 8 has not yet been constructed.
123230985
Off-shell states in the dual model
Abstract We present a class of Lorentz invariant, gauge invariant off-shell amplitudes for the ordinary Veneziano and Ramond-Neveu-Schwarz dual models. They correspond to interactions with the string which are local in space-time.
118961628
A LARGE HIGH CURRENT DENSITY SUPERCONDUCTING SOLENOID FOR THE TIME PROJECTION CHAMBER EXPERIMENT
TWO-WEEK LOAN COpy This is a Library irculating Copy which may be borrowed for two weeks. For a personal retention copy, call Tech. Info. Diuision, Ext. 6782
108163413
Progress on the MICE RFCC Module for the MICE Experiment
PROGRESS ON MICE RFCC MODULE FOR THE MICE EXPERIMENT* Allan DeMello, Nord Andresen, Michael Green, Derun L i , Heng Pan, Steve Virostek, Michael Zisman ( L B N L , Berkeley C A 94720, USA), Don Summers, Mike Reep (University of Mississippi, Oxford M S 38677, USA) An Bin Chen, Xiao-Kun Liu, Feng-Yu X u , Shi-Xian Zheng (HIT, Harbin, China), Yun Cao, Sen Sun, L i Wang, Lixin Y i n (SINAP, Shanghai, China) Abstract We describe the recent progress on the design and fabrication of the R F C C (RF and Coupling Coil) module for the international Muon Ionization Cooling Experiment (MICE). The M I C E cooling channel has two R F C C modules; each has four 201-MHz normal conducting R F cavities and one superconducting solenoid magnet. The magnet is designed to be cooled by three cryocoolers. Fabrication of the R F cavities is complete; design and fabrication of the magnets are in progress. The first magnet is expected to be finished by the end of 2011. pneumatic actuator (Fig. 3). Six flexure tuners are currently being fabricated (University of Mississippi) for a full cavity test of the R F tuner system. This test will include the electronic pressure control, EPICS software interface and the R F feedback system. This system will be assembled into a single cavity vacuum vessel (see below) for testing. INTRODUCTION M I C E is an international experiment designed to demonstrate muon beam cooling using ionization cooling (Fig. 1). Muons are captured in a strong magnetic field, cooled in 4D phase space and re-accelerated in the beamline direction by the normal conducting R F cavities in the R F C C . This demonstration is key to the success of a future Neutrino Factory or Muon Collider. The experiment is being hosted at Rutherford Appleton Laboratory ( R A L ) in the U K , where beamline commissioning is underway. Institutions participating in the collaboration include national laboratories and universities in Europe, the U.S., China, and Japan. Figure 2: 90° sectioned view of the M I C E cooling channel R F C C module. Figure 1 : The M I C E cooling channel. RFCC M O D U L E CAVITIES Lawrence Berkeley National Laboratory is responsible for the design of the R F Cavity and Coupling Coil (RFCC) module for M I C E (Fig. 2). Each R F C C module will contain four 201 M H z normal conducting R F cavities and one superconducting coupling coil magnet [4]. Each cavity will have its frequency actively tuned using six stainless steel flexure tuners moved with a dual action * This work was supported by the Office of Science, U.S. Department of Energy under D O E contract number DE-AC02-05CH11231. Figure 3: The prototype RF tuner flexure and actuator mounted on a 201-MHz cavity.
25645596
Correction of magnetization sextupole and decapole in a 5 centimeter bore SSC dipole using passive superconductor
Higher multipoles due to magnetization of the superconductor in 4-cm- and 5-cm-bore Superconducting Super Collider (SSC) superconducting dipole magnets have been observed. The use of a passive superconductor to correct the magnetization sextupole has been demonstrated on two dipoles built by the Lawrence Berkeley Laboratory. In the present work, it is shown how passive correction can be applied to the 5-cm SSC dipoles to remove sextupole and decapole caused by magnetization of the dipole superconductor. Two passive superconductor corrector options are presented. Both methods of passive superconductor correction will reduce magnetization sextupole at injection at 1 TeV or above any order magnitude or more over a wide range of operating temperatures. Increasing the diameter of the filament in block 1 increases the magnetization decapole at injection while the separate passive superconductor method reduces magnetization decapole. Both methods of correction reduce the magnetization sextupole whether the field is rising or falling. The change in magnetization sextupole and decapole due to flux creep decay of the superconductor during injection can be partially compensated for by using the passive superconductor.<<ETX>>
121794117
THE ROLE OF QUENCH BACK IN QUENCH PROTECTION OF A SUPERCONDUCTING SOLENOID
Abstract This report demonstrates the role of quench back in the quench protection of high current density superconducting solenoid magnets with well-coupled shorted secondary circuits. The phenomenon of ‘quench back’ can be used to greatly reduce the size of an external quench protection resistor or even to eliminate the need for an external quench protection system altogether. A comparison is made with conventional magnet quench protection systems with and without a closely coupled secondary circuit.
120781819
Cryogenic techniques for large superconducting magnets in space
Abstract A large superconducting magnet is proposed for use in a particle astrophysics experiment, ASTROMAG, which is to be mounted on the US Space Station. This experiment will have a two-coil superconducting magnet with coils which are 1.3 to 1.7 m in diameter. The two-coil magnet will have zero net magnetic dipole moment. The field 15 m from the magnet will approach earth's field in low earth orbit. The issue of high T c superconductor will be discussed in the paper. The reasons for using conventional niobium-titanium superconductor cooled with superfluid helium will be presented. Since the purpose of the magnet is to do particle astrophysics, the superconducting coils must be located close to the charged particle detectors. The trade-off between the particle physics possible and the cryogenic insulation around the coils is discussed. As a result, the ASTROMAG magnet coils will be operated outside the superfluid helium storage tank. The fountain effect pumping system which will be used to cool the coil is described in the report. Two methods for extending the operating life of the superfluid helium dewar are discussed. These include: (1) operation with a third shield cooled to 90 K with a sterling cycle cryocooler and (2) a hybrid cryogenic system where there are three hydrogen-cooled shields and cryostat support heat intercept points. Both methods will extend the ASTROMAG cryogenic operating life from 2 years to almost 4 years.