122261770
A model for pomeranchukon couplings
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.
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.
121755839
PHASE CONTOURS AND BOOTSTRAPS. I.
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.
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.
55066475
Structural Design and Thermal Analysis for Thermal Shields of the MICE Coupling Magnets
A superconducting coupling magnet made from copper matrix NbTi conductors operating at 4 K will be used in the Muon Ionization Cooling Experiment (MICE) to produce up to 2.6 T on the magnet centerline to keep the muon beam within the thin RF cavity windows. The coupling magnet is to be cooled by two cryocoolers with a total cooling capacity of 3 W at 4.2 K. In order to keep a certain operating temperature margin, the most important is to reduce the heat leakage imposed on cold surfaces of coil cold mass assembly. An intermediate temperature shield system placed between the coupling coil and warm vacuum chamber is adopted. The shield system consists of upper neck shield, main shields, flexible connections and eight supports, which is to be cooled by the first stage cold heads of two cryocoolers with cooling capacity of 55 W at 60 K each. The maximum temperature difference on the shields should be less than 20 K, so the thermal analyses for the shields with different thicknesses, materials, flexible connect...
122023958
Tests on large diameter superconducting solenoids designed for colliding beam accelerators
Two prototype large diameter thin coil solenoids which use the mechanical structure to moderate quenches, have been built and systematically tested. The solenoids are cooled by two phase helium flowing in tubes which form a part of the coil structure. The coils have been tested by inducing a series of quenches at various currents. The results of these tests are given in this paper.
136566290
MODELING OF PROXIMITY COUPLING BETWEEN SUPERCONDUCTING FILAMENTS IN SUPERCONDUCTING DIPOLE MAGNETS
There is strong experimental evidence for superconducting current coupling between filaments in fine filament multifilamentary Nb-Ti which has been proposed for the SSC. The coupling between the fine filaments appears to be a Type II superconducting coupling. As a result, a.c. loss and magnetization can increase as one reduces the filament size in a fine filamentary conductor. This paper presents a computer model which fits experimental data for proximity superconducting coupling between filaments in a superconductor matrix. Using this model, one can predict the effect of proximity coupling on the field uniformity of a dipole magnet for the SSC.
118142788
The Cryogenic refrigeration system for MICE
LBNL-51751 SCMAG-794 The Cryogenic Refrigeration System for MICE Michael A. Green Lawrence Berkeley National Laboratory The proposed cryogenic cooling system for MICE uses a single liquid helium refrigerator to cool the superconducting magnets, the liquid hydrogen absorbers, and the scintillating fiber detectors. It is proposed that the helium refrigerator cold box deliver two-phase helium at 4.4 K at the saturated liquid condition and 14 K helium at a pressure of 14 to 18 bars. The 4.4 K helium will be used to cool the seven superconducting magnet assemblies in the MICE magnet string and the fiber light detectors. The 14 K helium will be used to cool the liquid hydrogen absorbers, the magnet shields, and the gas cooled electrical leads that go from about 50 K to room temperature. Helium returns to the refrigerator from the magnet string and detector box at 4.3 K. The helium gas from the absorbers returns to the refrigerator as a gas at 18 K or lower. The helium that will be used to cool the magnet shields and leads will by pass the refrigerator cold box and return to the refrigerator compressor at about 293 K. Forced Two-phase Helium Cooling for the Magnets It is proposed that the superconducting coils for the MICE magnets be cooled by conduction from the magnet coil support structure. A number of large detector magnets are cooled this way. The magnet support structure will be cooled by two-phase helium in cooling tubes that have an ID about 10 mm. It is proposed that the solenoid magnets be cooled in series using a single cooling circuit that goes from the refrigerator through the magnets and back to the refrigerator. (See Figure 1.) The volume of liquid helium in the solenoids will be very low (of the order of a few liters). The advantages of two- phase helium cooling of the magnets are as follows: 1) The cool down of the magnet string is straightforward and well controlled. To first order, the magnet cool down rate is proportional to the magnet mass, proportional to the temperature difference between the flow circuit inlet and the outlet, and inversely proportional to the mass flow through the circuit. 2) The overall mass of a tubular cooled magnet and its cryostat is less than the mass of a magnet with helium bath cooling. 3) The amount of helium in contact with the magnet coil during a quench is limited to the amount of helium in the cooling tube. The safety hazard of liquid helium in tubes during a loss of vacuum or a magnet quench is small compared to a bath cooled cryostat. Tubes always have a higher pressure rating than a cryostat helium vessel. In general, tubes are not covered by the pressure vessel code; the helium vessel in a bath cryostat usually is covered by the pressure vessel code. 4) Helium services to the superconducting magnets can come into the cryostat from any direction. In other words, the helium services and leads do not have to come out of the top of the cryostat. The gas cooled electrical leads can be operated at any orientation including having the cold end up and the warm end down.
122299493
The Effect of Flux Creep on the Magnetization Field in the SSC Dipole Magnets
The sextupole fields of model SSC dipole magnets have been observed to change with time when the magnets are held at constant current under conditions similar to injection into the SSC accelerator. The changes in the sextupole component have close to a linear log time dependence, and is felt to be caused by flux creep decay of the magnetization currents in the superconductor filaments. Measurements of this decay have been made under various conditions. The conditions include various central field inductions and changes of field prior to when the decay was measured. The measured field decay in the dipole’s sextupole is proportional to the magnitude and sign of the sextupole due to magnetization which was measured at the start of the decay. This suggests that the decay is a bulk superconductivity flux creep. Proximity coupling appears to play only a minor role in the flux creep according to recent LBL measurements with a stable power supply.