122961674
Infinity Cancellations in SO(32) Superstring Theory
Abstract Type I superstring theory was previously shown to be anomaly-free if the gauge group is SO(32). Here it is demonstrated that the same group is also singled out by the requirement that infinities can be canceled by combining diagrams.
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.
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.
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.
25710510
How the Performance of a Superconducting Magnet Is Affected by the Connection Between a Small Cooler and the Magnet
As low temperature cryocoolers become more frequently used to cool superconducting magnets, it becomes increasingly apparent that the connection between the cooler and the magnet has an effect on the design and performance of the magnet. In general, the use of small coolers can be considered in two different temperature ranges; 1) from 3.8 to 4.8 K for magnet fabricated with LTS conductor and 2) from 18 to 35 K for magnets fabricated using HTS conductor. In general, both temperature ranges call for the use of a two-stage cooler. The best method for connecting a cooler to the magnet depends on a number of factors. The factors include: 1) whether the cooler must be used to cool down the magnet from room temperature, 2) whether the magnet must have one or more reservoirs of liquid cryogen to keep the magnet cold during a loss of cooling, and 3) constraints on the distance from the cooler cold heads and the magnet and its shield. Two methods for connecting low temperature coolers to superconducting magnets have been studied. The first method uses a cold strap to connect the cold heads directly to the loads. This method is commonly used for cryogen-free magnets. The second method uses a thermal siphon and liquid cryogens to make the connection between the load being cooled and the cold head. The two methods of transferring heat from the magnet to the cooler low temperature cold head are compared for the two temperature ranges given above
136567622
Ferromagnetic Material in the Superconductor and Its Effect on the Magnetization Sextupole and Decapole in the SSC Dipoles at Injection
It has been shown that the magnetization of a multi-filamentary superconductor can be altered by adding nickel to the composite strand. This report presents the results of calculations of the magnetization sextupole and higher multipoles in a 5 cm Superconducting Super Collider (SSC) dipole with and without nickel as part of the strand composite. The relative distribution of the nickel in the inner and outer coil conductors can be used to effectively eliminate sextupole and decapole at the SSC dipole injection field. Calculations of magnetization sextupole in the dipole are presented for strand with substituted nickel filaments and strand with electroplated nickel. The effect of nickel in the strand on the SSC dipole field quality at fields above the injection field is described. The effect of nickel in the strand on magnetization sextupole flux creep decay and the magnetization sextupole temperature dependence is also discussed.
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.
21404619
The Cold Mass Support System and the Helium Cooling System for the MICE Focusing Solenoid
The heart of the absorber focus coil (AFC) module for the muon ionization cooling experiment (MICE) is the two-coil superconducting solenoid that surrounds the muon absorber. The superconducting magnet focuses the muons that are cooled using ionization cooling, in order to improve the efficiency of cooling. The coils of the magnet may either be run in the solenoid mode (both coils operate at the same polarity) or the gradient (the coils operate at opposite polarity). The AFC magnet cold mass support system is designed to carry a longitudinal force up to 700 kN. The AFC module will be cooled using three pulse tube coolers that produce 1.5 W of cooling at 4.2 K. One of the coolers will be used to cool the liquid (hydrogen or helium) absorber used for ionization cooling. The other two coolers will cool the superconducting solenoid. This report will describe the MICE AFC magnet. The cold mass supports will be discussed. The reasons for using a pulsed tube cooler to cool this superconducting magnet will also be discussed.
122003703
Quench back in thin superconducting solenoid magnets
Abstract Superconducting magnets with well coupled, low resistance, secondary circuits have been observed to become fully normal faster than quench propagation in the coil would permit. This process is referred to as ‘quench back’. Quench back observed at the Lawrence Berkeley Laboratory (LBL) was caused by heating the secondary circuit from the current induced from the primary circuit as normal region in the superconducting coil propagated. This paper develops the theory for thermal quench back in thin solenoid magnets and compares this theory with measurements made in two one-meter diameter superconducting solenoid magnets.