16307657
D instanton partition functions
Duality arguments are used to determine {ital D}-instanton contributions to certain effective interaction terms of type II supergravity theories in various dimensions. This leads to exact expressions for the partition functions of the finite {ital N} {ital D}-instanton matrix model in d=4 and 6 dimensions that generalize our previous expression for the case d=10. These results are consistent with the fact that the Witten index of the {ital T}-dual {ital D}-particle process should only be nonvanishing for d=10. {copyright} {ital 1998} {ital The American Physical Society}
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.
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.
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.
111271489
QUENCH BACK IN SUPERCONDUCTING MAGNETS WITH SHORTED SECONDARY CIRCUITS
While testing a thin superconducting solenoid with a shorted secondary circuit, the coil was observed to become fully normal faster than quench propagation would permit. We call this process “quench back”. The quench back was caused by heating in the secondary circuit from current induced from the primary circuit. This paper presents a theoretical expression which can be used to estimate the quench back time in a solenoid with a well coupled secondary circuit. The calculation of quench back time is compared with measurements made on two one-meter diameter solenoid magnets.
38708797
The mechanical and thermal design for the MICE coupling solenoid magnet
The MICE coupling solenoids surround the RF cavities that are used to increase the longitudinal momentum of the muon beam that is being cooled within MICE. The coupling solenoids will have a warm-bore diameter of 1394 mm. This is the warm bore that is around the 200 MHz RF cavities. The coupling solenoid is a single superconducting coil fabricated from a copper matrix Nb-Ti conductor originally designed for MRI magnets. A single coupling magnet is designed so that it can be cooled with a single 1.5 W (at 4.2 K) cooler. The MICE cooling channel has two of these solenoids, which will be hooked together in series, for a magnet circuit with a total stored-energy of the order of 12.8 MJ. Quench protection for the coupling coils is discussed. This report also presents the mechanical and thermal design parameters for this magnet, including the results of finite element calculations of mechanical forces and heat flow in the magnet cold mass.
54990157
Does One Know the Properties of a MICE Solid or Liquid Absorber toBetter than 0.3 Percent
This report discusses the report discusses whether the MICE absorbers can be characterized to {+-}0.3 percent, so that one predict absorber ionization cooling within the absorber. This report shows that most solid absorbers can be characterized to much better than {+-}0.3 percent. The two issues that dominate the characterization of the liquid cryogen absorbers are the dimensions of the liquid in the vessel and the density of the cryogenic liquid. The thickness of the window also plays a role. This report will show that a liquid hydrogen absorber can be characterized to better than {+-}0.3 percent, but a liquid helium absorber cannot be characterized to better and {+-}1 percent.
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.
107306043
COMPUTER DESIGN AND OPTIMIZATION OF CRYOGENIC REFRIGERATION SYSTEMS
The design and optimization of a cryogenic refrigerator using the LBL computer program GEOTHM are described. This computer program has been used extensively to design and optimize geothermal power plants and power cycles of other types. GEOTHM can calculate the thermodynamics of a wide variety of cycles including refrigeration cycles. GEOTHM has an optimizer which permits single step multiparameter optimization of a thermodynamic cycle. A refrigeration cycle may be optimized for minimum cost refrigeration, or maximum thermodynamic performance using up to 55 optimizable parameters. The use of the optimizer in GEOTHM is demonstrated on two liquid nitrogen refrigeration cycles which are optimized for minimum refrigeration cost and minimum input power.