120308093
World Sheets for World Sheets
Abstract In this paper I suggest that the two-dimensional world sheet underlying the dynamics of relativistic strings may itself emerge from an approximation to a two-dimensional string theory. Coordinates that represent space-time and internal symmetries should emerge as wave functions of the massless states of that theory. This is motivated by studying various string theories with two-dimensional target spaces and internal symmetry which are related to generalized nonlinear sigma models.
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.
121755839
PHASE CONTOURS AND BOOTSTRAPS. I.
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.
119655108
The effect of muon decay on the design of dipoles and quadrupoles for a muon collider
The decay of muons to neutrinos and electrons can cause heating in the superconducting dipoles and quadrupoles in the muon collider acceleration rings and the colliding beam ring. The problem is particularly acute in the colliding beam ring where heating in the magnets can be as high as 2.4 kW per meter in the bending magnets of muon collider ring with 2 TeV mu plus and mu minus beams with 2.22×1012 particles per bunch at a repetition rate of 30 Hz. The energy deposited within the helium temperature region must be reduced at least three orders of magnitude in order for the refrigeration system to begin to keep up with the heat load. Beam heating from muon decay will require changes in dipole design from the traditional cosine theta (or intersecting ellipse) design used in the SSC magnets. Some dipole and quadrupole design options are presented in this report for both the accelerator rings and the colliding beam rings.
59453973
A superconducting focusing solenoid for the neutrino factory linear accelerator
A Superconducting Focusing Solenoid for the Neutrino Factory Linear Accelerator * M. A. Green, V. Lebedev, and B. P Strauss The 400-m long linear accelerator is divided into three sections. Upstream from the linear accelerator is a matching section that provides the first 60 MeV of muon acceleration. The end of the matching section consists of a pair of low stray field solenoids with adjustable currents for tuning. The first section has 4 short modules that are 5-meters long. Each short module has two cells of RF cavities. The second section has 16 medium length modules that are 8-meters long. Each intermediate module has two cells of RF cavities arranged in groups of two with a 1-meter space between groups. The short and intermediate modules have a 1-meter long focusing solenoid with a 1.25-meter long straight section at each end. The third acceleration section has 19 long modules that are 13-meters long. The long module has eight superconducting RF cells arranged in groups of two with a 1-meter space between cell groups. The focusing solenoid is 1.5 meters long with a 1.25-meter long space separating it from the adjacent RF cavity cells. The three types of acceleration modules used for the linear accelerator are illustrated in Figure 1. Unlike focusing quadrupoles, focusing solenoids can produce a stray field that exists some distance from the magnet. The superconducting RF cavities are sensitive to magnetic fields even at the level of 0.0001 T (versus 0.043 T for the smallest single solenoid in Table 1), so a key parameter in the focusing solenoid design is getting rid of the solenoid stray field in the RF cavities. The methods one can use to eliminate the stray field in the RF cavities are:1) The focusing solenoid should produce zero net magnetic moment[5,6]. This means that the coil that produces the field is bucked by a coil that is larger in diameter. 2) The field from the bucking coils should be distributed in the same way as the solenoid field. This suggests that the bucking solenoid be around the focusing solenoid so that the return flux from the focusing solenoid is returned between the focusing solenoid and the bucking solenoid[7]. 3) The nested solenoids should be surrounded by iron except where the muon beam passes through the solenoid. 4) An iron flux shield should be installed between the focusing solenoid and the RF cavities. 5) If the stray field is still not low enough, the RF cavities can be covered with a type 2 superconducting shield. This shield will trap earth’s magnetic field, but it will shield out the remaining stray flux from a nearby solenoid provided the cavities are cold (below 5 K) when the solenoid is turned on. An iron shielded actively shielded solenoid appears to be a minimum requirement in order to reduce the stray field to an acceptable level. Abstract--The proposed linear Accelerator that accelerates muons from 190 MeV to 2.45 GeV will use superconducting solenoids for focusing the muon beam. The accelerator will use superconducting RF cavities. These cavities are very sensitive to stay magnetic field from the focusing magnets. Superconducting solenoids can produce large stray fields. This report describes the 201.25 MHz acceleration system for the neutrino factory. This report also describes a focusing solenoid that delivers almost no stray field to a neighboring superconducting RF cavity. Index Terms—Superconducting Focusing Solenoid, Active Shielding, Superconducting RF Cavities I. I NTRODUCTION The proposed neutrino factory generates neutrinos from muon decay in a muon storage ring[1,2]. The muons are created from the decay of pions produced from the collision of protons on a fixed target. The pions are captured by a 20 T solenoid. The pions then decay to muons as they pass down a long channel. The muons are phase-rotated, bunched, and cooled before they can be accelerated and stored in the storage ring[3]. The first stage of acceleration is a linear accelerator that uses superconducting RF cavities[4]. Muon focusing during this acceleration occurs within superconducting solenoids. After the muons are accelerated to 2350 MeV, they enter a re- circulating linac that accelerates them to their final energy of 20 GeV. The 20 GeV muons are then stored in storage ring where they decay to two neutrinos and an electron or positron (depending on the charge of the originating muon type). II. F OCUSING S OLENOIDS FOR THE L INEAR A CCELERATOR The proposed linear accelerator that accelerates the muons from 190 MeV to 2350 MeV extends nearly 400 meters. The Linear accelerator will use high gradient superconducting RF cavities to accelerate the beam. These cavities will not only increase the acceleration gradient, but they will also save electric power. Between the RF cavities there will be superconducting solenoids that provide beam focusing. Received 26 September 2001 * This work was supported by the Office of Science, United States Department of Energy under DOE contract number DE-AC03-76SF00098 M. A. Green, is from the Lawrence Berkeley National Laboratory, Berkeley CA 94720, USA;V. Lebedev, is from the Thomas Jefferson National Laboratory, Newport News VA 23606, USA; B. P Strauss is from the U S Department of Energy, Germantown MD 20874, USA
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.
124315608
Proposal to Construct an anti-Proton Source for the Fermilab Accelerator
We propose to build a small storage ring for the accumulation of antiprotons produced in an external target. Stochastic and electron cooling will be used to reduce the transverse and longitudinal phase space of the antiprotons. The dynamics of stochastic and electron cooling will also be studied in this storage ring using circulating protons. The cooled antiprotons can be re-injected into the main ring or energy doubler ring; after simultaneous acceleration along with a proton bunch the accelerator will become a colliding {bar}pp machine with a center of mass energy range of 300-2600 GeV. Luminosities in the range 10{sup 29}-10{sup 32} cm {sup -2}sec{-1} are expected.
95431568
THE ROLE OF SUPERCONDUCTING MAGNETS IN NMR MEDICAL IMAGING
Modern medicine has become dependent on x-rays and various imaging techniques for the diagnosis of diseases. Within the last five yers, an imaging technique which uses NMR (Nuclear Magnetic Resonance) has been developed. NMR imaging will produce detailed pictures of soft tissues without the use of dangerous ionizing radiation. NMR imaging can be particularly useful for the detection of cancer and certain cardiovascular diseases. NMR imaging may well provide the first large-scale use of superconducting magnet technology by society as a whole. This paper describes the role of superconducting magnets in NMR imaging. The design criteria for super-conducting magnets suitable for whole-body imaging of humans are presented. A couple of magnet design approaches are discussed.