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
24392991
The Engineering Design of the 1.5 m Diameter Solenoid for the MICE RFCC Modules
The RF coupling coil (RFCC) module of MICE is where muons that have been cooled within the MICE absorber focus (AFC) modules are re-accelerated to their original longitudinal momentum. The RFCC module consists of four 201.25 MHz RF cavities in a 1.4 meter diameter vacuum vessel. The muons are kept within the RF cavities by the magnetic field generated by a superconducting coupling solenoid that goes around the RF cavities. The coupling solenoid will be cooled using a pair of 4 K pulse tube cooler that will generate 1.5 W of cooling at 4.2 K. The magnet will be powered using a 300 A two-quadrant power supply. This report describes the ICST engineering design of the coupling solenoid for MICE.
123081787
PROGRESS ON THE SUPERCONDUCTING MAGNET FOR THE TIME PROJECTION CHAMBER EXPERIMENT (TPC) AT PEP
The TPC (Time Projection Chamber) experiment at PEP will have a two meter inside diameter superconducting magnet which creatests a 1.5 T uniform solenoidal field for the TPC. The superconducting magnet coil, cryostat, cooling system, and the TPC gas pressure vessel (which operatests at 11 atm) were designed to be about two thirds of a radiation length thick. As a result, a high current density coil design was chosen. The magnet is cooled by forced flow two phase helium. The TPC magnet is the largest adiabatically stable superconducting magnet built to date. The paper presents the parameters of the TPC thin solenoid and its subsystems. Tests results from the Spring 1980 cryogenic tes are presented. The topics to be dealt with in the paper are cryogenic services and the tests of magnet subsystems such as the folded current leads. Large thin superconducting magnet technology will be important to large detectors to be used on LEP.
122748175
Calculation of the pressure rise in the cooling tube of a two-phase cooling system during a quench of an indirectly cooled superconducting magnet
Large superconducting detector magnets are indirectly cooled with two-phase helium flowing in cooling tubes attached to the coil or its support structure. Large detector magnets often quench such that most of the magnet stored energy ends up as heat stored in the coil package. The time constant for energy deposition in the coil and support structure is often quite short. This paper presents a method for calculating the peak pressure rise in the magnet two-phase cooling tube during a magnet quench. A comparison of calculated peak pressure rise and measured pressure rise for the PEP-4 solenoid is presented in this report. >
118834673
A Design for a Combined Function Superconducting Dipole for a Muon Collider FFAG Accelerator
The acceleration stages for a muon collider require that the muons be accelerated within a given ring in fewer than twenty turns. One type of accelerator that appears to be attractive for a synchrotron that accelerates the muon a factor of four in energy in a few turns is the Fixed Field Alternating Gradient (FFAG) type of accelerator. As the energy of the muon beam increases, the muons move toward a higher field region of a DC combined function dipole. The following dipole and quadrupole magnet characteristics are required for a muon FFAG machine to be successful: (1) The dipole will be a fixed field dipole with an impressed quadrupole and sextupole field. There may or may not be separate quadrupoles that mayor may not have added sextupole windings. (2) The horizontal aperture of the required good field region is wider than the vertical aperture of the required good field region. (3) The magnet is relatively short, so that the conventional SSC type of superconducting dipole or quadrupole ends can not be used. The field at the end of the magnet must fall off abruptly within the distance of less than one vertical aperture. For a magnet that is 400more » mm long, the end region can be no more than 80 mm long. (4) The structure of the integrated field within the end region must be the same as the structure of the two-dimensional filed at the center of the magnet. A very preliminary design concept for a FFAG combined function dipole is presented in this paper.« less
94844521
ACTIVE CENTER TAP QUENCH PROTECTION
15936820
One loop in eleven dimensions
Four-graviton scattering in eleven-dimensional supergravity is considered at one loop compactified on one, two and three-dimensional tori. The dependence on the toroidal geometry determines the known perturbative and non-perturbative terms in the corresponding processes in type II superstring theories in ten, nine and eight dimensions. The ultra-violet divergence must be regularized so that it has a precisely determined finite value that is consistent both with T-duality in nine dimensions and with eleven-dimensional supersymmetry.
123045249
The insertion of boundaries in world-sheets
Abstract This paper considers the operator that inserts a boundary in a string world-sheet on which the string coordinates satisfy either Neumann or constant Dirichlet boundary conditions. With an arbitrary open-string state attached to the boundary, this describes the vertex coupling an open string to a closed string (the “open-closed string vertex”). A boundary with no open strings attached can be viewed as a vacuum correction to closed-string theory. This factories into two open-closed string vertices joined together by an open-string propagator. BRST-invariant open-closed string vertices of the Neumann and Dirichlet theories are constructed in a “light-cone-like” frame (familiar from some formulations of covariant string field theory) as well as the “vertex operator” frame (in which a general open-string state is represented by a vertex operator attached to the world-sheet boundary). The vertices of the Neumann and Dirichlet theories are related to each other by space-time duality. The insertion of a closed Dirichlet boundary may be expressed in the light-cone-like gauge as an interaction vertex that acts at a fixed “time” and generates an explicit mass term connecting two arbitrary closed-string states. Some examples of how the presence of such boundaries modifies amplitudes for low-lying states are presented.
56468517
Eisenstein series for higher-rank groups and string theory amplitudes
Scattering amplitudes of superstring theory are strongly constrained by the requirement that they be invariant under dualities generated by discrete subgroups, E_n(Z), of simply-laced Lie groups in the E_n series (n<= 8). In particular, expanding the four-supergraviton amplitude at low energy gives a series of higher derivative corrections to Einstein's theory, with coefficients that are automorphic functions with a rich dependence on the moduli. Boundary conditions supplied by string and supergravity perturbation theory, together with a chain of relations between successive groups in the E_n series, constrain the constant terms of these coefficients in three distinct parabolic subgroups. Using this information we are able to determine the expressions for the first two higher derivative interactions (which are BPS-protected) in terms of specific Eisenstein series. Further, we determine key features of the coefficient of the third term in the low energy expansion of the four-supergraviton amplitude (which is also BPS-protected) in the E_8 case. This is an automorphic function that satisfies an inhomogeneous Laplace equation and has constant terms in certain parabolic subgroups that contain information about all the preceding terms.
120192541
Discrete and Abelian lattice gauge theories
Gauge-invariant discrete and Abelian (X-Y) spin models with compact degrees of freedom are studied in (D + 1) Euclidean (“space-time”) dimensions (D ⩽ 3). They are formulated in terms of quantum Hamiltonians on a D-dimensional spatial lattice. In this approach the periodic Gaussian and Abelian models are identical. 
 
Duality transformations are obtained which relate the topological excitations of one model to the fundamental quantum spin excitations of another. These motivate the extension of the usual gauge-invariant structure to “gauge invariance of the third kind” which involves degrees of freedom associated with the surfaces of the plaquettes. 
 
The nature of the excited states and the behaviour of the order (and disorder) parameters are discussed in various limits of the coupling constants. For both discrete and Abelian theories the behaviour of the order parameter (the Wilson loop) depends crucially on whether the spins in the theory carry the fundamental unit of charge or a multiple of it.
120913474
Quantum mechanics of a twisted superparticle
Abstract This paper is devoted to the quantization of the ten-dimensional superparticle in the formulation, due to Siegel, in which the local fermionic symmetry is implemented using explicit gauge fields and in which momentum coordinates conjugate to the fermionic superspace coordinates are introduced. Here, a truncation of the complete N = 1 superparticle is considered (the complete superparticle is analysed in a separate paper). This “truncated model” (which was the first modified superparticle considered by Siegel) is shown to be invariant under a “twisted” N = 2 space-time supersymmetry, and a light-cone gauge analysis shows that the physical spectrum is a representation of this algebra which includes negative norm states. The Batalin-Vilkovisky method is used to covariantly quantize the system in two ways, one with an infinite number of ghost fields and one with only a finite number. In both cases, the BRST cohomology is analysed in detail. Our results illustrate certain general features: (i) In a formulation with gauge fields for the fermionic symmetries the invariance can be fixed by imposing gauge conditions on the gauge fields. This results in a free quantum action, without the need for the problematic field redefinitions that arise in earlier formulations in which gauge conditions are imposed on the spinorial coordinates. (ii) There is an interesting pattern for the infinite number of ghost-for-ghosts, which naturally divide into two sets. The first is an infinite sequence of gauge fields while the second is a set of ghosts for the corresponding sequence of gauge invariances. (iii) The infinite set of quantum fields packages into simple infinite-dimensional spinor representations of the supergroup OSp(9, 1 | 2). The cohomology classes are particularly easy to describe in terms of OSp(9, 1 | 2) spinor notation.