125011989
Lessons Learned for the MICE Coupling Solenoid from the MICE Spectrometer Solenoids
LESSONS LEARNED FOR THE MICE COUPLING SOLENOID FROM THE MICE SPECTROMETER SOLENOIDS* M. A. Green a , L. Wang b , H. Pan c , H. Wu c , X. L. Guo c , S. Y. Li d , S. X. Zheng c , S. P. Virostek a , A. J. DeMello a , D. Li a , F. Trillaud a , and M. S. Zisman a , a) LBNL, Berkeley CA, USA, b) Shanghai Institute of Applied Physics, Shanghai, China c) ICST, HIT, Harbin, China, and d) Hilong University of Science and Technology, Harbin, China Abstract Tests of the spectrometer solenoids have taught us some important lessons. The spectrometer magnet lessons learned fall into two broad categories that involve the two stages of the coolers that are used to cool the magnets. On the first spectrometer magnet, the problems were centered on the connection of the cooler 2nd-stage to the magnet cold mass. On the first test of the second spectrometer magnet, the problems were centered on the cooler 1st- stage temperature and its effect on the operation of the HTS leads. The second time the second spectrometer magnet was tested; the cooling to the cold mass was still not adequate. The cryogenic designs of the MICE and MuCOOL coupling magnets are quite different, but the lessons learned from the tests of the spectrometer magnets have affected the design of the coupling magnets. This paper compares the magnet cryogenic design for the spectrometer magnet [4] and the coupling magnet [5]. The effect of magnetic fields on the high temperature superconductor (HTS) leads is discussed [6]. The experience gained from testing the spectrometer magnets has influenced the design of the coupling magnets. Lessons learned from the spectrometer magnets will likely affect the AFC magnet design [7] as well. SPECTROMETER AND COUPLING MAGNET DESIGN COMPARISON The spectrometer solenoid cryostat has an OD of 1.4 m and it is 2.7-m long. The coupling magnet cryostat has an OD of more than 2.2 m and a length of 0.49 m. The magnets are quite different. The spectrometer solenoid is long (2511 mm) compared to its coil ID of 516 mm. On other hand the coupling magnet coil is short (285 mm) compared to its coil ID of 1500 mm. As a result, the stray field outside the coupling magnet is large compared to the spectrometer magnet. The stray field of the coupling magnet affects the location and orientation of the HTS leads and it influences the design first-stage temperature for the coolers that cool the magnet. Table 1 compares the design heat loads for the two types of MICE magnets. Table 1: A Comparison of the Design Cryogenic Heat Loads for the Spectrometer and Coupling Magnets Parameter Spectro. Coupl. Number of 4.2 K coolers Total Lead Current (A) (No. Leads) Cold Mass Support Design Force (kN) Total Shield Area (m 2 ) Number of Wires to Shield Number of wires to Cold Mass Calculated 1st Stage Heat Loads Lead Conduction + I 2 R heating (W) Cold Mass Support heat Load (W) MLI Heat Load (W) Pipe and Sleeve Heat Load (W) Instrumentation Heat Load (W Total Design 1 st Stage Heat Load (W) Per Cooler 1 st Stage Heat Load (W) Calculated 2 nd Stage Heat Loads Lead Conduction + I 2 R heating (W) Cold Mass Support heat Load (W) MLI Heat Load (W) Pipe and Sleeve Heat Load (W) Instrumentation Heat Load (W) Total Design 2 nd Stage Heat Load (W) Per Cooler 2 nd Stage Heat Load (W) INTRODUCTION The muon ionization cooling experiment (MICE) will be a demonstration of muon cooling in a configuration that may be useful for a neutrino factory [1]. Stage 6 of MICE (the final MICE channel) consists of: 1) two spectrometer modules used for analyzing muon beam emittance before and after cooling; 2) three absorber focus coil (AFC) modules used for muon ionization cooling in the absorbers in the focusing magnets; and 3) two RF coupling coil (RFCC) modules are used for reaccelerating the muon beam between the AFC modules. The RFCC modules consist of a superconducting coupling solenoid, which surrounds a 1.4-meter diameter vacuum chamber that contains four separately powered conventional copper RF cavities that have a resonant frequency of 201.25 MHz. The individual RF cavity irises are closed by thin beryllium windows [2]. The coupling magnet will produce a large enough magnetic field to keep the beam within the iris of the RF cavities. The magnets used in the MICE cooling channel are all superconducting solenoids. All of the MICE cooling channel magnet modules are cooled using two-stage pulse tube coolers that develop 1.5 W of cooling at 4.2 K while generating 50 W of cooling at 45 K [3]. The channel magnets are continuously powered by one or more pairs of leads that go from 300 K to the cold mass. The magnet current leads between the first and second stages of the coolers are made from HTS conductor. The leads from 300 K to the cooler first-stages are conduction cooled. * This work is supported by the Office of Science, US Department of Energy under DOE contract DE-AC02-05CH11231. This work is also supported by funds of the cryogenic and technology innovation project under the “985-2” plan of the Harbin Institute of Technology.
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.
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. >
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.
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
119955549
Point-like structure and off-shell dual strings
Abstract We argue that in a consistent off-shell dual formalism the amplitude for the emission of a scalar off-shell state by a string consists of two components. One of these contains the particle poles in the off-shell leg and the other is intimately related to the insertion of a point-like energy density on the string. As a result, the amplitude for a string to emit a zero momentum scalar state into the vacuum (which may be relevant for spontaneous symmetry breaking) is described by the amplitude for a finite fraction of the energy in the string to collapse to a spatial point at some time (this fraction and its space-time position being integrated over). The off-shell amplitudes have an elegant formulation in terms of a set of “confined modes” which can be assigned quark flavour quantum numbers to reproduce the Chan-Paton scheme. We suggest the dual model be modified by allowing for the coupling of scalar closed strings to the vacuum and the resulting effect on the space-time structure of dual Green functions is described. We find that even the emission of a single zero-momentum closed string modifies the elastic amplitude in a significant manner, leading to a power-behaved fixed-angle cross section in contrast to the usual exponential decrease of the dual model. This arises from point-like scattering between energy densities accumulating in the colliding strings. The relationship between the fixed angle and Regge limits is discussed. The fixed angle behaviour is found to be the asymptotic limit in momentum transfer of a fixed pole that arises in the Regge limit.
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.
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.
121615877
Properties of the covariant formulation of superstring theories
Abstract The covariant two-dimensional action principle that describes the dynamics of free superstrings in a Minkowski background is reviewed. Covariant gauge conditions are formulated, which simplify the equations of motion of the superspace coordinates to free equations. In this gauge there are bosonic and fermionic constraints whose generators give a supersymmetric generalization of the Virasoro algebra. As in certain supersymmetric field theories, closure of the algebra requires using the equations of motion. Covariant constrained bracket relations are obtained for the classical theory, but it is very difficult to extend them to quantum mechanical commutation relations. Interaction vertices satisfying supersymmetry and the necessary gauge conditions are constructed. They reduce in a special frame to ones found in earlier work in the light-cone gauge, and then can be interpreted quantum mechanically.
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.