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
55539219
Cryogenic refrigeration requirements for superconducting insertion devices in a light source
LBNL-53578 SCMAG-823 Cryogenic Refrigeration Requirements for Superconducting Insertion Devices in a Light Source Michael A. Green Lawrence Berkeley National Laboratory ABSTRACT This report discusses cryogenic cooling superconducting insertion devices for modern light sources. The introductory part of the report discusses the difference between wiggler and undulators and how the bore temperature may affect the performance of the magnets. The steps one would take to reduce the gap between the cold magnet pole are discussed. One section of the report is devoted to showing how one would calculate the heat that enters the device. Source of heat include, heat entering through the vacuum chamber, heating due to stray electrons and synchrotron radiation, heating due to image current on the bore, heat flow by conduction and radiation, and heat transfer into the cryostat through the magnet leads. A section of the report is devoted to cooling options such as small cryo-cooler and larger conventional helium refrigerators. This section contains a discussion as to when it is appropriate to use small coolers that do not have J-T circuits. Candidate small cryo-coolers are discussed in this section of the report. Cooling circuits for cooling with a conventional refrigerator are also discussed. A section of the report is devoted to vibration isolation and how this may affect how the cooling is attached to the device. Vibration isolation using straps is compared to vibration isolation using helium heat pipes. The vibration isolation of a conventional refrigeration system is also discussed. Finally, the cool down of an insertion device is discussed. The device can either be cooled down using liquid cryogenic nitrogen and liquid helium or by using the cooler used to keep the devices cold over the long haul.
45506633
The superconducting solenoid magnets for MICE
The Muon Ionization Cooling Experiment (MICE) is a channel of superconducting solenoid magnets. The magnets in MICE are around the RF cavities, absorbers (liquid or solid) and the primary particle detectors [1], [2]. The MICE superconducting solenoid system consists of eighteen coils that are grouped in three types of magnet assemblies. The cooling channel consists of two complete cell of an SFOFO cooling channel. Each cell consists of a focusing coil pair around an absorber and a coupling coil around a RF cavity that re-accelerates the muons to their original momentum. At the ends of the experiment are uniform field solenoids for the particle detectors and a set of matching coils used to match the muon beam to the cooling cells. Three absorbers are used instead of two in order to shield the detectors from dark currents generated by the RF cavities at high operating acceleration gradients.
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.
119583895
Modifying the bosonic string vacuum
Abstract A nontrivial string vacuum can induce effects in open bosonic string theories which can be interpreted in terms of nonlocality of the mapping of the string world sheet into spacetime. This is achieved by modifying the sum over Riemann surfaces to include boundaries on which the bosonic fields satisfy a Dirichlet condition, as well as holes with the usual Neumann condition and crosscaps. Such effects profoundly alter the large-angle behaviour of string amplitudes. With suitable normalization, they also lead to a cancellation of the one-loop divergence associated with the vacuum emission of a soft dilaton.
119400372
Locality and currents for the dual string
Abstract We wish to describe the coupling of a local current to the dual string as the amplitude for the string to collapse to a point. At the quantum level we note that states which are localized in the transverse directions are forced by the gauge constraints to have longitudinal extension. The best we can do in the conventional model is, therefore, to construct off-shell states which have zero helicity (but no unique spin). We calculate the propagator for such states and compare it with the model of Schwarz. In their respective critical dimensions (26 for the string and 16 for the off-shell model of Schwarz) the two results become identical. We also calculate the Green functions for the coupling of one of our off-shell states to any number of on-shell particles by means of the functional formalism. Our results have a close connection with the previous models of Schwarz and Wu and of Corrigan and Fairlie.
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.
15960460
Instantons in supersymmetric Yang-Mills and D-instantons in IIB superstring theory
The one-instanton contributions to various correlation functions of superconformal currents in four-dimensional = 4 supersymmetric SU(2) Yang-Mills theory are evaluated to the lowest order in perturbation theory. Expressions of the same form are obtained from the leading effects of a single D-instanton extracted from the IIB superstring effective action around the AdS5 ? S5 background. This is in line with the suggested AdS/Yang-Mills correspondence. The relation between Yang-Mills instantons and D-instantons is further confirmed by the explicit form of the classical D-instanton solution in the AdS5 ? S5 background and its associated supermultiplet of zero modes. Speculations are made concerning instanton effects in the large-Nc limit of the SU(Nc) Yang-Mills theory.
121804056
A lattice formulation of the Reggeon Field Theory and its critical behaviour
Abstract We formulate a lattice description of the Reggeon Field Theory in terms of two-dimensional vector spins of unit length (as in the x − y model). We exhibit, within the context of mean field theory, the phase transition of the Reggeon Field Theory that occurs as the (imaginary) magnetic field and temperature are varied in our statistical mechanical model.