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.
94844521
ACTIVE CENTER TAP QUENCH PROTECTION
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.
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.
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
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. >
7549151
Vacuum values for auxiliary string fields
Abstract Auxiliary string fields are introduced in light-cone gauge string field theory in order to express contact interactions as contractions of cubic vertices. The auxiliary field in the purely closed-string bosonic theory may be given a non-zero expectation value, giving rise to a phase in which world-sheets have boundaries.
122496955
Anomaly-free chiral theories in six dimensions
Abstract The coupled N = 1 Yang-Mills plus supergravity theory in ten dimensions can be made anomaly-free for SO(32) or E 8 × E 8 . Only the case of SO(32) is known to correspond to a superstring theory, which is probably necessary for a fully consistent quantum theory. Anomaly-free chiral theories in lower dimensions can be obtained by considering nontrivial compactifications (involving nonzero background gauge fields) of the ten-dimensional theory that satisfy a topological consistency condition. This paper considers the compactification of four dimensions on the manifold K 3 without requiring that the equations of motion be satisfied. This leads to a large number of anomaly-free chiral supersymmetric six-dimensional theories, corresponding to various ways of embedding U(1) factors in SO(32) or E 8 × E 8 .
7533646
Ultraviolet properties of maximal supergravity.
We argue that recent results in string perturbation theory indicate that the four-graviton amplitude of four-dimensional N=8 supergravity might be ultraviolet finite up to eight loops. We similarly argue that the h-loop M-graviton amplitude might be finite for h<7+M/2.
119415557
Duality and higher derivative terms in M theory
Dualities of M-theory are used to determine the exact dependence on the coupling constant of the D6 4 interaction of the IIA and IIB superstring effective action. Upon lifting to eleven dimensions this determines the coefficient of the D6 4 interaction in eleven-dimensional M-theory. These results are obtained by considering the four-graviton two-loop scattering amplitude in eleven-dimensional supergravity compactified on a circle and on a two-torus — extending earlier results concerning lower-derivative interactions. The torus compactification leads to an interesting SL(2,)-invariant function of the complex structure of the torus (the IIB string coupling) that satisfies a Laplace equation with a source term on the fundamental domain of moduli space. The structure of this equation is in accord with general supersymmetry considerations and immediately determines tree-level and one-loop contributions to D64 in perturbative IIB string theory that agree with explicit string calculations, and two-loop and three-loop contributions that have yet to be obtained in string theory. The complete solution of the Laplace equation contains infinite series' of single D-instanton and double D-instanton contributions, in addition to the perturbative terms. General considerations of the higher loop diagrams of eleven-dimensional supergravity suggest extensions of these results to interactions of higher order in the low energy expansion.
124124262
SUPERSTRINGS AND THE UNIFICATION OF THE PHYSICAL FORCES