117251296
Preliminary study of a superfluid helium cryogenic system for the large hadron collider
55204249
A Cryogenic Axial-Centrifugal Compressor For Superfluid Helium Refrigeration
CERN's new project, the Large Hadron Collider (LHC), will use superfluid helium as coolant for its high-field superconducting magnets and therefore require large capacity refrigeration at 1.8 K. This may only be achieved by subatmospheric compression of gaseous helium at cryogenic temperature. To stimulate development of this technology, CERN has procured from industry prototype Cold Compressor Units (CCU). This unit is based on a cryogenic axial-centrifugal compressor, running on ceramic ball bearings and driven by a variable-frequency electrical motor operating under low-pressure helium at ambient temperature. The machine has been commissioned and is now in operation. After describing basic constructional features of the compressor, we report on measured performance.
118122719
DESIGN, TEST AND PERFORMANCE OF THE LIQUID HELIUM CRYOSTATS FOR THE LEP SUPERCONDUCTING QUADRUPOLE MAGNETS
The experimental areas of LEP, the high-energy electron-positron collider presently under construction at CERN, will be equipped with eight superconducting quadrupole magnets, housed in liquid helium cryostats embedded in the complex detector set-ups. To comply with transverse space restrictions, the 2.5 m-long slender cryostats feature a 130 mm diameter warm bore and a horizontally-oriented service funnel at one end, equipped with 2000 A current leads. The cryostats have been designed by CERN, manufactured and assembled by industry, and tested in the laboratory. Besides design principles and constructional features, results of tests and comparative performance data are presented.
122695581
TOWARDS COST-TO-PERFORMANCE OPTIMISATION OF LARGE SUPERFLUID HELIUM REFRIGERATION SYSTEMS
The field range of superconducting devices may be extended by lowering their operating temperature, using superfluid helium refrigeration systems which have to deliver working pressures down to 1.6 kPa. The corresponding pressure ratio can be produced by integral cold compression or using a combination of cold compressors in series together with "warm" compressors at room temperature. The optimisation of such a system depends on the number, arrangement and characteristics of cold and warm machines as well as on the operating scenario and turndown capability. The aim of this paper is to compare relative investment and operating costs of different superfluid helium cryogenic systems, with the aim of optimising their cost-to-performance ratio within the constraints of their operating scenario.
133673972
Investigation and qualification of thermal insulation systems between 80-K and 4.2-K
116929466
The superfluid helium model cryoloop for the CERN Large Hadron Collider (LHC)
The high-field superconducting magnets of the CERN Large Hadron Collider (LHC) will operate in static pressurized helium II at a maximum temperature of 1.9 K, irrespective of their position around the 26.7 km circumference of the machine ring. Their static and dynamic heat loads will be transported by conduction in the pressurized helium II, to a heat exchanger tube threading its way along the magnet string, in which flowing saturated helium II absorbs the heat in quasi-isothermal conditions. Following promising results obtained with heated flow tests on two-phase helium II, a full-scale 20 m-long thermohydraulic model of a LHC cryoloop was designed, built and operated, addressing key issues such as flow stability, steady-state heat transfer, transient response to varying loads, control strategies, and influence of slope. We present the results obtained and show that they validate the basic design choices of the proposed LHC cryogenic system.
121120449
Design and simulation of muon ionization cooling channels for the Fermilab Neutrino Factory feasibility study
In the past few years, the concept of a high intensity muon storage ring has been pursued as an option for the next generation neutrino source. To produce the high intensity muon beam needed for the successful operation of a neutrino source, on the order of 1020 muon decays per year, the phase space occupied by the muon beam must be significantly reduced before the beam is accelerated. The initial transverse emittance of the muon beam before acceleration is assumed to be 9p mm rad. Because of the time limitation imposed by the muon lifetime, the technique employed to accomplish the desired emittance reduction is ionization cooling. In this paper we present two ionization cooling lattice designs, which use solenoidal focusing elements and liquid hydrogen absorbers to reduce the muon beam phase space. We discuss the design concepts and engineering constraints for these lattices and present simulation results obtained using a detailed tracing code with a complete model of muon-matter interactions. The reduction in transverse emittance is approximately a factor of 5. This result is within a factor of 2 of the total cooling requirements for a successful neutrino factory design and within a factor of 1.4 of the requirements for the main cooling section specified in the conceptual design of this machine.
43442717
Recent results from Fermilab E687
Recent analyses from Fermilab fixed target photoproduction experiment 687 are summarized. Emphasis is placed on strong interaction studies performed on high statistics samples of Charm decays and light quark states. In particular, semi-leptonic measurements of form factors in Cabibbo suppressed modes are described. A Dalitz analysis of the D{sub s}{sup +}{yields}{pi}{sup +}{pi}{sup -}{pi}{sup +} has been performed and can be linked to recent results on scalar states decaying to {pi}{sup +}{pi}{sup -}. In addition, Charm-Anticharm asymmetries in high energy photoproduction have been measured. Finally, photoproduction of light quark states, such as the vector meson {rho}(1700) or the f{sub 0}(980) are discussed.
120234331
Performances of a preamplifier-silicon photodiode readout system associated with large BGO crystal scintillators
Abstract The characteristics of a hybridized low noise preamplifier are described. Performances of the preamplifier in combination with silicon photodiodes are discussed and results from laboratory tests and test runs with an assembly of large BGO crystals are presented.
41310630
Comments on frictional cooling and the zero energy options for cooling intense muon beams
It is shown that the proposed frictional cooling method is not directly applicable to intense ({approximately} 10{sup 12}) muon bunches, mostly due to space charge constraints. Other difficulties stem from the fact that the initial emittance must be quite small, compared to the nominal muon collider emittance. Excessive heat due to energy deposition in the foils, from the primary muon beam or from secondary electrons could also destroy the thin foils used as moderator. Other zero energy schemes are considered, separately for {mu}{sup {minus}} and {mu}{sup +}. All of them lead the authors to the study of exotic electrons-ions-muons plasma.
136953526
Performances of large BGO crystals below 20 MeV