121851945
Design, test and performance of the prototype superconducting quadrupole for the LEP low-beta insertions
The prototype of the superconducting quadrupoles for the low-beta insertions at the Large Electron-Positron collider has been tested successfully. This industry-built quadrupole, which has a warm bore of 130 mm and a magnetic length of 2 m, is required to provide a gradient of 36 T/m over a field aperture of 1000 mm diameter. It achieved its maximum operating current without training. While retaining the main characteristics of its ISR predecessors, the design of this magnet incorporates several novel features, due to constraints imposed by the environment of the LEP experiments. In particular the quadrupole is slender and ironless, and has a horizontally oriented cryogenic service funnel. Following a description of the major aspects of the design, the results are given of the magnetic and cryogenic tests and measurements. >
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.
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.
133673972
Investigation and qualification of thermal insulation systems between 80-K and 4.2-K
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.
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.
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.
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.
120522308
High energy cosmic muons and the calibration of the L3 electromagnetic calorimeter
Abstract A method to calibrate the L3 electromagnetic calorimeter with cosmic muons has been tested on a matrix of 100 tapered BGO crystals. Calibration constants in the energy range of 20–30 MeV were measured at the 2% level collecting about 200 muons per crystal. The results are in agreement with the calibration constant determined using a 10 GeV electron beam.
32930723
GEANT4 simulation and theoretical studies of a helical cooling channel
We present a conceptual design and detailed GEANT4 simulation of a helical ionization cooling channel proposed by Ya. Derbenev, which is able to cool in 3 dimensions (3-D). The lattice of the channel consists of a long solenoid (B=5 T, L=72 m, R=70 cm) and a transverse dipole magnetic field which rotates with a period of 1.8 m and an amplitude of 0.3 T. The cooling is achieved using lithium hydride wedge absorbers. Re-acceleration is performed by 201.25 MHz RF cavities which provide a 6.2 MeV per cooling cell. The parameters of the muon beam at the end of the channel are: transmission 85%, transverse and longitudinal emittances 0.6 cm and 2 cm, respectively.
93634723
Contribution à l'étude du calorimètre électromagnétique à cristaux de germanate de bismuth de l'expérience L3 sur LEP