120725124
Application of liquid helium cryoplants at CERN
In 1992, the liquid-helium cooling capacity installed at CERN was nearly tripled, passing from 6.8 to 19.7 kW/4.5 K (entropy equivalent*). Further tripling is expected in 1993. While the 6.8 kW available in 1991 were produced by 14 plants of moderate size (500 W/4.5 K average), two of the four plants added in 1992 have unit capacities of 6 kW/4.5 K. Four plants of 12 kW/4.5 K, upgradable to 18 kW/4.5 K in a later phase, are presently being installed. Most of the smaller plants are associated with particle physics experiments, cooling superconducting magnets of particle detectors and high-gradient focusing magnets of colliding-beam experiments. Six plants provide liquid helium for development laboratories and test facilities. The recently acquired multi-kW plants will be integral parts of the collider itself. Their present function is to cool superconducting RF cavities designed to increase the beam energy of the Large Electron Positron collider LEP from 50 to above 90 GeV. In the future, the same and additional plants will be available for the cooling of the superconducting magnet ring of the planned Large Hadron Collider LHC. To this end, they will be equipped with complementary 1.8 K final stages.
122643839
A pulsed superconducting magnet for a static magnetic refrigerator operating between 1.8 K and 4.5 K
Superfluid helium is increasingly used as a technical cooling medium in large-scale research projects involving high-field superconducting magnets, such as the CERN Large Hadron Collider (LHC). For refrigeration cycles operating below the normal boiling point of helium, a potentially interesting alternative to vapour compression is magnetic refrigeration, pioneered decades ago. In the framework of development for an industrial-size 1.8 K magnetic refrigerator using a static active material, we have designed, built and tested a pulsed superconducting magnet producing up to 3 T at a ramping rate of 6.5 T/s. The solenoid-type coil, wound with low-loss superconducting wire (small-filament NbTi in a composite Cu/Cu-Ni matrix), is internally cooled by normal boiling helium, and installed inside a toroidal yoke, made of tapered laminations of commercially pure iron. After describing design and construction of the magnet, we present test results and measurements of performance, field quality and pulsed-operation losses. >
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.
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.
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.
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.
1161525
Recent studies of dispersion matched steering for the ILC bunch compressor and main linac
The dispersion matched steering (DMS) method is studied in detail in the context of a curved main linac. In the absence of cavity tilts (rotations in the YZ plane), DMS provides a unique and stable solution with negligible emittance growth. If cavity tilts are about 300 murad, the algorithm is not very robust. The emittance growth through the entire linac for positrons is about 5 nm, if the system is strictly static and statistical averaging can be used to improve beam position measurements. This growth is mostly eliminated if the dispersion and its derivative at injection can be adjusted. If anticipated ground motion, beam and klystron jitter, beam position measurement resolution are introduced (i.e. dynamical case), the emittance preservation goal is currently not achieved by DMS alone. Mitigation strategies are outlined.
122661128
A first approach to mechanical construction and cooling of a composite 3D silicon vertex detector
Abstract This paper presents first results on mechanical and cooling studies for a 3D silicon vertex detector designed for B physics at a hadron collider. Prototype modules were built from raw silicon wafers. One module was instrumented with resistors to simulate readout electronics. Both module movement and temperature variations were recorded. A cooling method utilizing simple air/helium flow was investigated, but proved inadequate because of too large temperature anisotropies.
122472626
Recent results from Fermilab E687 on charm spectroscopy
Recent analyses of charm spectroscopy from Fermilab fixed target experiment 687 [1] are summarized. Emphasis is placed on the phenomenology of Cabibbo suppression in the meson sector. Such transitions have been observed in the semileptonic modes and hadronic modes. While the former transitions give us an opportunity to observe the weak current and the CKM matrix, a systematic comparison of the latter transitions allow us to study strong interaction effects, and possibly, light quark spectroscopy.
116611232
B Physics working group summary
Calculations of the B{sub c} spectrum of energy levels, transitions between levels, and weak decays of the ground state, as well as their production and observation at hadron colliders, are summarized. Also, recent experimental B Physics results from the CDF and D0 Tevatron experiments are reviewed and future prospects are discussed.