115884934
Operational experience with the LEP low-beta superconducting quadrupoles
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.
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. >
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
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.
17521917
Simulation of the Electron Flux Into the Main Injector Electron Cloud Retarding Field Analyzer Using Vorpal
We present results from precision simulations of the electron cloud (EC) in the Fermilab Main Injector (MI), focusing on the dynamics of the EC close to the Retarding Field Analyzer (RFA) detectors. Our simulations are based on the Vorpal plasma simulation package. We find that the presence of a parasitic, weak (few Gauss) magnetic field significantly alters the spatial distribution of electrons in the cloud. The detected flux can easily change by factors of two depending on the location of the RFA. Moreover, the growth rate of the EC is also sensitive to such magnetic fields. Therefore, we suggest to (i) upgrade the RFA preamplifier to ￻ 10 MHz bandwidth such that the change in EC growth rate during a complete MI bunch train can be detected; (ii) install a small solenoid (of ￻ 25 Gauss maximum) to optionally switch off the EC, and thereby cleanly establish the presence of low energy electrons in the pipe; and (iii) design an RFA that can be inserted in a ￻ 2 kGauss field, such that an EC signal can be seen in the environment that matters, i.e., in the MI dipoles.
23121089
A comparison and benchmark of two electron cloud packages
We present results from precision simulations of the electron cloud (EC) problem in the Fermilab Main Injector using two distinct codes. These two codes are (i)POSINST, a F90 2D+ code, and (ii)VORPAL, a 2D/3D electrostatic and electromagnetic code used for self-consistent simulations of plasma and particle beam problems. A specific benchmark has been designed to demonstrate the strengths of both codes that are relevant to the EC problem in the Main Injector. As differences between results obtained from these two codes were bigger than the anticipated model uncertainties, a set of changes to the POSINST code were implemented. These changes are documented in this note. This new version of POSINST now gives EC densities that agree with those predicted by VORPAL, within {approx}20%, in the beam region. The root cause of remaining differences are most likely due to differences in the electrostatic Poisson solvers. From a software engineering perspective, these two codes are very different. We comment on the pros and cons of both approaches. The design(s) for a new EC package are briefly discussed.
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.
120906556
THE BTEV TRIGGERS AND DATA ACQUISITION SYSTEMS
A coherent and complete suite of triggers and data compression stages for the BTeV experiment has been designed and prototyped. Level 1 considers all crossings, finds primary vertices, and searches for detached tracks from these primary vertives using only the pixel vertex detector. Muons with a relatively high transverse momentum will also be identified at that stage. Level 1 runs on dedicated processors. Level 2 selects events based on the pixel and the forward tracking systems, and will run on a conventional processor farm. Level 3 will use the complete BTeV detector information to reduce the background by a factor of factor 2 to 5 and to reduce significantly the event size.
54053068
Microwave Transmission Through the Electron Cloud at the Fermilab Main Injector: Simulation and Comparison with Experiment
Simulations of the microwave transmission properties through the electron cloud at the Fermilab Main Injector have been implemented using the plasma simulation code 'VORPAL'. Phase shifts and attenuation curves have been calculated for the lowest frequency TE mode, slightly above the cutoff frequency, in field free regions, in the dipoles and quadrupoles. Preliminary comparisons with experimental results for the dipole case are showed and will guide the next generation of experiments.