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.
56333052
Benchmarking/Crosschecking DFS in the ILC Main Linac
In an effort to compare beam dynamics and create a ''benchmark'' for Dispersion Free Steering (DFS) a comparison was made between different ILC simulation programs while performing DFS. This study consisted of three parts. First, a simple betatron oscillation was tracked through each code. Secondly, a set of component misalignments and corrector settings generated from one program was read into the others to confirm similar emittance dilution. Thirdly, given the same set of component misalignments DFS was performed independently in each program and the resulting emittance dilution was compared. Performance was found to agree exceptionally well in all three studies.
16599712
Comparison of tracking codes for the International Linear Collider
In an effort to compare beam dynamics and create a "benchmark" for Dispersion Free Steering (DFS) a comparison was made between different International Linear Collider (ILC) simulation programs while performing DFS. This study consisted of three parts. Firstly, a simple betatron oscillation was tracked through each code. Secondly, a set of component misalignments and corrector settings generated from one program was read into the others to confirm similar emittance dilution. Thirdly, given the same set of component misalignments, DFS was performed independently in each program and the resulting emittance dilution was compared. Performance was found to agree exceptionally well in all three studies.
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.
62352767
ASPECTS OF SCIENTIFIC VISUALIZATION FOR HEP ANALYSIS AT FERMILAB
33125511
Beam-Beam Effects in the Tevatron Run II
Electromagnetic long-range and head-on interactions of high intensity proton and antiproton beams are significant sources of beam loss and lifetime limitations in the Tevatron Collider Run II (2001-present). We present observations of the beam-beam phenomena in the Tevatron and results of relevant beam studies. We analyze the data and various methods employed in high energy physics (HEP) operation, predict the performance for planned luminosity upgrades and discuss ways to improve it.
121495790
Ionization loss in BGO
Abstract We report on a precise measurement of the energy loss through ionization by pions in bismuth germanate performed at several values of the incident particles momentum with a prototype of the L3 electromagnetic calorimeter. The experimental results are in good agreement with theoretical predictions showing the relativistic rise modified by density effect.
118077361
The Superfluid Helium Cryogenic System for the LHC Test String: Design, Construction and First Operation
A major milestone in the preparation of the Large Hadron Collider (LHC) project is the testing and operation of a 50-m long superconducting magnet string, representing a half-cell of the machine lattice. This also corresponds to the length of the elementary cooling loops providing refrigeration at the 1.9 K, 4.5-to-20 K, and 50-to-75 K levels to the LHC cryomagnets. Based on existing large-capacity cryogenic infrastructure, we have designed, built and are operating a dedicated cryogenic system feeding the LHC Test String, with installed capacities of 120 W @ 1.8 K and 10 g/s supercritical helium at 4.5 K. The system also includes 15 kA, 1.6 kA, 500 A, 250 A and 50 A current lead pairs for powering of main and auxiliary magnet circuits, as well as a 120 kW liquid nitrogen vaporizer for controlled cooldown of the 105 kg cold mass. The system is fully instrumented, controlled by dedicated industrial PLCs connected to an industrial supervision system. We report on performance in operation, including response of the system to transients such as current ramp and discharge, as well as magnet resistive transitions.
108668199
Operational Experience with a Cryogenic Axial-Centrifugal Compressor
The Large Hadron Collider (LHC), presently under construction at CERN, requires large refrigeration capacity at 1.8 K. Compression of gaseous helium at cryogenic temperatures is therefore inevitable. Together with subcontractors, Linde Kryotechnik has developed a prototype machine. This unit is based on a cryogenic axial-centrifugal compressor, running on ceramic ball bearings and driven by a variable-frequency electrical motor operating at ambient temperature. Integrated in a test facility for superconducting magnets, the machine has been commissioned without major problems and successfully gone through the acceptance test in autumn 1995. Subsequent steps were initiated to improve efficiency of this prototype. This paper describes operating experience gained so far and reports on measured performance prior and after constructional modifications.
59027060
ASSESSING RISK IN COSTING HIGH-ENERGY ACCELERATORS:FROM EXISTING PROJECTS TO THE FUTURE LINEAR COLLIDER
High-energy accelerators are large projects funded by public money, developed over the years and constructed via major industrial contracts both in advanced technology and in more conventional domains such as civil engineering and infrastructure, for which they often constitute one-off markets. Assessing their cost, as well as the risk and uncertainty associated with this assessment is therefore an essential part of project preparation and a justified requirement by the funding agencies. Stemming from the experience with large circular colliders at CERN, LEP and LHC, as well as with the Main Injector, the Tevatron Collider Experiments and Accelerator Upgrades, and the NOvA Experiment at Fermilab, we discuss sources of cost variance and derive cost risk assessment methods applicable to the future linear collider, through its two technical approaches for ILC and CLIC. We also address disparities in cost risk assessment imposed by regional differences in regulations, procedures and practices.
122883842
SUPERFLUID HELIUM AS A TECHNICAL COOLANT
The characteristics of superfluid helium as a technical coolant, which derive from its specific transport properties, are presented with particular reference to the working area in the phase diagram (saturated or pressurised helium II). We then review the principles and scaling laws of heat transport by equivalent conduction and by forced convection in pressurised helium II, thus revealing intrinsic limitations as well as technological shortcomings of these cooling methods. Once properly implemented, two-phase flow of saturated helium II presents overwhelming advantages over the previous solutions, which dictated its choice for cooling below 1.9 K the long strings of superconducting magnets in the Large Hadron Collider (LHC), a 26.7 km circumference particle collider now under construction at CERN, the European Laboratory for Particle Physics near Geneva (Switzerland). We report on recent results from the ongoing research and development programme conducted on thermohydraulics of two-phase saturated helium II flows, and on the validation of design choices for the LHC cooling system.