119232009
Plate fin heat exchanger model with axial conduction and variable properites
Future superconduction radio frequency (SRF) cavities, as part of Project X at Fermilab,will be cooled to superfluid helium temperatures by a cryogenic distribution system supplying cold supercritical helium. To reduce vapor fraction during the final Joule Thomson (J-T) expansion into the superfluid helium cooling bath, counter-flow, plate-fin heat exchanger are an effective option. However, at liquid helium temperatures requires consideration of axial heat conduction along the direction of flow, in addition to variable fluid properties. Here we present a numberical model that includes the effects of axial guide design decisions on heat exhanger material choice and geometry. In addition, the J-T expansion process is modeled with the heat exchanger to analyze the effect of heat load and cryogenic supply parameters.
109984057
Fermilab SRF cryomodule operational experience
Fermi National Accelerator Laboratory is constructing an Advanced Accelerator Research and Development facility at New Muon Lab. The cryogenic infrastructure in support of the initial phase of the facility consists of two Tevatron style standalone refrigerators, cryogenic distribution system as well as an ambient temperature pumping system to achieve 2 K operations with supporting purification systems. During this phase of the project a single Type III plus 1.3 GHz cryomodule was installed, cooled and tested. Design constraints of the cryomodule required that the cryomodule individual circuits be cooled at predetermined rates. These constraints required special design solutions to achieve. This paper describes the initial cooldown and operational experience of a 1.3 GHz cryomodule using the New Muon Lab cryogenic system.
122091552
NEUTRAL PION PHOTOPRODUCTION AND PROTON COMPTON SCATTERING AT LARGE ANGLES
121936146
Acceleration of Heavy Ions at the Princeton Particle Accelerator
Modifications to the Princeton Particle Accelerator (PPA) such as pulsed heavy ion source, extended range radiofrequency system, vacuum system improvements, allowed the adaptation of the 3 GeV proton synchrotron to the acceleration of heavier ions. Accele ation of nitrogen ions in a charge state of N5+ and N6+ to an energy of 4 and 7 GeV were achieved starting in July 1971. Present average intensities run at about 3 x 105 and 2 x 105 particles/sec. Expectations for acceleration of neon and argon in the near future will be discussed.
109689468
Spallation neutron source (SNS)
The Spallation Neutron Source [1], located at Oak Ridge, TN, is a state-of-the-art neutron-scattering facility presently under construction as a collaborative effort of six national laboratories. The facility is comprised of a high-power particle-accelerator system, a liquid-mercury target-moderator system, and a suite of world-class scientific instruments. One-ms-long negative-hydrogen-ion (H - ) pulses are produced by an ion source. The ion beam is accelerated to 185 MeV by normal conducting (NC) linear accelerator (linac) cavities, and further accelerated to 1 GeV by a superconducting linac [2]. The acceleration is accomplished by means of niobium superconducting radiofrequency (SRF) cavities that operate at 2.1K. The linac beam is stacked in a compressor ring, and 695-ns-long pulses are extracted onto the target at a 60-Hz rate. Neutrons are produced by spallation in the mercury, and their energy is moderated to useable levels, in part by supercritical hydrogen moderators. The simultaneous performance goals of more than one MW of initial proton beam power, 95% facility availability, and the desire for hands-on maintenance capability in the accelerator complex place significant demands on the performance and operational reliability of the technical and conventional systems. An overview of the SNS facility, including its purpose, major components, and a summary of the present status is presented, with particular emphasis on the superconducting linac and the cryogenic moderators.
119260064
MSSM dark matter measurements at the LHC without squarks and sleptons
We examine the case of neutralino dark matter in the focus point region of the MSSM, in which the scalar sparticles are too heavy to be produced at the LHC. Whilst it has been previously asserted that the LHC alone would fail to constrain the properties of the lightest neutralino for such a scenario, we find that one can obtain good predictions of astrophysical quantities such as the relic density, annihilation cross-section and direct search cross-sections by using the shape of the dilepton invariant mass spectrum to constrain neutralino mixing. We demonstrate our technique using a Bayesian analysis of the 24 parameter MSSM model space, and in the process introduce a novel way of improving the LHC results even without assumptions on which new sparticles are responsible for the kinematic features in the dilepton invariant mass distribution. Finally, we consider the interplay between direct search experiments and the LHC, and find that, even with a realistic estimate of the relevant astrophysical uncertainties, one could also combine current direct search exclusion limits with LHC data to constrain neutralino mixing and improve the predicition of other astrophysical quantities.
125390779
Proton compton scattering and neutral-pion photoproduction at large angles
The differential cross sections for ..gamma..p ..-->.. ..gamma..p and ..gamma..p ..-->.. ..pi../sup 0/p have been measured from abs. value (t) = 0.7 to 4.3 GeV/sup 2/ and for incident energies in the range 2 to 6 GeV. The energy dependence of Compton scattering is well described by parton model ideas. However, the energy dependences of ..pi../sup 0/ photoproduction and the ratio of Compton scattering to ..pi../sup 0/ photoproduction are not consistent with dimensional counting arguments.