58893353
FERMILAB BOOSTER CHARGE AS A FUNCTION OF LINAC INTENSITY
A common belief at Fermilab has been that the Booster performed best when the Linac operated at the highest possible beam currents. In order to provide these high currents the Linac has been running at least 50% above the design intensity since shortly after the Linac upgrade in 1993. Early in 2002 it was decided to investigate this dependence to see if the Booster operated more efficiently with a higher Linac current and a low number of turns.
119968235
Direct current surface plasma source with high emission current density
A surface plasma source for long-time dc operation with efficient production of negative ions and high emission current density has been designed and tested. Several modifications of the discharge system, beam extraction, cesium supply, and source design have been tested for long-time operation. The emission current density of H− ions has been increased to j=1 A/cm2 in the dc mode of operation with a discharge voltage, Ud=80 V; a discharge current, Id=0.9 A and a discharge power, P=70 W. Corresponding efficiency of the current density production S=j/P=15 A/cm2 kW is much higher than in modern positive ion sources. Source features determining an operational lifetime will be discussed.
121242219
Attainment of an MeV-range, DC electron beam for the Fermilab cooler
To prepare a beam generation device for Fermilab's future Recycler Electron Cooling system, an experimental set-up with a simplified beam line has been commissioned at Fermilab. Stable operation was achieved at an electron energy of 3.5 MeV and a DC beam current of up to 0.5 A. The main reason for interruptions of the operation was found to be microsecond long bursts of the cathode current. While the frequency of the interruptions is determined primarily by a flow of secondary ions, the resulting reduction in the duty factor depends on the beam optics, the protection systems, and the tube electric field strength.
118674965
Operation and improvements of the Fermilab 400 MeV Linac
The 400 MeV Fermilab Linac Upgrade commissioning began August 28, 1993. High energy physics collider operation (run 1b) began in November 1993 and ended March 1, 1996. The Linac, operating at 98% reliability, provided 400 MeV H{sup -} beam to the Booster and 66 MeV H{sup -} beam to the Neutron Therapy Facility. During this time, the beam intensity, which initially was administratively set to 35 MA, rose to a peak of 50 mA while losses decreased significantly. This paper discusses the Linac operation and reliability since the Upgrade.
123613871
Observations of the transverse and longitudinal nature of the Fermilab linac beam
The installation of nonintercepting beam position monitors (BPMs) in the 200 MeV linac at Fermilab has facilitated several new observations on the character of the linac beam. In particular, two interesting phenomena have been discovered: a high-frequency change in the beam position and a slow variation in the phase-lock loops during a 30 mu s beam pulse. Progress in initiating the Delta -t measurement is being made. The Delta -t procedure adjusts the RF phase and amplitude in each of the accelerating modules of a linac. The procedure uses beam-induced signals from linac BPMs to determine changes in the times of flight of beam bunches when the tuned module is turned off and when it is turned on.<<ETX>>
113925183
Factors Affecting H- Beam Performance in the Fermilab Linac
17272111
Effects of fermion localization in Higgsless theories and electroweak constraints
Abstract Extra-dimensional Higgsless models with electroweak symmetry breaking through boundary conditions generically have difficulties with electroweak precision constraints, when the fermions are localized to the “branes” in the fifth dimension. In this Letter we show that these constraints can be relaxed by allowing the light fermions to have a finite extent into the bulk of the fifth dimension. The T and U electroweak parameters can be naturally suppressed by a custodial symmetry, while the S parameter can be made to vanish through a cancellation, if the leakage into the bulk of the light gauge fields and the light left-handed fermion fields are of the same size. This cancellation is possible while allowing realistic values for the first two generations of fermion masses, although special treatment is probably required for the top quark. We present this idea here in the context of a specific continuum theory-space model; however, it can be applied to any five-dimensional Higgsless model, either with a flat or a warped background.
118744572
Baryon number and charge fluctuations from lattice QCD
Abstract We calculate electric and baryonic charge fluctuations on the lattice. Results have been obtained with the highly improved staggered quark action (HISQ) and almost physical quark masses on lattices with spacial extent of N τ = 6 , 8 , 12 . Higher order cumulants of the net-charge distributions are increasingly dominated by a universal scaling behavior, which is arising due to a critical point of QCD in the chiral limit. Considering cumulants up to the sixth order, we observe that they generically behave as expected from universal scaling laws, which is quite different from the cumulants calculated within the hadron resonance gas model. Taking ratios of these cumulants, we obtain volume independent results that can be compared to the experimental measurements. Such a comparison will unambiguously relate the QCD transition temperature that has been determined on the lattice with the freeze out temperature of heavy ion collision at LHC and RHIC.
13969763
Baryon number strangeness and electric charge fluctuations at zero and non-zero chemical potential
We present results on baryon number, strangeness and electric charge fluctuations in QCD at non-zero density and temperature obtained from lattice calculations with almost physical quark masses. At vanishing chemical potential, i.e. under conditions almost realized at RHIC and the LHC, quartic fluctuations of net baryon number and strangeness are large in a narrow temperature interval characterizing the transition region from the low to the high temperature phase. Our results are based on Taylor expansions in light and strange quark chemical potentials, i.e. we rigorously compute corrections to bulk thermodynamic quantities at non-vanishing chemical potential, by performing a Taylor expansion in μ/T. We find non-monotonic behavior for the radius of convergence of this series, which could be a hint for a critical end point in the (T, μ)-plane.
15351369
Charm production in deep inelastic scattering from threshold to high Q2
Charm final states in deep inelastic scattering constitute ~ 25% of the inclusive cross-section at small x as measured at HERA. These data can reveal important information on the charm and gluon structure of the nucleon if they are interpreted in a consistent perturbative QCD framework which is valid over the entire energy range from threshold to the high energy limit. We describe in detail how this can be carried out order-by-order in PQCD in the generalized MSbar formalism of Collins (generally known as the ACOT approach), and demonstrate the inherent smooth transition from the 3-flavor to the 4-flavor scheme in a complete order αs calculation, using a Monte Carlo implementation of this formalism. This calculation is accurate to the same order as the conventional NLO F2 calculation in the limit Q/mc >> 1. It includes the resummed large logarithm contributions of the 3-flavor scheme (generally known in this context as the fixed-flavor-number or FFN scheme) to all orders of αsln (mc2/Q2). For the inclusive structure function, comparison with recent HERA data and the existing FFN calculation reveals that the relatively simple order-αs (NLO) 4-flavor (mc≠0) calculation can, in practice, be extended to rather low energy scales, yielding good agreement with data over the full measured Q2 range. The Monte Carlo implementation also allows the calculation of differential distributions with relevant kinematic cuts. Comparisons with available HERA data show qualitative agreement; however, they also indicate the need to extend the calculation to the next order to obtain better description of the differential distributions.
117111536
THE DENSITY OF STATES METHOD AT FINITE CHEMICAL POTENTIAL.
We study the density of states method to explore the phase diagram of the chiral transition on the temperature and quark chemical potential plane. Four quark flavors are used in the analysis. Though the method is quite expensive small lattices show an indication for a triple-point connecting three different phases on the phase diagram.