37433006
Measurement and simulation of source-generated halos in the University Of Maryland Electron Ring (UMER)
One of the areas of fundamental beam physics that have served as the rationale for recent research on UMER is the study of the generation and evolution of beam halos. Recent experiments and simulations have identified imperfections in the source geometry, particularly in the region near the emitter edge, as a significant potential source of halo particles. The edge-generated halo particles, both in the experiments and the simulations are found to pass through the center of the beam a short distance downstream of the anode plane. Understanding the detailed evolution of these particle orbits is therefore important to designing any aperture to remove the beam halo.
23902126
The University of Maryland Electron Ring (UMER) enters a new regime of high-tune-shift rings
Beams with a high phase space density are useful for many modern applications such as free electron lasers, pulsed neutron sources, high-energy-density physics, and high-luminosity colliders. Production of such beams requires understanding the complex space charge dynamics at the low-energy end of the accelerator. The University of Maryland Electron Ring (UMER) has been designed and built with the purpose of investigating space charge effects using scaled low-energy electron experiments. We have recently circulated the highest- space-charge beam in a ring to date, achieving a breakthrough both in the number of turns and in the amount of current propagated. We have propagated a beam with an integer tune shift for over 100 turns, and other, even higher-current beams, for 5-50 turns albeit with some beam loss. One beam had a tune shift at injection of 5.0, which is several factors higher than anything propagated in the past. We report here as well on other interesting aspects of the UMER work.
109430895
Rotational Mismatches and Emittance Growth for the UMER Beam
This is a numerical study of the effects of a rotational mismatch of a beam at injection. A closely related type of mismatch is the presence of a skew quadrupole at some place in the transporting channel. In both cases, the initial mismatch implies that the emittance of the beam will increase as the beam is transported through an alternating focusing channel. In our simulations, we used the WARP computer code to simulate the University of Maryland Electron Ring (UMER) beam and we have indeed seen a substantial emittance growth (by a factor of 2–3) for mismatches of 10 degrees.
118277402
Recursive equations for arbitrary scattering processes at tree order and beyond
An examination subject is irradiated with a sequence of RF pulses. Negative gradient pulses Gz3 and Gy4, as well as a phase-coding gradient Gx2 are generated preceding each RF pulse. Negative gradient pulses Gz2 and Gy1, as well as a phase-coding gradient Gx1, are generated following each RF pulse. The phase-coding gradient Gx1 is inverted relative to the phase-coding gradient Gx2. The negative gradient pulse Gy1 is followed by a positive gradient pulse Gy2 which serves as a read-out gradient during which a first signal S1 is received. A positive gradient pulse Gy3 is generated preceding the negative gradient pulse Gy4, the positive gradient pulse Gy3 serving as a read-out gradient during which a second signal S2 is received. Two signals having different T2 weighting are thus obtained in each measuring sequence, without extending the measuring time. Two images having different T2 contrast, and thus increased diagnostic value, can thus be produced.
121078454
Astrophysics at n_TOF Facility at CERN
The neutron time of flight (n_TOF) facility at CERN is a spallation neutron source with white neutron energy spectrum (from thermal to several GeV), covering the full energy range of interest for nuclear astrophysics, in particular for measurements of the neutron capture cross section required in s-process nucleosynthesis. This contribution presents an overview on the astrophysical program carried on at the n_TOF facility, the main results and their implications.
59270303
High Accuracy 233U(n, f) Cross-Section Measurement at the White-Neutron Source n_TOF from Near-Thermal to 1 MeV Neutron Energy
The U-233(n, f) cross section has been measured at the white neutron source n_TOF in a wide energy range with a dedicated fission ionization chamber. We report here the results from similar to 30 meV to 1 MeV neutron energy. The U-233(n, f) cross section has been determined relative to a reference sample of U-235(n, f) measured simultaneously with the same detector. The very high instantaneous neutron flux and the intrinsically low background of the n_TOF installation result in an accuracy around 3 range, while the energy resolution of the neutron beam allows for an accurate description of the fission cross section by means of R-matrix analysis over a wide energy range. The results are, in general, in good agreement with the most recent high-accuracy measurement of this fission cross section, over the more limited range of the previous measurements, and indicated that even the latest evaluations underestimate the cross section in the epithermal region. The present high-quality data provide the basis for a more precise evaluation of the U-233 fission cross section and for improving the reliability of databases needed for the design of new energy systems based on the Th/U cycle.
119874447
Intermittency effects in a two-component model
Abstract We study the intermittency phenomenon in high-energy collisions assuming that a new component in particle production processes, corresponding to a higher-order phase transition in the Feynman-Wilson fluid, coexists incoherently with a conventional production mechanism characterized by standard, finite-range correlations in rapidity space. The complementary effects of these two components are investigated and the origin of the power-law behaviour of the scaled factorial moments in present experiments is discussed.
2891581
HELAC - A MONTE CARLO GENERATOR FOR MULTI-JET PROCESSES
The status of the multi-purpose event generator HELAC is briefly presented. The aim of this tool is the full simulation of events within the Standard Model (SM) at current and future high energy experiments, in particular the LHC. Some results related to the production of multi-jet final states at the LHC are also discussed.