Large aperture vibrating wire monitor with two mechanically coupled wires for beam halo measurements

Development of a new type of vibrating wire monitor (VWM), which has two mechanically coupled wires (vibrating and target), is presented. The new monitor has a much larger aperture size than the previous model of the VWM, and thus allows us to measure transverse beam halos more effectively. A prototype of such a large aperture VWM with a target wire length of 60 mm was designed, manufactured, and bench-tested. Initial beam measurements have been performed at the Fermilab High Intensity Neutrino Source facility, and key results are presented.open1

Vibrating Wire for Beam Profile Scanning

The method for measurement of transverse profile (emittance) of the bunch by detecting of radiation arising scattering at of the bunch on the scanning wire is wide-spread. In this work the information about scattering bunch is proposed to measure using the oscillation frequency of the tightened scanning wire. In such way the system of radiation (or secondary particles) extraction and measurement can be removed. Dependence of oscillations frequency on beam scattering is determined by several factors, including changes of wire tension caused by transverse force of the beam, influence of beam self field. Preliminary calculations show that influence caused by wire heating will dominate. We have studied strain gauges on the basis of vibrating wire from various materials (tungsten, beryl bronze, niobium zirconium alloys). A scheme of self oscillations generation by alternating current in autogeneration circuit with automatic frequency adjustment was selected. Special method of wire fixation and elimination of transverse degrees of freedom allow to achieve relative stability better than 1E-5 during several days. For a tungsten wire with a fixed end dependence of frequency on temperature was 1E-5/K. Experimental results and estimates of wire heating of existing scanners show, that the wire heats up to a few hundred grades, which is enough for measurements

Non-exciting wakefield structured bunches in a one-dimensional plasma model

A model of one-dimensional (1D) cold plasma with an external train of rigidly structured bunches with diverse charges has been introduced. In this model, a solution that cancels the wakefield after the train is found. The density of such bunches can be much greater than the density of the plasma, and a high amplitude electrical field arising inside the train can be used for charged-particle acceleration. In addition, analytical and numerical simulations have been performed

Superluminal synchrotron radiation

To avoid complex computations based on wide Fourier expansions, the electromagnetic field of synchrotron radiation (SR) was analyzed using Lienard-Wiechert potentials in this work. The retardation equation was solved for ultrarelativistic movement of rotating charge at distances up to the trajectory radius. The radiation field was determined to be constricted into a narrow extended region with transverse sizes approximately the radius of trajectory divided by the particle Lorentz factor (characteristic SR length) cubed in the plane of trajectory and the distance between the observation and radiation emission point divided by the Lorentz factor in the vertical direction. The Lienard-Wiechert field of rotating charge was visualized using a parametric form to derive electric force lines rather than solving a retardation equation. The electromagnetic field of a charging point rotating at superluminal speeds was also investigated. This field, dubbed a superluminal synchrotron radiation (SSR) field by analogy with the case of a circulating relativistic charge, was also presented using a system of electric force lines. It is shown that SSR can arise in accelerators from “spot” of SR runs faster than light by outer wall of circular accelerator vacuum chamber. Furthermore, the mentioned characteristic lengths of SR in orbit plane and in vertical direction are less than the interparticle distances in real bunches in ultrarelativistic accelerators. It is indicating that this phenomenon should be taken into account when calculating bunch fields and involved at least into the beam dynamic consideration

Dilation of the Giant Vortex State in a Mesoscopic Superconducting Loop

We have experimentally investigated the magnetisation of a mesoscopic aluminum loop at temperatures well below the superconducting transition temperature $T_{c}$. The flux quantisation of the superconducting loop was investigated with a $\mu$-Hall magnetometer in magnetic field intensities between $\pm 100 {Gauss}$. The magnetic field intensity periodicity observed in the magnetization measurements is expected to take integer values of the superconducting flux quanta $\Phi_{0}=h/2e$. A closer inspection of the periodicity, however, reveal a sub flux quantum shift. This fine structure we interpret as a consequence of a so called giant vortex state nucleating towards either the inner or the outer side of the loop. These findings are in agreement with recent theoretical reports.Comment: 12 pages, 5 figures. Accepted for publication in Phys. Rev.