A diode laser velocimeter based on laser self-mixing has been developed and characterized as a reliable, precise, comparably cheap, and compact monitor. The resolution of this sensor at different incident angles and for a variety of solid and liquid targets moving at velocities between 0.1 and 50 m/s is presented. This includes a theoretical analysis of the underlying measurement principle, highlighting possibilities to extend the measurement capabilities to even higher velocities by altering the sensor design. Finally, an outlook on future applications of the sensor for detailed studies of supersonic gas jets used in beam diagnostics and atomic physics applications is given.
Supersonic gas jets can be used as a profile monitor for charged particle beams, as well as a cold target for collision experiments. For the optimisation of these experiments, it is important to know the velocity and density distribution of the jet. In these applications, gas jet velocities can be up to 2000 m/s. A diode laser velocimeter based on laser self-mixing method is currently being developed as an easy to build and compact alternative measurement technique. The technique seems a promising way for a complete characterisation of the gas jet parameters. It should be pointed out, however, that laser self-mixing is usually used for measurement of low velocities and vibrations. In this contribution, the heterodyne principle and design of the laser diode velocimeter are first discussed. The laser velocimeter is a self-aligning device, based on the self-mixing method where the laser is both, transmitter and receiver of the signal. The here presented theoretical analysis shows the possibility to extend measurement capabilities also to high velocities by altering the design. Experimental results from measurements with different targets are presented. The set-up for testing the sensor allows investigations into the limitation of the method to be made as well as the amount of feedback which is required for a detailed study of a gas jet.
Synchrotron radiation is emitted whenever a beam of charged particles passes though a magnetic field. The power
emitted is strongly dependent on the relativistic Lorentz factor of the particles, which itself is proportional to the beam
energy and inversely proportional to the particle rest mass. Thus, synchrotron radiation is usually associated with
electron accelerators, which are commonly used as light sources. However the largest proton machines reach sufficiently
high energies to make synchrotron light useful for diagnostic purposes.
The Large Hadron Collider at CERN will accelerate protons up to an energy of 7TeV. An optical arrangement has been
made which focuses synchrotron light from two LHC magnets to image the cross-section of the beam. It is also planned
to use this setup to produce a longitudinal profile of the beam by use of fast Single Photon Counting. This is complicated
by the bunched nature of the beam which needs to be measured with a very large dynamic range.
In this contribution we present early experimental data of the transverse LHC beam profile together with a scheme for
measuring the longitudinal profile with a time resolution of 50 ps. It includes the use of a gating regime to increase the
dynamic range of the photon counter and a three-stage correction algorithm to compensate for the detector's deadtime,
afterpulsing and pile-up effects.
In future high intensity, high energy accelerators, beam losses have to be minimized to maximize performance and
reduce activation of accelerator components. It is imperative to have a clear understanding of the mechanisms that can
lead to halo formation and to have the possibility to test available theoretical models with an adequate experimental
setup. Measurements based on optical transition radiation (OTR) provide an interesting opportunity for high resolution
measurements of the transverse beam profile.
An imaging system based on a beam core-suppression technique, in which the core of the beam is deflected by means of
a micro mirror array, to allow for direct observation of the halo has been developed. In this contribution, a possible
layout of a novel diagnostic system based on adaptive optics is presented and the results of first tests carried out in our
optical lab are summarized.
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