Patrick G. O'Shea

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It is widely believed that harmonics are suppressed in helical wigglers. However, linear harmonic generation (LHG) occurs by an azimuthal resonance that excites circularly polarized, off-axis waves, where the hth harmonic varies as exp((ihtheta). Nonlinear harmonic generation (NHG) is driven by bunching at the fundamental and has different properites from(More)
∗ Research supported by the U.S. Department of Energy. † Abstract A new optics design for beam injection into the University of Maryland Electron Ring (UMER) is proposed for multi-turn operations. We review the previous method where two pulsed and physically overlapped Panofsky quadrupoles (one is centered on the injector and the other is(More)
Alignment of experimental components is critical to operation of The University of Maryland Electron Ring (UMER). Procedures and equipment used to align components of the electron ring are presented. The compact nature of UMER (ring diameter ≈ 4 m) presents unique challenges and advantages associated with the placement of vacuum components, confinement and(More)
Initial experimental results are presented for measurements of the emittance of an electron beam in the University of Maryland Electron Ring (UMER). Two independent sets of slit-collector systems are used to measure the emittance in the vertical and horizontal directions respectively. Results are then compared to the time integrated emittance measurements(More)
The University of Maryland Electron Ring (UMER) is a small-scale experiment on space-charge dominated beams. The 100 ns, 10 keV electron beam fills up nearly one-half of the ring circumference. Here we review two models for the evolution of such beams, and present some initial results of measurements of longitudinal beam expansion for two initial line(More)
Both galaxies and charged particle beams can exhibit collisionless evolution on surprisingly short time scales. This can be attributed to the dynamics of chaotic orbits. The chaos is often triggered by resonance caused by time dependence in the bulk potential, which acts almost identically for attractive gravitational forces and repulsive electrostatic(More)
Density modulation of charged particle beams may occur as a consequence of deliberate action, or may occur inadvertently because of imperfections in the particle source or acceleration method. In the case of intense beams, where space charge and external focusing govern the beam dynamics, density modulation may, under some circumstances, be converted to(More)
We report a new experimental study of the growth of longitudinal energy spread in a space-charge-dominated electron beam, with a beam energy of several keV and beam current of approximately 100 mA. At relatively low beam densities, we measure growing energy spreads with distance along the transport channel, which are in remarkably good agreement with the(More)