Physics

Permanent URI for this communityhttp://hdl.handle.net/1903/2269

Browse

Filter results by typing the first few letters
Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Design of a nonlinear quasi-integrable lattice for resonance suppression at the University of Maryland Electron Ring
    (2018) Ruisard, Kiersten; Koeth, Timothy; Thomas, Antonsen; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Conventional particle accelerators use linear focusing forces for transverse confinement. As a consequence of linearity, accelerating rings are sensitive to myriad resonances and instabilities. At high beam intensity, uncontrolled resonance-driven losses can deteriorate beam quality and cause damage or radio-activation in beam line components and surrounding areas. This is currently a major limitation of achievable current densities in state-of-the-art accelerators. Incorporating nonlinear focusing forces into machine design should provide immunity to resonances through nonlinear detuning of particle orbits from driving terms. A theory of nonlinear integrable beam optics is currently being investigated for use in accelerator rings. Such a system has potential to overcome the limits on achievable beam intensity. This dissertation presents a plan for implementing a proof-of-principle quasi-integrable octupole lattice at the University of Maryland Electron Ring (UMER). UMER is an accelerator platform that supports the study of high-intensity beam dynamics. In this dissertation, two designs are presented that differ in both complexity and strength of predicted effects. A configuration with a single, relatively long octupole magnet is expected to be more stabilizing than an arrangement of many short, distributed octupoles. Preparation for this experiment required the development and characterization of a low-intensity regime previously not operated at UMER. Additionally, required tolerances for the control of first and second order beam moments in the proposed experiments have been determined on the basis of simulated beam dynamics. In order to achieve these tolerances, a new method for improved orbit correction is developed. Finally, a study of resonance-driven losses in the linear UMER lattice is discussed.
  • Thumbnail Image
    Item
    Novel Emittance Measurement Through Experimental Study of Envelope Mode Resonance in a High-Intensity Particle Beam
    (2015) Stem, William Durst; Koeth, Timothy W; O'Shea, Patrick G; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    On-line monitoring of beam quality for high-intensity particle beams requires non-invasive transverse phase space diagnostics. Such diagnostics are in high demand for use in heavy ion accelerators and free-electron lasers (FELs). A technique to measure emittance using multi-turn resonant excitation of the quadrupole envelope mode has been demonstrated at the University of Maryland Electron Ring (UMER). The rms Kapchinsky-Vladimirsky (KV) equations predict the time-evolution of particle beam envelopes. Linear perturbations to the matched envelope solution of these equations excite normal modes at space-charge-dependent natural frequencies. This experiment employs periodic, impulsed perturbations to drive resonant excitations of these modes. Steady state resonance structure in the form of a lattice is predicted using analytic solutions of a delta-kicked simple harmonic oscillator (SHO). Numerical simulations of this SHO along with simulations from the WARP envelope solver and particle-in-cell (PIC) codes are documented. This dissertation presents the first proof-of-principle experimental resonant excitation of the quadrupole envelope mode in a high-intensity particle beam. To excite the mode experimentally, an rf-driven electric quadrupole is constructed and installed in UMER. The quadrupole fields are driven by a tunable resonant tank circuit designed and built for this experiment. After resonant excitation, the knockout imaging method is used to collect 3 ns synchronized transverse time slice images of the beam. Image moments are analyzed and show good agreement with simulation. Emittance can then be inferred from the measured natural frequencies of the envelope modes utilizing a conversion obtained through simulation. A direct emittance measurement is performed using a conventional pinhole scan at injection as an experimental validation of the envelope resonance method.
  • Thumbnail Image
    Item
    Structured Plasma Waveguides and Deep EUV Generation Enabled by Intense Laser-Cluster Interactions
    (2012) Layer, Brian; Milchberg, Howard M; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Using the unique properties of the interaction between intense, short-pulse lasers and nanometer scale van-der-Waals bonded aggregates (or `clusters'), modulated waveguides in hydrogen, argon and nitrogen plasmas were produced and extreme ultraviolet (EUV) light was generated in deeply ionized nitrogen plasmas. A jet of clusters behaves as an array of mass-limited, solid-density targets with the average density of a gas. Two highly versatile experimental techniques are demonstrated for making preformed plasma waveguides with periodic structure within a laser-ionized cluster jet. The propagation of ultra-intense femtosecond laser pulses with intensities up to 2x1017 W/cm2 has been experimentally demonstrated in waveguides generated using both methods, limited by available laser energy. The first uses a `ring grating' to impose radial intensity modulations on the channel-generating laser pulse, which leads to axial intensity modulations at the laser focus within the cluster jet target. This creates a waveguide with axial modulations in diameter with a period between 35 μm and 2 mm, determined by the choice of ring grating. The second method creates modulated waveguides by focusing a uniform laser pulse within a jet of clusters with flow that has been modulated by periodically spaced wire obstructions. These wires make sharp, stable voids as short as 50 μm with a period as small as 200 μm within waveguides of hydrogen, nitrogen, and argon plasma. The gaps persist as the plasma expands for the full lifetime of the waveguide. This technique is useful for quasi-phase matching applications where index-modulated guides are superior to diameter modulated guides. Simulations show that these `slow wave' guiding structures could allow direct laser acceleration of electrons, achieving gradients of 80 MV/cm and 10 MV/cm for laser pulse powers of 1.9 TW and 30 GW, respectively. Results are also presented from experiments in which a nitrogen cluster jet from a cryogenically cooled gas valve was irradiated with relativistically intense (up to 2x1018 W/cm2) femtosecond laser pulses. The original purpose of these experiments was to create a transient recombination-pumped nitrogen soft x-ray laser on the 2p3/2→1s1/2 (λ = 24.779 Å) and 2p1/2→1s1/2 (λ = 24.785 Å) transitions in H-like nitrogen (N6+). Although no amplification was observed, trends in EUV emission from H-like, He-like and Li-like nitrogen ions in the 15 - 150 Å spectral range were measured as a function of laser intensity and cluster size. These results were compared with calculations run in a 1-D fluid laser-cluster interaction code to study the time-dependent ionization, recombination, and evolution of nitrogen cluster plasmas.