Bulletin of the American Physical Society
2006 APS April Meeting
Saturday–Tuesday, April 22–25, 2006; Dallas, TX
Session B14: Particle Beam Physics and Technologies |
Hide Abstracts |
Sponsoring Units: DPB Chair: Joseph Bisognano, University of Wisconsin Room: Hyatt Regency Dallas Cumberland I |
Saturday, April 22, 2006 10:45AM - 10:57AM |
B14.00001: Experimental Investigation of Beam Breakup in the Jefferson Laboratory 10 kW FEL Upgrade Driver Christopher Tennant, David Douglas, Kevin Jordan, Lia Merminga, Eduard Pozdeyev, Haipeng Wang In energy recovery linacs the maximum average current can be limited by the multipass beam breakup (BBU) instability, which occurs when the electron beam interacts with the higher-order modes (HOMs) of an accelerating cavity on the accelerating pass and again on the energy recovered pass. Experimental characterization and observations of the instability at the Jefferson Laboratory 10 kW Free Electron Laser (FEL) Driver are presented. Methods to measure the threshold current for the instability were developed and the results were used to compare with the predictions of several BBU simulation codes. This represents the first time in which the codes have been definitively benchmarked. With BBU posing a threat to high current beam operation in the FEL Driver, several suppression schemes were successfully developed. These include direct damping of the dangerous HOM and appropriately modifying the electron beam optics so as to reduce the coupling between the beam and mode. [Preview Abstract] |
Saturday, April 22, 2006 10:57AM - 11:09AM |
B14.00002: Controlling wiggler harmonic radiation to minimize FEL cavity mirror damage S.L. Huang, Y.K. Wu Wigglers emit both fundamental and harmonic radiation. In UV-VUV oscillator FELs, harmonic radiation can cause serious damage to the downstream mirror of the FEL cavity. This work reports our studies of wiggler radiation loading on the FEL cavity mirror. A mechanism to control and reduce mirror damage using a set of controllable in-vacuum apertures is being developed for the Duke storage ring FELs. Two optical klystron FELs, one with a pair of horizontally polarized wigglers, the other with a pair of circularly polarized wigglers, will be studied in detail. We will report the effectiveness of the apertures in reducing the wiggler harmonic radiation loading on the FEL cavity mirror for both optical klystron FELs under various operation conditions and for different lasing wavelengths. [Preview Abstract] |
Saturday, April 22, 2006 11:09AM - 11:21AM |
B14.00003: Recent Studies of Coherent Bremsstrahlung Herbert Uberall The concept of coherent bremsstrahlung (CB), i.e., of X-rays generated by electrons in single crystals that exhibit monochromatic spikes was brought to light by Dyson and Uberall (Phys. Rev. 99, 1955, p. 604). Experimental studies were first carried out by Diambrini et al. (Rev. Mod. Phys. 40, 1968, p. 611) and repeated world-wide afterwards. These spikes are almost 100{\%} linearly polarized, such that CB is now being developed into a source of monochromatic polarized radiation in a way where no other method could accomplish that, and where many scientific investigations are now becoming possible due to its use, e.g. at Jefferson Lab., Newport News, VA. 5.7 GeV electrons produce 2-GeV photons with 84{\%} polarization at the peak energy. Experiments carried out with them involve production of $\rho $, $\zeta $ and $\omega $ mesons. Electrons of 189 GeV at CERN yield CB photons at 170 GeV. Studies are being carried out at 855-MeV Mainz electron accelerator MAMI, of the Mozley-de Wire effect, which, by collimating the emitted radiation, narrows the width of the CB peaks and enhances the CB linear polarization. [Preview Abstract] |
Saturday, April 22, 2006 11:21AM - 11:33AM |
B14.00004: Injection, focusing, and acceleration of electrons in the nonlinear 3D laser wakefield. Serguei Kalmykov, Leonid Gobunov, Patrick Mora, Gennady Shvets Accelerating and focusing phases of the nonlinear three-dimensional axi-symmetric laser wakefield can almost entirely overlap at some distance back from the laser pulse in homogeneous plasma. Field structure of this kind results from the curvature of phase fronts due to the radially inhomogeneous relativistic plasma frequency shift. Consequently, the number of trapped low-energy electrons can be much greater than that predicted by the linear wake theory. This effect is favorable for trapping and monoenergetic acceleration of considerable charge (several hundreds of pC) to about 1 GeV per electron in the plasma wakefield driven by the ultrashort (of order 30 fs) loosely focused (focal spot radius about 100 microns) petawatt laser pulse. [Preview Abstract] |
Saturday, April 22, 2006 11:33AM - 11:45AM |
B14.00005: Acceleration of a Train of Micro-Bunches Moving in a Dilute Resonant Active Medium Levi Schachter Adapting the frequency of a train of micro-bunches, injected into a resonant medium to the resonance of the latter, leads to an effective interaction between the electrons and the medium. Of particular interest is the case when the medium is active i.e. it stores energy since the train of micro-bunches may be accelerated. If the bandwidth of the resonant line is much narrower than that associated with the interference pattern of electromagnetic field of the $M$ micro-bunches, then the energy transferred is independent of the number of micro-bunches. Implying that all the bunches are uniformly accelerated. [Preview Abstract] |
Saturday, April 22, 2006 11:45AM - 11:57AM |
B14.00006: Electron Cloud Investigations in the Fermilab Main Injector Robert Zwaska, Weiren Chou, Ioanis Kourbanis, Alberto Marchionni, Vladimir Shiltsev, Xiaolong Zhang The Fermilab Main Injector currently accelerates 300 kW of 120 GeV protons for antiproton and neutrino production. We report on searches for the formation of an electron cloud within the Main Injector, and possible associated proton beam instabilities. Current capabilities and instrumentation upgrades will be discussed. These studies are performed with the anticipation that future plans could lead to a fourfold increase of the proton charge in the Main Injector. [Preview Abstract] |
Saturday, April 22, 2006 11:57AM - 12:09PM |
B14.00007: Characterization of Quasi-monoenergetic Neutron Beams from Deuteron Breakup at the 88-Inch Cyclotron Darren Bleuel, Margaret McMahan, Larry Ahle, Lee Bernstein, Lawrence Heilbronn A neutron irradiation facility is being developed at Lawrence Berkeley National Laboratory's (LBNL's) 88-inch cyclotron to measure neutron cross sections on radioactive targets important to nuclear astrophysics and stockpile stewardship. Quasi-monoenergetic neutron beams are produced in the 10-32 MeV range using the deuteron breakup reaction on various thin targets. Accurate characterization of these beams is needed before cross section measurements may be performed. To determine the neutron spectra produced by the breakup reaction on thin targets, three methods have been used, including activation foil measurements, direct neutron measurement using the time-of-flight technique with a Stilbene detector, and complimentary measurements of the associated protons using STARS, a silicon telescope array. Preliminary results indicate a good outlook for producing quasi-monoenergetic neutron beams with fluxes in the 10$^{6-8}$ n/cm$^{2}$/s range. [Preview Abstract] |
Saturday, April 22, 2006 12:09PM - 12:21PM |
B14.00008: Spatially resolved X-ray emission of heavy ion beam interaction with solid matter. Sergey Pikuz Jr., Olga Rosmej, Anatoly Faenov, Vladimir P. Efremov, Svitlana Korostiy, Abel Blazevic, Alexander Fertman, Igor Skobelev, Henry E. Norman, Dieter H.H. Hoffmann We have been investigated K-shell radiation of projectile ions and solid media during its interaction. The main advantage of the method consists in that the media is transparent for radiation applied for diagnostics, which provides the data acquisition directly from the interaction volume. The projectile and target spectra in the energy range of 1.5$^{ }-^{ }$8 keV were registered by means of spherically bend crystal spectrometers (FSSR) with a high spatial resolution along the beam propagation. The Ni, Ca and Mg ions accelerated in GSI UNILAC facility to the energies of 11.4 and 5.9 MeV/u were slowed down in solid quartz, quartz aerogels and aluminum media. Low-density (up to 0.02 g/cc) aerogel targets allowed expanding the interaction volume up to 100 times and, accordingly, to resolve the evolution of ion beam velocity and charge states inside the media. Simultaneously, the wavelengths and relative intensities of K$_{a}$ satellite lines radiated by Si and Al target ions with different charges were measured. This has been provided us to investigate the excited media of the heavy ion track on a timescale of radiation transitions lifetimes ($\sim $20 fs after excitation). Low beam current of 1 uA allowed us to consider the excitation process as a number of statistically independent acts of single heavy ion energy deposition to the media. [Preview Abstract] |
Saturday, April 22, 2006 12:21PM - 12:33PM |
B14.00009: An Active X-Band High Power RF Compression System Using an Ultrafast Silicon Switch Jiquan Guo, Sami Tantawi In this paper, we present the recent results of our research on the ultra-high power fast silicon RF switch and its application on active X-Band RF pulse compression systems. This switch is composed of a group of PIN diodes on a high purity silicon wafer. The wafer is inserted into a cylindrical waveguide operating in the TE01 mode. Switching is performed by injecting carriers into the bulk silicon through a high current pulse. Our current design uses a CMOS compatible process and the fabrication is accomplished at SNF (Stanford Nanofabrication Facility). The RF energy is stored in a room-temperature, high-Q 400 ns delay line; it is then extracted out of the line in a short time using the switch. The pulse compression system has achieved a gain of 11, which is the ratio between output and input power. Power handling capability of the switch is estimated at the level of 10MW. [Preview Abstract] |
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