Bulletin of the American Physical Society
2009 APS April Meeting
Volume 54, Number 4
Saturday–Tuesday, May 2–5, 2009; Denver, Colorado
Session R6: Imaging Advanced Accelerators |
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Sponsoring Units: DPP DPB Chair: Thomas Antonsen, University of Maryland Room: Governor's Square 16 |
Monday, May 4, 2009 1:30PM - 2:06PM |
R6.00001: Holographic Visualization of Wakefield Accelerator Structures Invited Speaker: |
Monday, May 4, 2009 2:06PM - 2:42PM |
R6.00002: Ultrafast terahertz generation and spectroscopy for accelerator diagnostics Invited Speaker: The generation of strong terahertz (THz) radiation has recently drawn considerable attention owing to the potential for intense THz excitation spectroscopy, nonlinear THz optics, as well as biomedical and security imaging. For these applications, THz field strength of MV/cm (or several microjoule under single-cycle, diffraction-limited focusing) is required. Such field strength can be obtained currently at electron accelerator facilities such as linacs, synchrotrons, and free electron lasers, as well as at laser-plasma accelerators, where all mediate highly relativistic electrons. Surprisingly, non-relativistic electrons can also generate intense coherent THz radiation. Recently, high-energy ($>$5 microjoule), super-broadband ($>$75 THz) THz radiation has been produced via ultrafast two-color photoionization [1]. In this scheme, a femtosecond laser's fundamental and its second harmonic pulses are mixed in a gas to generate a directional electron current on the time scale of sub-50 fs with simultaneous THz radiation in the far field. Another important THz application is diagnosing the temporal profiles of relativistic electron beams. As a noninvasive method, the longitudinal profile can be characterized from field-induced birefringence in an electro-optic crystal in the vicinity of the electron beam. To monitor the bunch profiles in real time, a chirped optical pulse can be used to map out the charge field onto the probe spectrum. Here, the temporal resolution, previously limited by the chirp, can be greatly improved with an in-line spectral interferometric algorithm [2]. The diagnostic can also provide 2D spatio-temporal imaging of ultrashort electron bunches in real time. Another single-shot diagnostic recently developed is an echelon-assisted spatial encoding method [3] which can provide a $>$10 ps time window with $\sim $25 fs temporal step sizes, with many advantages over other single-shot THz diagnostics. \\[4pt] [1] K. Y. Kim \textit{et al}., Nature Photon. \textbf{2}, 605 (2008)\\[0pt] [2] K. Y. Kim \textit{et al}., Appl. Phys. Lett. \textbf{88}, 041123 (2006)\\[0pt] [3] K. Y. Kim \textit{et al}., Opt. Lett. \textbf{32}, 1968 (2007). [Preview Abstract] |
Monday, May 4, 2009 2:42PM - 3:18PM |
R6.00003: Optical Diagnostics for Plasma-based Particle Accelerators Invited Speaker: One of the challenges for plasma-based particle accelerators is to measure the spatio-temporal characteristics of the accelerated particle bunch. ``Optical'' diagnostics are particularly interesting and useful because of the large number of techniques that exits to determine the properties of photon pulses. The accelerated bunch can produce photons pulses that carry information about its characteristics for example through synchrotron radiation in a magnet, Cherenkov radiation in a gas, and transition radiation (TR) at the boundary between two media with different dielectric constants. Depending on the wavelength of the emission when compared to the particle bunch length, the radiation can be incoherent or coherent. Incoherent TR in the optical range (or OTR) is useful to measure the transverse spatial characteristics of the beam, such as charge distribution and size. Coherent TR (or CTR) carries information about the bunch length that can in principle be retrieved by standard auto-correlation or interferometric techniques, as well as by spectral measurements. A measurement of the total CTR energy emitted by bunches with constant charge can also be used as a shot-to-shot measurement for the relative bunch length as the CTR energy is proportional to the square of the bunch population and inversely proportional to its length (for a fixed distribution). Spectral interferometry can also yield the spacing between bunches in the case where multiple bunches are trapped in subsequent buckets of the plasma wave. Cherenkov radiation can be used as an energy threshold diagnostic for low energy particles. Cherenkov, synchrotron and transition radiation can be used in a dispersive section of the beam line to measure the bunch energy spectrum. The application of these diagnostics to plasma-based particle accelerators, with emphasis on the beam-driven, plasma wakefield accelerator (PWFA) at the SLAC National Accelerator Laboratory will be discussed. [Preview Abstract] |
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