Ultrafast Electron Diffraction Device for Time-Resolved Chemical Imaging
Because of the need to operate in a space-charge-dominated regime, the generation and preservation of femtosecond electron beams is a major challenge for chemical dynamics and accelerator technology R & amp;D. Electrons from a photo-cathode radio frequency (RF) gun can be used as scattering particles to produce a time-dependent diffraction pattern containing femtosecond time-scale structural information. This technique is known as Ultrafast Electron Diffraction (UED). The higher electric field at the cathode of an RF gun delivers higher electron bunch density with even shorter time resolution than a DC gun, which is typically employed, due to a significant reduction in the space-charge interaction. The near-relativistic speed of the electrons further reduces the velocity mismatch in the sample and significantly improves the overall time resolution of the technique. We propose a novel UED device that employs radial bunch compression in an 11.42 GHz X-band RF electron gun. Very promising simulation results have already been demonstrated. A Phase I program will re-design the X-band gun using a coaxial line at the rear of the cathode. This will create space at the gun exit for the cathode drive laser and simplify the electron beam transport Optimization of the high-charge ultrafast electron beam and the overall compact single-shot UED system will be performed. AES hasdemonstrated the feasibility of a single-shot UED device with beam dynamics simulations. An X-band RF photocathode gun generates an ultrafast high-brightness electron beam with better performance than a standard S-band gun or a DC gun that is typically used today for UED experiments. In Phase I, AES will optimize the beam dynamics performance of the gun and modify the RF coupling to improve the overall compact footprint of the UED system. Thermo-structural and RF analysis of the gun will be completed. We will then perform a conceptual engineering design of the system to ensure the design concept is robust and readily manufactured. This will permit Phase II fabrication and validation testing of the UED system. Commercial Applications and Other Benefits: Ultrafast high-brightness electron beams are an important means of characterizing the atomic- scale molecular structure of samples in chemical imaging with femtosecond time-resolution. A single-shot X-band UED device will have improved bunch length and beam brightness while reducing the size and capital cost of the system. Such an affordable, compact RF gun could be used to drive laser wakefield accelerators, non-recirculating coherent synchrotron radiation sources and free electron lasers, opening up the possibility of such R & amp;D to a wider community of smaller user groups. By increasing the duty factor of a thermionic version of the gun, the lucrative Non Destructive Evaluation (NDE) and Homeland Security markets that seek compact electron sources could be accessed.
Small Business Information at Submission:
Advanced Energy Systems, Inc.
27 Industrial Blvd. Unit E Medford, NY 11763-2286
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