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Compact radiation sources for increased access to high brightness x-rays

  • Author(s): O'Shea, Finn Henry
  • Advisor(s): Rosenzweig, James B
  • et al.
Abstract

The successful operation of the x-ray free electron lasers at LCLS and SACLA are a boon for science. The increase in brightness of 10 orders of magnitude over synchrotron sources as well as the sub-picosecond time profile of the x-rays are opening new avenues of research in fields ranging from biology to solid state physics. However, synchrotrons and free electron lasers that produce x-rays are expensive, with price tags that measured hundreds of millions. Further, the standard unit of measure for the scale of these sources is kilometers. The sheer size and prohibitive cost of these devices means that such sources are out of the reach of universities and smaller laboratories.

The focus of this dissertation is in increasing access to x-ray sources by making them both smaller and, perhaps more importantly, cheaper. Current limitations to source size reduction are discussed which leads to the conclusion that smaller x-rays sources require short period undulators. In this context, two approaches to increasing access to x-rays are covered. The first is direct decrease in the period length of undulators through more advanced design and materials. This path begins with a discussion of the design and construction of a 9 mm period prototype. An analysis of the benefits of such a device, in reduced undulator and accelerator lengths at existing free electron lasers, is explored. And finally, the operation of the undulator in a realistic scenario is experimentally explored in a scaled experiment at optical frequencies.

The second method for decreasing the period length of the light source is to replace the undulator with a laser, making an inverse Compton scattering source. The relationship between undulator radiation and the inverse Compton scattering process is examined, as well as the characteristics of the source itself. Lastly, as a demonstration of the function of the inverse Compton scattering source at Brookhaven National Laboratory as a diagnostic tool rather than an experiment itself, the 9 keV x-rays from the source are Bragg reflected from a Silicon crystal as a precursor to a pump-probe experiment which uses the inverse Compton scattered x-rays as a diagnostic. The experiment shows that the characteristics of the produced x-ray beam can be predicted by the input parameters.

With sources like the LCLS accepting one quarter of proposals for beam time, it is clear that there is demand for high brightness x-ray sources. Both of these technologies have the potential to increase access not just to x-rays but also to the sources themselves, potentially allowing proliferation of the number of locations for users to access diagnostic tools as well as creating a community of university scale operators.

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