Use of capillary optics as a beam intensifier for a Compton x-ray source.

The use of Kumakhov capillary optics will significantly enhance the performance of near-monochromatic, Compton backscattered x-ray programs. The Vanderbilt University Medical Free-Electron Laser Center is developing the capability to create these tunable x rays for medical imaging. The present transport has only reflection optics, and the beam is quite large in diameter at the laboratory. Low loss collimation of this beam would allow higher x-ray intensities after transport. This article describes experimental and computer simulation results which predict the expected performance for a multifiber Kumakhov collimator for use in the x-ray beam transport. Estimates from our research are that a multifiber optic formed of individual polycapillary fibers could be used to capture the full 7 mrad of the Vanderbilt x-ray beam and collimate it to a 1-2 mrad divergence with approximately 40%-50% transmission efficiency. This optic should increase the x-ray intensity at the laboratory level by a factor of > or = 5 by decreasing the beam divergence and subsequent spot size. Additionally, analysis of monolithic optics of fused multicapillary fibers predicts an increase in the intensity of the x rays at the laboratory by a factor of 55. These optics can have tapered channels that greatly decrease their exit divergence. This will greatly enhance the capabilities of this unique x-ray source. This article reports the initial results from a collaboration between Vanderbilt, The Center for X-Ray Optics at University at Albany, SUNY, and X-Ray Optical Systems in Albany, NY.

Application of graphite mosaic monochromator crystals for x-ray transport.

The Vanderbilt University Free-Electron Laser Program is developing the capability to create near-monochromatic x rays for medical imaging and other purposes. For this experiment we feed back the normal infrared FEL light to collide with the electron beam. This causes Compton backscattering of the incident photons which creates x rays. This paper is particularly focused on the x-ray beam transport to be used with this experiment. This transport must redirect the x-ray beam to match a beam chase located in the accelerator vault ceiling at a 40° angle to the x-ray creation axis. It has been determined that the most efficient way to form this transport is by using multiple reflections from mosaic graphite crystals. Samples of these crystals have been obtained and reflection characteristics are being measured. Flat crystals have been investigated at this point. Curved crystals have also been obtained and these will be measured soon. All of these results will dictate the final form of the beam transport.

Current Status of the VU MFEL Compton X-Ray Program.

The Vanderbilt University medical FEL (free electron laser) Compton x-ray program is close to being operational. The FEL modifications necessary for this new capability are near completion. The transport and detection systems for electron and IR beams have been designed, delivered, and tested. We initially expect to produce 108 x-ray photons per second in the 15- to 20-keV region.