Generation and application of channeling X-rays using a novel, low-emittance electron beam—Status and plans

We plan to use very small emittance electron beams created from our novel, single tip cathodes to make a channeling-radiation X-ray source for X-ray imaging, especially phase contrast imaging. We calculate that we can preserve the electron emittance from the source to the crystal, and focus to a 40 nm spot on the crystal face for 40 MeV electrons. This yields an X-ray source with good coherence properties. We discuss our plan for experiments at Fermilab with 4.5 MeV electrons at the High Brightness Electron Source Laboratory, and with 40 MeV electrons at the Advanced Superconducting Test Accelerator. We also present the state of our art with cathode construction and testing. Electrons come from the cathodes by field-emission, with the electric field enhanced by geometric properties of a very small, robust diamond tip. This can create an electron beam with very small emittance. We estimate that the normalized emittance of such a beam at the cathode is 3 nm rad. We currently test the cathodes in DC, high-voltage test stands. We will begin experiments placing the cathodes in RF guns in early 2013.