Nonlinear laser synchrotron source experiment for tunable, monochromatic X-rays

Summary form only given. The laser synchrotron source (LSS) experiment at the Naval Research Laboratory generates X-rays using Thomson scattering of laser photons from a relativistic electron beam. Previous experiments utilized a thermionic RF electron gun operating at 2.856 GHz to produce electron beams with an energy of 4.1 MeV and average currents of 300 mA over the 300-nsec macropulse. A Nd:Glass laser (5 J, 10 nsec, 1.053 m wavelength) was used in a 180-degree scattering geometry. Experimental results included the generation of 372 eV photons with 2% bandwidth and 2/spl times/10/sup 7/ photons per pulse. A new experiment is underway to investigate nonlinear Thomson scattering using a new photocathode RF gun (BNL IV design) and the T/sup 3/ laser (/spl sim/1 J, 0.3 psec). When this laser is focused to a spot size of 10 /spl mu/m the peak intensity reaches 6/spl times/10/sup 18/ W/cm/sup 2/ with a corresponding laser strength parameter a/sub 0/=2.2. The quiver motion of an electron in such an intense field is relativistic, and the scattered radiation occurs at higher harmonics of the linear Doppler-upshifted frequency. The new experiment has two laser pulse compressors: one for the uv pulse which illuminates the photocathode and one for the main (scattering) laser pulse. This allows the electron beam and scattering beam pulse lengths to be varied independently. The nominal RF gun operating parameters are 4.5 MeV, 100 A peak current, <1 nC charge, pulse lengths of a few psec, and a normalized rms emittance of 3 /spl pi/-mm-mrad. Results will be presented on the conditioning and initial operation of the RF gun.