Compact broadband high-resolution Compton spectroscopy for laser-driven high-flux gamma rays

A compact broadband Compton spectrometer with high spectral resolution has been designed to detect spectra of laser-driven high-flux gamma rays.The primary detection range of the gamma-ray spectrum is 0.5 MeV–13 MeV,although a secondary harder gamma-ray region of 13 MeV–30MeV can also be covered.The Compton-scattered electrons are spectrally resolved using a curved surface detector and a nonuniform magnetic field produced by a pair of step-like magnets.This design allows a compact structure,a wider bandwidth,especially in the lower-energy region of 0.5 MeV–2 MeV,and optimum spectral resolution.The spectral resolution is 5%–10%in the range 4 MeV–13 MeV and better than 25%in the range 0.5MeV–4MeV(with an Al converter of 0.25mmthickness and a collimator of 1 cm inner diameter).Low-Z plastic materials are used on the inner surface of the spectrometer to suppress noise due to secondary X-ray fluorescence.The spectrometer can be adjusted flexibly via a specially designed mechanical component.An algorithmbased on a regularizationmethod has also been developed to reconstruct the gamma-ray spectrum from the scattered electrons.

Hard x-ray transmission curved crystal spectrometers(10–100 keV) for laser fusion experiments at the ShenGuang-Ⅲ laser facility

Two transmission curved crystal spectrometers are designed to measure the hard x-ray emission in the laser fusion experiment of Compton radiography of implosion target on ShenGuang-III laser facility in China. Cylindrically curvedα-quartz(10–11) crystals with curvature radii of 150 and 300 mm are used to cover spectral ranges of 10–56 and17–100 ke V, respectively. The distance between the crystal and the x-ray source can be changed over a broad distance from 200 to 1500 mm. The optical design, including the integral reflectivity of the curved crystal, the sensitivity, and the spectral resolution of the spectrometers, is discussed. We also provide mechanic design details and experimental results using a Mo anode x-ray source. High-quality spectra were obtained. We confirmed that the spectral resolution can be improved by increasing the working distance, which is the distance between the recording medium and the Rowland circle.

Gamma-ray generation from ultraintense laser-irradiated solid targets with preplasma

In the laser plasma interaction of quantum electrodynamics(QED)-dominated regime,γ-rays are generated due to synchrotron radiation from high-energy electrons traveling in a strong background electromagnetic field.With the aid of2 D particle-in-cell code including QED physics,we investigate the preplasma effect on theγ-ray generation during the interaction between an ultraintense laser pulse and solid targets.We found that with the increasing preplasma scale length,theγ-ray emission is enhanced significantly and finally reaches a steady state.Meanwhile,theγ-ray beam becomes collimated.This shows that,in some cases,the preplasmas will be piled up acting as a plasma mirror in the underdense preplasma region,where theγ-rays are produced by the collision between the forward electrons and the reflected laser fields from the piled plasma.The piled plasma plays the same role as the usual reflection mirror made from a solid target.Thus,a single solid target with proper scale length preplasma can serve as a manufactural and robustγ-ray source.