Development of a multispectral flat-field x-ray microscope with self-adjusting spectral response for the fusion plasma temperature diagnostics

The measurement of the electron temperature distribution of hotspot requires bremsstrahlung imaging with both spectral resolution and spatial resolution. The Kirkpatrick–Baez (KB) microscope is an important diagnostic device in inertial confinement fusion experiments, which can realize high spatial resolution imaging of multi-energy. However, conventional KB microscopes face a fundamental trade-off between achieving a quasi-monoenergetic response and maintaining uniform efficiency across the field of view. This inherent limitation leads to difficulties in efficiency calibration and can introduce distortion in hotspot images, thereby preventing their effective application in the quantitative measurement of hotspot radiation intensity. This paper proposes a four-energy-point KB microscope with a self-adjusting spectral response, in which the response energies adapt to the field-of-view position. The design simultaneously achieves a quasi-monoenergetic response and a uniform efficiency distribution, thereby mitigating hot-spot image distortion and simplifying efficiency calibration. Each channel of this microscope achieves a spectral resolution of ΔE/E ∼ 10%, and the efficiency uniformity (relative standard deviation: ση/η̄) within the ±150 μm field of view is 6.27%–9.63%. The spatial resolution at the center of the field of view is better than 5 μm. We deployed this microscope for implosion hotspot imaging, successfully acquiring images at four distinct energy points. These images are suitable for diagnosing hotspot electron temperature.