In inertial confinement fusion (ICF) experiments on the National Ignition Facility (NIF), measurements of average ion temperature using DT neutron time of flight broadening and of DD neutrons do not show the same apparent temperature. Some of this may be due to time and space dependent temperature profiles in the imploding capsule which are not taken into account in the analysis. As such, we are attempting to measure the electron temperature by recording the free-free electron-ion scattering-spectrum from the tail of the Maxwellian temperature distribution. This will be accomplished with the new NIF Continuum Spectrometer (ConSpec) which spans the x-ray range of 20 keV to 30
keV (where any opacity corrections from the remaining mass of the ablator shell are negligible) and will be sensitive to temperatures between ∼ 3 keV and 6 keV. The optical design of the ConSpec is designed to be adaptable to an x-ray streak camera to record time resolved free-free electron continuum spectra for direct measurement of the dT/dt evolution across the burn width of a DT plasma. The spectrometer is a conically bent Bragg crystal in a focusing geometry that allows for the dispersion plane to be perpendicular to the spectrometer axis. Additionally, to address the spatial temperature dependence, both time integrated and time resolved pinhole and penumbral imaging will be
provided along the same polar angle. The optical and mechanical design of the instrument is presented along with estimates for the dispersion, solid angle, photometric sensitivity, and performance.
One dimensional spatially resolved high resolution x-ray spectroscopy with spherically bent crystals and 2D pixelated
detectors is an established technique on magnetic confinement fusion (MCF) experiments world wide for Doppler
measurements of spatial profiles of plasma ion temperature and flow velocity. This technique is being further developed
for diagnosis of High Energy Density Physics (HEDP) plasmas at laser-plasma facilities and synchrotron/x-ray free
electron laser (XFEL) facilities. Useful spatial resolution (micron scale) of such small-scale plasma sources requires
magnification, because of the finite pixel size of x-ray CCD detectors (13.5 μm). A von-Hamos like spectrometer using
spherical crystals is capable of magnification, as well as uniform sagittal focusing across the full x-ray spectrum, and is
being tested in laboratory experiments using a tungsten-target microfocus (5-10 μm) x-ray tube and 13-μm pixel x-ray
CCD. A spatial resolution better than 10 μm has been demonstrated. Good spectral resolution is indicated by small
differences (0.02 – 0.1 eV) of measured line widths with best available published natural line widths. Progress and status
of HEDP measurements and the physics basis for these diagnostics are presented. A new type of x-ray crystal
spectrometer with a convex spherically bent crystal is also reported. The status of testing of a 2D imaging microscope
using matched pairs of spherical crystals with x rays will also be presented. The use of computational x-ray optics codes
in development of these instrumental concepts is addressed.
High resolution (λ/Δλ ~10,000) 1D imaging x-ray spectroscopy using a spherically bent crystal and a 2D hybrid pixelarray detector (PAD) is used world wide for Doppler measurements of ion-temperature (Ti) and plasma flow-velocityprofiles in magnetic confinement fusion (MCF) plasmas. Meter sized plasmas are diagnosed with cm spatial resolution and 10 ms time resolution. This concept can also be used as a diagnostic of small sources, such as inertial confinement fusion (ICF) plasmas and targets on x-ray light source beam lines, with spatial resolution of microns. A new concept of using matched pairs of spherically bent crystals for monochromatic stigmatic 2D x-ray imaging of mm sized sources offers the possibility of spatial resolution of microns and large solid angle, relative to that achieved with pinhole imaging. Other potential applications of the 2D imaging schemes include x-ray lithography and x-ray microscopy for biological and materials science research. Measurements from MFE plasmas, as well as laboratory experiments and ray tracing computations validating the 1D imaging spectroscopy and 2D x-ray imaging techniques will be presented.
Recent advances in x-ray detection technology and diagnostic design have dramatically improved the ability
of using x-ray imaging and spectroscopic diagnostics to accurately measure important parameters in magnetically
confined and laser produced fusion plasmas. With these advancements, the detailed characterization
of the diagnostic system properties has become ever more important. We present an overview of current
and future x-ray diagnostic requirements for fusion plasmas and describe, in particular, diagnostic systems
employing spherically bent crystals to resolving characteristic x-ray lines from trace impurities with energies
in the range 1-20keV. The requirements and challenges for the simulation of existing and planned diagnostic
installations and are discussed.
Simultaneous measurements of the integrated reflectivity of a mica crystal for different orders of reflection have been performed at a predefined Bragg angle of 45 degree(s) with use of a new method. The method is less time consuming than previous techniques and provides data with small statistical errors. It can be readily used for the calibration of x-ray crystal spectrometers. The paper presents experimental results for Bragg reflections up to the 22nd order. The obtained experimental results are compared with theoretical predictions.
A novel x-ray tube has been produced by using a line filament as a cathode. It is found that the electrons emitted form the filament arrive on the anode in a line perpendicular to the direction of the filament. The image of the x-ray emitting area on the anode obtained with a x-ray pinhole camera and a CCD detector shows a slightly curved line. The formation of this curved line is explained by Monte Carlo calculations, which include electric and magnetic fields in the x-ray tube as well as Joule heating, surface cooling, and thermal conduction in the cathode. The experimental result sand the result form the Monte Carlo calculations are presented.