= Solution
Use a sufficiently high SEM acceleration voltage to transmit through the particle/support combination and provide useful diffracted intensity; operation near the high-voltage end of the SEM range is a reasonable starting point. The supplied wavelength is used directly for the camera-length calculation, rather than assigning a precise voltage from an approximate wavelength relation.
Choose the smallest beam current consistent with usable counting statistics, because the stated source-size contribution obeys
$$
d_0=\frac{2\sqrt{i}}{\pi\sqrt{\beta}\alpha}.
$$
Higher gun brightness permits more current at the same small probe. A relatively short working distance can give a larger convergence semiangle and reduce this term. In the specified fixed lens-to-detector geometry, shortening working distance also increases the specimen-to-detector camera length, reducing the detector's collection angles.
The objective aperture should be optimized, not made arbitrarily large: increasing $\alpha$ reduces the source-size and diffraction contributions, but spherical/chromatic aberrations and angular broadening eventually worsen the probe or diffraction selectivity. A suitable aperture balances those effects while keeping the chosen diffraction rings within the annulus. Adjust specimen height to meet that angular condition, focus and align at the operating voltage, and control drift and contamination.
Low convergence favors angular discrimination of diffraction, whereas high convergence can favor probe size. The optimum therefore depends on whether spatial detail or sharply selected <Bragg diffraction> contrast is the limiting requirement.
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