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The performance of a 9-kW class magnetically shielded Hall thruster operating on xenon and krypton propellants is experimentally characterized. Thrust and efficiency measurements performed at discharge powers ranging from 4.5 to 9 kW indicate that the anode efficiency of krypton is 9%–18% lower than that of xenon. This difference is comparable to previous measurements reported for unshielded Hall thrusters, although it is found that unlike in previous studies, the efficiency ratio widens with increasing discharge voltage. Far-field probes are employed to measure the contributions to anode efficiency at conditions of 4.5 and 6  kW. These results indicate that mass utilization has the largest impact on the difference in performance between xenon and krypton. Assuming this mass utilization remains the dominant driver at higher voltages, it is proposed that the higher electron temperature of shielded thrusters along channel centerline coupled with the nonlinearity of the ionization cross section may explain why the efficiency gap widens with increasing voltage for shielded thrusters. The results are discussed in the context of optimizing magnetically shielded Hall thrusters for improved performance on krypton propellant.

Based on an original design by F. H. Attix, an improved free-air ionization chamber was constructed at the National Radiation Standard Laboratory of the Institute of Nuclear Energy Research (INER, Taiwan), as the primary standard for x-rays generated at energy levels between 50 keV and 300 keV. Various improvements were made to the Attix design, including modifications of the chamber structure and the measurement technique. The changes include: (i) a three-section design with fixed central cylinder; (ii) thickening of the shielding box; (iii) a circuitous mechanism for the operational handle, to avoid unwanted scattering; (iv) a ruler mechanism to provide fine position control; and (v) increased thickness of the aluminium wall of the chamber. After initial experimental verification, a comparison with the National Institute of Standards and Technology (NIST, USA) using a transfer standard chamber yielded differences in calibration factors of less than 1 %. In addition, the overall uncertainty for the x-ray measurement in terms of air kerma is less than 1 % at the 95 % confidence level. These results indicate that the improved free-air ionization chamber can serve as a primary standard at the NRSL.

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