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arXiv · 2609.04293

Design optimization, commissioning, and uncertainty analysis of the quadrupole resonator system at Jefferson Lab for SRF material characterization

Mingqi Ge·Sarra Bira·Kristof Brunner·Natalie Gale·Marco Garlasche·Valentin Giglia·Oleksandr Hryhorenko·Justin Kent·Peter Owen·Uttar Pudasaini·Guillaume Rosaz·Karol Scibor·Pramita Tiwari·Anne-Marie Valente-Feliciano·Lorena Vega Cid·Walter Venturini·Haipeng Wang
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Abstract

A quadrupole resonator (QPR) provides a sample-based platform for characterizing materials for superconducting radio-frequency (SRF) applications under controlled field, frequency, and temperature conditions. This paper presents the design optimization, commissioning, and validation of the Jefferson Lab QPR system, including a quantitative assessment of measurement uncertainty. The resonator geometry was re-optimized from the CERN version-II design to improve quadrupole-mode separation and enable four usable modes at 400, 806, 1221, and 1640 MHz. The measurement system combines self-excited-loop RF operation, cable-loss-corrected power calibration, decay-based external-Q calibration, and RF-DC thermal-substitution calorimetry to determine the peak surface magnetic field Bpk and sample surface resistance Rs. Commissioning measurements on bulk Nb and Nb3Sn-Ta-Cu samples validated the system response over a broad range of frequency, temperature, and RF field. The extracted superconducting energy-gap parameters are consistent with the reported values for Nb and Nb3Sn, as well as with those obtained from single-cell cavity measurements. The commissioned system operates from 1.8 K to near the superconducting transition temperature of the sample, with accessible Bpk values from approximately 5 mT to a sample- and temperature-dependent heater-power-budget limit; a maximum field of 60 mT was demonstrated for bulk Nb at 400 MHz and 4 K. The combined relative standard uncertainties are 8.3% for Bpk and below 18% for Rs when r = PDC2/PDC1 is less than 0.9. The worst-case Bpk resolution at the 95% confidence level is approximately 1.35 mT, while the Rs resolution is below 1 nOhm at 10 mT and 2 K. These results establish the JLab QPR as a calibrated, multi-frequency platform with quantified measurement uncertainty for SRF material characterization.

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Mingqi Ge, Sarra Bira, Kristof Brunner, Natalie Gale, Marco Garlasche, Valentin Giglia, Oleksandr Hryhorenko, Justin Kent, Peter Owen, Uttar Pudasaini, Guillaume Rosaz, Karol Scibor, Pramita Tiwari, Anne-Marie Valente-Feliciano, Lorena Vega Cid, Walter Venturini, Haipeng Wang. 2026-09-03. Design optimization, commissioning, and uncertainty analysis of the quadrupole resonator system at Jefferson Lab for SRF material characterization. https://arxiv.org/abs/2609.04293

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