A thermostatic chamber for doppler-broadening thermometry of mercury vapors

We present an isothermal chamber designed and realized at the Italian Metrological Institute (INRiM) to stabilize the temperature of a quartz cell for Doppler-broadened precision spectroscopy of mercury atoms in the UV region for the practical realization of the new definition of kelvin. The challenge of this apparatus is the capability to control, with great accuracy, the temperature of a non-cylindrical quartz cavity containing the mercury vapors. The temperature was actively controlled and maintained stable within 0.05 mK at the triple point of water for 15 h, but longer periods are possible. The spatial uniformity was also characterized. The traceability of temperature measurements and the complete uncertainty budget are discussed.