Positive column of the Cs–Ar low-pressure discharge

The optically pumped, vapor-cell atomic clock is a work horse of precise timekeeping, finding applications onboard global navigation satellites as well as at cellular communications base stations. At the heart of the device is the relatively simple alkali rf-discharge lamp, which enables the production of the atomic-clock signal and the sensing of the atoms' response to resonant microwaves. In the lamp, electrons extract energy from an rf-field via elastic collisions with noble-gas buffer atoms; the energetic electrons then ionize Rb atoms; finally, resonant light for optical pumping is produced through Rb + /electron recombination at the lamp's glass walls. Unfortunately, recent research has shown that alkali rf-discharge lamps slowly lose their buffer gas, giving rise to a life-limiting mechanism for the rf-discharge lamp and hence the atomic clock. Here, we review the literature on buffer-gas loss in alkali rf-discharge lamps and discuss a likely mechanism for the process. We then discuss the dependence of the discharge's electron temperature on rf-frequency, and how this might be used as a critical test of the proposed mechanism.Index Terms-Alkali discharge lamp, atomic clocks, inductively-coupled plasma, noble-gas ionization, Rb atomic clock.

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“…Evaluating this expression at an upper bound electron temperature, T e = 5000 K [25], [26], we obtain…”

Section: A General Considerationsmentioning

confidence: 99%

Noble-Gas Loss in Alkali Rf-Discharge Lamps and Its Possible Dependence on Electron Temperature

Encalada

Jaduszliwer

Lybarger

et al. 2014

IEEE Trans. Instrum. Meas.

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“…The rest of the tube cross section was filled with a homogeneous positive column. The positive column with the filament was the third PC mode [27,[36][37][38]. Xenon was excited and ionized in the filament, and bright xenon atom lines along with the cesium atom lines were observed in its emission spectrum.…”

Section: Plasma Slab Generation Using a Cs-xe DC Discharge And Experimentioning

confidence: 99%

A Technique for Time-Resolved Imaging of Millimeter Waves Based on Visible Continuum Radiation from a Cs-Xe DC Discharge — Fundamentals and Applications

Gitlin¹

2016

Plasma Science and Technology - Progress in Physical States and Chemical Reactions

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The chapter presents a review of a highly sensitive technique for time-resolved imaging and measurement of the 2D intensity profiles of millimeter waves (MMW) based on the use of visible continuum radiation (VCR) from the positive column (PC) of a medium pressure Cs-Xe DC discharge (VCRD technique). The review focuses on the operating principles, fundamentals, and applications of this new technique. The design of a discharge tube and an experimental setup which were used to create a wide homogeneous PC plasma slab are described. The MMW effects on the plasma slab are studied. The mechanism of microwave-induced variations in the VCR intensity and the causes of violation of the local relation between the visible continuum emissivity and the MMW intensity are discussed. The main characteristics, e.g., spatial and temporal resolution, and sensitivity of the VCRD technique have been evaluated. Experiments on imaging of the field patterns of horn antennas and quasioptical beams demonstrated that the VCRD technique can be used for a good-quality imaging of the MMW beams in the entire MMwavelength band. The VCRD technique was applied for imaging of output field patterns of the MMW electron tubes and determination of some of their characteristics, as well as for active real-time imaging and nondestructive testing using MM waves.

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“…More important, however, is the high degree of linearity between ln[S 828 /S nom ] and (P nom -P rf )/P rf P nom , which provides evidence for the thermalization hypothesis embodied in Eq. (31). The shorter dashed line passing through the data in Fig.…”

Section: -15mentioning

confidence: 99%

“…First, and perhaps most important, the values of T Xe obtained for normal rf-power levels (i.e., P rf > 2.5 W) are roughly about 4000 K. This is very much in line with the expected electron temperature for the rf-discharge based on measurements by van Tongeren for a Cs positive column. 31 We take this as evidence that the values of T Xe are a good surrogate for T e .…”

Section: A Surrogate For Electron Temperature: T Xementioning

confidence: 99%

“…4 provides an illustrative example of the radial electron distribution for a range of likely 2β values. For the computations, we considered an rf-discharge lamp with the following parameters: P rf = 0.5 W, Q = 100, 30 ν o = 10 2 MHz, R = 0.4 cm, L = 1 cm, T e = 5000 K, 31 and T L = 110 o C, which implies [Rb] = 1.9×10 13 cm -3 . These parameters yield η = 7.6%, and from the figure we see that increasing values of β tend to flatten the electron distribution for ρ < 0.5.…”

Section: Estimation Of the Rb Light Emissionmentioning

confidence: 99%

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Spectral emission from the alkali inductively-coupled plasma: Theory and experiment

2018

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The weakly-ionized, alkali inductively-coupled plasma (ICP) has a long history as the light source for optical pumping. Today, its most significant application is perhaps in the rubidium atomic frequency standard (RAFS), arguably the workhorse of atomic timekeeping in space, where it is crucial to the RAFS’ functioning and performance (and routinely referred to as the RAFS’ “rf-discharge lamp”). In particular, the photon flux from the lamp determines the signal-to-noise ratio of the device, and variations in ICP brightness define the long-term frequency stability of the atomic clock as a consequence of the ac-Stark shift (i.e., the light-shift). Given the importance of Rb atomic clocks to diverse satellite navigation systems (e.g., GPS, Galileo, BeiDou) – and thereby the importance of alkali ICPs to these systems – it is somewhat surprising to find that the physical processes occurring within the discharge are not well understood. As a consequence, researchers do not understand how to improve the spectral emission from the lamp except at a trial-and-error level, nor do they fully understand the nonlinear mechanisms that result in ICP light instability. Here, we take a first step in developing an intuitive, semi-quantitative model of the alkali rf-discharge lamp, and we perform a series of experiments to validate the theory’s predictions.

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Positive column of the Cs–Ar low-pressure discharge

Cited by 27 publications

References 25 publications

Noble-Gas Loss in Alkali Rf-Discharge Lamps and Its Possible Dependence on Electron Temperature

Noble-Gas Loss in Alkali Rf-Discharge Lamps and Its Possible Dependence on Electron Temperature

A Technique for Time-Resolved Imaging of Millimeter Waves Based on Visible Continuum Radiation from a Cs-Xe DC Discharge — Fundamentals and Applications

Spectral emission from the alkali inductively-coupled plasma: Theory and experiment

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