Lamb-shift and electric field measurements in plasmas

Doveil, Fabrice; Chérigier-Kovacic, Laurence; Ström, Petter

doi:10.1088/0741-3335/59/1/014020

Cited by 3 publications

(2 citation statements)

References 19 publications

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“…We have already measured the absolute value of the static electric field profile between two polarised plane electrodes in vacuum with a good agreement with a numerical calculation of the field. We have applied the same technique to measure the static electric field between two polarised plane electrodes in a plasma, where the field is null (quasineutrality) except in the sheath near the polarised electrode [4]. The sheath thickness has been related to the plasma density.…”

Section: Introductionmentioning

confidence: 99%

Estimation of the Lyman-α signal of the EFILE diagnostic under static or radiofrequency electric field in vacuum

Poggi¹,

Guillaume²,

Doveil³

et al. 2018

Plasma Sci. Technol.

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The EFILE diagnostic (Electric Field Induced Lyman-α Emission) aims to provide a non intrusive and precise measurement of the electric field in plasma, using a beam of hydrogen atoms prepared in the metastable 2s state. The metastable particles are obtained by means of a proton beam extracted from a hydrogen plasma source, and neutralised by interaction with vaporised caesium.When a 2s atom enters a region where an electric field is present, it undergoes a transition to the 2p state (Stark mixing). It then quickly decays to the ground level, emitting Lyman-α radiation, which is collected by a photomultiplier. The 2s → 2p transition rate is proportional to the square of the magnitude of the electric field, and depends on the field oscillation frequency (with peaks around 1 GHz). By measuring the intensity of the Lyman-α radiation emitted by the beam it is possible to determine the magnitude of the field in a defined region.In this work, an analysis of the behaviour of the diagnostic under static or radiofrequency electric field is presented. Electric field simulations obtained with a finite element solver of Maxwell equations, combined with theoretical calculations of the Stark mixing transition rate, are used to develop a model for the interpretation of photomultiplier data. This method shows good agreement with experimental results for the static field case, and allows to measure the field magnitude for the oscillating case.

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Section: Introductionmentioning

confidence: 99%

Estimation of the Lyman-α signal of the EFILE diagnostic under static or radiofrequency electric field in vacuum

Poggi¹,

Guillaume²,

Doveil³

et al. 2018

Plasma Sci. Technol.

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“…In general, strong electric fields can be measured with deflections of particle beams [94,95] or spectroscopic techniques, such as Stark effect [96] and Lamb shift [97]. Weaker field measurements, on the other hand, are mostly obtained with probes or antennas [98].…”

Section: Double-tip Electric-field Probementioning

confidence: 99%

Validation of a Lagrangian model for laser-induced fluorescence

Chu¹

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To my parentsii v Since man is not born with knowledge, who can be without doubts? If one has doubts and is not willing to learn from a teacher, his doubts will never be resolved. Those who were born before me must have learned the Tao earlier than me, and I take them as my teachers. Those who were born after me may also have learned the Tao earlier than me, and I take them as my teachers. Since the Tao is what I desire to learn, why should I care if my teachers were born before or after me? Therefore, whether a man is noble or lowly, old or young, where there is the Tao, there is my teacher.vi ABSTRACT Extensive information can be obtained on wave-particle interactions and wave fields by direct measurement of perturbed ion distribution functions using laserinduced fluorescence (LIF). For practical purposes, LIF is frequently performed on metastable states that are produced from neutral gas particles and ions in other electronic states. If the laser intensity is increased to obtain a better LIF signal, then optical pumping can produce systematic effects depending on the collision rates which control metastable population and lifetime. We numerically simulate the ion velocity distribution measurement and wave-detection process using a Lagrangian model for the LIF signal. The simulations show that optical pumping broadening affects the ion velocity distribution function (IVDF) f 0 (v) and its first-order perturbation f 1 (v, t) when laser intensity is increased above a certain level. The results also suggest that ion temperature measurements are only accurate when the metastable ions can live longer than the ion-ion collision mean free time. For the purposes of wave detection, the wave period has to be significantly shorter than the lifetime of metastable ions for a direct interpretation. Experiments are carried out to study the optical pumping broadening and metastable lifetime effects, and the results are compared with the simulation in order to validate the Lagrangian model for LIF. It is more generally true that metastable ions may be viewed as test-particles. As long as an appropriate model is available, LIF can be extended to a range of environments. vii PUBLIC ABSTRACTIn laser-induced fluorescence (LIF), measurements of spontaneous light emission after laser excitation of plasma particles provides useful insight into some its qualities, like its ion temperature and wave-particle interaction dynamics.Usually physicists analyze LIF results with the fixed coordinate-based Eulerian approach. But in this thesis, we apply a Lagrangian approach to LIF analysis using newly written code to follow each individual ion orbit. We found the Lagrangian model, with which we numerically simulated the ion velocity and wave-detection process, is more efficient and revealing than the Eulerian approach. It computationally allows a separation of the quantized description of ionic states from the classical dynamics of the ion center of mass. Also, some key calculations can be done by hand and included readily, leading to large tim...

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Summary of basic plasma physics sessions at the first Asia Pacific Plasma Conference, 2017

Sen

2018

Rev. Mod. Plasma Phys.

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Lamb-shift and electric field measurements in plasmas

Cited by 3 publications

References 19 publications

Estimation of the Lyman-α signal of the EFILE diagnostic under static or radiofrequency electric field in vacuum

Estimation of the Lyman-α signal of the EFILE diagnostic under static or radiofrequency electric field in vacuum

Validation of a Lagrangian model for laser-induced fluorescence

Summary of basic plasma physics sessions at the first Asia Pacific Plasma Conference, 2017

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