Lyman-<i>α</i> radiation of a metastable hydrogen beam to measure electric fields

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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“…when ω = ω L , and the quadratic dependence on the electric field amplitude was confirmed in previous works [11].…”

supporting

confidence: 68%

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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“…We experimentally observe a factor of this order of magnitude between the signal measured when the electric field is resonant with the Lamb shift frequency and when the electric field is constant. 14 Calculating the quenched level 2s lifetime is a major issue since the probe H(2s) beam will start to interact with the perturbing field as soon as it is sent through the explored medium. One has to be sure that the probe beam is not totally quenched before it reaches the region of interest.…”

Section: Physical Principlesmentioning

confidence: 99%

“…The beam is then passed through a cesium (Cs) cell 21,22 which can be heated to produce Cs vapor to create metastable atoms in the 2s state by a charge exchange collision 23 H + + Cs −→ H(2s) + Cs + with a maximum cross section at 500 eV. If the cesium cell is not heated, the Lyman-α emission is significantly lower 14 but the diagnostic is still working well, as metastable atoms are being produced by collisions between ions and the residual gas along the path to the test chamber. This case will be referred in the following as ion beam measurements.…”

Section: A the Hydrogen Ion Sourcementioning

confidence: 99%

Electric field induced Lyman-α emission of a hydrogen beam for electric field measurements

Chérigier-Kovacic

Ström

Lejeune

et al. 2015

Review of Scientific Instruments

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Electric field induced Lyman-α emission is a new way of measuring weak electric fields in vacuum and in a plasma. It is based on the emission of Lyman-α radiation (121.6 nm) by a low-energy metastable H atom beam due to Stark-quenching of the 2s level induced by the field. In this paper, we describe the technique in detail. Test measurements have been performed in vacuum between two plates polarized at a controlled voltage. The intensity of emitted radiation, proportional to the square of the field modulus, has been recorded by a lock-in technique, which gives an excellent signal to noise ratio. These measurements provide an in situ calibration that can be used to obtain the absolute value of the electric field. A diagnostic of this type can help to address a long standing challenge in plasma physics, namely, the problem of measuring electric fields without disturbing the equilibrium of the system that is being studied.

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“…We also observe the strong enhancement of the signal when the field is oscillating at the Lamb shift frequency. This technique is applied in a plasma, offering an alternative way to measure weak electric fields by direct and non-intrusive means [2].…”

mentioning

confidence: 99%

Lyman-α radiation of a probing metastable hydrogen beam to measure electric fields in diluted fluids and plasmas

2013

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The interaction between a metastable H(2s) atomic hydrogen beam and an external electric field leads to the emission of the Lyman-α line. It originates in the Stark mixing of the near-degenerate 2s1/2 and 2p1/2 levels separated by the Lamb shift. The quenched radiation proportional to the square of the electric field amplitude is recovered in vacuum by using such an atomic probe beam. For larger electric field, saturation is observed and related to the beam finite transit time. We also observe the strong enhancement of the signal when the field is oscillating at the Lamb shift frequency. This technique is applied in a plasma, offering an alternative way to measure weak electric fields by direct and non-intrusive means.

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Lyman-α radiation of a metastable hydrogen beam to measure electric fields

Cited by 7 publications

References 10 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

Electric field induced Lyman-α emission of a hydrogen beam for electric field measurements

Lyman-α radiation of a probing metastable hydrogen beam to measure electric fields in diluted fluids and plasmas

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