Updating Plasma Scattering of Electromagnetic Radiation

Sheffield, John

doi:10.1088/1742-6596/227/1/012001

Cited by 12 publications

(17 citation statements)

References 42 publications

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“…5d) has two ion acoustic peaks which appear when the value of ZT e becomes larger than T i . The separation of the two peaks is related to ZT e , while their width is determined by T i [13]. The theoretical fit to the spectrum gives T i =400±50 eV and T e =70±8 eV with Z=8.…”

Section: Fig 2: (A)mentioning

confidence: 95%

“…The scattering spectrum has a broad Gaussian-like shape with a spectral width of ∼4Å. The presence of a single peak suggests that T i >ZT e in the plasma [13], a result of the high kinetic energy of the W ions in the ablation flow. The theoretical fit to the spectrum gives T i =20±5 keV.…”

Section: Fig 2: (A)mentioning

confidence: 99%

“…2c. Each spectrum represents the so-called ion feature in the collective scattering signal [13]. In the ablation flow from W wires the ion feature has a single peak whose width is dependent on T i and also on the spread of the flow velocities inside the scattering volume.…”

Section: Fig 2: (A)mentioning

confidence: 99%

“…Fig. 4b shows radial profiles of the ion temperature, determined by fitting a theoretical scattered spectrum [13] convolved with the apparatus function of the spectrometer. It is seen that at early times (∼150 ns) the ion temperature near the array axis is ∼5 keV.…”

Section: Fig 2: (A)mentioning

confidence: 99%

“…The measurements were obtained using an optical Thomson scattering diagnostic working in the collective scattering regime [13]. The Doppler shift of the ion feature in the scattered spectrum allowed measurements of the flow velocity of the ablated plasma while the shape of the spectrum provided measurements of the ion (T i ) and electron (T e ) temperatures of the plasma [13]. The measured radial velocity profiles show that the plasma flow undergoes additional acceleration inside the arrays, consistent with the presence of current and magnetic fields in the array interior [14].…”

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confidence: 99%

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Optical Thomson Scattering Measurements of Plasma Parameters in the Ablation Stage of Wire ArrayZPinches

et al. 2012

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A Thomson scattering diagnostic has been used to measure the parameters of cylindrical wire array Z pinch plasmas during the ablation phase. The scattering operates in the collective regime (α>1) allowing spatially localised measurements of the ion or electron plasma temperatures and of the plasma bulk velocity. The ablation flow is found to accelerate towards the axis reaching peak velocities of 1.2-1.3×10 7 cm/s in aluminium and ∼1×10 7 cm/s in tungsten arrays. Precursor ion temperature measurements made shortly after formation are found to correspond to the kinetic energy of the converging ablation flow.Wire array Z pinch implosions can efficiently convert stored electrical energy into powerful bursts of soft xrays. Experiments on the 20 MA Z pulsed power generator [1] have achieved peak powers of 280-300 TW with a >2 MJ yield at 20% efficiency [2] by imploding cylindrical arrays consisting of hundreds of fine metallic wires. It was found [3][4][5] that in wire array Z pinches the wires remain stationary for the first 60-80% of the implosion time and steadily ablate plasma which is accelerated by the j×B force. This ablation flow distributes mass in the array interior which sets the initial conditions for the implosion phase. The ablation mass distribution depends on the ablation rate, dm/dt, and on the flow velocity, which are related via force -momentum balance. However, the flow velocity was not measured in past experiments apart from the velocity of the initial part of the flow which was inferred from the time of plasma appearance on the array axis and from end-on interferometry measurements, giving V∼1.5×10 7 cm/s [6] [7]. The velocity of the ablation flow in the later stages, when the majority of the ablated material is moving into the array interior, is not known. Instead, the ablation rate and mass redistribution is often discussed using the so-called 'ablation velocity', introduced in the rocket model [3] via momentum balance arguments, which is inferred from the implosion dynamics or from unfolds of x-ray radiography measurements of mass distribution in the array interiorNumerical simulations [10][11] show that velocity is changing both with time and with the radial position of the flow, indicating that the flow is accelerated by the j×B force acting on the plasma in the array interior. However, these simulations do not model the initial heating of the wires and the process of conversion of initially cold metallic wires into a plasma. Instead, simulations start from wire material already converted into plasma at some initial temperature and density, and these initial conditions are adjusted to produce agreement of the simulated implosion dynamics with experimental observations. Direct measurements of the ablation flow velocity and density are needed to allow verification of these numerical models. Knowledge of the flow velocity is also important for other applications of different wire array Z pinch configurations, used e.g. in laboratory astrophysics [12] and other HEDP basic science research.In th...

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Section: Fig 2: (A)mentioning

confidence: 95%

Section: Fig 2: (A)mentioning

confidence: 99%

Section: Fig 2: (A)mentioning

confidence: 99%

Section: Fig 2: (A)mentioning

confidence: 99%

mentioning

confidence: 99%

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Optical Thomson Scattering Measurements of Plasma Parameters in the Ablation Stage of Wire ArrayZPinches

et al. 2012

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On the theory of the incoherent scatter gyrolines

2017

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The incoherent scatter spectrum feature referred to as the “gyroline” is investigated theoretically and experimentally. The gyroline is associated with the dispersion relation for electrostatic whistler waves. Earlier treatments by Trulsen and Bjørna (1978, and references therein) derive the frequency and growth rate for these waves, but their derivation is only accurate for very small magnetic aspect angles, i.e., for wave vectors close to perpendicular to the geomagnetic field. Their expression for the frequency has the form of a low‐order Padé approximate, but we find that a simple formula of this kind accurate for arbitrary magnetic aspect angles does not exist. We therefore analyze the incoherent scatter gyroline feature computationally. The analysis is supported by range‐resolved incoherent scatter spectrograms measured recently at Arecibo. The gyroline feature is shown to be strongest in the midlatitude E and valley regions where the electron temperature is low enough to avoid cyclotron damping.

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Particle-in-cell simulation of incoherent scatter radar spectral distortions related to beam-plasma interactions in the auroral ionosphere

et al. 2011

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[1] An electrostatic parallel particle-in-cell (EPPIC) code that allows for particle beam injections and multiple boundary conditions is used to investigate the beam-plasma interaction and its manifestations in the incoherent scatter (IS) spectrum. Specifically, the code is used to investigate anomalous enhancements in the ion acoustic line through the destabilization of the plasma by injection (or precipitation) of low-energy electron beams. This enhancement of the ion acoustic line is a form of IS distortion commonly observed in the vicinity of auroral arcs called the naturally enhanced ion-acoustic line (NEIAL). Simulations confirm the parametric decay of Langmuir waves as a plausible mechanism, assuming a mechanism for the formation of dense low-energy (<10 eV) electron beams in the ionosphere. The spectral distortions are similar at aspect angles as large as ±15°from the beam direction. Simulations also show that the first Langmuir harmonic can have a power intensity higher than that of the ion acoustic line of a thermal plasma. Conditions which would allow the detection of Langmuir harmonics with existing incoherent scatter radars are discussed.

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Updating Plasma Scattering of Electromagnetic Radiation

Cited by 12 publications

References 42 publications

Optical Thomson Scattering Measurements of Plasma Parameters in the Ablation Stage of Wire ArrayZPinches

Optical Thomson Scattering Measurements of Plasma Parameters in the Ablation Stage of Wire ArrayZPinches

On the theory of the incoherent scatter gyrolines

Particle-in-cell simulation of incoherent scatter radar spectral distortions related to beam-plasma interactions in the auroral ionosphere

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