Production of radiatively cooled hypersonic plasma jets and links to astrophysical jets

Lebedev, S. V.; Ciardi, A.; Ampleford, D. J.; Bland, S. N.; Bott, S. C.; Chittenden, J. P.; Hall, G. N.; Rapley, J.; Jennings, C. A.; Sherlock, M.; Frank, Adam; Blackman, Eric G.

doi:10.1088/0741-3335/47/12b/s33

Cited by 69 publications

(51 citation statements)

References 40 publications

(52 reference statements)

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“…Lebedev 2005;Ampleford et al 2008) have also shown the development of conical shocks forming at the base and along the axis of the developed jet.…”

Section: Jets and Multiple Oblique Shocksmentioning

confidence: 99%

Active galactic nuclei jets and multiple oblique shock acceleration: starved spectra

Meli¹,

Biermann

2013

A&A

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Context. Shocks in jets and hot spots of active galactic nuclei (AGN) are one prominent class of possible sources of very high-energy cosmic-ray particles (above 10 18 eV). Extrapolating their spectrum to their plausible injection energy from some shock implies an enormous hidden energy for a spectrum of index ∼−2. Some analyses suggest the particles' injection spectrum at source to be as steep as −2.4 to −2.7, which exacerbates the problem, by a factor of 10 6 . Nevertheless, it seems implausible that more than at the very best 1/3 of the jet energy goes into the required flux of energetic particles, thus one would need to allow for the possibility that there is an energy problem, which we would like to address in this work. Aims. Sequences of consecutive oblique shock features, or conical shocks, have been theoretically predicted and eventually observed in many AGN jets. Based on that, we use by analogy the Comptonization effect and propose a scenario of a single injection of particles consecutively accelerated by several oblique shocks along the axis of an AGN jet. Methods. We developed a test-particle approximation Monte Carlo simulations to calculate particle spectra by acceleration at such a shock pattern while monitoring the efficiency of acceleration by calculating differential spectra. Results. We find that the first shock of a sequence of oblique shocks establishes a low-energy power-law spectrum with ∼E −2.7 . The following consecutive shocks push the spectrum up in energy, rendering flatter distributions with steep cut-offs, and characteristic depletion at low energies, which could explain the puzzling apparent extra source power. Conclusions. Our numerical calculations show a variation of spectral indices, a general spectral flattening, and starved spectra, which connect to the relativistic nature of the shocks, the multiple shock acceleration conditions, and the steepness of the magnetic field to the shock normal. This helps in understanding the jet-magnetic field geometry and the irregular or flat spectra observed in many AGN jets (e.g., CenA, 3C 279, PKS 1510-089). Furthermore, the E −2.4 − E −2.7 ultra-high-energy cosmic-ray injected source spectra claimed by many authors might be explained by the superposition of several, perhaps many, emission sources, all of which end their particle shock-acceleration sequence with flatter, starved spectra produced by two or more consecutive oblique shocks along their jets. It might also imply a mixed component of the accelerated particles above 10 19 eV. Moreover, the present acceleration model can explain the variability of inverted gamma-ray spectra observed in high redshifted flaring extragalactic sources.

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“…Lebedev 2005;Ampleford et al 2008) have also shown the development of conical shocks forming at the base and along the axis of the developed jet.…”

Section: Jets and Multiple Oblique Shocksmentioning

confidence: 99%

Active galactic nuclei jets and multiple oblique shock acceleration: starved spectra

Meli¹,

Biermann

2013

A&A

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“…By employing a small, dedicated low inductance pulser to drive the xpinch, such as the one described by Mesyats et al, 19 one could couple this diagnostic to a wide range of laser plasma and pulsed power experiments. Examples include the study of conditions in hydrodynamic 20,21 and magnetically driven jets, [22][23][24] materials in WDM state, 11,12 and the structure of radiative shocks. 21,25 Additionally, the excellent spectral resolution makes it possible to improve and expand upon data previously taken of spectral opacities in highly controlled samples such as those found in Refs.…”

Section: Resultsmentioning

confidence: 99%

High resolution absorption spectroscopy of exploding wire plasmas using an x-pinch x-ray source and spherically bent crystal

Knapp

Pikuz

Shelkovenko

et al. 2011

Review of Scientific Instruments

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We present here the use of absorption spectroscopy of the continuum radiation from x-pinch-produced point x-ray sources as a diagnostic to investigate the properties of aluminum plasmas created by pulsed power machines. This technique is being developed to determine the charge state, temperature, and density as a function of time and space under conditions that are inaccessible to x-ray emission spectroscopic diagnostics. The apparatus and its characterization are described, and the spectrometer dispersion, magnification, and resolution are calculated and compared with experimental results. Spectral resolution of about 5000 and spatial resolution of about 20 μm are demonstrated. This spectral resolution is the highest available to date in an absorption experiment. The beneficial properties of the x-pinch x-ray source as the backlighter for this diagnostic are the small source size (<5 μm), smooth continuum radiation, and short pulse duration (<0.1 ns). Results from a closely spaced (1 mm) exploding wire pair are shown and the general features are discussed.

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“…An even simpler way to explore this concept would be in a fan-shaped planar wire array in which the wires are more closely spaced at the cathode than at the anode (the 2D analog of a conical array). Like a conical wire array [58] or radial array [59], one would expect the implosion to start at the cathode where the magnetic field is higher. Multiple implosions initiating at this cathode contact point due to current restrike are often observed in radial wire arrays.…”

Section: Chapter 4 Conclusion and Future Directionsmentioning

confidence: 99%

Compact wire array sources: power scaling and implosion physics.

Serrano¹,

Chuvatin

Jones³

et al. 2008

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A series of ten shots were performed on the Saturn generator in short pulse mode in order to study planar and small-diameter cylindrical tungsten wire arrays at ∼5 MA current levels and 50-60 ns implosion times as candidates for compact z-pinch radiation sources. A new vacuum hohlraum configuration has been proposed in which multiple z pinches are driven in parallel by a pulsed power generator. Each pinch resides in a separate return current cage, serving also as a primary hohlraum. A collection of such radiation sources surround a compact secondary hohlraum, which may potentially provide an attractive Planckian radiation source or house an inertial confinement fusion fuel capsule. Prior to studying this concept experimentally or numerically, advanced compact wire array loads must be developed and their scaling behavior understood. The 2008 Saturn planar array experiments extend the data set presented in Ref.[1], which studied planar arrays at ∼3 MA, 100 ns in Saturn long pulse mode. Planar wire array power and yield scaling studies now include current levels directly applicable to multi-pinch experiments that could be performed on the 25 MA Z machine. A maximum total x-ray power of 15 TW (250 kJ in the main pulse, 330 kJ total yield) was observed with a 12-mm-wide planar array at 5.3 MA, 52 ns. The full data set indicates power scaling that is sub-quadratic with load current, while total and main pulse yields are closer to quadratic; these trends are similar to observations of compact cylindrical tungsten arrays on Z. We continue the investigation of energy coupling in these short pulse Saturn experiments using zero-dimensional-type implosion modeling and pinhole imaging, indicating 16 cm/μs implosion velocity in a 12-mm-wide array. The same phenomena of significant trailing mass and evidence for resistive heating are observed at 5 MA as at 3 MA. 17 kJ of Al K-shell radiation was obtained in one Al planar array fielded at 5.5 MA, 57 ns and we compare this to cylindrical array results in the context of a K-shell yield scaling model. We have also performed an initial study of compact 3 mm diameter cylindrical wire arrays, which are alternate candidates for a multi-pinch vacuum hohlraum concept. These massive 3.4 and 6 mg/cm loads may have been impacted by opacity, producing a maximum x-ray power of 7 TW at 4.5 MA, 45 ns. Future research directions in compact x-ray sources are discussed. 4 AcknowledgmentWe thank M. Lopez (1675), G. T. Liefeste (1675), and J. L. Porter (1670) for providing load hardware and diagnostic support; L.B. Nielsen-Weber (1675) and D.S. Nielsen (1675) for extensive support of diagnostic installation, fielding, and film processing;

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Production of radiatively cooled hypersonic plasma jets and links to astrophysical jets

Cited by 69 publications

References 40 publications

Active galactic nuclei jets and multiple oblique shock acceleration: starved spectra

Active galactic nuclei jets and multiple oblique shock acceleration: starved spectra

High resolution absorption spectroscopy of exploding wire plasmas using an x-pinch x-ray source and spherically bent crystal

Compact wire array sources: power scaling and implosion physics.

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