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Signatures of hot electrons and fluorescence in Mo Kα emission on Z

Physics of Plasmas

Hansen, Stephanie B.; Ampleford, David A.; Cuneo, M.E.; Ouart, N.; Jones, Brent M.; Jennings, C.A.; Dasgupta, A.; Coverdale, Christine A.; Rochau, G.A.; Dunham, Gregory S.; Giuliani, J.L.; Apruzese, J.P.

Recent experiments on the Z accelerator have produced high-energy (17 keV) inner-shell K-alpha emission from molybdenum wire array z-pinches. Extensive absolute power and spectroscopic diagnostics along with collisional-radiative modeling enable detailed investigation into the roles of thermal, hot electron, and fluorescence processes in the production of high-energy x-rays. We show that changing the dimensions of the arrays can impact the proportion of thermal and non-thermal K-shell x-rays. © 2014 AIP Publishing LLC.

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TYPE Conference YEAR 2014
ScopusOSTI

Diagnostic constraints on the amount of cold mass in imploded argon pinches on Z

AIP Conference Proceedings

Apruzese, J.P.; Jones, Brent M.; Giuliani, J.L.; Ouart, N.D.; Thornhill, J.W.; Harvey-Thompson, Adam J.; Ampleford, David A.; Jennings, C.A.; Hansen, Stephanie B.; Moore, N.W.; Lamppa, Derek C.; Coverdale, C.A.; Cuneo, M.E.; Rochau, G.A.

The refurbished Z machine at Sandia National Laboratories has been successfully configured to drive gas-puff Z pinches. A series of experiments using Ar loads produced K-shell yields of 330 ± 9% kJ, with highly reproducible K-shell spectra and power pulses. Using spectroscopic and power data, we are able to constrain the properties of both the cold, non-K-shell radiating mass as well as the hot K-shell component of the pinch plasma. As in previous gas-puff shots on the original version of Z, only about 1/4 to 1/3 of the load mass was heated to temperatures sufficient to produce K-shell x-rays.

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TYPE Conference Poster YEAR 2014
ScopusOSTI

Two dimensional RMHD modeling of effective ion temperatures in recent ZR argon experiments

AIP Conference Proceedings

Giuliani, J.L.; Thornhill, J.W.; Apruzese, J.P.; Jones, Brent M.; Harvey-Thompson, Adam J.; Ampleford, David A.; Dasgupta, A.; Jennings, C.A.; Hansen, S.B.; Moore, N.W.; Lamppa, D.C.; Coverdale, Christine A.; Cuneo, M.E.; Rochau, G.A.

Radiation magnetohydrodynamic r-z simulations are performed of recent Ar shots on the refurbished Z generator to examine the effective ion temperature as determined from the observed line width of the He-γ line. While many global radiation properties can be matched to experimental results, the Doppler shifts due to velocity gradients at stagnation cannot reproduce the large experimentally determined width corresponding to an effective ion temperature of 50 keV. Ion viscous heating or magnetic bubbles are considered, but understanding the width remains an unsolved challenge.

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TYPE Conference Poster YEAR 2014
ScopusOSTI

X-ray power and yield measurements at the refurbished Z machine

Review of Scientific Instruments

Jones, Brent M.; Ampleford, David A.; Cuneo, M.E.; Hohlfelder, Robert J.; Jennings, C.A.; Johnson, Drew J.; Jones, Brent M.; Lopez, M.R.; Macarthur, J.; Mills, Jerry A.; Preston, T.; Rochau, G.A.; Savage, Mark E.; Spencer, D.; Sinars, Daniel S.; Porter, J.L.

Advancements have been made in the diagnostic techniques to measure accurately the total radiated x-ray yield and power from z-pinch implosion experiments at the Z machine with high accuracy. The Z machine is capable of outputting 2 MJ and 330 TW of x-ray yield and power, and accurately measuring these quantities is imperative. We will describe work over the past several years which include the development of new diagnostics, improvements to existing diagnostics, and implementation of automated data analysis routines. A set of experiments on the Z machine were conducted in which the load and machine configuration were held constant. During this shot series, it was observed that the total z-pinch x-ray emission power determined from the two common techniques for inferring the x-ray power, a Kimfol filtered x-ray diode diagnostic and the total power and energy diagnostic, gave 449 TW and 323 TW, respectively. Our analysis shows the latter to be the more accurate interpretation. More broadly, the comparison demonstrates the necessity to consider spectral response and field of view when inferring x-ray powers from z-pinch sources. © 2014 AIP Publishing LLC.

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TYPE Journal Article YEAR 2014
ScopusOSTIDOI

Larger sized wire arrays on 1.5 MA Z-pinch generator

AIP Conference Proceedings

Safronova, A.S.; Kantsyrev, V.L.; Weller, M.E.; Shlyaptseva, V.V.; Shrestha, I.K.; Esaulov, A.A.; Stafford, A.; Chuvatin, A.S.; Coverdale, Christine A.; Jones, Brent M.

Experiments on the UNR Zebra generator with Load Current Multiplier (LCM) allow for implosions of larger sized wire array loads than at standard current of 1 MA. Advantages of larger sized planar wire array implosions include enhanced energy coupling to plasmas, better diagnostic access to observable plasma regions, and more complex geometries of the wire loads. The experiments with larger sized wire arrays were performed on 1.5 MA Zebra with LCM (the anode-cathode gap was 1 cm, which is half the gap used in the standard mode). In particular, larger sized multi-planar wire arrays had two outer wire planes from mid-atomic-number wires to create a global magnetic field (gmf) and plasma flow between them. A modified central plane with a few Al wires at the edges was put in the middle between outer planes to influence gmf and to create Al plasma flow in the perpendicular direction (to the outer arrays plasma flow). Such modified plane has different number of empty slots: it was increased from 6 up to 10, hence increasing the gap inside the middle plane from 4.9 to 7.7 mm, respectively. Such load configuration allows for more independent study of the flows of L-shell mid-atomic-number plasma (between the outer planes) and K-shell Al plasma (which first fills the gap between the edge wires along the middle plane) and their radiation in space and time. We demonstrate that such configuration produces higher linear radiation yield and electron temperatures as well as advantages of better diagnostics access to observable plasma regions and how the load geometry (size of the gap in the middle plane) influences K-shell Al radiation. In particular, K-shell Al radiation was delayed compared to L-shell mid-atomic-number radiation when the gap in the middle plane was large enough (when the number of empty slots was increased up to ten).

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TYPE Conference Poster YEAR 2014
ScopusOSTI

K-α emission spectroscopic analysis from a Cu Z-pinch

High Energy Density Physics

Jones, Brent M.; Ampleford, David A.; Hansen, Stephanie B.

Advances in diagnostic techniques at the Sandia Z-facility have facilitated the production of very detailed spectral data. In particular, data from the copper nested wire-array shot Z1975 provides a wealth of information about the implosion dynamics and ionization history of the pinch. Besides the dominant valence K- and L-shell lines in Z1975 spectra, K-α lines from various ionization stages were also observed. K-shell vacancies can be created from inner-shell excitation and ionization by hot electrons and from photo-ionization by high-energy photons; these vacancies are subsequently filled by Auger decay or resonance fluorescence. The latter process produces the K-α emission. For plasmas in collisional equilibrium, K-α emission usually occurs from highly charged ions due to the high electron temperatures required for appreciable excitation of the K-α transitions. Our simulation of Z1975 was carried out with the NRL 1-D DZAPP non-LTE radiation-hydrodynamics model, and the resulting K- and L-shell synthetic spectra are compared with measured radiation data. Our investigation will focus on K-α generation by both impacting electrons and photons. Synthetic K-α spectra will be generated either by self-consistently calculating the K-shell vacancy production in a full Z-pinch simulation, or by post-processing data from a simulation. The analysis of these K-α lines as well as K- and L-shell emission from valence electrons should provide quantitative information about the dynamics of the pinch plasma.

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TYPE Journal Article YEAR 2013
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Results 76–100 of 293
Results 76–100 of 293