Magnetic field measurements via visible spectroscopy on the Z machine

Gómez, M. R.; Hansen, Stephanie B.; Peterson, Kyle; Bliss, David E.; Carlson, A. L.; Lamppa, Derek C.; Schroen, D. G.; Rochau, G. A.

doi:10.1063/1.4891304

Cited by 28 publications

(15 citation statements)

References 12 publications

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“…The sodium is attributed to unintended direct human-electrode contact. Negligibly small quantities (nanograms) have been readily observed in visible spectra from other experiments on Z [53]. The dominance of contaminants in the convolute plasma inventory is consistent with spectroscopic observations in previous pulsed-power systems (electron-beam diodes, ion-beam diodes, MITLs) [54].…”

Section: A Composition and Locationsupporting

confidence: 85%

Experimental study of current loss and plasma formation in the Z machine post-hole convolute

Gómez

Gilgenbach

Cuneo

et al. 2017

Phys. Rev. Accel. Beams

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The Z pulsed-power generator at Sandia National Laboratories drives high energy density physics experiments with load currents of up to 26 MA. Z utilizes a double post-hole convolute to combine the current from four parallel magnetically insulated transmission lines into a single transmission line just upstream of the load. Current loss is observed in most experiments and is traditionally attributed to inefficient convolute performance. The apparent loss current varies substantially for z-pinch loads with different inductance histories; however, a similar convolute impedance history is observed for all load types. This paper details direct spectroscopic measurements of plasma density, temperature, and apparent and actual plasma closure velocities within the convolute. Spectral measurements indicate a correlation between impedance collapse and plasma formation in the convolute. Absorption features in the spectra show the convolute plasma consists primarily of hydrogen, which likely forms from desorbed electrode contaminant species such as H 2 O, H 2 , and hydrocarbons. Plasma densities increase from 1 × 10 16 cm −3 (level of detectability) just before peak current to over 1 × 10 17 cm −3 at stagnation (tens of ns later). The density seems to be highest near the cathode surface, with an apparent cathode to anode plasma velocity in the range of 35-50 cm=μs. Similar plasma conditions and convolute impedance histories are observed in experiments with high and low losses, suggesting that losses are driven largely by load dynamics, which determine the voltage on the convolute.

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Section: A Composition and Locationsupporting

confidence: 85%

Experimental study of current loss and plasma formation in the Z machine post-hole convolute

Gómez

Gilgenbach

Cuneo

et al. 2017

Phys. Rev. Accel. Beams

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“…1 The development of this technique for Na absorption is described in detail in Ref. [75]. The amount of Zeeman splitting gives a measure of the magnetic field strength in regions where the background continuum is being absorbed.…”

Section: Streaked Visible Spectroscopy (Svs): Svs For Measuring Zeemamentioning

confidence: 99%

Implementing and diagnosing magnetic flux compression on the Z pulsed power accelerator

McBride

Bliss

Gómez

et al. 2015

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We report on the progress made to date for a Laboratory Directed Research and Development (LDRD) project aimed at diagnosing magnetic flux compression on the Z pulsed-power accelerator (0-20 MA in 100 ns). Each experiment consisted of an initially solid Be or Al liner (cylindrical tube), which was imploded using the Z accelerator's drive current (0-20 MA in 100 ns). The imploding liner compresses a 10-T axial seed field, B z (0), supplied by an independently driven Helmholtz coil pair. Assuming perfect flux conservation, the axial field amplification should be well described by B z (t) = B z (0) × [R(0)/R(t)] 2 , where R is the liner's inner surface radius. With perfect flux conservation, B z (t) and dB z /dt values exceeding 10 4 T and 10 12 T/s, respectively, are expected. These large values, the diminishing liner volume, and the harsh environment on Z, make it particularly challenging to measure these fields. We report on our latest efforts to do so using three primary techniques: (1) micro B-dot probes to measure the fringe fields associated with flux compression, (2) streaked visible Zeeman absorption spectroscopy, and (3) fiber-based Faraday rotation. We also mention two new techniques that make use of the neutron diagnostics suite on Z. These techniques were not developed under this LDRD, but they could influence how we prioritize our efforts to diagnose magnetic flux compression on Z in the future. The first technique is based on the yield ratio of secondary DT to primary DD reactions. The second technique makes use of the secondary DT neutron time-of-flight energy spectra. Both of these techniques have been used successfully to infer the degree of magnetization at stagnation in fully integrated Magnetized Liner Inertial Fusion (MagLIF) experiments on Z [

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“…There is the matter of most methods used to obtain large fields being destructive in their nature, thus complicating the experimental reproducibility. In such experiments, the Zeeman splitting of energy levels in alkalimetal atoms is used to observe field strengths of the order of tens/hundreds of Tesla via spectroscopic techniques [32][33][34]. Non-destructive techniques for producing * francisco.s.ponciano-ojeda@durham.ac.uk these large fields also exist, and this has enabled work in large pulsed magnetic fields up to 58 T with similar alkaliatom systems [35,36].…”

Section: Introductionmentioning

confidence: 99%

Absorption spectroscopy and Stokes polarimetry in a $^{87}$Rb vapour in the Voigt geometry with a 1.5 T external magnetic field

Ponciano-Ojeda,

Logue,

Hughes

2020

Preprint

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Magnetic field measurements via visible spectroscopy on the Z machine

Cited by 28 publications

References 12 publications

Experimental study of current loss and plasma formation in the Z machine post-hole convolute

Experimental study of current loss and plasma formation in the Z machine post-hole convolute

Implementing and diagnosing magnetic flux compression on the Z pulsed power accelerator

Absorption spectroscopy and Stokes polarimetry in a $^{87}$Rb vapour in the Voigt geometry with a 1.5 T external magnetic field

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