Charge-Exchange Atoms and Ion Source Divergence in a 20 TW Applied-<i>B</i>Ion Diode

Filuk, A.B.; Bailey, James E.; Carlson, A. L.; Johnson, D. J.; Lake, P.; Mehlhorn, T. A.; Mix, L. P.; Renk, Timothy Jerome; Stygar, W. A.; Maron, Y.

doi:10.1103/physrevlett.77.3557

Cited by 15 publications

(5 citation statements)

References 17 publications

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“…Lithium was chosen because it was not observed in any previous spectra, so if observed, the source of the signal could be isolated. Additionally, there is a strong neutral lithium line at 6708 Å, which has been observed previously in highpower diodes [44,45]. In this experiment, the bottom of the SVS probe was coated with 1 μm of LiF.…”

Section: A Composition and Locationsupporting

confidence: 52%

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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: 52%

“…Visible emission from the convolute region was collected and transported via fiber optic to two streaked-visiblespectroscopy (SVS) diagnostics. Similar systems have been used at Sandia to understand applied-B ion diodes [44,45] and shocks in liquid deuterium [46]. Details of the SVS diagnostics are given in Appendix B.…”

Section: Spectral Measurementsmentioning

confidence: 99%

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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“…This is significantly higher than the previously reported threshold of 5ϫ10 5 W cm Ϫ2 for the Li I 2p -4d line, 8 and higher still than the LIBORS based prediction 21 of 3ϫ10 4 W cm Ϫ2 for a 1-2 mm layer of Li vapor at 10 17 cm Ϫ3 . While all of the models considered here 1,4,20 predict a lowering of the threshold on resonance, no observable difference could be ascertained in our experiments.…”

Section: E Thresholds For Ion Productioncontrasting

confidence: 64%

“…Rather, it arises as a result of electrons gaining energy in superelastic collisions with resonantly excited atoms. However problems with beam divergence 8 have led to renewed interest in generating lithium ions by laser produced plasmas. 5 LIBORS may prove useful in ion source development for inertial confinement fusion.…”

Section: Introductionmentioning

confidence: 99%

Spatially resolved spectra of resonantly pumped laser produced plasmas of lithium

McCormack

O’Sullivan

1999

Review of Scientific Instruments

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Spatially resolved visible spectra emitted from a plasma formed by focusing the output of a flashlamp pumped dye laser onto solid targets of lithium have been recorded. The effects of laser wavelength on plasma formation have been analyzed by tuning the laser to the first resonance transition in lithium at 6708 Å and comparing the results with those obtained at an off resonance wavelength of 6728 Å. Laser energies varied from 430 to 645 mJ and were focused to a spot diameter of 300 m with a pulse length of 850 ns. Light from the plasma was focused onto the slit of a Hilger spectrograph, which incorporated a Pellin-Broca prism whose output was focused onto a charge-coupled device camera. Electron densities of 10 16 -10 18 cm Ϫ3 were deduced from Stark width and shift measurements of the Li II 2s -2p line at 5485 Å and from the Li I 2 p -4d line at 4603 Å. In this way the electron density could be mapped as a function of distance from the target. By observing emission at 5485 Å the electron density was observed to increase when the laser was tuned on resonance compared to off. This was not the case when the neutral Li I 2 p -4d line was used as a diagnostic. The anomaly is accounted for by referring to both the ionization rates involved and the temporal profile of the emission.

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“…Stimulated desorption is important in (i) the initiation of events on anode and cathode surfaces at low temperature, (ii) under special conditions with high current densities or avalanches of low energy (=1-100 eV) electrons, and (iii) with particular contaminants with high elastic scattering cross section [34]. Stimulated desorption possibly accounts for temperature independent anode particle production early in the power pulse in several works [8,18,35], may be a dominant effect in insulator flashover [36,37], in cavities for RF accelerators [19,38], and in microwave devices.…”

Section: Pulsed Desorption From Electrodesmentioning

confidence: 99%

The effects of electrode cleaning and conditioning on the performance of high-energy, pulsed-power devices

Cuneo

Proceedings ISDEIV. 18th International Symposium on Discharges and Electrical Insulation in Vacuum (Cat. No.98CH36073)

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-High-energy pulsed-power devices routinely access field strengths above those at which broad-area, cathode-initiated, high-voltage vacuum-breakdown occur (> le7 -3e7 V/m). Examples include magnetically-insulatedtransmission-lines and current convolutes, high-currentdensity electron and ion diodes, high-power microwave devices, and cavities and other structures for electrostatic and RF accelerators. Energy deposited in anode surfaces may exceed anode plasma thermal-desorption creation thresholds on the time-scale of the pulse. Stimulated desorption by electron or photon bombardment can also lead to plasma formation on electrode or insulator surfaces. Device performance is limited above these thrFsholds, particularly in pulselength and energy, by the formation and expansion d plasmas formed primarily fiom electrode contaminants. Insitu conditioning techniques to modify and eliminate the contaminants through multiple high-voltage pulses, low base pressures, RF discharge cleaning, heating, surface coatings, and ion-and electron-beam surface treatment allow access to new regimes of performance through control of plasma formation and modification of the plasma properties. Experimental and theoretical progress h m a variety of devices and small scale experiments with a variety of treatment methods will be reviewed and recommendations given for future work.

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Charge-Exchange Atoms and Ion Source Divergence in a 20 TW Applied-BIon Diode

Cited by 15 publications

References 17 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

Spatially resolved spectra of resonantly pumped laser produced plasmas of lithium

The effects of electrode cleaning and conditioning on the performance of high-energy, pulsed-power devices

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