Investigation of plasma formation and propagation in relativistic electron beam diodes

Johnston, Mark D.; Oliver, B.V.; Portillo, S.; Mehlhorn, T. A.; Welch, D. R.; Rose, D. V.; Bruner, N.; Droemer, D.; Maron, Y.; Klodzh, E.; Bernshtam, V.; Stambulchik, E.; Heathcote, A.; Critchley, A.

doi:10.1109/plasma.2008.4590862

Cited by 6 publications

(3 citation statements)

References 2 publications

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“…Even considering differences in the chordal lines of sight (figure 8), it is apparent that the on-axis plasma is much brighter (denser) than the off-axis plasma. Since absolute calibrations were not performed on these shots, it was decided to calibrate the data by using the late-time spectra measured at large radii, and relating it back to the early-time on-axis continuum spectra (see "region analyzed" in figures 3,4,6, and 7) [23]. With a spectral resolution of 12 Angstroms, we observed line broadening for both aluminum and carbon lines (determined to be Stark broadening), indicating the presence of high electron densities (>10^17 cm -3 ).…”

Section: Experimental Results: (Shots 409-416)mentioning

confidence: 99%

Optical Spectroscopy Results for the Self-Magnetic Pinch Electron Beam Diode on the RITS-6 Accelerator

Johnston

Oliver

Hahn

et al. 2012

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Experiments have been conducted at Sandia National Laboratories' RITS-6 accelerator facility [1] (operating at 7.5 MV and 180 kA) investigating plasma formation and propagation in relativistic electron beam diodes used for flash x-ray radiography. High resolution, visible and ultraviolet spectra were collected in the anode-cathode (A-K) vacuum gap of the Self-Magnetic Pinch (SMP) diode [2-4]. Time and space resolved spectra are compared with time-dependent, collisional-radiative (CR) calculations [5-7] and Lsp, hybrid particle-in-cell code simulations [8,9]. Results indicate the presence of a dense (>1x10 17 cm-3), low temperature (few eV), on-axis plasma, composed of hydrocarbon and metal ion species, which expands at a rate of several cm/s from the anode to the cathode. In addition, cathode plasmas are observed which extend several millimeters into the A-K gap [10]. It is believed that the interaction of these electrode plasmas cause premature impedance collapse of the diode and subsequent reduction in the total radiation output. Diagnostics include high speed imaging and spectroscopy using nanosecond gated ICCD cameras, streak cameras, and photodiode arrays.

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Section: Experimental Results: (Shots 409-416)mentioning

confidence: 99%

Optical Spectroscopy Results for the Self-Magnetic Pinch Electron Beam Diode on the RITS-6 Accelerator

Johnston

Oliver

Hahn

et al. 2012

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“…The result is plotted in figure 12 (brown curve). Figure 13 shows an experimental streaked spectrum from a Self-Magnetic Pinch (SMP) shot on the RITS-6 accelerator [11]. Time goes from top to bottom; three lines have been placed on the spectrum to show when current first reaches the diode (0ns), the mid-point of the radiation pulse (55ns), and the end of the radiation pulse (96ns).…”

Section: Calibration Of Streaked Arc Lamp Spectramentioning

confidence: 99%

Absolute calibration method for nanosecond-resolved, time-streaked, fiber optic light collection, spectroscopy systems

Johnston

Oliver

Droemer

et al. 2012

Review of Scientific Instruments

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This paper describes a convenient and accurate method to calibrate fast (<1 ns resolution) streaked, fiber optic light collection, spectroscopy systems. Such systems are inherently difficult to calibrate due to the lack of sufficiently intense, calibrated light sources. Such a system is used to collect spectral data on plasmas generated in electron beam diodes fielded on the RITS-6 accelerator (8-12MV, 140-200kA) at Sandia National Laboratories. On RITS, plasma light is collected through a small diameter (200 μm) optical fiber and recorded on a fast streak camera at the output of a 1 meter Czerny-Turner monochromator. For this paper, a 300 W xenon short arc lamp (Oriel Model 6258) was used as the calibration source. Since the radiance of the xenon arc varies from cathode to anode, just the area around the tip of the cathode ("hotspot") was imaged onto the fiber, to produce the highest intensity output. To compensate for chromatic aberrations, the signal was optimized at each wavelength measured. Output power was measured using 10 nm bandpass interference filters and a calibrated photodetector. These measurements give power at discrete wavelengths across the spectrum, and when linearly interpolated, provide a calibration curve for the lamp. The shape of the spectrum is determined by the collective response of the optics, monochromator, and streak tube across the spectral region of interest. The ratio of the spectral curve to the measured bandpass filter curve at each wavelength produces a correction factor (Q) curve. This curve is then applied to the experimental data and the resultant spectra are given in absolute intensity units (photons/sec/cm(2)/steradian/nm). Error analysis shows this method to be accurate to within +∕- 20%, which represents a high level of accuracy for this type of measurement.

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“…Corrected 300W xenon arc lamp raw streaked spectrum (brown curve) overplotted with measured bandpass filter curves. Figure 13 shows an experimental streaked spectrum from a Self-Magnetic Pinch (SMP) shot on the RITS-6 accelerator [11]. Time goes from top to bottom; three lines have been placed on the spectrum to show when current first reaches the diode (0ns), the mid-point of the radiation pulse (55ns), and the end of the radiation pulse (96ns).…”

Section: Calibration Of Streaked Arc Lamp Spectramentioning

confidence: 99%

Absolute calibration method for fast-streaked, fiber optic light collection, spectroscopy systems.

Johnston¹,

Frogget

Oliver³

et al. 2010

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This report outlines a convenient method to calibrate fast (<1ns resolution) streaked, fiber optic light collection, spectroscopy systems. Such a system is used to collect spectral data on plasmas generated in the A-K gap of electron beam diodes fielded on the RITS-6 accelerator (8-12MV, 140-200kA). On RITS, light is collected through a small diameter (200 micron) optical fiber and recorded on a fast streak camera at the output of 1 meter Czerny-Turner monochromator (F/7 optics). To calibrate such a system, it is necessary to efficiently couple light from a spectral lamp into a 200 micron diameter fiber, split it into its spectral components, with 10 Angstroms or less resolution, and record it on a streak camera with 1ns or less temporal resolution. One method of doing this is with a DC short arc lamp. For this report, a 300W xenon arc lamp (Oriel Model 6258) was used. Since the radiance of the xenon arc varies from the cathode to the anode, just the area around the tip of the cathode ("hotspot") was imaged onto the fiber producing the highest intensity output. To compensate for chromatic aberrations, the signal was optimized at each wavelength measured. Output power at each wavelength was measured using 10nm bandpass interference filters and a calibrated photodetector. These measurements give power at discrete wavelengths across the spectrum, and when linearly interpolated, provide a calibration curve for the lamp. The fiber is then attached to the entrance of the monochromator and a spectrum is taken. The shape of the spectrum is determined by the collective responsivity of the optics, monochromator, and streak tube across the spectral region of interest. The ratio of this curve to the measured bandpass filter curve at each

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Investigation of plasma formation and propagation in relativistic electron beam diodes

Cited by 6 publications

References 2 publications

Optical Spectroscopy Results for the Self-Magnetic Pinch Electron Beam Diode on the RITS-6 Accelerator

Optical Spectroscopy Results for the Self-Magnetic Pinch Electron Beam Diode on the RITS-6 Accelerator

Absolute calibration method for nanosecond-resolved, time-streaked, fiber optic light collection, spectroscopy systems

Absolute calibration method for fast-streaked, fiber optic light collection, spectroscopy systems.

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