J. McGurn

Sandia National Laboratories, Albuquerque, New Mexico, United States

Are you J. McGurn?

Claim your profile

Publications (72)77.04 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The effect of short-circuit across the final anode-cathode gap of powerful pulsed current generators could hamper efficient power delivery to the Z-pinch plasma. To study this effect, a novel EUV diagnostics of plasmas created in the final section of the transmission line (the anode-cathode gap near the main load) of the Z-Machine high-current generator (Sandia National Laboratories, United States) was developed. The work included developing spectroscopic instruments, theoretical and experimental studies of EUV spectra of iron ions in well-diagnosed laser-produced plasmas, and a comparison of these spectra with those of plasmas created in the final anode-cathode gap of the transmission line. The EUV spectra of highly charged Fe ions in the spectral range λ ∼ 20–800 Å were investigated. In experiments performed at Sandia National Laboratories, spectra of FeXIII-FeXVII ions were observed. A comparison of the measured and calculated spectra shows that the electron plasma temperature in the anode-cathode gap is T e ∼ 200 eV.
    Plasma Physics Reports 10/2008; 34(11):944-954. · 0.66 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The effect of a short circuit across the final anode-cathode (A-K) gap of the powerful Z-Accelerator could hamper effective power delivery to z-pinch plasmas. The objective of this work is to develop an extreme ultraviolet (EUV) diagnostic technique for diagnosis of the low-temperature plasmas created in the final transmission line (A-K gap near the load) of the Z-Accelerator at the Sandia National Laboratories (SNL). The purpose of this effort is to help in understanding and mitigating this potentially serious problem. This work includes developing EUV grazing incidence spectrometers, investigation of the EUV spectra of highly charged ions in well diagnosed laser-produced plasmas, and the comparison of these laser plasma spectra with the spectra of plasmas created in the inner transmission line. Spectra of highly-charged iron (Fe) ions were investigated using EUV spectroscopy methods in a spectral range of 2 to 80 nm. Experiments at SNL have shown that the most stripped ion observed in the spectra is FeXVII. Comparison of the experimental spectra of FeIII through FeXVII ions with theoretical calculations gives an electron temperature T e of ∼ 200 eV.
    Pulsed Power Conference, 2007 16th IEEE International; 07/2007
  • [Show abstract] [Hide abstract]
    ABSTRACT: Summary form only given. The goal of this work is to develop theoretical support for advanced EUV diagnostics for magnetic insulation transmission line (MITL) study at SNL and for Z-pinch plasma study in general. EUV spectra of carbon and oxygen ions have been generated by a laser plasma source at the Z-pinch and laser-plasma X-ray/EUV facility at UNR. This source was designed for testing and calibration of the new X-ray/EUV devices. Polyethylene and mylar slabs attached to the computer-controlled 2D translation stage were used as targets. EUV spectra were collected by a spectrograph with a sliced multilayer grating which can cover a broad spectral region of 130-280 Aring. To increase sensitivity of the spectrograph and to add spatial resolution, glass capillary optics was employed. Non-LTE kinetic models developed for low-Z elements have been tested and used to identify the spectra and to provide plasma parameters. Application of these models and synthetic spectra to the existing and future MITL experiments on the 20 MA Z accelerator at SNL is discussed
    01/2006;
  • [Show abstract] [Hide abstract]
    ABSTRACT: We have developed wire-array z -pinch scaling relations for plasma-physics and inertial-confinement-fusion (ICF) experiments. The relations can be applied to the design of z -pinch accelerators for high-fusion-yield (approximately 0.4 GJ/shot) and inertial-fusion-energy (approximately 3 GJ/shot) research. We find that (delta(a)/delta(RT)) proportional (m/l)1/4 (Rgamma)(-1/2), where delta(a) is the imploding-sheath thickness of a wire-ablation-dominated pinch, delta(RT) is the sheath thickness of a Rayleigh-Taylor-dominated pinch, m is the total wire-array mass, l is the axial length of the array, R is the initial array radius, and gamma is a dimensionless functional of the shape of the current pulse that drives the pinch implosion. When the product Rgamma is held constant the sheath thickness is, at sufficiently large values of m/l, determined primarily by wire ablation. For an ablation-dominated pinch, we estimate that the peak radiated x-ray power P(r) proportional (I/tau(i))(3/2)Rlphigamma, where I is the peak pinch current, tau(i) is the pinch implosion time, and phi is a dimensionless functional of the current-pulse shape. This scaling relation is consistent with experiment when 13 MA < or = I < or = 20 MA, 93 ns < or = tau(i) < or = 169 ns, 10 mm < or = R < or = 20 mm, 10 mm < or = l < or = 20 mm, and 2.0 mg/cm < or = m/l < or = 7.3 mg/cm. Assuming an ablation-dominated pinch and that Rlphigamma is held constant, we find that the x-ray-power efficiency eta(x) congruent to P(r)/P(a) of a coupled pinch-accelerator system is proportional to (tau(i)P(r)(7/9 ))(-1), where P(a) is the peak accelerator power. The pinch current and accelerator power required to achieve a given value of P(r) are proportional to tau(i), and the requisite accelerator energy E(a) is proportional to tau2(i). These results suggest that the performance of an ablation-dominated pinch, and the efficiency of a coupled pinch-accelerator system, can be improved substantially by decreasing the implosion time tau(i). For an accelerator coupled to a double-pinch-driven hohlraum that drives the implosion of an ICF fuel capsule, we find that the accelerator power and energy required to achieve high-yield fusion scale as tau(i)0.36 and tau(i)1.36, respectively. Thus the accelerator requirements decrease as the implosion time is decreased. However, the x-ray-power and thermonuclear-yield efficiencies of such a coupled system increase with tau(i). We also find that increasing the anode-cathode gap of the pinch from 2 to 4 mm increases the requisite values of P(a) and E(a) by as much as a factor of 2.
    Physical Review E 09/2005; 72(2 Pt 2):026404. · 2.31 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present observations for 20-MA wire-array z pinches of an extended wire ablation period of 57%+/-3% of the stagnation time of the array and non-thin-shell implosion trajectories. These experiments were performed with 20-mm-diam wire arrays used for the double- z -pinch inertial confinement fusion experiments [M. E. Cuneo, Phys. Rev. Lett. 88, 215004 (2002)] on the Z accelerator [R. B. Spielman, Phys. Plasmas 5, 2105 (1998)]. This array has the smallest wire-wire gaps typically used at 20 MA (209 microm ). The extended ablation period for this array indicates that two-dimensional (r-z) thin-shell implosion models that implicitly assume wire ablation and wire-to-wire merger into a shell on a rapid time scale compared to wire acceleration are fundamentally incorrect or incomplete for high-wire-number, massive (>2 mg/cm) , single, tungsten wire arrays. In contrast to earlier work where the wire array accelerated from its initial position at approximately 80% of the stagnation time, our results show that very late acceleration is not a universal aspect of wire array implosions. We also varied the ablation period between 46%+/-2% and 71%+/-3% of the stagnation time, for the first time, by scaling the array diameter between 40 mm (at a wire-wire gap of 524 mum ) and 12 mm (at a wire-wire gap of 209 microm ), at a constant stagnation time of 100+/-6 ns . The deviation of the wire-array trajectory from that of a thin shell scales inversely with the ablation rate per unit mass: f(m) proportional[dm(ablate)/dt]/m(array). The convergence ratio of the effective position of the current at peak x-ray power is approximately 3.6+/-0.6:1 , much less than the > or = 10:1 typically inferred from x-ray pinhole camera measurements of the brightest emitting regions on axis, at peak x-ray power. The trailing mass at the array edge early in the implosion appears to produce wings on the pinch mass profile at stagnation that reduces the rate of compression of the pinch. The observation of precursor pinch formation, trailing mass, and trailing current indicates that all the mass and current do not assemble simultaneously on axis. Precursor and trailing implosions appear to impact the efficiency of the conversion of current (driver energy) to x rays. An instability with the character of an m = 0 sausage grows rapidly on axis at stagnation, during the rise time of pinch power. Just after peak power, a mild m = 1 kink instability of the pinch occurs which is correlated with the higher compression ratio of the pinch after peak power and the decrease of the power pulse. Understanding these three-dimensional, discrete-wire implosion characteristics is critical in order to efficiently scale wire arrays to higher currents and powers for fusion applications.
    Physical Review E 04/2005; 71(4 Pt 2):046406. · 2.31 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We have imploded the first foil load on the accelerator Z, and compared its implosion characteristics to a wire-array load of the same mass. The copper foil load was 1.5-µm thick, 2-cm in diameter, and 1-cm long, weighing 8.3-mg/cm. The same mass wire-array consisted of 300 20-µm diameter copper wires. The peak radiated power for the wire-array implosion was 60-TW with a 10-ns width, the peak radiated power for the foil implosion was 30-TW with a 20-ns width. Both the foil and the wire-array were backlit with 1.865 keV photons when the load current was 8.8-MA, the time at which the loads are predicted by 0D modeling to begin to implode. The backlit images show the development of axial instability at the edge of the loads. The instability appears to be more pronounced for the foil load. The foil is observed to have a delayed implosion trajectory with respect to the wire array. For the 300-wire-array the wire cores are observed to expand to a 50-µm diameter at the time of 8.8-MA load current.
    11/2004;
  • [Show abstract] [Hide abstract]
    ABSTRACT: A bottom axial diagnostic package has recently been developed and fielded on the 100 ns, 20 MA pinch-driver Z. The bottom package was developed to measure the power radiated to the bottom of Z and compare it to the power radiated to the top of Z on dynamic hohlraum pinch loads. When an up∕down power asymmetry was measured, the bottom package was expanded in an effort to determine the source of the asymmetry. The bottom package contains one port directly on axis, six ports at 3.4° to the axis, and four ports at 9° to the axis. Typical diagnostics fielded on the bottom package are a time-resolved pinhole camera, time-integrated spatially resolved convex crystal spectrometers, a time-resolved crystal spectrometer, x-ray diodes, bolometers, and photoconducting detectors. We will present some typical data from these bottom diagnostics on dynamic hohlraum shots on Z and briefly discuss their relevance to the up∕down power asymmetry.
    Review of Scientific Instruments 10/2004; 75(10):3684-3686. · 1.60 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We have measured the x-ray power and energy radiated by a tungsten-wire-array z pinch as a function of the peak pinch current and the width of the anode-cathode gap at the base of the pinch. The measurements were performed at 13- and 19-MA currents and 1-, 2-, 3-, and 4-mm gaps. The wire material, number of wires, wire-array diameter, wire-array length, wire-array-electrode design, normalized-pinch-current time history, implosion time, and diagnostic package were held constant for the experiments. To keep the implosion time constant, the mass of the array was increased as I2 (i.e., the diameter of each wire was increased as I), where I is the peak pinch current. At 19 MA, the mass of the 300-wire 20-mm-diam 10-mm-length array was 5.9 mg. For the configuration studied, we find that to eliminate the effects of gap closure on the radiated energy, the width of the gap must be increased approximately as I. For shots unaffected by gap closure, we find that the peak radiated x-ray power P(r) proportional to I1.24+/-0.18, the total radiated x-ray energy E(r) proportional to I1.73+/-0.18, the x-ray-power rise time tau(r) proportional to I0.39+/-0.34, and the x-ray-power pulse width tau(w) proportional to demonstrate that the internal energy and radiative opacity of the pinch are not responsible for the observed subquadratic power scaling. Heuristic wire-ablation arguments suggest that quadratic power scaling will be achieved if the implosion time tau(i) is scaled as I(-1/3). The measured 1sigma shot-to-shot fluctuations in P(r), E(r), tau(r), tau(w), and tau(i) are approximately 12%, 9%, 26%, 9%, and 2%, respectively, assuming that the fluctuations are independent of I. These variations are for one-half of the pinch. If the half observed radiates in a manner that is statistically independent of the other half, the variations are a factor of 2(1/2) less for the entire pinch. We calculate the effect that shot-to-shot fluctuations of a single pinch would have on the shot-success probability of the double-pinch inertial-confinement-fusion driver proposed by Hammer et al. [Phys. Plasmas 6, 2129 (1999)]. We find that on a given shot, the probability that two independent pinches would radiate the same peak power to within a factor of 1+/-alpha (where 0< or =alpha<1) is equal to erf(alpha/2sigma), where sigma is the 1sigma fractional variation of the peak power radiated by a single pinch. Assuming alpha must be < or =7% to achieve adequate odd-Legendre-mode radiation symmetry for thermonuclear-fusion experiments, sigma must be <3% for the shot-success probability to be > or =90%. The observed (12/2(1/2))%=8.5% fluctuation in P(r) would provide adequate symmetry on 44% of the shots. We propose that three-dimensional radiative-magnetohydrodynamic simulations be performed to quantify the sensitivity of the x-ray emission to various initial conditions, and to determine whether an imploding z pinch is a spatiotemporal chaotic system.
    Physical Review E 04/2004; 69(4 Pt 2):046403. · 2.31 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Results from the first solid foil implosion on the 18-MA Z accelerator are reported. The foil implosion is compared to a 300-wire-array implosion with the same material and the same diameter, height, and total mass. Though both the foil and the array produced comparable x-ray yields, the array's radiation burst was twice as powerful and half as long as the foil's. These data along with x-ray backlighting images and inductance measurements suggest that the foil implosion was more unstable than the wire-array implosion.
    Physics of Plasmas 01/2004; 11. · 2.38 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Summary form only given. In previous current-scaling experiments performed by William A. Stygar, the load masses were 5.8 mg for 90 kV charging of the Marx generators and 2.7 mg for 60 kV charging, resulting in implosion times of the order of 95 ns. The observed average peak radiated powers and energies were respectively 132TW and 1.625MJ for the 90-kV shots and 82.3TW and 0.841MJ for the 60-kV shots. The peak radiated X-ray power was proportional to the 1.24th power of the load current (P∝I<sup>1.24</sup>), and the total radiated X-ray energy was proportional to the 1.73rd power of the load current (E∝I<sup>1.73</sup>). In the present current scaling experiments the purpose is to look at current scaling of X-ray energy and power at shorter implosion times. The wire number (300), the array diameter (20 mm) and the height (1 cm) were the same as in previous studies. However the load masses were half the previous ones and equal to 2.5 and 1.25 mgr. This caused the arrays to pinch faster: ∼80 ns into the current pulse. The power output at full charging of the Marx's (90 kV) and the standard 100 ns current drive of Z driver was quite high for a single 20-mm diameter W wire array and equal to 170TW. The total radiated energy was equal to 1.14MJ. We fired one shot at full 90 kV charge (Z_1142) and a second one at 60 kV (Z_1143). The pinches were of very high quality as witnessed by the output X-ray pulses and framing cameras. The FWHM of both shots were 3.9 ns and the rise times 2.5 and 3.1 ns. The peak load currents were respectively 16.45 and 11.09MA. The radiated power ratio is equal to the current ratio to the 1.88th power (P∝I<sup>1.88</sup>) while the ratio of the total radiated energy is almost the same and equal to the 1.90th power of the current ratio (E∝I<sup>1.90</sup>). Despite the fact that fast pinches do not use all the available Z driver energy and consequently deliver less total radiated X-ray energy, they however yield more radiated power and tighter stagnations than the slower, higher mass pinches. This may be most important for ICF loads. More shots are planned to further validate and confirm these scoping results.
    Plasma Science, 2004. ICOPS 2004. IEEE Conference Record - Abstracts. The 31st IEEE International Conference on; 01/2004
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A dynamic hohlraum is formed when an imploding annular cylindrical Z-pinch driven plasma collides with an internal low density convertor. This collision generates an inward traveling shock wave that emits x rays, which are trapped by the optically thick Z-pinch plasma and can be used to drive an inertial fusion capsule embedded in the convertor. This scheme has the potential to efficiently drive high yield capsules due to the close coupling between the intense radiation generation and the capsule. In prior dynamic hohlraum experiments [J. E. Bailey et al., Phys. Rev Lett. 89, 095004 (2002)] the convertor shock wave has been imaged with gated x-ray pinhole cameras. The shock emission was observed to be very circular and to be quite narrow in the radial direction. This implies that there is minimal Rayleigh–Taylor imprinting on the shock wave. Thus, the dominant source of radiation asymmetry is not random and in principle could be significantly decreased by proper design. Due to the closed geometry of the dynamic hohlraum, the most convenient way to diagnose the radiation symmetry is to image the x rays from the core of an imploded capsule. However, the core temperatures in the prior experiments were not high enough to obtain images. Using numerical simulations we have redesigned the dynamic hohlraum to obtain higher capsule core temperatures. This has enabled us to obtain x-ray pinhole images and Ar K-shell spectra from the imploded cores of 1.7–2.0 mm diameter CH-wall capsules filled with either D2 or CD4 and doped with a small amount of Ar. These capsules absorbed approximately 20 kJ of x-ray energy from the radiation drive, which peaked at a temperature of about 200 eV. Core temperatures of approximately 1 keV were inferred from the Ar spectrum. Our present understanding of the physics of dynamic hohlraums is presented along with our plans to improve this system.
    Physics of Plasmas 05/2003; 10(5). · 2.38 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present a technique for experimentally measuring two-dimensional radiation temperatures in dynamic Hohlraums on Z. In principle the technique can be applied to any radiation source. Total radiated power from the source is measured by normalizing the area under an x-ray diode signal to energy yield measured by a bolometer. The radiated power as a function of time, which is just the normalized x-ray diode signal, can then be used to normalize gated microchannel plate x-ray pinhole camera images. The procedure is most accurate when the gated x-ray pinhole camera has the same filter as the x-ray diode and when the filter is transmissive near the peak of the Planckian radiation temperature being measured. We present results for two-dimensional radiation temperatures as a function of time for dynamic Hohlraum experiments on Z. In these experiments a z pinch consisting of nested tungsten wire arrays driven by the 20 MA, 100 ns Z accelerator implodes onto cylindrical foam located on axis. X-ray diodes and bolometers located along the axis measure the power radiated along the pinch axis. Pinhole-imaged time-resolved microchannel plate framing cameras located on axis measure the spatial distribution of this radiation. Results from the analysis of many shots taken on Z show that a symmetrical strongly radiating shock wave is launched in the foam. The shock wave stagnates to less than 1 mm diameter with radiation temperatures exceeding 300 eV. Applications for this source include driving inertial confinement fusion capsules within the dynamic Hohlraum and weapons physics experiments that use the dynamic Hohlraum as a radiation source. © 2003 American Institute of Physics.
    Review of Scientific Instruments 02/2003; 74(3):2211-2214. · 1.60 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present results from crystal spectroscopic analysis of silicon aero-gel foams heated by dynamic hohlraums on Z. The dynamic hohlraum on Z creates a radiation source with a 230-eV average temperature over a 2.4-mm diameter. In these experiments silicon aero-gel foams with 10-mg/cm3 densities and 1.7-mm lengths were placed on both ends of the dynamic hohlraum. Several crystal spectrometers were placed both above and below the z-pinch to diagnose the temperature of the silicon aero-gel foam using the K-shell lines of silicon. The crystal spectrometers were (1) temporally integrated and spatially resolved, (2) temporally resolved and spatially integrated, and (3) both temporally and spatially resolved. The results indicate that the dynamic hohlraum heats the silicon aero-gel to approximately 150-eV at peak power. As the dynamic hohlraum source cools after peak power the silicon aero-gel continues to heat and jets axially at an average velocity of approximately 50-cm/μs. The spectroscopy has also shown that the reason for the up/down asymmetry in radiated power on Z is that tungsten enters the line-of-sight on the bottom of the machine much more than on the top.
    Journal of Quantitative Spectroscopy and Radiative Transfer 01/2003; · 2.38 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In the fast ignitor approach to inertial fusion [Tabak et al., Phys. Plasmas 1, 1626 (1994)], ignition is produced by heating highly-compressed fuel with a fast, ultra-high power laser pulse. By separating the fuel compression and fast heating processes, symmetry and energy requirements for ignition are significantly relaxed. Laser propagation issues can be avoided by maintaining a plasma-free path for the short-pulse laser [Kodama et al., Nature 412, 798 (2001)]. In experiments on the Z accelerator at Sandia, we are exploring a fast ignitor hohlraum geometry uniquely adapted to fuel compression with a single-sided z-pinch radiation drive [Hanson et al., Phys. Plasmas 9, 2173 (2002)]. In this geometry, a hemispherical capsule mounted on a pedestal (short-pulse laser channel) is symmetrically imploded in a cylindrical secondary hohlraum heated by a single-wire-array z-pinch. Z-Beamlet point projection backlighter images of initial hemispherical capsule implosions on Z will be presented.
    11/2002;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Three hohlraum concepts are being pursued at Sandia National Laboratories (SNL) to investigate the possibility of using pulsed power driven magnetic implosions (Z pinches) to drive targets capable of fusion yields in the range 200-1000 MJ. This research is being conducted on SNL's Z facility, which is capable of driving peak currents of 20 MA in various Z pinch load configurations that produce implosion velocities as high as 7.5 × 107cm/s, X ray energies of 1-2 MJ and X ray powers of 100-250 TW. The first concept, denoted dynamic hohlraum, has achieved a temperature of 180 ± 14 eV in a configuration suitable for driving capsules. In addition, this concept has also achieved a temperature of 230 ± 18 eV in an arrangement suitable for driving an external hohlraum. The second concept, denoted static walled hohlraum, has achieved temperatures of ~80-100 eV. Experimental investigation of the third concept, denoted Z pinch driven hohlraum, has recently begun. The article discusses each of these hohlraum concepts and provides an overview of the experiments that have been conducted on these systems to date.
    Nuclear Fusion 05/2002; 39(9Y):1283. · 2.73 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A double Z pinch driving a cylindrical secondary hohlraum from each end has been developed which can indirectly drive intertial confinement fusion capsule implosions with time-averaged radiation fields uniform to 2%-4%. 2D time-dependent view factor and 2D radiation hydrodynamic simulations using the measured primary hohlraum temperatures show that capsule convergence ratios of at least 10 with average distortions from sphericity of /r<or=30% are possible on the Z accelerator and may meet radiation symmetry requirements for scaling to fusion yields of >200 MJ.
    Physical Review Letters 05/2002; 88(21):215004. · 7.94 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The Z-pinch-driven hohlraum (ZPDH) [J. H. Hammer et al., Phys. Plasmas 6, 2129 (1999)] is a promising approach to high yield inertial confinement fusion currently being characterized in experiments on the Sandia Z accelerator [M. E. Cuneo et al., Phys. Plasmas 8, 2257 (2001)]. Simulations show that capsule radiation symmetry, a critical issue in ZPDH design, is governed primarily by hohlraum geometry, dual-pinch power balance, and pinch timing. In initial symmetry studies on Z without the benefit of a laser backlighter, highly-asymmetric pole-hot and equator-hot single Z-pinch hohlraum geometries were diagnosed using solid low density foam burnthrough spheres. These experiments demonstrated effective geometric control and prediction of polar flux symmetry at the level where details of the Z-pinch implosion and other higher order effects are not critical. Radiation flux symmetry achieved in Z double-pinch hohlraum configurations exceeds the measurement sensitivity of this self-backlit foam ball symmetry diagnostic. To diagnose radiation symmetry at the 2%–5% level attainable with present ZPDH designs, high-energy x rays produced by the recently-completed Z-Beamlet laser backlighter are being used for point-projection imaging of thin-wall implosion and symmetry capsules. © 2002 American Institute of Physics.
    Physics of Plasmas 04/2002; 9(5):2173-2181. · 2.38 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In order to estimate the radiated power that can be expected from the next-generation z-pinch driver such as ZR at 28 MA, current-scaling experiments have been conducted on the 18-MA driver Z. We report on the current scaling of single 40-mm diameter tungsten 240-wire arrays with a fixed 110-ns implosion time. The wire diameter is decreased in proportion to the load current. The load current is reduced by reducing the charge voltage on the Marx banks. On one shot firing only 3 of the 4 levels of the Z machine further reduced the load current. The radiated energy scales as the current squared as expected but the radiated power scales as the current to the 3.5 power due to increased pinch instability at lower current. As the current is reduced the rise-time of the x-ray pulse increases and at the lowest current value of 10.4 MA a shoulder appears on the leading edge of the x-ray pulse. We will report on experiments in February 2002 which will attempt to image the pinch along the axis to determine the nature of the reduced stability at lower currents.
    Plasma Science, 2002. ICOPS 2002. IEEE Conference Record - Abstracts. The 29th IEEE International Conference on; 02/2002 · 2.38 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: An experimental study of high current (3–15 MA), high fidelity (multiple atomic number) and long implosion time (100–200 ns) gas puff loads using the 1–2–3–4 cm double-shell gas puff is in progress at Titan/PSD. Results of experiments conducted on Double-EAGLE, Saturn, Decade Quad and the Z accelerators will be analyzed and presented. The principal observations are: (1) The overall pinch quality and radiative characteristics of all the argon double shell z-pinches are quite satisfactory. The Ar K-shell yields varies from the expected I4 scaling in the inefficient regime for 3 to 7 MA to I2 scaling in the efficient regime from 7 to 15 MA. (2) On all experiments from 3–15 MA, selective seeding of the shells demonstrates that the hottest mass of the pinch originates from the inner shell. This suggests that mixing between the two plasma shells during their collision and final implosion is limited. (3) On the 15 MA Sandia Z accelerator, with a load mass of 0.8 mg/cm, the K-shell x-ray output reached 275 kJ in a 15 TW peak power, 12 ns pulse. The analyzed ion and electron densities reach 5 × 1019 and 1.0 × 1021 /cc and the highest electron temperature observed is up to 2.2 keV with a 2.0 keV continuum
    High-Power Particle Beams (BEAMS), 2002 14th International Conference on; 01/2002
  • [Show abstract] [Hide abstract]
    ABSTRACT: We report on the first experiments to measure the implosion dynamics of wire arrays on Z (M.E. Cuneo, et al., 3rd Wire Array Workshop, Abingdon, England, UK, April 2001). We use chordally- and axially-resolved visible and x-ray self-emission diagnostics. These experiments show implosion trajectories somewhat delayed (10-20 ns) from 0-D behavior near the initial array radius, but intercepting 0-D by half the initial radius. We observe a precursor pinch on the axis of the wire array at least 50 ns prior to the final stagnation, consistent with early acceleration of wire corona material. These experiments may indirectly indicate the presence of trailing mass at final stagnation. Comparisons of the data with a variety of 0-D models and 1- and 2-D radiation MHD simulations will be presented. These observations may impact our understanding of array power scaling and methods for array radiation pulseshaping for ICF. Sandia is a multiprogram laboratory operated by Sandia Corp., a Lockheed Martin Company, for the USDOE under contract DE-AC04-94AL85000.
    10/2001;