Plasma-filled Rod-pinch Diode Research Articles

The K x-ray line structures of the 3d-transition metals in warm dense plasma

The shapes and positions of the Kα1 and Kα2 x-ray lines for 3d-transition metals can vary substantially as electrons are stripped from the outer-shells. This paper shows the detailed line shapes for nickel and zinc, obtained by calculations with a multiconfiguration Dirac–Fock method that includes Breit interaction and quantum electrodynamics corrections. The line shapes can be useful in interpreting hot, dense plasmas with energetic electrons for which the K x-ray lines are optically thin, as may be produced by pulsed power machines such as the plasma-filled rod pinch diode or the plasma focus, or in short-pulsed high power laser plasmas.

预充等离子体密度对杆箍缩二极管特性的影响

预充等离子体密度对杆箍缩二极管特性的影响

Tungsten L transition line shapes and energy shifts resulting from ionization in warm dense matter

Spectra of the W L transitions in the energy range 8–12 keV from warm dense plasmas generated by the Naval Research Laboratory's Gamble II pulsed power machine were recorded by a newly developed high-resolution transmission-crystal X-ray spectrometer with ±2 eV accuracy. The discharges have up to 2 MV voltage, 0.5 MA current, and produce up to 2.4 MJ/cm−3 energy density. The plasma-filled rod pinch (PFRP) diode produces a plasma with Ne ≈ 1022 cm−3 and Te ≈ 50 eV during the time of maximum X-ray emission. By analyzing the line shapes, it was determined that the Lβ2 inner-shell transition from the 4d5/2 level was shifted to higher energy by up to 23 eV relative to nearby Lβ transitions from n = 3 levels. In addition, the Lβ2 transition was significantly broader and asymmetric compared to the n = 3 transitions. The energy shift of the Lβ2 transition results from the ionization of electrons outside the 4d shell that perturbs the transition energies in the ions to higher values. The increased line width and asymmetry result from unresolved transitions from a range of ionization states up to +28. The ionization distribution was determined by comparison of the measured energy shifts and widths to calculated transition energies in W ions, and the ionization was correlated with Gamble discharge parameters such as the anode type and the high voltage delay time. This work demonstrates a new hard X-ray spectroscopic diagnostic technique for the direct measurement of the ionization distribution in warm dense plasmas of the heavy elements W through U that is independent of the other plasma parameters and does not require interpretation by hydrodynamic, atomic kinetics, and radiative simulation codes.

Experiments with a plasma-filled rod-pinch diode on the MIG generator

Experimental data for creating an X-ray source several millimeters in size on the basis of a plasmafilled rod-pinch diode are reported. Experiments are carried out on the MIG high-current generator. A voltage pulse applied to the diode is sharpened and shortened by injecting plasma into the interelectrode gap up to the plasma-filled diode. Radiation extraction from the vacuum chamber in the paraxial direction is provided by inverting the positions of the cathode and anode using a post-hole vacuum convolute. It is demonstrated that the energy of a low-impedance high-current generator can be deposited with a high efficiency into an electron beam focused on the 1-mm2 tip of the rod-shaped anode. With a tapered tungsten rod 1.5 mm in diameter used as an anode, a pulsed X-ray source about 1 mm in size generating 30-ns-long pulses is obtained. The absorbed dose per pulse measured with a LiF thermoluminescent dosimeter behind a 5-mm-thick aluminum screen 1 m away from the source reaches 0.042 Gy.

K -line spectra from tungsten heated by an intense pulsed electron beam

The plasma-filled rod-pinch diode (PFRP) is an intense source of x-rays ideal for radiography of dense objects. In the PRFP megavoltage electrons from a pulsed discharge concentrate at the pointed end of a 1 mm diameter tapered tungsten rod. Ionization of this plasma might increase the energy of tungsten's Kα(1) fluorescence line, at 59.3182 keV, enough for the difference to be observed by a high-resolution Cauchois transmission crystal spectrograph. When the PFRP's intense hard bremsstrahlung is suppressed by the proper shielding, such an instrument gives excellent fluorescence spectra, albeit with as yet insufficient resolution to see any effect of tungsten's ionization. Higher resolution is possible with various straightforward upgrades that are feasible thanks to the radiation's high intensity.

Flash X-ray radiography source based on plasma-filled rod pinch diode

Results of experiments on the formation of a high-power focused electron beam in a plasma-filled rod pinch diode driven by a high-current MIG generator (maximum voltage, 1.3 MV; impedance, 0.65 Ω) are presented. The proposed diode with a sharpened 1.5-mm-thick tungsten rod anode provides an X-ray source for flash radiography with a size of ∼1 mm, which is capable of producing a radiation dose of 2.4 rad per pulse at a distance of 1 m. The results of comparative experiments with and without plasma injection into the diode are presented.

Radiographic Properties of Plasma-Filled Rod-Pinch Diodes

The plasma-filled rod-pinch diode (PFRP) is a new X-ray source appropriate for pulsed hydrodynamic radiography with endpoint voltage in the 1-2 MV range. The use of a plasma prefill in a rod-pinch-electrode configuration results in intense concentration of a 150-300 kA, ~2 MeV, ~100 ns electron beam at the tip of a tapered tungsten rod, producing an X-ray source with a submillimeter diameter and a dose of 25 rad (CaF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) at a distance of 1 m. These parameters are superior to conventional vacuum diodes used for radiography in this electron-beam energy range. The narrow X-ray source distribution and enhanced emission of X-rays with energies less than 300 keV are unique features of the PFRP that may be exploited for improved resolution and dynamic range for radiographic applications.

Ultra-high electron beam power and energy densities using a plasma-filled rod-pinch diode

The plasma-filled rod-pinch diode is a new technique to concentrate an intense electron beam to high power and energy density. Current from a pulsed power generator (typically ∼MV, MA, 100 ns pulse duration) flows through the injected plasma, which short-circuits the diode for 10–70 ns, then the impedance increases and a large fraction of the ∼MeV electron-beam energy is deposited at the tip of a 1 mm diameter, tapered rod anode, producing a small (sub-mm diameter), intense x-ray source. The current and voltage parameters imply 20–150 μm effective anode-cathode gaps at the time of maximum radiation, much smaller gaps than can be used between metal electrodes without premature shorting. Interferometric diagnostics indicate that the current initially sweeps up plasma in a snowplow-like manner, convecting current toward the rod tip. The density distribution is more diffuse at the time of beam formation with a low-density region near the rod surface where gap formation could occur. Particle simulations of the beam formation phase are dominated by rapid field penetration along the anode and radial J×B forces leading to gap formation and high-energy beam propagation to the rod tip. Beam deposition at the rod tip produces a high thermal energy-density (∼0.75 MJ/cm3), highly ionized (Z∼10, T∼25 eV) expanding tungsten plasma. Potential applications of this technique include improved radiography sources, high-energy-density plasma generation, and intense 10–100 keV x-ray production for nuclear-weapon-effects testing.