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Direct irradiation of materials by electron beams (e-beams) has been used to study material response.2,3 The desire to utilize high-power (∼ TW) generators to achieve higher specific energy deposition over larger areas has led to several approaches. One approach utilizes a monolithic e-beam diode with an external magnetic field (B field). The external B field allows the diode to operate in the bipolar,...
There is an interest in 10 keV to 100 keV radiation sources for some types of radiation-interaction studies. The approach presented here uses non-thermal radiation from single-wire radiators (SWRs). An SWR is a high-Z exploding wire that produces many small, bright radiation sources along its length during a fast (< 100 ns) high-current (∼ MA) discharge. In previous experiments,2 tungsten wires...
Measurements of the breakdown field of vacuum gaps have been made with a 1-MV, 50-ns test stand [1]. The first set of experiments was performed with planar, bare metal electrodes [2]. This geometry had an enhanced anode edge that affected measurements. Here, we report on a new set of measurements using anodes without field enhancement. Diagnostics include current and voltage probes, x-ray detector,...
We are studying species separation and magnetic field penetration in current-carrying plasmas in a coaxial plasma opening switch geometry1. PIC modeling has shown that these processes are dependent upon the radial density gradient and multi-species composition of the plasma2. Historically, flashboards, cable guns3, or an inverse pinch source4 have been used to inject plasma into the switch region...
Understanding the interaction of a strong magnetic field with a plasma is one of the fundamental problems in plasma physics. In this talk we report on a new systematic study using two-dimensional particle-in-cell simulations designed to explore the interplay between magnetic pushing1 (MHD time scales) and magnetic field penetration due to the Hall effect2. A two-ion-species plasma that consists of...
Magnetic field penetration in current-carrying plasmas is being studied in a plasma opening switch geometry. Several Marshall guns1 are used to inject single or multi-species plasmas between coaxial conductors connected to the output of NRL's Hawk pulsed-power generator. Following injection of the plasma, the generator is used to apply an electrical pulse with a peak current of 700 kA, a peak voltage...
Mercury, a 2-TW inductive voltage adder located at the Naval Research Laboratory in Washington, DC, had previously been converted from negative to positive polarity output by rotating each of the cells[1]. Positive polarity was needed to field an ion-beam diode.[2] However, rotating the cells takes about 2 to 3 weeks and is very labor intensive. So, when we next needed to operate in positive polarity,...
Pulsed bremsstrahlung from the Hermes-III generator1 produces photofission for research in Intense Pulsed Active Detection (IPAD)2. Hermes-III is operated in three modes producing bremsstrahlung with different endpoint energies: 8, 12, and 16 MeV, all with 30 ns x-ray pulse width. The electron-beam current increases with output voltage, from 300 kA at 8 MV to 600 kA at 16 MV. Previous experiments3...
There is ongoing interest in the use of an intense bremsstrahlung pulse to induce photofission in fissionable material.1, 2 To optimize the radiation for inducing fissions in the forward direction, electrons should approach normal incidence and their charge on the anode converter should be maximum. Here, these are optimized on the 8-MeV, 200-kA, 50-ns Mercury inductive voltage adder3 by varying the...
Mercury, a 2-TW inductive voltage adder located at the Naval Research Laboratory in Washington, DC, had previously been converted from negative to positive polarity output by rotating each of the cells1. Positive polarity was needed to field an ion-beam diode.2 However, rotating the cells takes about 2 to 3 weeks and is very labor intensive. So, when we next needed to operate in positive polarity,...
An intense bremsstrahlung x-ray pulse is generated by the 8-MeV, 200-kA, 50-ns Mercury inductive voltage adder.1 A study of the diode configuration was undertaken to optimize the forward-directed radiation. To this end, the diode AK gap was varied between 23 and 43 cm and an ID-reducing insert in the vacuum chamber wall was added to adjust the incidence angle and the electron charge at the tantalum...
An ongoing programme investigating the active detection of special nuclear material (SNM) is being undertaken by the Atomic Weapons Establishment (AWE) in collaboration with the Naval Research Laboratory (NRL). The programme is funded through the UK Home Office, Ministry of Defence and Cabinet Office and the Naval Research Laboratory supported primarily through the US Defence Threat Reduction Agency...
An ongoing programme looking at the active detection of special nuclear material (SNM) is being undertaken by the Atomic Weapons Establishment (AWE) in collaboration with the Naval Research Laboratory (NRL). As part of this programme, pulsed-power driven neutron experiments were conducted at the NRL Mercury accelerator. Mercury was used in a positive polarity mode to produce and accelerate protons...
We investigate the use of pulsed bremsstrahlung as a standoff active interrogation tool for the production of neutron and gamma signatures in fissionable materials.1 Photons are generated by an electron beam striking a Ta converter on the 16 MV Hermes III facility at Sandia National Laboratories, and propagate to a target location 19 m from the electron beam diode, at which various materials are placed...
Proton-beam-generation experiments have been conducted on the NRL Mercury pulsed-power generator operating in positive polarity with a lithium metal target embedded in the cathode. The accelerating voltage was limited to below 2.7 MV in order to limit the energy of neutrons produced in the 7Li(p,n)7Be reaction (Q = 1.88 MeV) to below 1 MeV. Analyses based on published results1 and calculations presented...
A series of experiments has been performed on the Mercury generator (8 MV, 200 kA, 50 ns) to investigate the use of a single, intense radiation pulse to induce photo fission.1 In these studies, a plate of depleted uranium (DU) is irradiated by the 8 MV-endpoint bremsstrahlung pulse produced by Mercury. Within this x-ray pulse, photons whose energies lie above the threshold of 5.26 MeV induce fission...
A 640 kV Marx bank and plasma opening switch (POS) produce an intense pulse of MeV protons that stop in a fluorine-bearing target. The 19F(p,αγ)16O reaction produces 6- to 7-MeV characteristic γ-rays that can induce fission reactions in fissionable materials, such as depleted uranium (DU). Some fission reactions are also induced by neutrons generated by proton and/or deuteron reactions in the target,...
In intense, pulsed active detection, a single, intense pulse of radiation is used to induce photofission in fissionable material, increasing its detectability. The Mercury pulsed-power generator was converted to positive polarity (+3.7 MV, 325 kA, 50-ns FWHM) to drive an intense, pulsed radiation source based on the FIGARO active detection concept. The probing radiation source consisted of an ion-beam...
The detection of fissile material by passive and active techniques is an area of intense interest. Many active approaches detect the products of fission induced by photon and/or neutron irradiation.1 One such approach has focused on using intense, pulsed, beam-target interactions to produce an irradiation source of 6.13-, 6.92-, and 7.13-MeV characteristic gamma rays from the 19F(p, αγ)16O reaction...
Summary form only given. Nuclear reactions in pulsed-power ion-diodes are usually induced by proton- or deuteron-projectiles accelerated to high energy by the voltage across the anode-cathode (A-K) gap. Reactions for which the incident projectile has a larger atomic number (Z > 2) are inhibited by the Coulomb barrier and are not usually detected. This work documents the detection of several heavy-ion...
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