The Infona portal uses cookies, i.e. strings of text saved by a browser on the user's device. The portal can access those files and use them to remember the user's data, such as their chosen settings (screen view, interface language, etc.), or their login data. By using the Infona portal the user accepts automatic saving and using this information for portal operation purposes. More information on the subject can be found in the Privacy Policy and Terms of Service. By closing this window the user confirms that they have read the information on cookie usage, and they accept the privacy policy and the way cookies are used by the portal. You can change the cookie settings in your browser.
Previous proof-of-principle experiments at NRL used the Mercury IVA facility to test a self-magnetic-pinch (SMP) diode in conjunction with a pulsed resistive heating treatment that cleaned the SMP's anode surface. This heating treatment was tested as a method for mitigating the negative effects of low-Z ions, such as post-shot activation and potentially reduced diode impedance. These low-Z ions can...
The Gamble II generator at the Naval Research Laboratory produces ∼100 ns pulse duration, relativistic-electron beams with peak energies on the order of 1MV and peak currents of about 800 kA with annular beam areas between 40–80 cm2. This gives peak current densities ∼10 kA/cm2. For many different applications, a nitrogen gas in the 1 Torr range is used as a charge- and current-neutralizing background...
Magnetic field penetration in electron-magneto-hydrodynamics (EMHD) can be driven by density gradients through the Hall term. Here we describe the effect of electron inertia on simplified one- and two-dimensional models of a magnetic front. Nonlinear effects due to inertia cause the 1D model to develop peaked solitary waves, while in 2D a shear-driven Kelvin-Helholtz (KH) like instability causes the...
High-power diodes that generate intense electron beams are useful in many applications such as generating intense microwave radiation, pumping lasers for driving inertial fusion targets, and producing bremsstrahlung x-rays for flash radiography and nuclear weapon effects simulations. The core component of a high-power diode consists of a two-electrode acceleration gap in which a high voltage pulse...
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...
The behavior of intense electron beams (those with current densities on the order of hundreds of kA/cm2 and beam rise times on the order of 100 ns) traveling through gaseous media depends strongly on the transport properties of the media. For example, the conductivity of a gas, which depends sensitively on its ionization state and temperature, has a strong influence on the beam behavior through the...
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...
The current models of the plasma formation processes are relatively simple. Most PIC codes allow for space-charge limited electron emission once an electric-field threshold is exceeded but do not self-consistently model the physics of the cathode surface or the subsequent expansion of the cathode plasma. The model used for ion emission from the anode enables emission once the temperature rise from...
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,...
The self-magnetic-pinch (SMP) electron beam diode is being developed for 4 to 10 M V, 30 to 50 ohms, 50 ns, flash radiography of explosively driven objects by AWE1, SNL2, and NRL3. The goal is a reproducible < 2-mm FWHM diameter radiographic spot at several hundred Rads (Si) at 1 m. In this talk a new approach is proposed where the outer diameter of an ∼50-ohm vacuum impedance MITL is tapered down...
For many applications, control and manipulation of the electron orbits in a high-current electron beam is desirable. This is especially true when a weakly-self-pinched, multi-MV electron-beam is used to make bremsstrahlung radiation. In this case, the radiation pattern is highly peaked along the direction that the electron beam makes when it strikes the x-ray target. Therefore, to maximize the number...
Non-neutral magnetic vortices have been observed in electromagnetic particle-in-cell (PIC) simulations of plasmas where density gradients exist. When plasma dynamics on the length scale of the electron inertial length (c/ωpe) and the time scale of electron motion (t∼1/ωpe) is considered, charge separation and electron inertia effects become important. Relativistic effects may also be important in...
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...
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 reflex triode consists of two grounded cathodes on either side of a positive-high-voltage, tantalum anode. Emitted electrons interact with the tantalum to produce bremsstrahlung and line radiation. By making the tantalum much thinner than the electron range, the self absorption of the x-rays by the tantalum can be reduced. The reflex triode configuration makes the electrons pass through the tantalum...
We propose and analyze computationally the Intense Pulsed Active Detection (IPAD) of fissile materials. This approach employs bremsstrahlung photons from a single intense 100-ns interrogating pulse produced by a pulsed-power generator. The IPAD system requires only 3 s to detect delayed neutrons. In contrast, a multiple-pulse-train LINAC system requires several minutes. Because of the much smaller...
Set the date range to filter the displayed results. You can set a starting date, ending date or both. You can enter the dates manually or choose them from the calendar.