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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...
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 use the Briggs-Bers criterion to examine the absolute instability at the lower and upper band edges of a coupled cavity TWT. We find that the lower band-edge is not subjected to absolute instability. At the upper band-edge, we find a threshold beam current beyond which absolute instability is excited. In general, an absolute instability would occur in a linear beam tube if the cold-tube circuit...
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...
This paper will present results of our analysis of the onset of absolute instability at the lower band edge of a traveling wave tube (TWT). We begin with the study of an electron beam propagating in a dielectric waveguide because the exact dispersion relation is easily formulated, and it is similar to that of a gyrotron-traveling wave amplifier in which the occurrence of an absolute instability was...
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...
Random fabrication errors in the slow wave circuits may have detrimental effects on the performance of traveling-wave tubes (TWTs) of all types [1]. Pengvanich et. al. [2] considered the evolution of the three forward waves in a TWT in which the Pierce parameters vary randomly along the tube axis. A peculiar feature of the results in Ref. [2] is that, in the statistical evaluation of a large number...
University of Michigan, Ann Arbor, MI 48109, USA Random fabrication errors due to fabrication tolerances in the manufacture of slow wave circuits may have detrimental effects on the performance of traveling-wave tubes (TWTs) of all types [1–3]. Such errors will pose an increasingly serious problem as TWTs are designed and built to operate in the sub-millimeter wavelength regime and beyond. In this...
The magneto-Rayleigh-Taylor instability (MRT) is important to peta-watt pulsed-power system development, wire-array z-pinches and magnetized target fusion, and equation-of-state studies using flyer plates or isentropic compression [1,2]. It is also important to the study of the crab nebulae [3]. In this paper, MRT in a finite slab is studied analytically using the ideal MHD model. The slab may be...
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