Magnetic cutoff in high-current diodes

Quasiequilibrium power flow in two radial magnetically insulated transmission lines (MITLs) coupled to a vacuum post-hole convolute is studied at 50 TW-200 TW using three-dimensional particle-in-cell simulations The voltages assumed for this study result in electron emission from all cathode surfaces. Electrons emitted from the MITL cathodes upstream of the convolute cause a portion of the MITL current to be carried by an electron sheath. Under the simplifying assumptions made by the simulations, it is found that the transition from the two MITLs to the convolute results in the loss of most of the sheath current to anode structures. The loss is quantified as a function of radius and correlated with Poynting vector stream lines which would be followed by individual electrons. For a fixed MITLconvolute geometry, the current loss, defined to be the difference between the total (i.e. anode) current in the system upstream of the convolute and the current delivered to the load, increases with both operating voltage and load impedance. It is also found that in the absence of ion emission, the convolute is efficient when the load impedance is much less than the impedance of the two parallel MITLs. The effects of space-charge-limited (SCL) ion emission from anode surfaces are considered for several specific cases. Ion emission from anode surfaces in the convolute is found to increase the current loss by a factor of 2-3. When SCL ion emission is allowed from anode surfaces in the MITLs upstream of the convolute, substantially higher current losses are obtained. Note that the results reported here are valid given the spatial resolution used for the simulations.

Section: Introductionmentioning

confidence: 99%

Steady-state modeling of current loss in a post-hole convolute driven by high power magnetically insulated transmission lines

Madrid

Rose

Welch

et al. 2013

“…where the following dimensions were applied: [17][18][19][20]. Using these values, L total ¼ 7:1 nH.…”

Section: Conical Power Feed and Experimental Chamber Designmentioning

confidence: 99%

250 kA compact linear transformer driver for wire arrayz-pinch loads

Bott

Haas

Madden

et al. 2011

We present the application of a short rise ($150 ns) 250 kA linear transformer driver (LTD) to wire array z-pinch loads for the first time. The generator is a modification of a previous driver in which a new conical power feed provides a low inductance coupling to wire loads. Performance of the new design using both short circuit and plasma loads is presented and discussed. The final design delivers $200 kA to a wire array load which is in good agreement with SCREAMER calculations using a simplified representative circuit. Example results demonstrate successful experiments using cylindrical, conical, and inverse wire arrays as well as previously published work on x-pinch loads.

“…The transmission-line voltages on RITS-6 are calculated using Mendel's pressure balance theory [6,15] and the Creedon model [28], which are both functions of the cathode boundary and anode currents. A common problem in MITL simulations is accurately modeling the cathode boundary-to-sheath current ratio before and after the retrapping wave has passed.…”

Section: Transmission-line Power Flowmentioning

confidence: 99%

Modeling particle emission and power flow in pulsed-power driven, nonuniform transmission lines

Bruner

Genoni

Madrid

et al. 2008

Pulsed-power driven x-ray radiographic systems are being developed to operate at higher power in an effort to increase source brightness and penetration power. Essential to the design of these systems is a thorough understanding of electron power flow in the transmission line that couples the pulsed-power driver to the load. In this paper, analytic theory and fully relativistic particle-in-cell simulations are used to model power flow in several experimental transmission-line geometries fielded on Sandia National Laboratories' upgraded Radiographic Integrated Test Stand [IEEE Trans. Plasma Sci. 28, 1653 (2000)]. Good agreement with measured electrical currents is demonstrated on a shot-by-shot basis for simulations which include detailed models accounting for space-charge-limited electron emission, surface heating, and stimulated particle emission. Resonant cavity modes related to the transmission-line impedance transitions are also shown to be excited by electron power flow. These modes can drive oscillations in the output power of the system, degrading radiographic resolution.