Evolving approaches to pulsed X-ray sources

Abstract

Production of pulsed radiation in the kiloelectronvolt-to-megaelectronvolt range for simulation of nuclear weapon effects uses pulsed power generators with output powers of the order of 1-10 TW. Radiation in the high-energy (gamma and hot) part of the spectrum has been obtained using intense electron beams incident on solid targets of high-material to produce radiation with continuous bremsstrahlung spectra. Magnetically driven plasma implosions have been used to obtain radiation in the keV (cold) part of the spectrum, characterized by strong line emission. The efficiency of radiation, required for Defense Threat Reduction Agency tasks, relative to stored pulser energy, is only a few percent. Radiation yields in the range of 5 to 60 keV are especially low, regardless of which method of radiation production is used. This article discusses the evolving approaches to producing hot and cold X-rays, to seeking more efficient radiators of cold and warm X-rays, and to improving the spectral and temporal characteristics of the hot radiation. Integration of the pulsed power drivers, with innovative radiator load concepts, is utilized to expand the cold and hot X-ray test capability, to increase the warm X-ray yields, as well as to reduce capital costs of the test facilities.Index Terms-Plasma implosions, pulsed power, X-rays.

Implosion dynamics and radiative characteristics of a high yield structured gas puff load

“…The expectation, supported by previous data, 34 has been that the K shell yield for any particular element decreases with implosion time, or equivalently, with the size of the nozzle. This can be seen as a consequence of the RayleighTaylor instability.…”

“…33 As noted in the Introduction, a simple Y ϳ I n scaling law is a convenient method for comparing results and is empirically seen to be generally applicable, even when the current pulse shape is varied; large changes in implosion time ͑from the Յ100 ns regime to the Ն ϳ 200 ns regime͒ have, heretofore, required a different proportionality factor in the power law scaling. 27,34 …”

Efficient Radiation Production in Long Implosions of Structured Gas-PuffZPinch Loads from Large Initial Radius

“…In addition, for a fixed load mass that provides the desired value of at given I m , a constant compression ratio implies Y K 1=R 0 1=. If this scaling, supported by some experimental data [7], always holds, the long implosions would be inherently inferior to the short implosions. To increase the initial radius of the load without sacrificing its radiative performance, we have to improve, rather than maintain, the quality of its implosion.…”

“…We have to increase the compression ratio and axial uniformity of the pinch and enhance the energy coupling to the stagnated radiating plasma. While conventional wisdom [7] indicates that this is hardly possible, the purpose of this Letter is to demonstrate how it can be done.Our strategy is to suppress the RT instability of implosion by shaping the peripheral load density profiles as described in [8][9][10][11][12] and at the same time to separate the dual role of the plasma in a conventional Z pinch that requires it to both couple energy during the run-in phase and then radiate at high [13] at implosion. The role of the outer region plasma (''pusher'') is to carry current during the rise time of the current drive and push as it implodes.…”

“…We have to increase the compression ratio and axial uniformity of the pinch and enhance the energy coupling to the stagnated radiating plasma. While conventional wisdom [7] indicates that this is hardly possible, the purpose of this Letter is to demonstrate how it can be done.…”