Publications

Results 26–50 of 60
Skip to search filters

Investigations of shot reproducibility for the SMP diode at 4.5 MV

Cordova, S.; Johnston, Mark D.; Leckbee, Joshua L.; Kiefer, Mark L.; Nielsen, D.S.; Renk, Timothy J.; Webb, Timothy J.; Ziska, Derek Z.

In experiments conducted on the RITS-6 accelerator, the SMP diode exhibits sig- ni cant shot-to-shot variability. Speci cally, for identical hardware operated at the same voltage, some shots exhibit a catastrophic drop in diode impedance. A study is underway to identify sources of shot-to-shot variations which correlate with diode impedance collapse. To remove knob emission as a source, only data from a shot series conducted with a 4.5-MV peak voltage are considered. The scope of this report is limited to sources of variability which occur away from the diode, such as power ow emission and trajectory changes, variations in pulsed power, dustbin and transmission line alignment, and di erent knob shapes. We nd no changes in the transmission line hardware, alignment, or hardware preparation methods which correlate with impedance collapse. However, in classifying good versus poor shots, we nd that there is not a continuous spectrum of diode impedance behavior but that the good and poor shots can be grouped into two distinct impedance pro les. This result forms the basis of a follow-on study focusing on the variability resulting from diode physics. 3

More Details
TYPE SAND Report YEAR 2013
OSTIDOI

Textured coatings as first-wall materials : exposure to energetic ions on RHEPP-1

Renk, Timothy J.

The level of energy deposition on future inertial fusion energy (IFE) reactor first walls, particularly in direct-drive scenarios, makes the ultimate survivability of such wall materials a challenge. We investigate the survivability of three-dimensional (3-D) dendritic materials fabricated by chemical vapor deposition (CVD), and exposed to repeated intense helium beam pulses on the RHEPP-1 facility at Sandia National Laboratories. Prior exposures of flat materials have led to what appears to be unacceptable mass loss on timescales insufficient for economical reactor operation. Two potential advantages of such dendritic materials are (a) increased effective surface area, resulting in lowered fluences to most of the wall material surface, and (b) improvement in materials properties for such micro-engineered metals compared to bulk processing. Several dendritic fabrications made with either tungsten and tungsten with rhenium show little or no morphology change after up to 800 pulses of 1 MeV helium at reactor-level thermal wall loading. Since the rhenium is added in a thin surface layer, its use does not appear to raise environmental concerns for fusion designs.

More Details
TYPE Conference YEAR 2010
OSTI

Characterization of deuterium beam operation on RHEPP-1 for future neutron generation applications

Renk, Timothy J.

We investigate the potential for neutron generation using the 1 MeV RHEPP-1 intense pulsed ion beam facility at Sandia National Laboratories for a number of emerging applications. Among these are interrogation of cargo for detection of special nuclear materials (SNM). Ions from single-stage sources driven by pulsed power represent a potential source of significant neutron bursts. While a number of applications require higher ion energies (e.g. tens of MeV) than that provided by RHEPP-1, its ability to generate deuterium beams allow for neutron generation at and below 1 MeV. This report details the successful generation and characterization of deuterium ion beams, and their use in generating up to 3 x 10{sup 10} neutrons into 4{pi} per 5kA ion pulse.

More Details
TYPE SAND Report YEAR 2009
OSTIDOI

Ultra-thin multilayer capacitors

Renk, Timothy J.

The fabrication of ultra-thin lanthanum-doped lead zirconium titanate (PLZT) multilayer ceramic capacitors (MLCCs) using a high-power pulsed ion beam was studied. The deposition experiments were conducted on the RHEPP-1 facility at Sandia National Laboratories. The goal of this work was to increase the energy density of ceramic capacitors through the formation of a multilayer device with excellent materials properties, dielectric constant, and standoff voltage. For successful device construction, there are a number of challenging requirements including achieving correct stoichiometric and crystallographic composition of the deposited PLZT, as well as the creation of a defect free homogenous film. This report details some success in satisfying these requirements, although 900 C temperatures were necessary for PLZT perovskite phase formation. These temperatures were applied to a previously deposited multi-layer film which was then post-annealed to this temperature. The film exhibited mechanical distress attributable to differences in the coefficient of thermal expansion (CTE) of the various layers. This caused significant defects in the deposited films that led to shorts across devices. A follow-on single layer deposition without post-anneal produced smooth layers with good interface behavior, but without the perovskite phase formation. These issues will need to be addressed in order for ion beam deposited MLCCs to become a viable technology. It is possible that future in-situ heating during deposition may address both the CTE issue, and result in lowered processing temperatures, which in turn could raise the probability of successful MLCC formation.

More Details
TYPE SAND Report YEAR 2009
OSTIDOI
Results 26–50 of 60
Results 26–50 of 60