Ion extraction capabilities of two-grid accelerator systems

An experimental investigation into the ion extraction capabilities of two-grid accelerator systems common to electrostatic ion thrusters is described. This work resulted in a large body of experimental data which facilitates the selection of the accelerator system geometries and operating parameters necessary to maximize the extracted ion current. Results suggest that the impingement-limited perveance is not dramatically affected by reductions in screen hole diameter to 0.5 mm. Impingement-limited performance is shown to depend most strongly on grid separation distance, accelerator hole diameter ratio, the discharge-to-total accelerating voltage ratio, and the net-to-total accelerating voltage ratio. Results obtained at small grid separation ratios suggest a new grid operating condition where high beam current per hole levels are achieved at a specified net accelerating voltage. It is shown that this operating condition is realized at an optimum ratio of net-to-total accelerating voltage ratio which is typically quite high. The apparatus developed for this study is also shown to be well suited measuring the electron backstreaming and electrical breakdown characteristics of two-grid accelerator systems

Composite heat pipe development status: Development of lightweight prototype carbon-carbon heat pipe with integral fins and metal foil liner

This report discusses development and proof-of-concept testing of a new lightweight carbon-carbon (C-C) space radiator heat pipe, carried out under the NASA Civil Space Technology Initiative (CSTI) High Capacity Power Program. The prototype heat pipe, equipped with a niobium-zirconium foil liner, was filled with potassium working fluid and tested for 11 hours, including startup from ambient temperature with the working fluid initially in the frozen state to near 700 K condenser temperature. Steady-state heat pipe input power during testing was facility limited to about 300 watts. Post test inspection showed the heat pipe to be in excellent condition after eight thermal cycles from ambient to steady-state operating temperature. Utilization of other liner materials and working fluids would greatly extend the spectrum of service temperatures for this technology, with potential applications ranging from small spacecraft heat rejection to aircraft and terrestrial uses

Carbon-Carbon Heat Pipe Testing and Evaluation

This report discusses development and proof-of-concept testing of a new lightweight carbon-carbon (C-C) space radiator heat pipe developed under the NASA Civil Space Technology Initiative (CSTI) High Capacity Power Program. The heat pipe was filled with potassium working fluid and tested for 11 hours including startup from ambient temperature with the working fluid initially in the frozen state to near 700 K condenser temperature. Steady-state heat pipe input power during testing was facility limited to about 300 watts, representing about 50 percent of the design input power. Post test inspection showed the heat pipe to be in excellent condition after eight thermal cycles from ambient to steady-state operating temperature. Potential applications, ranging from small spacecraft heat rejection to aircraft and terrestrial uses, are discussed

Pencil-like mm-size electron beams produced with linear inductive voltage adders (LIVA)

This paper presents design, analysis, and first results of the high brightness electron beam experiments currently under investigation at Sandia. Anticipated beam parameters are: energy 12 MeV, current 35-40 kA, rms radius 0.5 mm, pulse duration 40 ns FWHM. The accelerator is SABRE, a pulsed LIVA modified to higher impedance, and the electron source is a magnetically immersed foilless electron diode. 20 to 30 Tesla solenoidal magnets are required to insulate the diode and contain the beam to its extremely small sized (1 mm) envelope. These experiments are designed to push the technology to produce the highest possible electron current in a submillimeter radius beam. Design, numercial simulations, and first experimental results are presented

Development of a Dynamic Spot Size Diagnostic for Flash Radiographic X-Ray Sources

There has been considerable work in recent years in the development of high-brightness, high-dose flash x-ray radiographic sources. Spot size is one of several parameters that helps characterize source performance and provides a figure of merit to assess the suitability of various sources to specific experimental requirements. Time-integrated spot-size measurements using radiographic film and a high-Z rolled-edge object have been used for several years with great success. The Advanced Radiographic Technologies program thrust to improve diode performance requires extending both modeling and experimental measurements into the transient time domain. A new Time Resolved Spot Detector (TRSD) is under development to provide this information. In this paper we report the initial results of the performance of a 148-element scintillating fiber array that is fiber-optically coupled to a gated streak camera. Spatial and temporal resolution results are discussed and the data obtained from the Sand ia National Laboratories (SNL) RITS-3 (Radiographic Integrated Test Stand) accelerator are presented

Operational characteristics and analysis of the immersed-Bz diode on RITS-3.

The immersed-B{sub z} diode is being developed as a high-brightness, flash x-ray radiography source. This diode is a foil-less electron-beam diode with a long, thin, needle-like cathode inserted into the bore of a solenoid. The solenoidal magnetic field guides the electron beam emitted from the cathode to the anode while maintaining a small beam radius. The electron beam strikes a thin, high-atomic-number anode and produces bremsstrahlung. We report on an extensive series of experiments where an immersed-B{sub z} diode was fielded on the RITS-3 pulsed power accelerator, a 3-cell inductive voltage generator that produced peak voltages between 4 and 5 MV, {approx}140 kA of total current, and power pulse widths of {approx}50 ns. The diode is a high impedance device that, for these parameters, nominally conducts {approx}30 kA of electron beam current. Diode operating characteristics are presented and two broadly characterized operating regimes are identified: a nominal operating regime where the total diode current is characterized as classically bipolar and an anomalous impedance collapse regime where the total diode current is in excess of the bipolar limit and up to the full accelerator current. The operating regimes are approximately separated by cathode diameters greater than {approx}3 mm for the nominal regime and less than {approx} 3 mm for the anomalous impedance collapse regime. This report represents a compilation of data taken on RITS-3. Results from key parameter variations are presented in the main body of the report and include cathode diameter, anode-cathode gap, and anode material. Results from supporting parameter variations are presented in the appendices and include magnetic field strength, prepulse, pressure and accelerator variations

Lawson criterion for ignition exceeded in an inertial fusion experiment

For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion

High voltage high brightness electron accelerator with MITL voltage adder coupled to foilless diode

The design and analysis of a high brightness electron beam experiment under construction at Sandia National Laboratory is presented. The beam energy is 12 MeV, the current 35-40 kA, the rms radius 0.5 mm, and the pulse duration FWHM 40 ns. The accelerator is SABRE a pulsed inductive voltage adder, and the electron source is a magnetically immersed foilless diode. This experiment has as its goal to stretch the technology to the edge and produce the highest possible electron current in a submillimeter radius beam