Craig N. Boyer

Metal vapor vacuum arc ion source

A two-wire metal vapor vacuum arc (MeVVA) vacuum head includes an upper housing and a lower vacuum housing. The lower vacuum housing includes a plurality of ports, a vacuum space, and a first grid positioned in the vacuum space. A plurality of electrodes are positioned in the ports with a first end with an electrical contact area extending into the upper housing, and a second end extending into the vacuum space with an exposed electrical discharge area spaced from the first grid. An electrode of opposite polarity is positioned in one of the lower housing ports with a first end extending into the upper housing and a second end attached to the first grid. An extractor grid is positioned adjacent to the first grid, an electrode selector is operatively connected to the plurality of electrodes, and a trigger generator circuit is connected to an input of the electrode selector.

On-blaze operation of a Mo/Si multilayer-coated, concave diffraction grating in the 136–142-Å wavelength region and near normal incidence

The efficiency and resolving power of a concave, 2400-groove/mm, blazed diffraction grating that had a Mo/Si multilayer coating were determined. The multilayer coating had a peak reflectance of 55% at 140-A near normal incidence. The efficiency of the multilayer grating for wavelengths in the 136-139-A range was 2% near normal incidence. This efficiency was a factor of 150 greater than the efficiency of a sister replica Au-coated grating in the same wavelength region. The resolving power of the multilayercoated grating in the third order of a V viii transition with a first-order wavelength of 140.451 A was 9100. Comparisons with the Au-coated grating indicated that the application of the multilayer coating did not affect the resolving power or the blaze angle.

Portable hard x-ray source for nondestructive testing and medical imaging

A portable hard x-ray source has been developed for nondestructive testing, medical imaging, and flash x-ray radiography. The source is powered by a Marx generator that produces a 200 kV, 1.2 kA pulse of 60 ns full width at half maximum. The x-ray tube is composed of a tungsten anode and a mesh cathode. The time dependence of the voltage, current, and x-ray emission were measured and were in good agreement with computer simulations. The simulation model accounted for the 15 capacitors and 15 spark gap switches of the Marx generator and the perveance of the electron flow across the anode–cathode gap. The simulations indicated that the 5 J energy that was stored in the Marx generator was efficiently delivered to the x-ray tube. The measured x-ray exposure, 34 mR at a distance of 30 cm, was in good agreement with the calculated exposure. X-ray images are presented that demonstrate the capabilities of the x-ray source for medical imaging, nondestructive testing, and flash x-ray radiography.

Dual-waveband operation of a multilayer-coated diffraction grating in the soft x-ray range at near-normal incidence

A concave diffraction grating (2400 grooves/mm) coated with a Si/Mo multilayer has an efficiency of 2.5% at 290 A and a resolving power of 14,000 in third order of 156 A.

Automatic Multishot Operation of an Electromagnetic Launcher

The Naval Research Laboratory has developed an automatic electromagnetic launcher system for countermeasure deployment. The launcher operates at 1 Hz and can fire bursts of one to six 44-mm2 projectiles. The launcher is controlled from a computer that permits selection of the bank charging voltage and the number of shots. The present experimental setup consists of a railgun, an autoloader, and a rapid charger with computer control.

Temperature dependence of the EUV responsivity of silicon photodiode detectors

Responsivity of silicon photodiodes was measured from -100 C to +50 C in the 3 to 250 nm wavelength range using synchrotron and laboratory radiation sources. Two types of silicon photodiodes were studied, the AXUV series having a thin nitrided silicon dioxide surface layer and the SXUV series having a thin metal silicide surface layer. Depending on the wavelength, the responsivity increases with temperature with the rates 0.013%/C to 0.053%/C for the AXUV photodiode and 0.020%/C to 0.084%/C for the SXUV photodiode. The increase in responsivity is consistent with the decrease in the silicon bandgap energy which causes a decrease in the pair creation energy. These results are particularly important for dose measurement in extreme ultraviolet (EUV) lithography steppers and sources since the detector temperature often increases because of the high EUV intensities involved.

Design of Low-Current High-Efficiency Augmented Railguns

Properly designed augmented railguns (ARGs) can operate at significantly lower currents and higher efficiency than conventional non-ARGs. This paper analyzes the performance of a two-turn and a three-turn ARG showing the design parameters that are needed to achieve low-current high-efficiency operation. The ARG of this paper has a 40-mm square bore and is 820 mm long. Typical operating currents are from 150 to 300 kA with pulsewidths of approximately 6 to 8 ms. Projectile mass is typically in the range of 130 to 400 g. Projectile velocity is variable from 50 to 250 m/s. Experimental performance is compared with the theoretical predictions of the recently developed electromagnetic launcher (EML) equation. There is a good agreement between measured efficiency and theoretical predictions providing further confirmation of the EML equation. Deviations between measured efficiency and theoretical predictions are attributed to a poor sliding contact. The data also provide further evidence of the recently reported velocity-skin-effect in the contact.

Development of a 150-kW, Battery Powered, Rapid Capacitor Charger for a Small Railgun in Burst Mode Operation at 3 RPS

A battery powered rapid charger for the capacitor bank of a small, low velocity railgun is being developed to allow burst mode operation at 3 RPS in a compact system. Recent improvements in railgun efficiency have reduced the charge voltage requirement from 2.3 to 2.0 kV, thereby reducing the average charger power from 200 to 150 kW. The goal is to charge a 15-mF capacitor bank to 2.0 kV in 200 ms to allow countermeasure deployment in bursts of several rounds at a rate of 3 RPS (rounds per second). One module can currently produce 58 kW so three modules are required to meet the goal. Methods of increasing the module output to 75 kW so that only two modules are required are explored.

K-line spectra from tungsten heated by an intense pulsed electron beam

The plasma-filled rod-pinch diode (PFRP) is an intense source of x-rays ideal for radiography of dense objects. In the PRFP megavoltage electrons from a pulsed discharge concentrate at the pointed end of a 1 mm diameter tapered tungsten rod. Ionization of this plasma might increase the energy of tungstens Kα(1) fluorescence line, at 59.3182 keV, enough for the difference to be observed by a high-resolution Cauchois transmission crystal spectrograph. When the PFRPs intense hard bremsstrahlung is suppressed by the proper shielding, such an instrument gives excellent fluorescence spectra, albeit with as yet insufficient resolution to see any effect of tungstens ionization. Higher resolution is possible with various straightforward upgrades that are feasible thanks to the radiations high intensity.

Intense nanosecond duration source of 10-250 keV x rays suitable for imaging projectile-induced cavitation in human cadaver tissue

The design, fabrication, and performance of a repetitive nanosecond x-ray source having a pumped field-emission x-ray tube are described. A compact Marx generator, 61 cm in length and storing 12 J energy, directly drives the field-emission tube with voltage pulses >380kV and with <4ns rise time from an equivalent generator impedance of 52Ω. The x-ray dose is 520 μSv at a distance of 30.5 cm. A numerical simulation model is used in which the x-ray tube’s cathode width and anode-cathode gap spacing are permitted to change with time, while electron flow between the cathode and anode is space charge limited and nonrelativistic. The x-ray tube model is coupled to an equivalent circuit representation of the Marx generator that includes the capacitance variation with charging voltage of the BaTiO3 capacitors. The capabilities of the x-ray source for flash radiography have been demonstrated by the study of the evolution of cavitation in human cadaver legs induced by high-velocity projectiles.