Schematic of the experimental setup. Diagnostics include: (1) flat crystal spectrograph; (2) and (3) x-ray detectors (Si diode or DRD); (4) optical framing photography; (6) current monitor; (1) and (4) x-ray pinhole cameras. The current (quarter period of ∼1 μs) is obtained with a R-C integrated B-dot probe. A typical current signal above shows some residual noise from the discharge system.
Transmission curves for the filters used in these measurements.
A sequence of 2 ns optical photographs of the X-pinch assembled from different shots. Plasma growth and expansion speeds could be determined from such photographs. (Light scattering by the electrodes and the walls of the compact stainless steel vacuum vessel is responsible for the increased background gray level as the light intensity increases.)
X-ray pinhole photographs for a 2-wire 25 μm tungsten X-pinch, showing the progression from a relatively “soft” filter to a “harder” filter. The cathode is at the top and the anode at the bottom in all the images. The filter used in each case is as follows: (a) 10 μm Al (b) 12.5 μm Ti (c) 10 μm Cu (d) 30 μm Cu (e) 50 μm Cu (f) 12.5 μm Ti + 50 μm Cu. Typically, with the combined Ti and Cu filter as in case (f), the image of the X-pinch is almost non-existent.
(a) Two identical AXUV-HS1 Si diodes filtered with 25 μm Be and viewing the X-pinch from ports 2 and 3 (with an angular displacement of 45°). (b) Comparing the time response of an AXUV-HS1 diode (Si 1) and an AXUV-HS5 diode (Si 2) both filtered with 25 μm Be. The signals in 5(b) have been displaced for clarity. The AXUV-HS5 diode was often used with filters with a lower x-ray transmission in a certain spectral range in order to retain a high signal to noise ratio.
(a) Si diode 1 is filtered with 25 μm Be; Si diode 2 is filtered with 12.5 μm Ti + 12.7 μm Cu. The first x-ray pulse is predominantly soft x-rays since it is barely observed through the Ti/Cu filter. The second set of four pulses, occurring in a time span of about 100 ns, consist mostly of photons with energy hν ≈ 8 keV or hν ≥ 10 keV. (b) Signals obtained from a different shot with the same filters on Si 1 and Si 2 as in Fig. 6(a) . Such reproducibility is often observed on the microsecond X-pinch.
Si diode results from a 25 μm constantan X-pinch. In both (a) and (b), the tall peaks were obtained with 25 μm Be. In (a), the low peak was obtained with 12.7 μm Cu and in (b), with 25 μm Cu. The signals obtained with the Cu filters in this case are barely above the level of the noise due to EM pick up by the diodes which shows up as a low frequency oscillation. It is evident from such results that the x-ray emissions have a dominant component of soft x-rays (observable through 25 μm Be but barely through 25 μm Cu).
Si diode results from a 25 μm tungsten X-pinch. Si 1 was filtered with 12.7 μm Ti and Si 2 was filtered with 50 μm Cu. The second set of x-ray pulses after the first peak cannot have energy hν ≥ 15 keV since in that case Si 1 will show the stronger signal because of the transmission properties of 12.7 μm Ti in this spectral range.
X-ray emission observed using a Si diode and a DRD both of which are filtered with 25 μm Be. In this shot, only the first x-ray pulse was observed. The detectors show nearly identical signals, suggesting that the emitted x-rays are predominantly “softer” radiation in the 1–8 keV range. (Due to the lower sensitivity of the DRD, a lower signal-to-noise was often observed. In the above figure, the low frequency noise causes the DRD signal to cross the 0 V line. Nevertheless, the x-ray response is clearly distinguishable above the noise level.)
(a) X-ray image of a PMMA fiber capillary tubing with inner and outer diameters of 50 μm and 100 μm, respectively, obtained with point projection photography with a magnification of 2.3 using a 12.5 μm Ti filter. A 25 μm tungsten wire was included for comparison. The optical density profiles obtained at points 1 and 2 on the image and shown in Fig. 10(b) , demonstrate a resolution of the tubular end of the fiber, indicating an x-ray source of small spatial dimensions.
(a) X-ray image of a nickel-chromium wire gauze. The wire diameter is 250 μm. (b) X-ray image of a small common cockroach. Each of these images was obtained in a single shot with a 12.5 μm Ti filter and a magnification close to 1.0.
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