A low energy (3 kJ) plasma focus device energized by a single 32 uF capacitor charged at 12 kV with filling gases H2, Ne, and Ar is investigated as an X-ray source. Experiments are conducted with Cu and Al anode. Specifically, attention is given to tailor the radiation in different energy windows i.e. 1.23-1.30 KeV, 1.30-1.56 KeV, 2.50-4.99 KeV and Cu-Ka line radiations.
With the argon filling, the attention is paid to determine the system efficiency for argon K-lines and Cu-Ka line emission at different filling pressures, and to identify the radiation emission region. The highest argon line emission found at 1.5 mbar is about 30 mJ and the corresponding efficiency is 0.0015%. The same pressure is suitable for high Cu-Ka emission, which is about 70 mJ in 41t geometry and the system efficiency is 0.003%. The bulk of X-radiation is emitted from the region close to the anode tip, whereas some radiation emissions take place from the formed hot spot along the focus axis.
The device is operated in an enhanced Cu-Ka line emission mode. The anode is modified which enhanced the interaction of electrons in the current sheath with the anode tip. The Cu-Ka line radiation of 0.4 J/sr. is recorded in the side-on direction, which steadily increases in the end-on direction and attains the value of 0.8 J/sr. It is estimated about 40 J of energy is radiated as X-rays, out of which 8 J is in the form of Cu-Ka emission in 41t geometry. The radiation yield represents a system efficiency of 1.7% for overall X-ray emission, and 0.35% for the Cu-Ka line. For experiments with neon filling, two anode configurations are used: the conventional cylindrical anode, and tapered slightly toward the open end. The latter geometry enhances soft X-ray emission by three folds. The emission is pressure dependent and in both cases, the highest emission is observed at 3-3.5 mbar pressures. For the cylindrical anode, the soft X-ray emission is up to 7 J per shot, which is from a pinch plasma column, 5-6 mm long. For the tapered anode, up to 80 J per shot soft X-ray yield in 4n geometry is recorded, which corresponds to 4% wall plug efficiency. The diameter of the X -ray emission filament is much larger compared with the cylindrical anode. The bulk of emitted radiation is in 1.23-1.30 ke V energy window, which is thought to arise from recombination of H-like (Ne X) ions with the low energy electrons.
With the Al anode, the experiment is conducted both with the H2 and Ne gases. For H2 filling, the highest emission in 1.23-1.30 KeV range approaches as high as 0.9 J/sr. at 1.5 mbar. This emission flux corresponds to about 10 J in 4n geometry, in excess of 0.4% wall plug efficiency. The Al-Ka line emission attains maximum value of about 120-130 mJ/sr. at 2.0 mbar. In the experiment with Ne filling, the emission in 1.23-1.30 KeV energy window is highest at 0.5 mbar and equaled approximately 200 mJ/sr., whereas the maximum Al-Ka emission is about 60-65 mJ/sr. at the same pressure. The X-ray yield in 4n geometry did not exceed 2.5 J, which is equivalent to 0.1 % wall plug efficiency.