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46
Journal of Science and Technology in the Tropics (2010) 6: 43-47
this EUV pulse, the total photon energy emitted from
the plasma (assuming isotropic source) in the range
of 12 to 18 nm could be estimated to be about 50 mJ.
While the detection of the X-ray pulse for the 12.5
kV discharge is known to indicate the formation of a
focused plasma with temperature of probably greater
than 1 keV, the absence of X-ray radiation in a 8 kV
discharge is believed to indicate a lower temperature
plasma. The set of similar signals (Fig. 5) obtained
for an 8 kV discharge at 0.5 mbar argon is shown in
Figure 6. In this discharge, the length of the electrodes
of the UNU/ICTP PFF was shortened to 9 cm. This
discharge displays several features of its radiation
emission which are distinctly different from that of
the 12.5 kV discharge. Firstly, no X-ray was detected
for this discharge indicating lower temperature
plasma. The voltage signal showed multiple spikes
with low amplitudes. The corresponding EUV signal
also consisted of multiple pulses which occurred over
duration of more than 2 µs. The peak amplitude of the
pulse, however, was much lower than those observed
for discharges at 12.5 kV. However, due to long pulse
width, the area under this pulse corresponded to total
photon energy of about 100 mJ. The input energy of
the UNU/ICTP PFF was further tuned down to 540
J by operating at condition of V = 6.5 kV and L =
7.5 cm. The output EUV pulse was insignificantly
low as compared to those operated at 8 kV discharge
voltage.
In order to fine tune the EUV output from the
plasma focus at the three discharge voltages tested,
namely V = 12.5 kV, 8 kV and 6 kV, the operating
SXUV (V) Voltage (kV)
5
4
3
2
1
0
-1
3.0x10 -6
5
4
3
2
1
0
-1
3.0x10 -6
4.0x10 -6
4.0x10 -6
SXUV
BPX65
5.0x10 -6
5.0x10 -6
Time(s)
6.0x10 -6
6.0x10 -6
7.0x10 -6
5
4
3
2
1
0
-1
7.0x10 -6
Figure 6. The voltage, EUV and X-ray signals
obtained simultaneously for a 8 kV discharge of a
plasma focus with electrode length L = 9 cm and
operated with 0.5 mbar argon.
BPX65 (V)
pressure was varied from 0.5 mbar to 2.5 mbar for
a series of discharges. From the area under the EUV
pulse, the total photon energy emitted in the range of
12 to 18 nm was estimated and plotted (Fig. 7). It can
be seen that discharges with higher input energy of
2.3 kJ was able to produce EUV pulses with higher
amplitudes and shorter duration, but the total energy
corresponding to the photons emitted within the
spectral range of 12 to 18 nm was lower than those
emitted from discharges at 960 J input energy. EUV
energy of up to 100 mJ can be obtained from a 8 kV
discharge operated with 0.5 mbar argon.
CONCLUSION
By adjusting the operating parameters of the UNU/
ICTP PFF operated with argon from its originally
designed values of discharge voltage V = 15 kV,
electrode length L = 16 cm and P = 0.5 to 2.5 mbar
argon, we have obtained the possible experimental
conditions to operate it to produce plasmas with
conditions sufficient for emission up to the EUV
spectral range of 12 to 18 nm. The radiation energy
corresponding to this spectral range emitted from
a discharge with V = 12.5 kV, L = 16 cm and P =
0.5 to 2.5 mbar may be up to 95 mJ. This emission,
however, is accompanied by emission of X-ray
photons in the wavelength range of 0.3 to 3 nm. The
plasma produced under this condition is expected
to have achieved an electron temperature of up to
several keV. However, when the same plasma focus
device is operated at a scaled down condition of V
Figure 7. The variation of output EUV energy for
three sets of operation condition of discharge voltage
V and electrode length L at various pressure P. (i) V
= 12.5 kV, L = 16 cm; (ii) V = 8 kV, L = 9 cm; and (iii)
V = 6.5 kV, L = 7.5 cm.
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