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0 25 50 75 100 125 150 175 200
Applied DC Voltage (V)
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(a) 0W
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Applied DC Voltage (V)
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(b) 50W
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Applied DC Voltage (V)
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(c) 100W
0 25 50 75 100 125 150 175 200 Energy (eV)
0 25 50 75 100 125 150 175 200
Applied DC Voltage (V)
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(d) 150W
Figure 5.6: Distributions for the tension sweeps done for four different applied RF powers 0W, 50W, 100W and 150W. The lineEb=qVDCis plotted for comparison.
0 25 50 75 100 125 150 175 200
DC VoltageVDC(V)
0 25 50 75 100 125 150 175 200
BeamEnergyEb(eV)
0W 50W 100W 150W
(a)
Figure 5.7: Measured average beam energy Eb for the tension sweeps for each of the four selected VDCs0W, 50W, 100W and 150W.
When looking at figure 5.7(b) we can distinguishing two regions where the behaviour is different.
After around VDC = 80V the increase is linear but before that value we see the curves tending to a constant value.
Discharge current Id is plotted in Figure 5.8(a) alongside it’s oscillation frequencies in 5.8(b). We that in all cases the discharge current tends to a plateau aboveVDC= 75V. Before this plateau and for
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DC VoltageVDC(V)
0.0 0.2 0.4 0.6 0.8 1.0
DischargeCurrentId(A)
0W 50W 100W 150W
(a) Discharge current - black line indicates the ideal full ionization current for6sccm of Xenon,0.43A.
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RF PowerPRF(W)
0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0
IdOscillationFrequency(kHz)
0W 50W 100W 150W
(b)
Figure 5.8: Discharge currentIdand it’s oscillation frequency for theVDCsweeps.
the values ofVDC that could not hold the plasma withPRF = 0W we see an increase ofId withVDC. The oscillations exist only for the cases ofPRF = 0W and50W. Their frequencies clearly increase with VDCofPRF = 0W but not forPRF = 50W, where they are roughly constant.
Ion temperaturesTi were also taken using the tools described in section 4.4.2 and are displayed in Figure 5.9. As it was also seen in figure 5.6Tiis higher in the lower powers and seem to remain constant and below0.5eV for allVDCs for the two higher appliedPRFs.
5.3.2 Effect of Injected RF Power
The converse of the previous procedure was then carried out: for different fixed values of the applied DC voltageVDCwe swept the injected RF power from the minimum possible operating values to a maximum of 200W injected RF power.
0 25 50 75 100 125 150 175 200 DC Voltage (V)
0.0 0.5 1.0 1.5 2.0 2.5
Ion Temperature (eV)
Double Gaussian Fit
0W50W 100W150W
Figure 5.9: Evolution of ion temperatureTi(FWHM) with applied DC voltageVDC. Different peaks within a single distribution are differentiated using different point styles.
All the distributions are plotted in figure 5.10 along with the lineE =qVDC again as it was in figure 5.6. We can see now that, where we saw an increase in peak energy whenVDCwas swept, we now see a roughly constant value in the power sweeps, again in accordance with the referenceE=VDCline as it is also clear in Figure 5.11. Again there are two regimes that were seen in Figures 5.6 and 5.7. In the first, forVDC = 0V and50V,Eb > qVDC, the second in for then remaining, higher voltages whereEb
remains bellowVDC but approaches it with increasingPRF. The distributions are also becoming wider with higherVDC and in eachPRF sweep we see them getting narrower with increasedPRF.
These distributions were also fit to single and double Gaussian peak models allowing for the extrac- tion of the ion temperatureTishown in Figure 5.12. As expected from having analyzed Figure 5.10 we see that even taking into account two separate distributions for most cases,Tigets lower as morePRF is absorbed and is constant afterPRF = 100W. Note that for the case ofVDC = 0V there is only one peak.
Id is also seen to show two behaviours. In the cases ofVDC = 0V and 50 V we see the current steadily increasing towards the full ionization currentIf ull. When applying higher DC voltages however we see there are two regimes: with PRF < 100W the current decreases with power and oscillates (Figure 5.14) in the kHz range. After this threshold the current tends to a plateau. The same can be seen in the current measured by the RPA in Figure 5.15.
Low Power Study
During the course of experiment we noticed that there were oscillations in the discharge current in the KHz range. These oscillations were not present when higher ICP powers were applied but at very low powers we could still observe them. We swept the injected power from 0W to 10W and plotted the
0 20 40 60 80 100 120 Energy (eV)
0 20 40 60 80 100 120 140 160
Absorbed RF Power (W)
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(a) 0V
0 20 40 60 80 100 120
Energy (eV) 0
20 40 60 80 100 120 140
Absorbed RF Power (W)
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(b) 50V
0 20 40 60 80 100 120 140
Energy (eV) 0
20 40 60 80
Absorbed RF Power (W)
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(c) 100V
0 25 50 75 100 125 150 175 200 Energy (eV)
0 20 40 60 80 100 120 140
Absorbed RF Power (W)
0 50000 100000 150000 200000 250000
(d) 150V
Figure 5.10: Distributions for the power sweeps led usingVDC =0V, 50V, 100V and 150V in (a), (b), (c) and (d) respectively. The lineEb =qVDC is also plotted for comparison.
resulting frequencies (fig 5.17). We can see that oscillations disappear for specific RF powers and, looking at their corresponding distributions in Figure 5.16 we see that these correspond to the narrowest distributions.
5.3.3 Influence of Anode Position
The effect of the anode position of the ID-HALL’s plume was also studied. The anode ring was re- positioned to the different points along the channel indicated in figure 5.18 and for each RPA and anode current measurements were taken with an appliedVDC = 120V. The distributions are shown in figure 5.19.
For all the distributions, the peak energy is roughly constant along the sweep but presents a minimum around 2.3cm ans relative maximum at 3.1cm for the cases where 100W and 200W were applied to the ionization stage. ForPRF = 50W we see a narrowing of the distributions between 1.6cm and 2.6. As in the previous studies, distributions’s FWHM decreases with applied RF power.
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Coupled RF PowerPRF(W)
0 20 40 60 80 100 120 140
BeamEnergyEb(eV)
0V 50V 100V 150V
(a)
0 20 40 60 80 100 120
Coupled RF PowerPRF(W)
−40
−30
−20
−10 0 10 20 30
OffsetofEbtoVDC(eV)
0V 50V 100V 150V
(b)
Figure 5.11: Average beam energyEb for the power sweeps for 0 V, 50 V, 100 V and 150 V (a). The difference to the appliedVDC is plotted in (b).