Chapter 3 Front Panel Control
The extractor, focus 1 and focus 2 settings are all scaled relative to the beam energy (see "Energy" on page 13). For
this reason, when you set the extractor parameter, you specify a percentage value which is relative to the energy value.
You can set a value in the range 60–99.99 %.
There are some restrictions, based on other dependencies. The repeller is 80 V less than the filament to repel the elec-
trons in their path. The anode is 120 V more than the filament.
Running in MODIFY mode, the information presented on the display is different from other operational states1. In
MODIFY, you see a percentage value which is related to the parameter ENERGY. The selectable range spans
from 60 % to 99.99 %. If you exit MODIFY mode, the real voltages applied are shown. In both cases the
extractor current is displayed.
The idea behind this is as follows: If the voltages EXTRACTOR, FOCUS1, FOCUS2 are adjusted to a good performance of
the ion source, a change of the voltage ENERGY would require a readjustment of the voltages. For avoiding such a task,
scaling of the voltages EXTRACTOR, FOCUS1, FOCUS2 proportional to ENERGY is performed.
The EXTRACTOR parameter cannot be selected totally independently. The repeller (see figure 2) is 80 V less than the fil-
ament to repel the electrons in their path. The anode is 120 V more than the filament. If the difference between
EXTRACTOR and ENERGY voltage is less than 200 V (- 80 V and + 120 V) a larger extractor current can be established.
If the difference between EXTRACTOR and ENERGY is reduced to values approx. 200 eV or below and if the
EXTRACTOR current is monitored, the sharp increase of this current can be observed. In this case a current flow takes
place by electron transport from EXTRACTOR to anode. The total value of this current depends on gas pressure and the
gas type. The electron backflow to the anode can be compensated by measuring resistor networks within smaller limits.
Over the limit the electron backflow results in an increase of the anode voltage.
Therefore the EXTRACTOR voltage cannot have in all cases the same %-value compared to ENERGY. If the ENERGY
value is decreased then the %-value for EXTRACTOR has to be reduced as well.
For example: For 5000 eV ENERGY, the EXTRACTOR value can be up to 95 % for Ar at optimized pressure. For other
gases with different ionization probabilities (e.g. He, Ne) this value has to be reduced. For 1000 eV ENERGY the
EXTRACTOR value can be up to 86 % for Ar at optimized pressure.
The EXTRACTOR value has to also be reduced if an excessive gas pressure would be applied by the operator by mistake
or for any reason.
Don’t make any disconnections without turning off the mains supply switch of the Power Unit. Wait at least 30 seconds
after switching off before disconnecting, at risk of serious injury or death!
PU IQE 12/383.0
April 26, 2013
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