11-065 Ion Gun Controller Emission Switch Operation

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The emission scale switch on the 11-065 ion gun control is used to change the scale of the emission to three levels: 100% (X1), 10%(X.1) and 1%(X.01).  The effect of changing the emission switch is to reduce the emission current, which in turn reduces the ionization (pressure reading) and ion (target) current proportionally.

Initially, the emission needs to be set to 25mA in the X 1 scale and the leak valve is adjusted to achieve 15 to 25 mpA of pressure.

25 mA of emission current
Adjust Argon to get 15 t0 25 mPa of gas pressure

 The graph below shows the target current vs. time and the effect of changing the emission current from X 1 to the X.1 and X.01 scales.

Ion current in uA

When changing the emission scale switch, the emission reading on the 11-065 front panel meter will not change, but the actual emission current will be reduced by a factor of 10 (X.1 scale ) or 100 (X .01 scale). So for example if the emission is set to 25 and the emission scale switch is changed to X .1, the meter still indicates 25mA but the actual emission is 25mA X .1 = 2.5mA.   The pressure display will be reduced by a factor of 10 as well since the number of ions being generated are reduced proportionally to the emission current.  Ideally, the target current will also be reduced by to 10% of the X1 value when the emission scale switch is changed to X.1.  In the graph above we see that the target current drops from about 4.25uA to .8uA as the emission drops from 25mA to 2.5mA.  As expected, the target current drops a factor of 10ish to 70 nA as the emission scale switch is changed to the X .01 position.    

The picture below shows that the pressure drops to about 2mPa as the emission scale is changed to X.1

Emission scale x .1

This picture shows the pressure dropping to .2mPa as the emission scale switch is changed to the X.01 position.    

Emission scale x .01

The emission scale switch is an easy way to reduce the ion target current by a factor of 10 or 100 in order to achieve lower sputter rates.

Note that Balzers RVG 050 thermovalve controllers cannot be used on older 11-065s  in the X .1 or X .01 emission scale positions since they depend on the pressure reading for feedback.  Newer 11-065s have a circuit that compensates so that the pressure output is correct at each emission scale setting.

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