Determining the Size of a Plasma

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Determing the size of a plasma in a vacuum vessel may seem to be difficult on the account that there is no first hand measurements being taken. But, with the use of geometrical methods, the task is easily done.

The key is to find a characteric of the vessel that can be seen by the camera and be measured from outside of the vessel. This same object can be measure on the image and a scaling constant can be determined. This constant can be used to determine the size and shape of any plasma in the vessel.

In position #1, there is a port to the left of the limiter that is visible to the camera and that can be measured from the outside of the vessel. The measurement from the center of the limiter and the outside of this port is b=35.47cm (+/-) 0.5cm. Therefore, on any image, a measurement from the center of the limiter and the outside of the same port will give a measurement "a". (b/a) gives the scaling factor and using the following equation, any measurement of size in the vacuum vessel can be determined:

dr= (b/a)*di

Where dr in the real size measurement, and di is the measurement taken from the corresponding part on the image.