IG7 Page 11
cation. In our case the terminal will be around 3 to 5 kV with the IG7. How do
we reduce the potential energy of these charged ions to make it safer for elec-
trical components? We use a simple device called an ion tube.
Ion Tubes
Ion tubes serve a few special functions and are luckily easy to construct. A
tube consists of a grounded piece of conductive tubing with a sharp pin that is
centered at one end to emit the high voltage ions we are looking for. The pin
should not be positioned so close to the edge of the tube that you draw a
spark however. The configuration generates a strong electrical gradient
formed by the proximity of the needle tip to that of the grounded tube and
helps to draw off more ions at a much lower voltage potential than otherwise
required with a dull tip. When the ions leave the needle tip and are repelled
away from it, they are drawn to the edges of the pipe. In the process this ac-
celerates some surrounding air as the ions bump into other molecules on their
way to the pipe edge. As the air accelerates, it pushes the ions further down
the tube and allows them to accelerate even more air in the further distance
they travel. This action renders a decent amount of air motion that is mostly
limited by frictional forces and the initial energy in the ions. Some ions that are
released in the center of the tube manage to escape the tubing altogether and
are released out into the open air. As the ions accelerate the air, they loose
some of their potential energy to the form of kinetic energy (movement of the
air particles). This helps to further reduce the high energy potential of the ions
to a much lower level so that we don’t have to worry as much about damaging
sensitive electronics. Because of this, we can leave our ion tubes running in a
room without many worries other than someone sticking his/her finger in it!
One point to note is If you make the tube longer, you can achieve a bit more
air flow and release fewer ions with more likelihood of them being drawn to the
grounded pipe edges. Conversely, making the tube shorter can release more
ions that retain a much higher voltage potential into the surrounding air!
In this kit we will be building an array ion tubes with a variable distance be-
tween the needle points to the end of the tubes. This adjustability allows for
various features while experimenting.
-5kV
Dotted lines indicate
Ion paths,
arrows indicate air flow
direction.
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