[Sneap] Negative terminal operation conversion

[Johan Janse van Rensburg]

Hi,

 

I am working with a model AN 2000 HVE van de Graaff accelerator and is considering doing modifications to be able to obtain an accelerated electron beam.

The intended application is to irradiate semiconductor materials with > 1 MeV electrons to study point defect formation and its properties. Very low doses are needed and therefore only requires very low beam currents ( < 50 nA).

 

In the operating manual of the accelerator gets referred to an instant electron conversion kit, which converts the accelerator instantly to negative operation. Can anyone provide me with some more information on this.

 

As I understand it, the following things will have to be done to convert the accelerator to negative operation :

1)      The high voltage belt charge power supply polarity will have to be reversed from negative to positive.

2)      The probe terminal voltage for the RF ion source polarity need to change from positive to negative.

3)      The polarity of the focus electrode will have to change from negative to positive.

4)      Current meters polarity will have to be reversed.

5)      Extra radiation safety precautions in target room.

 

I assume one can run the accelerator then only using the GVM and not the corona control, since that is solely designed for positive operation. Small fluctuations in energy would not be a problem for the intended application. Does the GVM need any polarity changes?

 

Are there any other important modifications that would need to be done as well? 

 

Any help would be appreciated

 

Kind regards

 

Johan Janse van Rensburg

Department of Physics

University of Pretoria

Pretoria

South Africa
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