2 MeV heavy ion beam probe system for text upgrade

A 2 MeV Heavy Ion Beam Probe is being fabricated for installation on TEXT-Upgrade. One of the unique features of this beam probe system is that it is, in effect, two complete systems that share a single accelerator. Two separate primary beam lines and energy analyzers are used to permit measurements of most of the plasma cross section. It will be possible to switch from one line to the other by electrically controlled switching plates. Since TEXT-Upgrade will be capable of operating in either a signal null or double null divertor configuration, the HIBP system was designed so that it could make measurements at all three possible null points. The parallel plate electrostatic energy analyzers for the 2 Me V system have to be operated at a minimum voltage of 335 kV. A shaped top plate and a shaped vacuum chamber will be used to provide a uniform field region and thereby eliminate the need for guard rings. The dimensions of the top plate and ground plane are approximately 45 cm by 150 cm with a 17 cm gap between the plates. The biggest problem we have run into so far is bringing the prototype energy analyzer up to voltage. The prototype has been brought up to full operating conditions, but it was still drawing about 75 μamps of current and making large quantities of x-rays. The analyzer tests show that the operation is both voltage and field dependent, i.e., we can bring the top plate up to voltage if the ground plane is moved far away and we can bring the field up to 30 kV/cm if we reduce the gap between the plates and lower the voltage.