December 16th, 1999, Madison, Wisconsin

Today is the run day for the hibp on the MST. A few modifications were made before today's run.

• An 1" aperture has been installed right under the beam profile monitor. This reduces the area, which is exposed to the plasma, to 1/4 of the previous area.
• Two modified gain=-10^5 V/A current to voltage convertors were used to monitor the beam on the 10 kV toroidal plates in the primary beam line.
• A 200M Ohm resistor is connected from the extractor donut to the ground. A 300M Ohm resistor is connected from the Pierce donut to the ground.
• A schematic of the test setup is here.

The results are quite positive. The beam signals can be seen very clearly on the detector plates. ( Here the detectors mean the two 10kV toroidal plates). Below is some typical results:

• 70keV Na+ beam, raw data without smoothing.
• 70keV Na+ beam, with smoothing. (100pt average)
• 33keV Na+ beam, raw data without smoothing.
• 33keV Na+ beam, with smoothing. (100pt average)

If the ion beam is assumed has Gaussian distribution profile, a simple calculation can be done to predict what the beam signals should look like on the 10kV toroidal plates when sweeping the beam toroidally. Click here to see the simulation result. Notice that if ignore the secondary electrons effect, the simulated results will nicely match the test results.