Let's take a look at varying frequency versus beam current for 16O2+. Starting RF values shown below. FC6 = 1.09enA.

What I did: Pan RF frequency between about 12.5GHz and 14GHz. Plasma seemed to extinguish at a frequency under 13GHz.

What I found: Two peaks on the low side, right around 13GHz.

How I proceeded: I panned across those two peaks for stability. I found that the stronger peak in fact was noisier, and also at risk of losing plasma.

Screengrabs:

1. Starting RF settings

2. Lower window of "good" RF frequency.

3. Higher window of "good" RF frequency.

4. Original beam plot.

5. Beam plot at middle of "good" frequency range.

6. Beam after frequency restored to starting value.

7. Frequency survey correlation plot.

As it turns out and as you can see, the original frequency not only provides the same intensity of beam, the beam is also visibly more stable. (Keerthi found this one.)

Lesson learned: Discovery of the ideal frequency is an iterative process. At least three passes, each successively finer, are required.