No abstract

The effects of audio sidebands from the main rf of the NSLS VUV storage ring on beam motion and specifically on spectral reproducibility in the infrared region were investigated. For this spectral region it is advantageous to use Michelson interferometers because of their high throughput (Jacquinot advantage). A second advantage is that interferometers inherently give a multiplex or Felgett advantage, since one is always looking at all the wavelengths for all of the measuring time, even though there is only one detector. In such instruments it is beneficial to scan the moving mirror at a fast rate so that any mechanical or other low-frequency noise shows up as a slow modulation in the interferogram and disappears altogether in the Fourier transform from the spectral region of interest. However, audio-frequency sidebands appear from the rf energy restoring cavity as noise on the beam. These always occur at multiples of 60 Hz and can thus be readily identified. They can also be confirmed by changing the mirror velocity which changes where they appear in the spectra in a predictable way. In the present work, spectra were measured while simultaneously reducing and shifting the sidebands in the rf and thus the effects were correlated and ultimately eliminated as a source of noise. Ultimately reproducibilities of <1% in 15 s of scanning time across the entire spectral region from 800 to 4000 cm−1 with a sample throughput of only 10−10 m2 sr were achieved.

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A third RF system was commissioned and the existing two systems were modified. Included in the revisions were a new 100 kW, 50 MHz power amplifier, an infra-red heat sensor monitoring the accelerating cavity temperature to compensate for water film coefficient thermal loss, and the isolation of vacuum-RF seals on the accelerating cavity. The results of these changes will be detailed.

No abstract