LLRF9 Commissioning at ELSA

As reported earlier, LLRF9/500 was commissioned at ELSA in October 2013. The accelerator successfully operated with the new LLRF system through June 2014. During the week of June 9–13, 2014 the loaner unit was replaced with one purchased by ELSA. The week of installation and commissioning included tests of several new features and diagnostics. These include improved network/spectrum analyzer with variable sweep speed. The new analyzer is capable of making transfer function and spectral measurements within 27 Hz of the carrier.

Another new diagnostic, triggered waveform acquisition, opens new possibilities in system configuration (transient time-domain response measurements) and adds support for post-mortem diagnostics. Waveform acquisition of 16k samples per channel can operate with hardware or software triggers. Hardware trigger sources include external trigger inputs, ramp start signal, and interlock trip. Both pre- and post-trigger acquisition is supported.

Plot below shows closed-loop response of ELSA RF system to 5% amplitude and 5° phase steps. Response to amplitude step is underdamped, while phase step shows some overshoot. Most likely the difference is caused by klystron saturation, which mainly affects amplitude modulation response.