Characterizing betatron tune knobs at Duke storage ring
A good control of the electron beam betatron tune is critical for the operation of a storage ring. As the driver for Duke free-electron lasers (FELs) and the High Intensity Gammaray Source (HIGS), the Duke storage ring is operated in a wide energy range (0.3 GeV - 1.2 GeV), with several different electromagnetic wiggler configurations. This creates the challenge of controlling the betatron tune in a global manner. As the the first step, the feedforward tune compensation schemes were designed and implemented to the real-time computer control system to compensate the tune change caused by the wiggler field. To further increase the flexibility of the operation, a set of tune knob schemes are designed for various wiggler configurations. The β function changes caused by these knobs are constrained within the south straight section where the tune knob is located, minimizing the impact on the electron beam dynamics (i.e. injection and lifetime). The tune and β function measurements show a good agreement with the calculation. In addition, it is found that some tune knob schemes are effective for new wiggler configurations that are not originally designed for.
