Post date: Mar 28, 2014 3:37:14 AM
Ishi-san updated us on the ion source filament problem, which first arose late yesterday. It possible that the control system could be changed so that the current rather than voltage is used. However, its not clear how well this fix would
work and for how long. The lower risk solution, but one which would take a few days, would be to change the filament and recondition. A decision will be made this afternoon.
Suzie presented some results on ring dispersion measurements. The COD is measured at three probes at various loss times. The time was converted to momentum using the rf pattern. The slope of the closed orbit versus momentum, which is close to linear over the measured momentum range, provides a dispersion measurement. Suzie calculated the dispersion in this way for various corrector coil settings.
Shinji gave a presentation on the dispersion at the foil. The equivalent momentum was varied by first changing the F magnet and then changing the D to restore the tune to nominal. The foil position was moved to various points and the first turn peak voltage recorded. The shift in the pattern of peak voltage versus foil position allow us to measure the shift in the beam at the foil, and so make a measurement of the relative dispersion at that point. It could be seen that the beam moves inward with higher equivalent momentum, meaning the dispersion is negative. It was also noted that the percentage change in the measured ToF was much lower than the change in the equivalent momentum. After some discussion it was decided that this is down to the fact that gamma doesn't change when the equivalent momentum is changed.