5 replies on “Experimental Investigation of Accelerator Beam Dynamics with a Linear Paul Trap”
The potential of the rods in the Paul trap is presumably not perfectly linear. Are you able to see those nonlinear effects at all in the experiment?
On slide 12, what determines the envelope of the variation of the ion number with cell tune? Is it just a beta function, space charge, or a weak nonlinearity? And similarly, is it a weak nonlinearity or space charge that drives the resonances? If a weak nonlinearity, is it systematic (what I referred to in my previous question) of from imperfections?
Nice talk. I just want to make a comment from the history of the coherent/incoherent controversy. There was a time when the peak incoherent tune shift was used to evaluate whether the beam would be affected by resonances in its proximity. This is the tune for zero amplitude particles. For a gaussian dist., this tuneshift IIRC is twice larger than the ‘rms’ tune shift. This peak tuneshift is what used to be called the ‘incoherent tune’. No longer, thankfully.
Hi – sorry for the lack of clarity here – yes the trapping potential is slightly nonlinear due to the shape of the rods. You can indeed see the effect of this in the experiment, on slide 12 I show a tune scan taken at very low ion number. The resonances we see there are driven by the nonlinearities in the trap, as the ion number is far too low to see space charge effects!
Great question. The envelope of the variation of the ion number with cell tune on slide 12 is mainly due to the beta function as we’re at low ion number in this plot. At the extremes of cell tune, the beta function is either larger on average, or has a large maximum point, resulting in ions scraping on the rods and being lost. Large values of alpha (as in the Twiss parameter) can also result in fewer ions being detected due to the ions spreading out before they reach the faraday cup, but this is less of a problem when we use the MCP as the ions are then accelerated out of the trap. I think I’ve answered the rest in the answer to your previous question, but please let me know if I can add anything else!
FFA'20
5 replies on “Experimental Investigation of Accelerator Beam Dynamics with a Linear Paul Trap”
The potential of the rods in the Paul trap is presumably not perfectly linear. Are you able to see those nonlinear effects at all in the experiment?
On slide 12, what determines the envelope of the variation of the ion number with cell tune? Is it just a beta function, space charge, or a weak nonlinearity? And similarly, is it a weak nonlinearity or space charge that drives the resonances? If a weak nonlinearity, is it systematic (what I referred to in my previous question) of from imperfections?
Nice talk. I just want to make a comment from the history of the coherent/incoherent controversy. There was a time when the peak incoherent tune shift was used to evaluate whether the beam would be affected by resonances in its proximity. This is the tune for zero amplitude particles. For a gaussian dist., this tuneshift IIRC is twice larger than the ‘rms’ tune shift. This peak tuneshift is what used to be called the ‘incoherent tune’. No longer, thankfully.
Hi – sorry for the lack of clarity here – yes the trapping potential is slightly nonlinear due to the shape of the rods. You can indeed see the effect of this in the experiment, on slide 12 I show a tune scan taken at very low ion number. The resonances we see there are driven by the nonlinearities in the trap, as the ion number is far too low to see space charge effects!
Great question. The envelope of the variation of the ion number with cell tune on slide 12 is mainly due to the beta function as we’re at low ion number in this plot. At the extremes of cell tune, the beta function is either larger on average, or has a large maximum point, resulting in ions scraping on the rods and being lost. Large values of alpha (as in the Twiss parameter) can also result in fewer ions being detected due to the ions spreading out before they reach the faraday cup, but this is less of a problem when we use the MCP as the ions are then accelerated out of the trap. I think I’ve answered the rest in the answer to your previous question, but please let me know if I can add anything else!