Studying intense-beam physics in a compact Paul trap: the Paul Trap Simulator Experiment


Erik Gilson, Research Physicist
Princeton Plasma Physics Laboratory


Accelerators are used in many areas: medicine, high-energy particle physics, materials science, and fusion energy to mention a few examples.  As modern and next-generation accelerators make use of increasingly intense particle beams, the beams become more difficult to control.  Since accelerators are typically large expensive facilities that are “mission oriented,” its good to have a simple, compact, flexible facility to perform studies of the basic properties of intense beams.  Our Paul trap is a good example.


Our research is carried out in a 2-meter-long, 20-cm-diameter cylindrical pipe that is cut into four segments and operates as a linear Paul trap in a vacuum chamber.  A cesium-containing ceramic button is heated and cesium ions come off and fill the pipe and are trapped in the pipe by 200 V, 60 kHz signals put on the walls of the pipe.  A PC changes the amplitude and frequency of the oscillating voltage and we measure the resulting effects on the trapped ions. The results of our experiments simulate what happens when the magnet strength and spacing is changed in an accelerator system because the two systems turn out to be Lorentz transforms of each other.


We have shown that it is possible to efficiently simulate what happens to a particle beam traveling through an accelerator that uses an array of magnets to confine the beam.  The oscillating voltage on the walls of our trap simulates the array of magnets.  Experiments have been performed that establish how quickly the beam can be compressed without causing excess heating.  We have studied how robust the beam propagation is when there is random noise in the system.  Recent results have explored the self-oscillations of the beam and how they interact with the trapping system.

To better answer questions about how to quiescently transport intense beams over large distances, more research will be carried out where we significantly increase the number of ions in the trap to increase the self-electric field of the charge bunch.  Improved diagnostics will allow us to more carefully measure the positions and velocities of the ions to better understand the physics of intense beams, and also to look for particles as they are lost to the walls of the trap.

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