Rotating wall technique

This technique has found extensive use in improving the quality of these traps and in tailoring of both positron and antiproton (i.e. antiparticle) plasmas for a variety of end uses.

[8][9] The “rotating wall (RW) technique” uses rotating electric fields to compress SCP in PM traps radially to increase the plasma density and/or to counteract the tendency of plasma to diffuse radially out of the trap.

1, the RW technique uses an azimuthally segmented cylindrical electrode covering a portion of a plasma.

This is necessary to overcome asymmetry-induced transport which acts as a drag on the plasma and tends to oppose the RW torque.

For high quality PM traps with little asymmetry induced transport, one can access a so-called “strong drive regime.

[14] The technique was also used to phase-lock the rotation frequency of laser cooled single-component ion crystals.

One important application is the creation of specially tailored antiparticle beams for atomic physics experiments.

This has been crucial in experiments to study dense gases of positronium (Ps) atoms and formation of the Ps2 molecule (e+e−e+e−) [5-7].

[4] In particular, this technique, dubbed SDREVC (strong drive regime evaporative cooling),[20] was successful to the extent that it increased the number of trappable antihydrogen by an order of magnitude.

Fig. 1. Apparatus used to radially compress electron plasmas in a Penning–Malmberg trap using the RW technique by applying phased sinusoidal electrical signals to a segmented (RW) electrode.
Fig. 2. Radial compression of an electron plasma vs time with the RW fields turned on at t = 0. Note the log scale for density and the flat density profiles, before and after compression, that are characteristic of rigid plasma rotation
Fig. 2. Radial compression of an electron plasma vs time with the RW fields turned on at t = 0. Note the log scale for density and the flat density profiles, before and after compression, that are characteristic of rigid plasma rotation.
Fig. 3. Density of a positron plasma as a function of applied RW frequency. The solid line corresponds, characteristic of the strong drive regime. For this experiment, B = 0.04 T, and the maximum density achieved is 17% of the Brillouin density limit, which is the maximum possible density for a SCP confined in a field of strength B.
Fig. 3. Density of a positron plasma as a function of applied RW frequency. The solid line corresponds to f E = f RW , characteristic of the strong drive regime. For this experiment, B = 0.04 T, and the maximum density achieved is 17% of the Brillouin density limit, [ 5 ] which is the maximum possible density for a SCP confined in a field of strength B.