content_image/369381.jpg
<img src='content_image/369381.jpg'>

cluster width y$_{rms}$ exhibits power law behavior vs α 2 following the zigzag transition. The Debye shielding parameter is found by comparison to the model, and Debye shielding is shown to be important. 

The dusty plasma was studied in the DONUT (Dusty Ohio Northern University exper- imenT) apparatus (Fig. 1) [7, 8, 12, 16, 18, 19]. Argon gas was leaked into the vacuum chamber and the pressure was stabilized at 15.4 mtorr. At this pressure normal modes of the dust clusters are under damped [18]. Inside the chamber a capacitively-coupled rf electrode is used both to sustain the discharge and to levitate the dust particles. The rf frequency was 13.56 MHz, the forward rf power was ∼ 7 W and the dc self-bias on the electrode was − 90 V. 

The confining well (Fig. 1) is produced by a rectangular aperture placed on the 89-mm diameter aluminum electrode, creating a biharmonic well in the horizontal ( x - y ) plane [3]. The aperture is made of four aluminum bars, each with a cross section of 6.35 mm × 12.7 mm. The depth of the trap is 6.35 mm, the length is fixed at 50.8 mm, and the width d is adjustable 

