Linear trap with three orthogonal quadrupole fields for dust charging experiments

Abstract

Investigations of charging processes on a single dust grain under controlled conditions in laboratory experiments are the unique way to understand the behavior of dust grains in complex plasma (in space, in laboratory, or in technological applications). An electrodynamic trap is often utilized for both holding a single grain and continuously measuring its charge-to-mass ratio. We propose a modified design of the linear quadrupole trap with the electrodes split into two parts; each of them being supplied by a designated source. The paper presents basic calculations and the results of the trap prototype tests. These tests have confirmed our expectations and have shown that the suggested solution is fully applicable for the dust charging experiments. The uncertainty of determination of the dust grain charge does not exceed 10(-3). The main advantages of the suggested design in comparison with other traps used for dust investigations can be summarized as: The trap (i) is more opened, thus it is suitable for a simultaneous application of the ion and electron beams and UV source; (ii) facilitates investigations of dust grains in a broader range of parameters; and (iii) allows the grain to move along the axis in a controlled way.

Laboratory Simulation of the Positron–Dust Interaction and its Implication for Interstellar Dark Clouds

“…One can see two types of grain charge variations. The smooth and small changes, like those observed during first 30 hr of the experiment, are partly caused by drifts of the recording electronics and partly by changes of the temperature in the laboratory leading to changes of the dimensions of the trap, affecting the conversion of the grain oscillation frequency to its charge (Beránek et al 2012). Above it, one can identify steplike variations of different heights that are caused by charging events.…”

“…We selected a collection of spherically shaped SiO 2 grains with diameters ranging from 1 to 3 μm as analogues of interstellar dust. A single grain was caught in an electrodynamic quadrupole trap situated inside a vacuum chamber with a working pressure of less than 10 −5 Pa (Beránek et al 2012). The grain oscillation frequency is the only measurable quantity, and we have developed several techniques to determine the grain mass, charge, capacitance, and other parameters (Pavlůet al 2004).…”

“…In our laboratory simulations, each grain was kept in the linear electrodynamic quadrupole trap (Beránek et al 2012) for 1-2 months and its charging by the interaction with the positron beam was monitored. Note that measurements were time consuming and took hundreds of hours.…”