The electric field strength e (V/m) is a value obtained by dividing the potential difference Vn between adjacent electrodes configured for ion trapping by the arrangement pitch p (m) of the electrodes configured for ion trapping as represented by equation (2). That is, e=Vn/p ??(2).
The potential difference Vn between adjacent electrodes configured for ion trapping is equivalent to double the effective voltage VE of the AC signals, and thus the following equation (3) is derived.
That is, e=2VE/p ??(3).
Note that, as in Example 1 illustrated in 
By inserting equation (3) into equation (1), the moving speed v (m/s) of the ionic impurities is represented by equation (4). That is, v=2μVE/p ??(4).
The time td of the ionic impurities moving between adjacent electrodes configured for ion trapping is a value obtained by dividing the arrangement pitch p of adjacent electrodes configured for ion trapping by the moving speed v of the ionic impurities as represented by equation (5). That is, td=p/v=p2/2μVE ??(5).
Thus, a preferable frequency f (Hz) is obtained by the scrolling of electric field in accordance with the time td of the ionic impurities moving between adjacent electrodes configured for ion trapping. The time of the scrolling of electric field is equivalent to the difference Δt in phase between the AC signals, and when Δt is 1/n period, a preferable frequency f (Hz) is derived from the following equation (6). That is, f=l/n/td=2μVE/np2 ??(6)