Apparatus and methods are disclosed for manipulating charged particles. The charged particles are directed from a source thereof into a zone. A first electrical potential is generated in the zone. Simultaneously, a second electrical potential is generated outside the zone. The second electrical potential penetrates into the zone and combines with the first electrical potential to form an oscillating electric potential field having predetermined characteristics sufficient to manipulate the charged particles. The manipulating of the charged particles includes, e.g., transporting, collisional cooling, collisional induced dissociating and collisional focusing. In one embodiment an apparatus comprises a hollow first element and a hollow second element. The second element is disposed within the first element. The second element has at least two openings in a wall thereof. The openings are elongated and radially disposed with respect to the axis of the second element. The length of the openings is at least about 20% of the length of the second element The first element and the second element each are adapted independently to receive a voltage to generate within the second element an electric potential having predetermined characteristics. The apparatus and methods of the invention have particular application to the field of mass spectrometry.