A sonotrode for the ultrasonic welding of plastic components (G, B) of an electronic cigarette, comprising: a body having a longitudinal development along an axis; the body comprising a first end connectable to an ultrasound generator, and a second end opposite to the first end; a cavity for at least partially receiving a plastic component of an electronic cigarette to be welded, developing from the second end of the body towards the first end of the body along an axis parallel to said longitudinal development axis; the cavity defining an opening at the second end of the body, communicating with the outside of the sonotrode; characterised in that: the cross section of the cavity at the opening has an outline comprising: a first portion that has the shape of a first arc of a reference circumference and that comprises a first end and a second end, opposite each other; and a second portion, that has the shape of a second arc of said reference circumference and that comprises a first end and a second end, opposite each other; the first end of the second portion being proximal to the first end of the first portion, and the second end of the second portion being proximal to the second end of the first portion; a third portion, connected to the first end of the first portion and to the first end of the second portion, that develops externally to said reference circumference; a fourth portion, connected to the second end of the first portion and to the second end of the second portion, that develops externally to said reference circumference. a body having a longitudinal development along an axis; the body comprising a first end connectable to an ultrasound generator, and a second end opposite to the first end; a cavity for at least partially receiving a plastic component of an electronic cigarette to be welded, developing from the second end of the body towards the first end of the body along an axis parallel to said longitudinal development axis; the cavity defining an opening at the second end of the body, communicating with the outside of the sonotrode; characterised in that: the cross section of the cavity at the opening has an outline comprising: a first portion that has the shape of a first arc of a reference circumference and that comprises a first end and a second end, opposite each other; and a second portion, that has the shape of a second arc of said reference circumference and that comprises a first end and a second end, opposite each other; the first end of the second portion being proximal to the first end of the first portion, and the second end of the second portion being proximal to the second end of the first portion; a third portion, connected to the first end of the first portion and to the first end of the second portion, that develops externally to said reference circumference; a fourth portion, connected to the second end of the first portion and to the second end of the second portion, that develops externally to said reference circumference. a first portion that has the shape of a first arc of a reference circumference and that comprises a first end and a second end, opposite each other; and a second portion, that has the shape of a second arc of said reference circumference and that comprises a first end and a second end, opposite each other; the first end of the second portion being proximal to the first end of the first portion, and the second end of the second portion being proximal to the second end of the first portion; a third portion, connected to the first end of the first portion and to the first end of the second portion, that develops externally to said reference circumference; a fourth portion, connected to the second end of the first portion and to the second end of the second portion, that develops externally to said reference circumference.