A quadrupole rod assembly, comprising: at least four electrically conductive rods elongated along a longitudinal axis, the rods being circumferentially spaced from each other in a transverse plane orthogonal to the longitudinal axis, and positioned at a radius R o from the longitudinal axis, each rod comprising a plurality of rod contact surfaces (242, 244, 246, 248) in the transverse plane; an electrically insulating first ring coaxially surrounding and spaced from the rods by a first radial gap, the first ring comprising a first ring face and an opposing second ring face in the transverse plane; an electrically insulating second ring coaxially surrounding and spaced from the rods by a second radial gap, the second ring comprising a third ring face and an opposing fourth ring face in the transverse plane; a first clamping system comprising a plurality of first clamping faces in the transverse plane and a plurality of second clamping faces in the transverse plane, wherein each first clamping face spans the radial gap and is in contact with the first ring face and a respective rod contact surface, each second clamping face spans the radial gap and is in contact with the second ring face and a respective rod contact surface, and the first ring and the rods are clamped between the first clamping faces and the second clamping faces such that the first ring and the rods are spatially fixed relative to each other; and a second clamping system comprising a plurality of third clamping faces in the transverse plane and a plurality of fourth clamping faces in the transverse plane, wherein each third clamping face spans the radial gap and is in contact with the third ring face and a respective rod contact surface, each fourth clamping face spans the radial gap and is in contact with the fourth ring face and a respective rod contact surface, and the second ring and the rods are clamped between the third clamping faces and the fourth clamping faces such that the second ring and the rods are spatially fixed relative to each other. at least four electrically conductive rods elongated along a longitudinal axis, the rods being circumferentially spaced from each other in a transverse plane orthogonal to the longitudinal axis, and positioned at a radius R o from the longitudinal axis, each rod comprising a plurality of rod contact surfaces (242, 244, 246, 248) in the transverse plane; an electrically insulating first ring coaxially surrounding and spaced from the rods by a first radial gap, the first ring comprising a first ring face and an opposing second ring face in the transverse plane; an electrically insulating second ring coaxially surrounding and spaced from the rods by a second radial gap, the second ring comprising a third ring face and an opposing fourth ring face in the transverse plane; a first clamping system comprising a plurality of first clamping faces in the transverse plane and a plurality of second clamping faces in the transverse plane, wherein each first clamping face spans the radial gap and is in contact with the first ring face and a respective rod contact surface, each second clamping face spans the radial gap and is in contact with the second ring face and a respective rod contact surface, and the first ring and the rods are clamped between the first clamping faces and the second clamping faces such that the first ring and the rods are spatially fixed relative to each other; and a second clamping system comprising a plurality of third clamping faces in the transverse plane and a plurality of fourth clamping faces in the transverse plane, wherein each third clamping face spans the radial gap and is in contact with the third ring face and a respective rod contact surface, each fourth clamping face spans the radial gap and is in contact with the fourth ring face and a respective rod contact surface, and the second ring and the rods are clamped between the third clamping faces and the fourth clamping faces such that the second ring and the rods are spatially fixed relative to each other.