An apparatus comprising: a plurality of coaxial collection tubes extending substantially parallel to a major axis , wherein each tube of the plurality of coaxial collection tubes comprises: a first end defining an orifice , wherein the first end is disposed at a first position on a plane substantially orthogonal to the major axis , a second end coupled to an end of a respective outlet tube of a plurality of outlet tubes , the respective outlet tube comprising an outlet tube wall , and a collection tube wall extending from the first end to the second end , wherein the collection tube wall at the first end comprises a first diameter, wherein the collection tube wall at a second position between the first end and the second end comprises a second diameter greater than the first diameter, wherein the collection tube wall extending from the second position to the first position tapers toward the major axis at a first angle relative an axis orthogonal to the major axis , wherein a first coaxial collection tube of the plurality of coaxial collection tubes is disposed radially inward from a second coaxial collection tube of the plurality of coaxial collection tubes , characterized in that a first outlet tube wall of the plurality of outlet tubes extends through a second outlet tube wall of the plurality of outlet tubes , and wherein the first outlet tube wall is shaped as a teardrop or a triangular prism to reduce accumulation of particles on the outer surface of the first outlet tube wall . wherein each tube of the plurality of coaxial collection tubes comprises: a first end defining an orifice , wherein the first end is disposed at a first position on a plane substantially orthogonal to the major axis , a second end coupled to an end of a respective outlet tube of a plurality of outlet tubes , the respective outlet tube comprising an outlet tube wall , and a collection tube wall extending from the first end to the second end , wherein the collection tube wall at the first end comprises a first diameter, wherein the collection tube wall at a second position between the first end and the second end comprises a second diameter greater than the first diameter, wherein the collection tube wall extending from the second position to the first position tapers toward the major axis at a first angle relative an axis orthogonal to the major axis , a first end defining an orifice , wherein the first end is disposed at a first position on a plane substantially orthogonal to the major axis , a second end coupled to an end of a respective outlet tube of a plurality of outlet tubes , the respective outlet tube comprising an outlet tube wall , and a collection tube wall extending from the first end to the second end , wherein the collection tube wall at the first end comprises a first diameter, wherein the collection tube wall at a second position between the first end and the second end comprises a second diameter greater than the first diameter, wherein the collection tube wall extending from the second position to the first position tapers toward the major axis at a first angle relative an axis orthogonal to the major axis , wherein a first coaxial collection tube of the plurality of coaxial collection tubes is disposed radially inward from a second coaxial collection tube of the plurality of coaxial collection tubes , characterized in that a first outlet tube wall of the plurality of outlet tubes extends through a second outlet tube wall of the plurality of outlet tubes , and wherein the first outlet tube wall is shaped as a teardrop or a triangular prism to reduce accumulation of particles on the outer surface of the first outlet tube wall . <EOS>