Patent ID: 7609139

Claim:
An electromagnet, comprising: a. a cylinder of conductive material having a central axis, a first end, a second end, a mid plane positioned between said first and second ends, and a central bore passing through said cylinder from said first end to said second end; b. at least one port passing from said central bore to the exterior of said cylinder in a direction substantially perpendicular to said central axis; and c. a helical gap following a helical path along said central axis from said first end of said cylinder to said second end of said cylinder, wherein said helical gap passes from said central bore to said exterior of said cylinder in a direction substantially perpendicular to said central axis wherein said at least one port lies on said mid plane, and wherein a pitch of said helical path varies, and wherein said pitch of said helical path is relatively shallow proximate said first end and said second end; and said pitch of said helical path is relatively steep proximate said mid plane, and wherein said at least one port assumes an elliptical form which diverges when proceeding from said central axis toward said exterior of said cylinder.