- Email: [email protected]
Scattering phenomena in double-direction focusing electromagnetic mass separators
NUCLEAR
INSTRUMENTS
AND
METHODS
38 (1965) 59; © N O R T H - H O L L A N D
PUBLISHING
CO.
SCATTERING P H E N O M E N A IN DOUBLE-DIRECTION FOCUSING E L E C T R O M A G N E T I C MASS SEPARATORS M. MENAT
Atomic Energy Commission of Israel, Hakirya, Tel-Aviv, Israel
A series of experiments have shown that both elastic and charge exchange scattering of a directed ion beam by residual gas are dominant factors causing contamination in electromagnetic mass separators. The contamination caused by elastic scattering has been calculated by making use of simple geometrics and assuming a reliable interaction potential between the fast moving ions and the residual gas atoms or molecules. In the case of close encounters between the fast moving ions and the residual gas molecules, charge exchange scattering may occur, and the ions are changed into fast moving atoms or, as they are generally called, neutrals. The contaminating ions originate from the entire region between source and collector; the contaminating neutrals, on the other hand, come from a rather limited region in the vicinity of the exit magnet boundary. The scattering phenomena in one-direction focusing electromagnetic isotope separators have been treated earlier1'2). Since then interest in double-direction focusing machines has grown steadily, and at last three methods have been used with the aim of achieving z-direction focusing in addition to radial focusing: 1. Electrostatic methods 3'4). 2. Non-homogeneous fields, having an inhomogeneity index of ½, ref. 5). 3. Fringing field focusing, based on the non-perpendicular direction of the ion beam at the entrance and/or the exit boundary of a sector field 6- 9). The scattering phenomena have been treated for each of the above types of separators 1°) and significant expressions for the fractional contaminations as caused
by these scattering phenomena have been derived. The fractional contaminations thus obtained are functions of: a. the residual gas molecule concentration, b. the fractional mass difference A M/M, c. the collector area, d. the magnet radius Ro, e. a configuration factor T(q~0), f. some constants which appear in the expressions for the differential cross-sections. The reciprocal value of the sum of fractional contaminations imposes an upper limit to the enhancement factor. By performing the various integrations in a different sequence, general expressions for the transmission from source to collector are obtained. References 1) M. Menat, in: Conf. Physics of electromagnetic separation methods (Internal report, Orsay, 1962). z) M. Menat, Can. J. Phys. 42 (1964) 164. 3) j. Koch (ed.), Eleetromagnetie isotope separato'rs with applications of eleetromagnetieally enriched isotopes (North Holland Publ. Comp., Amsterdam, 1958) 47. 4) N. J. Freeman and I. Pagden, in: Conf. Physics of electromagnetic separation methods (Internal report, Orsay, 1962). 5) F. P. Viehb6ck in: M. J. Higatsberger and F. P. Viehb6ck (ed.) Electromagnetic separation of radioactive isotopes (Springer Verlag, Vienna, 1961) 91. 6) W. G. Cross, Rev. Sci. Instr. 22 (1951) 717. 7) M. Camac, Rev. Sci. Instr. 22 (1951) 197. 8) G. Anderson, B. Hedin and G. Rudstam in: M. J. Higatsberger and F. P. Viehb6ck (ed.) Electromagnetic separation of radioactive isotopes (Springer Verlag, Vienna, 1961) 103. 9) G. Anderson, B. Hedin and G. Rudstam, Nucl. Instr. and Meth. 28 (1964) 245. 10) M. Menat and G. Frieder, Can. J. Phys. 43 (1965) 1525.
59 II. ION OPTICS, ETC.
INSTRUMENTS
AND
METHODS
38 (1965) 59; © N O R T H - H O L L A N D
PUBLISHING
CO.
SCATTERING P H E N O M E N A IN DOUBLE-DIRECTION FOCUSING E L E C T R O M A G N E T I C MASS SEPARATORS M. MENAT
Atomic Energy Commission of Israel, Hakirya, Tel-Aviv, Israel
A series of experiments have shown that both elastic and charge exchange scattering of a directed ion beam by residual gas are dominant factors causing contamination in electromagnetic mass separators. The contamination caused by elastic scattering has been calculated by making use of simple geometrics and assuming a reliable interaction potential between the fast moving ions and the residual gas atoms or molecules. In the case of close encounters between the fast moving ions and the residual gas molecules, charge exchange scattering may occur, and the ions are changed into fast moving atoms or, as they are generally called, neutrals. The contaminating ions originate from the entire region between source and collector; the contaminating neutrals, on the other hand, come from a rather limited region in the vicinity of the exit magnet boundary. The scattering phenomena in one-direction focusing electromagnetic isotope separators have been treated earlier1'2). Since then interest in double-direction focusing machines has grown steadily, and at last three methods have been used with the aim of achieving z-direction focusing in addition to radial focusing: 1. Electrostatic methods 3'4). 2. Non-homogeneous fields, having an inhomogeneity index of ½, ref. 5). 3. Fringing field focusing, based on the non-perpendicular direction of the ion beam at the entrance and/or the exit boundary of a sector field 6- 9). The scattering phenomena have been treated for each of the above types of separators 1°) and significant expressions for the fractional contaminations as caused
by these scattering phenomena have been derived. The fractional contaminations thus obtained are functions of: a. the residual gas molecule concentration, b. the fractional mass difference A M/M, c. the collector area, d. the magnet radius Ro, e. a configuration factor T(q~0), f. some constants which appear in the expressions for the differential cross-sections. The reciprocal value of the sum of fractional contaminations imposes an upper limit to the enhancement factor. By performing the various integrations in a different sequence, general expressions for the transmission from source to collector are obtained. References 1) M. Menat, in: Conf. Physics of electromagnetic separation methods (Internal report, Orsay, 1962). z) M. Menat, Can. J. Phys. 42 (1964) 164. 3) j. Koch (ed.), Eleetromagnetie isotope separato'rs with applications of eleetromagnetieally enriched isotopes (North Holland Publ. Comp., Amsterdam, 1958) 47. 4) N. J. Freeman and I. Pagden, in: Conf. Physics of electromagnetic separation methods (Internal report, Orsay, 1962). 5) F. P. Viehb6ck in: M. J. Higatsberger and F. P. Viehb6ck (ed.) Electromagnetic separation of radioactive isotopes (Springer Verlag, Vienna, 1961) 91. 6) W. G. Cross, Rev. Sci. Instr. 22 (1951) 717. 7) M. Camac, Rev. Sci. Instr. 22 (1951) 197. 8) G. Anderson, B. Hedin and G. Rudstam in: M. J. Higatsberger and F. P. Viehb6ck (ed.) Electromagnetic separation of radioactive isotopes (Springer Verlag, Vienna, 1961) 103. 9) G. Anderson, B. Hedin and G. Rudstam, Nucl. Instr. and Meth. 28 (1964) 245. 10) M. Menat and G. Frieder, Can. J. Phys. 43 (1965) 1525.
59 II. ION OPTICS, ETC.