Progress in Superconducting Beam Handling and Accelerator Structures Since November 1966

Abstract

At an earlier meeting1 a full-scale superconducting quadrupole which was under construction at Brookhaven National Laboratory was described. The results of tests2 on that quadrupole will be described here. Also, at the meeting a year ago calculations were reported concerning the possibility of constructing a FFAG field with Nb3–Sn, for a 200 BeV accelerator. Those calculations assumed a circular cross section for the geometry of the coil. Since then the calculations3 have been extended to include an elliptical4 cross section for dipole, quadrupole, and diquadrupole superconducting structures. One advantage for the elliptical geometry is that it reduces the cost of the necessary Nb3–Sn by about a ratio of (a+b)/2r where a and b are the semimajor and minor axes of the ellipse and r=a, the radius of the circle for the circular case. Results of the calculations for dipoles, quadrupoles, and diquadrupole fields in elliptical cross-section geometries will be presented. These can all be used in accelerator designs with separated function elements or with combined function elements provided the elements are not pulsed. Pulsing produces losses which are not well understood at present. Theoretically4 the turn distribution for a dipole-ellipse is given by N ∝ (a+b) {Δ[sin(θp)]}, where θp is the parametric angle for an ellipse and is related to the central angle of an ellipse by tanθ=(b/a) tanθp. N is the number of turns per Δθ angle interval and θ is the central angle of the ellipse. The field in the elliptical case for an actual turn distribution of Nb3Sn ribbon is calculated in a way similar to that for the circular case.5 Now, however, ρ is the distance from the axis of the ellipse to the surface of the ellipse at some central θ and the point P, at which the field is calculated is specified by a distance r from the axis of the ellipse to the point but at an angle θi, the initial angle at which calculation is commenced. Then the program calculates the field contribution at the point P from each ribbon, takes the vector sum, and calculates the resultant field. Pictures of a mock-up model will be used to illustrate the type of construction which might be used for a suitable FFAG coil configuration. Various coil configurations of large size including one suitable for a 1000 BeV accelerator will be discussed. Costs for the necessary Nb3–Sn for various coil configurations are estimated assuming present prices, sizes of ribbon, and critical current values. Calculations for bucking coils to produce effective cancellation of the magnetic fields outside of the structures also have been considered.