Correcting Emittance Growth Due to Stray Sextupole Fields

This paper discusses the emittance growth produced by sextupole fields in conjunction with a solenoidal focusing. The sextupole emittance is derived and compared with numerical simulations using a measured sextupole field for a vacuum chamber in a solenoidal field. It is found that the sextupole emittance is dominated by the field's radial non-linearity and the growth due to the skew angle is much smaller. It is shown that a corrector sextupole placed after the sextupole-solenoid system is effective at cancelling this emittance growth. Leaving only the growth due to the solenoid's spherical aberration.