CHESS-U Sextupole Studies

This page serves to catalog and archive results of studies using the sextupole magnets in the CHESS-U ring. Machine studies shifts are documented here, including procedures for measuring phase functions, orbits, tunes as functions of sextupole settings.

Of particular interest is the possibility to measure the beam size in sextupoles. The basic idea is that sextupole offsets introduce a quadrupole error via the first derivative of the field, so the tune shift can be used to measure the offset. Then the second derivative provides a dipole error which depends on the summed squares of the offset and the beam size, so the tune shift can be used to isolate the beam size. A discussion of the derivation of the relationship between the beam size and the tune and orbit changes, including a test using the CHESSU lattice, can be found here). A Mathematica notebook showing derivations is available here).

An additional benefit of these studies is obtaining calibration constants (sextupole field strength versus current setting) and position offsets of the sextupole magnets relative to the design orbit.

The studies also include investigations into the measurement accuracy for the phase functions, orbits, and betatron tune values obtained via various methods, in particular comparing the Digital Tune Tracker to analysis of turn-by-turn data.

J.A. Crittenden, W. Carbonell, K. Deitrick, H. Duan, A. Fagan, G. Hoffstaetter, V. Khachatryan, I. Mishra, D. Sagan, A. Shaked, and S. Wang / 27 February 2024