MAGNET FIDUCIALIZATION WITH COORDINATE MEASURING MACHINES

H. FRIEDSAM, W. OREN, M. PIETRYKA

Stanford Linear Accelerator Center Stanford University, Stanford, CA.

1．Introduction

One of the fundamental alignment problems encountered when building a par­ticle accelerator is the transfer of a component’s magnetic centerline position to external fiducials. This operation, dubbed fiducialization, is critical because it can contribute significantly to the alignment error budget. The fiducialization process requires two measurements:

from magnetic centerline to mechanical centerline, and

from mechanical centerline to external fiducials.

This paper will focus on methods for observing the second measurement. Two Stanford Linear Collider (SLC) examples are presented.

2．Goals

The object of magnet fiducialization is to relate the magnet-defined beamline position to exterior reference surfaces. To be useful for later component alignment, this relationship must be established in a manner consistent with overall positioning tolerances The error budget for the SLC’s component to component alignment tolerance is as follows：

magnetic centerline to mechanical centerline δ=±30μm

mechanical centerline to fiducial marks δ=±50μm

fiducial marks to adjacent components δ=±80μm

TOTAL δ=±100μm

The offset between the mechanical and magnetic centerlines of well-known mag­nets is generally smaller than the measurement tolerance. It is commonly assumed to be zero without measurement. When this tiny value must be mea­sured, extreme care is necessary to avoid obscuring the offset with measurement tool registration errors. In contrast, the mechanical centerline to fiducial measure­ment must be performed on every magnet. The tolerance for this operation is only slightly larger and pushes conventional surveying technology to its limit. Work supported by Department of Energy contract DE-AC02-76SF00515 .This has forced the search for other means of measuring these quantities reliably and accurately.

3．Methodology

To complete the transfer for mechanical centerline to the fiducials, a magnet coordinate system must be defined. This includes establishing its origin and the three orientation angles of the rigid body. Often the X and Y origins are determined by the centerline of the pole tips while the zero coordinate for Z is the longitudinal center of the magnet. Roll is set by the midplane of symmetry and yaw and pitch are defined by locating the center of the pole tips at both ends of the magnet.

All measurement systems used to make this transfer establish this coordinate system. Then all fiducial coordinates are defined within this coordinate system.

4．Tools

The measurement tools for transferring the pole-defined centerline to outside reference marks must have some basic capabilities. They must be able to measure the size and shape of the poles as well as the midplane of symmetry.