LCLS Conceptual Design Report - Stanford Synchrotron Radiation ...

g ( )
First field Integral(G-cm)
L C L S C O N C E P T U A L D E S I G N R E P O R T
80
60
40
20
0
-20
-40
-60
50
J1p
100
J1n
150
200
250
Magnet
Figure 8.5 First vertical field integral through the half-period fixture when the same magnet block
is oriented with its vertical moment positive (blue +) and negative (red –) for a few of
the magnets. The positive orientation usually gives a higher integral, but not always.
Another characteristic of the assembled magnetic structure that cannot be predicted from
the Helmholtz coil measurements is the phase variation. This can be seen in Figure 8.6. The
vertical component of the field in the fixture has been measured for both orientations of the
vertical moment of the magnet block (the direction of the main component of the block’s moment
is the same). The difference between these two measurements is plotted. The plot also includes
the result of a calculation that assumes a uniform distribution of magnetization. The difference
seen between the measurement and calculation can affect the contribution to the phase error from
the magnet block.
Figure 8.6 Difference in vertical on-axis field when a magnet block is rotated to change the
vertical component of the field, plotted vs. z. The measured effect may differ from the
calculation if the distribution of the vertical magnetization in the magnet block is not
uniform; this can affect the phase errors.
300
350
400
450
U N D U L A T O R ♦ 8-19