New beam position monitor system design for the APS injector. Page: 2 of 8
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The system design philosophy was to simplify the topology so the same basic
design can be used as the universal replacement for all injector position monitoring
applications. The other general design constraint was to make it as reliable and
maintainable as possible. The design choice was a log-ratio system with the
subtraction function being done in software. The basic expression for the log-ratio
beam position [3,4] is:
Np = [(log(A) - log(B)]= log(A /B) = tanh1L[A B(
where Np is the normalized position and A and B is the induced voltages on the
stripline pick-up. This technique adds some flexibility to the system design. The
algorithm to calculate the beam position can be changed or adjusted in the future as
new techniques develop.
The BPM system was partitioned into subsystems as shown in Figure 1. The
stripline detector, bandpass filters, and front-end board make up the major differences
between applications. This partitioning allows the use of most of the components for
operation at either 352 MHz or 2856 MHz. The stripline sensitivity and system
calibration factor can be calculated by the following equations [3,4]:
80 1 (2)
where S = stripline sensitivity (dB/mm) and b = half aperture (mm), and
X(mm)z ~ xV.,, (3)
S X Gsysem
where X(mm) = normalized position (mm), Gsystem = system gain (which is set to
36mV/dB), and V., = log amplifier module output (mV).
Table 1 describes the location and number of BPMs that will be upgraded. These
applications are transport lines between the linac and the storage ring. This table also
describes the type of detector, sensitivity, and system calibration factor.
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Lill, R.; Singh, O. & Arnold, N. New beam position monitor system design for the APS injector., article, May 15, 2002; Illinois. (digital.library.unt.edu/ark:/67531/metadc741928/m1/2/: accessed May 27, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.