COUPLING MEASUREMENT AND CORRECTION AT RHIC. Page: 2 of 3
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where E is the 2x2 off diagonal coupling matrix of the
4x4 1-turn matrix. For N skew quadrupoles of strength k
and length L wired into a family, neglecting beta and
phase differences, we can write the following relation:
AQm ~ - kL l.T/(7
The operational way to correct coupling is to reach the
minimum separation via a tune scan to bring the tunes
together. At the minimum, a pair of orthogonal skew
quadrupole families are varied to reduce the separation,
ideally limited only by the resolution of the tune
2.1 The global coupling application package
An application package (DQMIN) has been developed for
global linear decoupling for Run 2001. It consists of a
series of tcl scripts, able to interface with the tune
measurement systems (Tune Meter, Schottky monitor,
and PLL) and the power supply control software (Ramp-
Editor) respectively for tune and skew quadrupole
families control. In more detail, the script functionality
" Setting of the desired tunes
" Monitoring magnet current changes
" Getting measured tunes from the existing tune
" Visualization of tune scans vs. set-tunes
" Setting of skew quads family strengths
2.2 Performance during Run 2001
The global coupling correction system has been used
during run 2001 almost exclusively to correct the residual
coupling in the machine, after the local correction in the
IR triplets . The system could correct coupling in the
machine to the tune measurement system precision of
0.001-0.0005 using the tune meter and the HF Schottky
monitor. Use of the PLL use for decoupling, potentially
providing a much higher resolution (~.0-), will be
discussed in Section 3. Although the ultimate correction
quality in 2001 has been to AQ,=.005, it has been our
experience that for operations the coupling had to be
typically controlled to AQmid~0.005. Global coupling
corrections were performed at injection and flattop.
Global coupling readjustment was required after tune
changes (as the global correction is valid only in the
vicinity of the tunes where the tune scan is performed),
and after orbit correction, that generate tune shift.
Table 1. Global decoupling performance Run 2001.
Blue Blue Yellow Yellow
injection flattop injection Flattop
AQmin 0.0005 0.006 0.004 0.0005
Skew 0 0- 0 0.00005
Quad 0.0006 0.0005 0.0001 -0.0005
(kL) 0 0.0001 0 0.0005
Measured 28.2207 28.228 28.208 28.2169
tunes 29.2202 29.234 29.2124 29.2164
Tune Artus Artus Artus HF
system FFT FFT Schottky
Date 7/12/01 7/2101 10/12/01 11/16/01
The global decoupling system performance for the gold
run after dedicated tune and family scans are summarized
in Table 1. Similar performances were obtained during
the polarized proton run.
Coupling correction in run 2001 was done exclusively
at injection and flattop, with the injection settings
propagated during ramping. The skew quadrupole
families settings over the life of run 2001 (both An and
PP) at injection are shown in Figure 2, showing more
correction activity at the run start and during polarized
protons operations. Figure 3 shows a typical tune scan to
bring the tunes together, in this example at flattop in
Yellow, during the polarized proton run.
Global coupling skew quadrupole correctors
Blue and Yellow Rings - Injetion
-0.0010 -__ y-sq
)Tap-v Im-09 Ng~-B Sop-1 0 ct-7 Dc-0
Tmen in the run
Figure 2. Skew family strengths during Run 2001
Figure 3. Scan to bring the tune together, Yellow ring,
polarized proton operation, High Frequency Schottky
3. DEVELOPMENTS FOR RUN~ 2003
The planning of the RHIC Run 2003, to start in
November 2002, was initiated at the RHlIC Retreat in
March 2002. Operational experience from 2001 stressed
that we need faster coupling correction capabilities, and a
library of correction configurations, for example, for
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PILAT,F.; BEEBE-WANG,J.; FISCHER,W.; PTITSYN,V. & SATOGATA,T. COUPLING MEASUREMENT AND CORRECTION AT RHIC., article, June 2, 2002; Upton, New York. (digital.library.unt.edu/ark:/67531/metadc741860/m1/2/: accessed November 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.