Tracking studies on the effects of magnet multipoles on the aperture of the RHIC heavy ion collider Page: 4 of 4
This article is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to Digital Library by the UNT Libraries Government Documents Department.
The following text was automatically extracted from the image on this page using optical character recognition software:
Fig. 3 Momentum scans at points "B" (single dipole
per half cell) and "B’" (two dipoles per half cell).
Values represent the worst case for ten different sets
of random multipole errors.
This study was also made at point "A". A stability
limit of 19+0.3 mm was obtained when the arc quadru-
poles had their nominal coil ID and the radii of all
other elements were increased by 10%. In addition,
(a^.b^) was set to zero in all other elements other
than the three quadrupoles to Q3 near the crossing
point—in these elements (85,bj) was set to zero.
Further study of the upper allowed limits of the deca-
pole and dodecapole errors have not been made; the
main emphasis has been to determine the maximum sta-
bility limit when all elements have their nominal ID's.
At point "B" a stability limit of 19 mm was ob-
tained with both programs when all magnets had their
nominal radii and random multipoie errors. A momentum
scan was made at this tune; the results appear in
Fig. 3. As before, tracking runs were made with ten
different sets of random multipole errors, and the
worst case was used as the stability limit. A stabil-
ity limit of 19 mm (6a) was obtained at AP/P = 0,0,
and the stability limit at AP/P = +0.5% is reduced-by
■v3 mm to 5o. This is the maximum momentum spread of
the stored beam. During acceleration the momentum
spread will increase to 1.2% at transition, but as
this will be a temporary situation, the 12 mm (4a)
stability limit is not considered unreasonable.
A second set of runs has been made to determine
whether or not increasing the number of dipoles im-
proves the aperture—whether the effects of the ran-
dom multiples scale as 1//2N, with N being the number
of dipoles. In all the previous studies there was a
multipole kick at each end of every dipole. The ORBIT
program uses the same multipole at each end of the
dipole, while the default version of PATRICIA assigns
a different multipole to each end of a dipole. In the
second study the dipoles were split in two with a
multipole element at each end of every half dipole.
In addition, PATRICIA was changed so that the multi-
poles at boch ends of a dipole could be the same or
different. By using split dipoles with the option of
having the same multipole at both ends, the sequence
of random multipoles was unchanged from what it had
been in the first study. The stability limit was not
determined for point "A". For point "C" the stability
limit is the same at AP/P = 0.0 with one or two dipoles
per half cell. At points ”B” (single) and "B”' (two)
the stability limits at AP/P * 0.0 differ by 0.6 mm
and are considered to be consistent. The results of
the "B’" scan also appear in Fig. 3. No significant
difference has been found between having one or two
dipoles per half cell. \s doubling the number of units
increases the cost, this does not seem to be a promis-
ing avenue for improving the performance of the lattice.
The data presented in this report represent the
present status of the aperture studies on RHIC. The
results are not final; more studies will be performed
that will look at alternate working points at the
effects of including a^, bj, at the effects of sys-
tematic multipoles, and at corrector systems. The
manner in which beam-beam tune shift and amplitude
dependent tune shift combine has not been fully
Finally, the random errors used in this study
were generated from a rather simple model using an
assumed rms coil displacement of 0.002 inches and
are to be considered as reasonable but not final.
Tracking studies are intended to explore the sensi-
tivity to particular random multipole errors so that
efforts can be made to reduce those multipole errors
during the construction phase. Once magnet construc-
tion is started a set of actual random multipole
errors will be obtained, and magnet shuffling may be
used to reduce the effects of a single undesirable
1. S. Y. Lee, Present Conference.
2. H. Wiedemann, PEP-220, Stanford Linear Accelerator
Center, September, 1976.
3. G. Parzen, Brookhaven National Laboratory,
This article can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Article.
Dell, G.F. & Parzen, G. Tracking studies on the effects of magnet multipoles on the aperture of the RHIC heavy ion collider, article, January 1, 1985; Upton, New York. (https://digital.library.unt.edu/ark:/67531/metadc1093926/m1/4/: accessed March 25, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.