An Interactive Beam Line Simulator Module for RHIC Page: 2 of 4
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AN INTERACTIVE BEAM LINE SIMULATOR MODULE FOR RHIC*
W. W. MacKay, Brookhaven National Laboratory, Upton NY, 11973-5000
This paper describes the interactive simulation engine, bl,
designed for the RHIC[l] project. The program tracks as
output to shared memory the central orbit, Twiss and dis-
persion functions, as well as the 6 x 6 beam hyperellipsoid.
Transfer matrices between elements are available via inter-
active requests. Using a 6-d model, optical elements are
modeled with a linear transfer matrix and a vector. The
vector allows simulation of misalignments, shifts in field
strengths, and beam rigidity. Currently only a linear model
is used for elements. In addition to the usual magnets, a
foil element is included which can shift the beam's rigidity
(resulting from a change of charge and energy loss), as well
as increase the momentum spread and emittance. Running
as a Glish client, bi can be interfaced to other programs,
such as an orbit plotter and a power supply application to
give a quick prediction of the beam orbit from actual op-
erating currents in the accelerator. Various strengths and
offsets may be changed by sending Glish events to bl.
My intention in writing this program was to provide a pro-
gram that would quickly track a beam through a section of
beam line. Of particular interest are modeling of injection
and first turn in RHIC. The requirements were that:
1. It should track the central trajectory, beam envelope,
and optics functions for various magnet settings and
initial beam conditions.
2. It should read the standard RHIC lattice definition
files, with additional information on how to combine
these files using a database.
3. It should be interactive, so that it could be used as
a simulator. Initial conditions and various elements
should be able to be tweaked with a quick turn-a-
round from retracking the beam. It should be able to
return requested transfer matrices between elements.
4. It should be able to be interfaced into the control sys-
5. It should produce binary output, both to disk files and
to shared memory.
The program does not print out results or plot them; sep-
arate programs have been written for these purposes. An
X-windows plotting program, plot.bl, plots the data from
shared memory and can be tied to bl through Glish.
* Work performed under the auspices of the US DOE.
Glish is a system with three components: a scripting
language specifying what programs to run and how to
interconnect them, libraries that can be linked with pro-
grams to allow them to communicate by sending and re-
ceiving events, and an interpreter process for executing
Glish scripts and providing interprocess communication
via Glish events.
' 0 design trajecory
Fig. 1 Schematic of an offset element.
2 TRACKING METHOD
The program bl is fully 6-dimensional with the transpose
of a trajectory vector given by
XT =(x x' y y' z 6),
where 6 = Ap/p is the fractional momentum deviation
from the design particle. The program tracks the central
trajectory through the ith element by the equation:
X(si) = MiX(s.i-) + U,
where Mi is the usual linear matrix for the element, si is
the path length at the downstream end of the element, and
U4 is a constant vector for that element. The vector U/ may
be used to specify misalignment of the element. For an
offset misalignment given by Wi (see Fig. 1), the corre-
sponding vector is
The 6 x 6 beam hyperellipsoid E is tracked by the equation
Ei = MiEi_1M.
The Twiss functions: Q,,, ax, -y, /y, ay, yy, dispersion
functions: 1k, ?', qy, ry, vZ, and phase advances: 0, oy
may also be tracked through the beam line.
In order to keep calculations to a minimum, three sepa-
rate Glish events are used to invoke independent tracking
of trajectory, hyperellipsoid, and optics functions, since the
user may not want all the possible information. If only a
steering magnet is changed, the user may care to retrack
just the trajectory.
i = (I-- Mi)Wi.
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W., MacKay. An Interactive Beam Line Simulator Module for RHIC, report, May 9, 1997; United States. (digital.library.unt.edu/ark:/67531/metadc871273/m1/2/: accessed November 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.