Tracking ions inside PRISMA
E.FarneaINFN Sezione di Padova
The PRISMA Magnetic SpectrometerThe PRISMA Magnetic Spectrometer
E. Fioretto
INFN - LNL
E. Fioretto
INFN - LNL
195 MeV 195 MeV 3636S + S + 208208Pb, Pb, lablab = 80 = 80oo
E (a.u.)E (a.u.)
E (
a.u
.)E (
a.u
.)Z=16Z=16
Z=28Z=28
XY
X position X position
Y Y positionposition
E/E
< 2
%
E/E
< 2
%
Z/Z/Z
~ 6
0 fo
r Z=
20
Z ~ 6
0 fo
r Z=
20
t <
500
t < 5
00
ps
ps
X =
1 m
m
X =
1 m
m
Y =
2
Y = 2
m
mm
mt ~
350
ps,
t ~ 3
50 p
s,
X =
1 m
m
X =
1 m
m
Y =
1 m
m
Y = 1
mm
MCP
QDipol
e
MWPPAC IC
Z, A, of the recoils through combination of: Energy TOF Focal plane position
Direction from the start detector
A possible approachIn principle, once a detailed 3D map of the fields is known, the transportation through PRISMA is fully determined by the entrance position and by the magnetic rigidity:
Where MD, MQ are called transportation matrices. In practice,
high-order polynomial expansions are used (see eg A.Lazzaro, NIM A570, 192 (2007)) to invert the matrices and determine the trajectory of the ions.
MMMQDfp yxMMx ,,
The present approach
In the case of PRISMA, we can take a simplified approach:1) Ideal magnetic elements are considered, reabsorbing fringe
effects with a redefinition of the geometry (effective length)2) The trajectory from the dipole to the focal plane is essentially in
the dispersion plane (~20cm vertical displacement vs ~400cm path)
3) Given the size of the MCP start detector, the trajectories entering the quadrupole are essentially para-axial
4) Once the magnetic rigidity of the ions is fixed, their motion is determined by the ratio of the magnetic fields, BD/BQ rather than
their exact values
In practice an iterative procedure is followed
The iterative procedure
Guess rigidity(curvature
radius)
Transport to quadrupole(straight line)
Transport through
quadrupole
Transport to dipole
(straight line)
Transport through dipole(arc of circle)
Focal plane coincides with
observed?
New guess rigidity
Validate event with IC information
No
Yes
C++ and FORTRAN versions availableC++ and FORTRAN versions available
ResultsOriginal algorithm Present algorithm
The results with experimental PRISMA data are of the same quality as those obtained with the original algorithm used in GSORT
Few iterations per cycle are needed, fast enough for on-line (spy) implementation
The PRISMA presort library User just needs to create an instance of a
prismaManager object prismaManager takes care of creating instances
of other relevant objects Experiment-specific configuration decoded from
configuration files User just asks for information to
prismaManager, which will “forward the question to” the proper object
Data need to be formatted in a native format (not ADF, not yet available at the time of developing the library)
Implementation into Narval Just completed, results soon to be seen …
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