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 …