1. Dipole Magnetic Field Effect on the Antiproton Beam
June 15th, 2009 | T. Randriamalala, J. Ritman and T. Stockmanns

2. The Why of the Topic
Where should the luminosity monitor be located when the dipole field is on?
How does the B field act on the trajectory of the antiproton beam?
The beam pipe bend should match the curvature of the antiproton trajectory so that antiproton scattered with q < 8 mrad do not hit the beam pipe.

3. Luminosity Monitor Position
For the dipole:
Trajectory curvature radius inside the dipole region:
The angle between the z-axis direction and the antiproton beam trajectory after the bend is 40 mrad.
The dipole is located at about z = 4.5 m
At z =10 m, the luminosity monitor is at x ~ 21cm

4. According to the Magnets TDR:
400 mm
Antiproton beam trajectories corresponding to the momentum of1.5 GeV/c to 15 GeV/c.
The leftmost line is for a 15 GeV/c beam,
the rightmost line is for a 3 GeV/c beam.
The maximum distance between these trajectories at z = 10 m is about 0.4 mm.

5. ! Working with pandaroot:
At z = 10 m, the luminosity monitor was shifted at x = 21 cm and rotated with an angle of 40 mrad.
Run the simulation macro for the luminosity monitor for different values of beam momentum.
With some of these values, no hits are observed. !

6. The Dipole Field Maps in PandaRoot
Test of the dipole field maps by running a simple simulation:
Put one active plane at z =10 m.
No detector, or beam pipe.
Switch all the magnetic field on: solenoid , dipole, transition region.
Run for different values of beam momentum (1.5 GeV/c, 4.6 GeV/c, 8.9 GeV/c, GeV/c and 15 GeV/c).

7. Hit x-position for 5000 events
Only hits corresponding to 1.5 GeV/c and 15 GeV/c sit at the right position.
~ 325 mm
Agree with the Magnets TDR (~ 370 mm)

8. The corresponding intensity of magnetic fields for 4. 06 GeV/c and 11
The corresponding intensity of magnetic fields for 4.06 GeV/c and GeV/c are not “strong” enough to redirect beam in the correct position.
In contrast, for 8.9 GeV/c, the magnetic field intensity is too high.

9. Dipole Region Solenoid Region
Different dipole field maps implemented in pandaroot:
1.5 GeV/c
Bz(z) [Tesla]
By(z) [Tesla]
Z [cm]
Solenoid Region
Dipole Region
In the Magnet TDR:
Field distribution along the z-axis for different dipole settings for a 1.5GeV/c (solid black line and left scale) and a 15 GeV/c beam (dashed blue line and right scale).
By(z) [Tesla]
15 GeV/c
Bz(z) [Tesla]
15 GeV/c
Same shape and same scale !
Z [cm]

10. 8.9 GeV/c Abrupt increase of the magnetic field intensity
By(z) [Tesla]
Abrupt increase of the magnetic field intensity
Bz(z) [Tesla]
Z [cm]
Antiprotons are bent too much!

11. Antiprotons are not bent enough !
4.06 GeV/c
By(z) [Tesla]
Bz(z) [Tesla]
Z [cm]
Presence of cut
Antiprotons are not bent enough !
By(z) [Tesla]
11.91 GeV/c
Bz(z) [Tesla]
11.91 GeV/c
Z [cm]

12. Conclusion Magnetic field maps inside pandaroot were tested.
It does not work as well as what is described in the Magnets TDR. In particular those ones corresponding to the beam momentum 4.6 GeV/c, 8.9 GeV/c and GeV/c.
This was already reported to the forum.