Optics and magnetic field calculation for the Hall D Tagger

Guangliang YangGlasgow University

Contents

1. Magnetic field calculated using Opera 3D. 2. Tagger optics calculated using Opera 3D. 3. Tagger optics along the straight line focal

plane. 4. Conclusion.

Part 1. Magnetic field calculation.

The magnetic field of the Hall D Tagger is calculated by using a finite element software- Opera 3D, version 10.025

Two identical dipoles and one quadupole are included in the same mesh model.

More than 2 million elements and 1.5 million nodes have been used in the calculation.

The magnetic fields have been checked along various electron trajectories.

Magnetic field calculated by using Opera 3D, version 10.025.

Mesh used by Tosca for magnetic field calculation .

Mid-plane magnetic field histogram calculated by TOSCA.

Magnetic field along a line perpendicular to the magnet output edge.

TOSCA Magnetic Field Calculation.

Magnetic field along electron beam trajectories between 3.9 and 5.0 GeV.

Y-component of stray field at focal plane position.

Minimum distance between focal plane detector and EFB

Component of stray field normal to y-direction at focal plane position.

Minimum distance between focal plane detector and EFB

Part 2. Optics calculated using Opera 3D.

• The electron trajectories of various energies have been evaluated using the calculated magnetic field.

• By using the calculated electron trajectories, optical properties of the Tagger are determined.

• Electron trajectories have been calculated using Opera 3 D post processor.

• The focal plane position is determined by using the calculated electron trajectories and spot sizes.

Beam trajectories (1-9 GeV) and the straight line focal plane position

Tosca.

Different colours indicate

different energies

Calculated electron trajectories (81 per ray bundle).

Beam trajectories calculated from TOSCA in the mid plane for 3 GeV and 8 GeV. Those trajectories having the same direction focus on position 1, and those trajectories having the same starting position focus on position 2. ( Electrons travelling in the direction shown by the top arrow ).

Electron trajectory bundles according to their directions at the object position (Angle variations span 4 theta_C).

(3 GeV) (8 GeV)

1 21

2

Object Image

Sketch showing the two focusing positions

Position 1Position 2

Lens

From the TOSCA calculation, the best location for a straight line focal plane is close to position 2 for the lower electron energies. For high electron energies the best location is close to position 1.

Beam trajectories calculated by TOSCA in a vertical plane for 3 GeV electrons.

Exit edge

Exit edge

Focal plane

Focal plane

Without quadrupole With quadrupole

Rays with different starting points but with a common angle

Y position depends on emission angle of bremsstrahlung electrons.

Bundles are well separated at focal plane

(without quadrupole)

Par 3. Tagger optics along the straight line focal plane.

1. The optical properties have been determined using Tosca ray tracing .

2. The optical properties meet the requirements of GlueX.

Straight line focal plane position

Main beam

Magnet 1Magnet 1

Photon beam

Straight thin window flange (parallel to the straight line focal plane determined by TOSCA ray tracing)

Comparison of optical properties along the Straight Line focal plane (without and with quadrupole).

(quadrupole field optimized for 3 GeV electrons.)

Resolution. Half vertical height.

Dispersion. Beta.

Comparison of optical properties along the Straight Line focal plane (without and with quadrupole).

Beta is the angle between an outgoing electron trajectory and the focal plane.

(Perpendicular to electron trajectory)

Conclusions

• The magnetic field of the Hall D Tagger has been calculated by using a finite element software- Opera 3D.

• The electron trajectories of various energies have been evaluated using the calculated magnetic field.

• By using the calculated electron trajectories, optical properties of the Tagger are determined.

• The optical properties along the straight line focal plane of the two identical magnets Tagger meet the GlueX specifications.