1. Solenoid Performances in Different Situations

2. Outline The request of double polarity arose
a study to evaluate the effect of hysteresis on the magnetic field has been performed
The request of running at lower field with respect to the design one arose
the field has been calculated at different currents
“Curiosity” about the possibility of running the magnet without the iron yoke is in the air
the field of the bare solenoid has been calculated

3. Polarity Reversal
The effect of hysteresis has been simulated changing the magnetisation curve
In fact, this is a conservative assumption, since it is equivalent to complete magnetisation in all the iron yoke
We expect complete magnetisation in a large part of the iron yoke but not necessarily everywhere
The hysteresis curve has been designed on the basis of literature values for low carbon steel
the net change is a proper translation to the left or the right of the magnetisation curve

4. Reference Field

5. After the Second Energisation

6. After Polarity Change

7. Summary
This analysis of the effect of polarity change shows that a minor effect is expected in the central tracker region
the change in B is few parts ‰
A larger effect is foreseen inside the iron yoke
this is partially due to the assumptions I made to perform this calculations
anyhow, this could affect the muon chambers tracking capability

8. Lower Field Operations
The magnet behaviour has been evaluated at 20%, 40%, 60%, 80% of the nominal current
For each configuration the uniformity and the radial field integral have been evaluated in the outer tracker region
The effect of saturation in the downstream door is evident even if small
The quality of the field is almost in the requirements for each configuration

9. 20% of the Nominal Current

10. 40% of the Nominal Current

11. 60% of the Nominal Current

12. 80% of the Nominal Current

13. Reference Field

14. Summary
The magnet can be operated at every current, lower with respect to the design one
The field quality is very similar at every current
The little variations in the radial field integral distributions is probably due to the saturation in the downstream door

15. No Iron Solenoid

16. Summary of the Summaries
The magnet can be operated in both polarities without significant effect
can the field variation in the iron affect the muons tracking? to be investigated
The magnet can be operated at every current lower than the design one
the field quality is almost unaffected and the central field is reasonably linear with the current density
The magnet cannot be operated without the iron
the disperse field is too large
the magnetic forces acting on the coils are too large