Effect of CTOF, CND, and HTCC Detector Shield on the Hall-B Solenoid Magnet

Transcription

1 Effect of CTOF, CND, and HTCC Detector Shield on the Hall-B Solenoid Magnet, Engineering Division, JLAB October 14 th 2013; Revision-0 1. Introduction This document is based on the calculations done for the Hall-B solenoid magnet. Hall-B solenoid magnet is a 5-T actively (self) shielded magnet. This magnet is being designed and manufactured by Everson Tesla, Inc. (ETI). All the coil dimensions in this report are based on ETI-PDR report submitted in February All the calculations presented in this report are reproduced making the model in VF-Cobham software. The solenoid magnet consists of 5 coils- 2 inner coils, 2 middle (or intermediate) coils and one shield coil. In this report field and force calculations for the magnet are summarized. The physical cold dimensions of the coils are shown in Fig. 1. Hall B Solenoid Magnet: Coil Dimensions mm mm mm mm mm mm -Z +Z mm mm mm mm mm Fig.1: The physical cold dimensions of the solenoid coils Page 1 of 19

2 The solenoid magnet has detectors fitted around it. There are 3 types of detector around the magnet. a. CTOF (Central time of flight) b. CND (Central Neutron Detector) c. HTCC (High Threshold Cherenkov counter) These detectors are sensitive to magnetic field and need shielding from the magnetic field, but these shields might have an effect on the magnetic field of the solenoid and might exert force on the coils. In this document the effects of CTOF, CND, and HTCC detector shields are considered. Fig.2 shows the CTOF fitted around the solenoid. Fig.3 shows the CTOF shield detail. This shield has 3 layers of material. In this report initially only the outer layer is considered, and then an equivalent simplified shield is considered. Fig.4 shows the equivalent simplified shield area and calculations for packing fraction. Fig.5 shows the CND shield, equivalent shield and calculations for packing fraction. Fig.6 shows the HTCC shield, equivalent shield and calculations for packing fraction. Fig.2: Position of the CTOF detector around the solenoid magnet Page 2 of 19

3 Fig.3: Details of CTOF shield Fig.4: Equivalent shield area and packing fraction for simplified CTOF shield Page 3 of 19

4 Fig.5: CND shield with equivalent area and packing fraction for simplified CND shield Fig.6: HTCC shield with equivalent area and packing fraction for simplified HTCC shield Page 4 of 19

5 Bmod (T) 2. Coil only calculation Coil only model includes all the 5 coils. The coil dimensions and current density is based on ETI PDR report. Fig. 7 shows coil only model in Opera. Fig.7: Coil only Model In the coil only model field along the axis of the magnet, coil forces, maximum field in the coils, SSP (short sample percentage) and current sharing temperature are plotted. These are shown in Fig.8 to Fig. 11 and table 1. SSP and current sharing temperature values are based on conductor data at 4.2 K and assuming all the coils are at 4.2 K Bmod (T) Bmod (T) Distance along the beam direction (mm) Fig. 8: Field along the magnet axis in coil only model Page 5 of 19

6 Fig. 9: Maximum field in the coils in coil only model Coil only Coil No. Fx (N) Fy (N) Fz N) All Coils Coil only Coil No. Tx (N-mm) Ty (N-mm) Tz (N-mm) All coils Table 1: Coil forces and torques in coil only model Page 6 of 19

7 Fig. 10: SSP distribution in the coil only model Fig.11: Current sharing temperature distribution in coil only model 3. Calculation with CTOF shield (outer layer) For this analysis only the outer layer of CTOF shield is considered. Fig.12 shows the coil model with CTOF outer shield. In the model field along the axis of the magnet, coil forces, maximum field in the coils, SSP (short sample percentage) and current sharing temperature are plotted. These are shown in Fig.13 to Fig. 16 and table 2. Page 7 of 19

8 Bmod (T) Fig.12: Solenoid model with coil and CTOF outer shield 6.00 Bmod with CTOF shield outer layer only Bmod with CTOF outer shield (T) Distance along the beam direction (mm Fig. 13: Field along the magnet axis in model with CTOF outer shield Fig. 14: Maximum field in the coils in model with CTOF outer shield Page 8 of 19

9 CTOF Outer shield Coil No. Fx (N) Fy (N) Fz N) All Coils Coil No. Tx (N-mm) Ty (Nmmmm) Tz (N All coils Table 2: Coil forces and torques in model with CTOF outer shield Fig. 15: SSP distribution in model with CTOF outer shield Fig.16: Current sharing temperature distribution in model with CTOF outer shield Page 9 of 19

10 Field (T) 4. Calculations with CTOF equivalent shield For this analysis equivalent shape, size and area of CTOF shield is considered. Fig.17 shows the coil model with CTOF equivalent shield. In this model field along the axis of the magnet, coil forces, and maximum field in the coils are plotted. These are shown in Fig.18, Fig. 19 and table 3. Fig.17: Solenoid model with coil and CTOF equivalent shield 6.00 Bmod with Equivalent CTOF shield (T) Bmod with Equivalent CTOF shield (T) Distance along the beam direction (mm) Fig. 18: Field along the magnet axis in model with CTOF equivalent shield Page 10 of 19

11 Fig. 19: Maximum field in the coils in model with CTOF equivalent shield CTOF simplified shield Coil No. Fx (N) Fy (N) Fz N) All Coils Coil No. Tx (N-mm) Ty (N-mm) Tz (N-mm) All coils Table 3: Coil forces and torques in model with CTOF equivalent shield Page 11 of 19

12 Field (T) 5. Calculations with CND shield For this analysis equivalent shape, size and area of CND shield is considered. Fig.20 shows the coil model with CND equivalent shield. In this model field along the axis of the magnet, coil forces, and maximum field in the coils are plotted. These are shown in Fig.21, Fig. 22 and table 4. Fig.20: Solenoid model with coil and CND equivalent shield 6.00E+00 Bmod with Equivalent CND shield (T) 5.00E E E+00 Bmod with Equivalent CND shield (T) 2.00E E E Distance along the beam direction (mm) Fig. 21: Field along the magnet axis in model with CND equivalent shield Page 12 of 19

13 Fig. 22: Maximum field in the coils in model with CND equivalent shield CND simplified shield Coil No. Fx (N) Fy (N) Fz N) All Coils Coil No. Tx (N-mm) Ty (N-mm) Tz (N-mm) All coils Table 4: Coil forces and torques in model with CND equivalent shield Page 13 of 19

14 Field (T) 6. Calculations with CTOF and CND together For this analysis equivalent shape, size and area of CTOF and CND shields is considered. Fig.23 shows the coil model with CTOF and CND equivalent shield. In this model field along the axis of the magnet, coil forces, and maximum field in the coils are plotted. These are shown in Fig.24, Fig. 25 and table 5. Fig.23: Solenoid model with coil and equivalent CTOF and CND shield 6.00 Bmod with Equivalent CTOF and CND shield (T) Bmod with Equivalent CTOF and CND shield (T) Distance along the beam direction (mm) Fig. 24: Field along the magnet axis in model with equivalent CTOF and CND shield Page 14 of 19

15 Fig. 25: Maximum field in the coils in model with equivalent CTOF and CND shield CTOF and CND simplified shield Coil No. Fx (N) Fy (N) Fz N) All Coils Coil No. Tx (N-mm) Ty (N-mm) Tz (N-mm) All coils Table 5: Coil forces and torques in model with equivalent CTOF and CND shield 7. Calculation with HTCC shield (alone and with CTOF and CND) For this analysis equivalent shape, size and area of HTCC shield is considered. The HTCC are located in very low field, therefore, only forces are calculated for this case. Fig.26 shows the coil model with CTOF, CND, and HTCC equivalent shields. In this model only coil forces are calculated. These are given in table 6 and table 7. Page 15 of 19

16 Fig. 26: Solenoid model with coil and equivalent CTOF, CND, and HTCC shield HTCC simplified shield Coil No. Fx (N) Fy (N) Fz N) All Coils Coil No. Tx (N-mm) Ty (N-mm) Tz (N-mm) All coils Table 6: Coil forces and torques in model with equivalent HTCC shield Page 16 of 19

17 CTOF, CND and HTCC simplified shield Coil No. Fx (N) Fy (N) Fz N) All Coils Coil No. Tx (N-mm) Ty (N-mm) Tz (N-mm) All coils Table 7: Coil forces and torques in model with equivalent CTOF, CND and HTCC shield 8. Comparison of field and field homogeneity For all the above simulation central field and field homogeneity in the central region (ɸ25 mm x 40 mm) is also calculated. Comparison of field and field homogeneity for all the simulation is given in table 8. Field homogeneity in the center region gets slightly worse. In ETI design homogeneity is just within the specification without any margin there (89 ppm instead of 100 ppm), this issue needs to be discussed with ETI during discussion for the correction coils. The design capabilities of correction coil needs to be studied in detail to address this issue. Page 17 of 19

18 Coils only With outer CTOF shield With equivalent CTOF shield With equivalent CND shield With equivalent CTOF and CND shields Table 8: Field and field homogeneity comparison With equivalent CND shield With equivalent CTOF and CND shields Central field (T) Maximum field in Z=-20 to +20 and r=12.5 mm Minimum field in Z=-20 to +20 and r=12.5 mm db (mt) Field homogeneity (db/b) (ppm) Field homogeneity with margin (db/b)*1.5 (ppm) Comparison of coil forces and torques For all the above simulation forces and torques on the coils are calculated. The torque is calculated around the center of the magnet. The total forces on the magnet dues to CTOF, CND, and HTCC detector shield is about 12 kn. These forces are higher than the actual forces from the individual shields. The comparison between CTOF outer shield calculation and CTOF equivalent shield force calculation shows that these forces are probably double of the forces from the individual shield. This value of forces will be good number to consider for structural analysis, this will give sufficient margin. Comparison of forces and torques for all the simulation is given in table 9. Coil only CTOF outer shield only CTOF simplified shield CND simplified shield CTOF and CND simplified shield Coil Fx No. (N) Fy (N) Fz N) Fx (N) Fy (N) Fz N) Fx (N) Fy (N) Fz N) Fx (N) Fy (N) Fz N) Fx (N) Fy (N) Fz N) Fx (N) Fy (N) Fz N) Fx (N) Fy (N) Fz N) All Coils Coil Tx (Nmmmmmmmmmmmmmm) Ty (N- Tx (N- Ty (N- Tx (N- Ty (N- Tx (N- Ty (N- Tx (N- Ty (N- Tx (N- Ty (N- Tx (N- Ty (N- Tz (N-m) Tz (N-m) Tz (N-m) Tz (N-m) Tz (N-m) Tz (N-m) No. Tz (N-m) All coils Table 9: Comparison of coil forces and torques HTCC simplified shield CTOF, CND and HTCC simplified shield Page 18 of 19

19 10. Conclusion In this technical note effect of detector shield on the Hall-B magnet is studies in detail. The effect on the magnetic field, field homogeneity, forces and torques is calculated. A simplified model using the equivalent volume of the CTOF, CND and HTCC is used for the analysis. Following conclusions can be drawn based on the above study: Field homogeneity gets slightly worse and out of specification. ETI in their design has not considered any margin on the field homogeneity, according to ETI design field homogeneity is 89 ppm, if a standard factor of 1.5 is used; homogeneity in ETI design without shield is also out of specification (133 ppm). The homogeneity with all the detector shield is around 165 ppm (with 50% margin otherwise 110 ppm). Net force on the magnet due to CTOF, CND and HTCC detector shield is approximately 12kN (in the simplified model). This number given enough safety margin for designing the axial support for the magnet system. There is some iron in the Hall-B structure and the force on the solenoid due to that structure is around 500 N. That should also be added to this value. There are some other SS tubes inside the bore of the magnet; they will be made with non-magnetic SS. Page 19 of 19