1. Hall C Users Meeting 31 January 2009
SHMS Optics Update
Tanja Horn
Hall C Users Meeting
31 January 2009

2. SHMS Optics Configuration
Need charged particle detection with momenta up to the beam energy (11 GeV) at forward angles down to 5.5° even with HMS at small angles
Most reasonable configuration: HBQQQD
Focal Plane HB Q1 Q2 Q3
DIPOLE
Deflection=3 °
Deflection= 18.4 °

3. Collimator reduces uncertainties due to opticsQ1 Q2 Q3 D
+10% < δ < +15%
Event loss at Q1 due to geometric effects
Acceptance at dipole entrance depends on aperture and δ
Events at negative δ are focused more
Collimator can eliminate events that would be lost inside the dipole
Reduces model dependent systematic uncertainty

4. Sieve Slit for Spectrometer Optics
Sieve slit is used to understand the optics properties the spectrometer
Figures show HMS sieve slit reconstruction data
HMS
X’ (individual holes)
1.8 mr
X’ (columns) mr
Y’ (individual holes) mr
Y’ (rows) mr
Y (mean)
2 mm
H. Blok, T. Horn, G. Huber et al., Phys. Rev. C78 (2008)

5. HMS collimator/slit system
Sieve slit
0.508 cm holes in 7 (9) columns at cm (2.540 cm) intervals in the horizontal (vertical) direction
Center of sieve slit at 168 cm from target center
No holes at / cm and cm/-5.080cm for orientation checks
Outermost holes are at ± cm (±60.5 mr)
Octagonal collimators
6.35 cm thick heavymet (90% W, 10% CuNi)
HMS Collimator box D Q1 Q2 Q3

6. SHMS collimator/sieve system
Sieve collimator in front of HB: standard optics calibration may be complicated
Aperture defining slits: best location in front of HB
Sieve collimator in front of Q1: optics modeling straightforward, but have to assume that perturbations due to HB are small
Possible sieve collimator locations y HB Q1 Q2 Q3 D x
Design will be octagonal shape
Dimensions depend on location in z

7. Place SHMS collimator after HBQ1
SHMS collimator box
No room before HB for collimator box with collimator(s) and sieve slit
Assume front of collimator is at 82 cm after the HB center or at 2.58 m from the pivot
Collimator is then ±0.055*258=±14.2 cm high and
±0.030*258=±7.7 cm wide
Assume heavymet material for ±5cm at least need 40cm by 25cm per collimator

8. Slit Box Design Limitations: Width
SHMS
HMS Q1 HB Q2
Slit box
Guiding rod options:
35-cm wide slit box is possible
Move horizontally from SHMS left to beam axis
Mechanical (surveyed) stop at SHMS right
Guiding rods (w/ tooling balls) on top and bottom
Two options: guiding rods in the back or to sides

9. Slit Box Design Limitations: Depth
Analogous to HMS design, assume octagonal collimator thickness 6.4 cm
Sieve slit is thinner (e.g., HMS: cm thick)
Two octagonal collimators
Also take into account additional material for support etc.
Type
Thickness
Box material thickness
0.9 cm
Empty space for motion
0.6 cm
Collimator thickness
6.4 cm
Rod/tooling ball space
4.6 cm
Box/material thickness
Total depth of slit box
13.4 cm
Sieve slit

10. SHMS Slit Box in Hall C Slit box fits between HB and Q1
Front of slit box is 80 cm after the HB center, or at 2.56 m from target center
Sufficiently far away from HB to have minimum stray field

11. SHMS sieve slit design
Standard calibrations of SHMS with the sieve before Q1 possible
Preliminary simulations show small distortions of mid-plane symmetry
FP pattern of sieve before HB shows strong delta dependence of the bending
z=120cm
z=258cm
Size of sieve holes: 3 mrad
For comparison: HMS sieve holes diameter is 0.504cm (3 mrad)
Further studies of the focal plane patterns will determine the optimal design for optics reconstruction

12. Additional Sieve Slit before HB
Special calibration sieve slit HB Q1
120 cm from target center
Assume front of sieve slit is 56 cm in front of HB center or at 1.20 m from the pivot
Need to cover at least ±0.055*120cm=±6.6 cm high and
±0.030*120cm=±3.6cm wide for a point target
Assume heavymet material for ± 5 cm at least at the edges
Assume 30 cm wide by 25 cm high sieve (note: HB gap is 35cm by 36 cm)
Weighs about 40 kg, so movable by hand

13. Design Limitation: height of the sieve slit
SHMS
HMS Q1 HB Q2
Special Sieve Slit
Type
Thickness
Wall thickness
0.9 cm (x2)
Rod/tooling ball thickness
4.6 cm (x2)
Sieve slit height
25.0 cm
Total height of slit box
36.0 cm
Additional sieve slit (simple hand motion) before HB
Move horizontally from SHMS left to beam axis
Only inserted for special calibration runs

14. Design Limitation: depth of the sieve slit
Analogous to HMS design, assume octagonal sieve slit thickness 3.2 cm
But cannot forget about additional materials for support
Type
Thickness
Thickness of guide before sieve
0.5 cm
Sieve slit thickness
(but rod/tooling bar thickness)
3.2 cm
5.1 cm
Thickness of guide after sieve
Back wall material thickness
0.9 cm
Total depth of slit box
6.5 cm

15. Next Steps
Additional studies for understanding the optical properties of the SHMS including HB
Look how HB distorts the “image” of a collimator or sieve slit in front of it.
How does an entrance octogonal look like in position and angle space at the planned location at the entrance of Q1 – can easily be done using HB TOSCA
HMS Q2
Q1’
Beamline
Bender
Short report on simulation results
Optimization of the distance between and the size of the Q1 sieve holes and the special calibration sieve slit before HB
HMS Q1
Additional techniques for calibration techniques
Possibilities of H(e,e’p) for calibrations especially the HB part
Target

16. Backup material

17. Q1 sieve

18. Special calibration sieve

19. Target Region Slot in Q2 for Beamline Slot in Q1’ for Beamline
Vertical Slot in HB for HMS Q1 at 12°
Slot in HB for Beamline