Hall C Users Meeting

1
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 18.4
Deflection3
3
Collimator reduces uncertainties due to optics
10 lt d lt 15

• Event loss at Q1 due to geometric effects
• Acceptance at dipole entrance depends on aperture
  and d
• Events at negative d 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
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 1.524 cm
  (2.540 cm) intervals in the horizontal (vertical)
  direction
• Center of sieve slit at 168 cm from target center
• No holes at 1.524/2.540 cm and -1.524
  cm/-5.080cm for orientation checks
• Outermost holes are at 10.160 cm (60.5 mr)

• Octagonal collimators
• 6.35 cm thick heavymet (90 W, 10 CuNi)

HMS Collimator box
D
Q2
Q1
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
Q1
Q2
Q3
HB
D
x

• Design will be octagonal shape
• Dimensions depend on location in z

7
Place SHMS collimator after HB
HB
Q1
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 0.05525814.2 cm high and
• 
  0.0302587.7 cm wide

• Assume heavymet material for 5cm at least need
  40cm by 25cm per collimator

8
Slit Box Design Limitations Width
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 3.175 cm thick)

• Also take into account additional material for
  support etc.

Two octagonal collimators
Sieve slit
10
SHMS Slit Box in Hall C

• 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

z120cm
z258cm

• 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
Q1
HB
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 0.055120cm6.6 cm high
  and
• 
  0.030120cm3.6cm 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
Special Sieve Slit

• 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

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

HMS Q1

• Optimization of the distance between and the size
  of the Q1 sieve holes and the special calibration
  sieve slit before HB

• Additional techniques for calibration techniques
• Possibilities of H(e,ep) 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