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

T. Horn, SHMS Optics UpdateT. Horn, SHMS Optics Update

SHMS Optics Update

Tanja Horn

Hall C Users Meeting

31 January 2009

User

T. Horn, SHMS Optics Update

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

HB Q1 Q2 Q3 DIPOLE

Focal Plane

Deflection= 18.4 °Deflection=3 °


Collimator reduces uncertainties due to optics

• Event loss at Q1 due to geometric effects

• Acceptance at dipole entrance depends on aperture and δ– Events at negative δ are focused more

+10% < δ < +15%

• Collimator can eliminate events that would be lost inside the dipole– Reduces model dependent

systematic uncertainty

Q1

Q2

Q3

D


Sieve Slit for Spectrometer Optics

• Sieve slit is used to understand the optics properties the spectrometer

• Figures show HMS sieve slit reconstruction data

H. Blok, T. Horn, G. Huber et al., Phys. Rev. C78 (2008)

X’ (individual holes) 1.8 mr

X’ (columns) 1.8-2.1 mr

Y’ (individual holes) 0.3-0.7 mr

Y’ (rows) 0.8-1.0 mr

Y (mean) 2 mm

HMS


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

Q1 Q2 Q3D


SHMS collimator/sieve system

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

Q1 Q2 Q3HB D

Possible sieve collimator locations

y

x

• 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


Place SHMS collimator after HB

• 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

HB Q1

SHMS collimator box

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


Slit Box Design Limitations: Width

SHMS

HMS

Q1HB

Q2

• 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

Slit box

Guiding rod options:


Slit Box Design Limitations: Depth

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 0.9 cm

Total depth of slit box 13.4 cm

• 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.

Sieve slit

Two octagonal collimators


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

Slit box fits between HB and Q1


SHMS sieve slit design

• 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

z=120cm z=258cm• 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


Additional Sieve Slit before HB

• 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

Q1HB

Special calibration sieve slit

120 cm from target center


Design Limitation: height of the 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

SHMS

HMS

Q1HB

Q2Special Sieve Slit


Design Limitation: depth of the sieve slit

Type Thickness

Thickness of guide before sieve 0.5 cm

Sieve slit thickness (but rod/tooling bar thickness)

3.2 cm5.1 cm

Thickness of guide after sieve 0.5 cm

Back wall material thickness 0.9 cm

Total depth of slit box 6.5 cm

• Analogous to HMS design, assume octagonal sieve slit thickness 3.2 cm

• But cannot forget about additional materials for support


Bender

Q1’

Target

HMS Q1

HMS Q2

Beamline

• 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

Next Steps

• Short report on simulation results

• Additional techniques for calibration techniques– Possibilities of H(e,e’p) for calibrations especially the HB part

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


Backup material


Q1 sieve


Special calibration sieve


Target Region

Slot in HB for Beamline

Vertical Slot in HB for HMS Q1 at 12°

Slot in Q1’ for Beamline

Slot in Q2 for Beamline

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

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