HYSPEC HYSPEC INSTRUMENT DESIGN – OUTLINE  The two “models” considered for HYSPEC – inside & outside (Mark)  A breakdown of the components of the two models (Mark)  Estimates of the cost (Mark)  COFFEE BREAK  Simulating the two models (Vinita) - MCNP considerations for shielding drum & T0 chopper - McStas flux at sample considerations  Engineering the drum shield & the detector vessel (Bill) - Available angular ranges  Polarization analyzer system (Igor)

HYSPEC The Generic Layout of HYSPEC T1A chopper T1B chopper Drum shield

HYSPEC Model one: BL14B, 25m from moderator (inside hall) Straight guide 4cm(w) x 15cm(h) 4.5m sample to detector

HYSPEC Model two: BL14B, ~37m from moderator (outside hall) Curved guide 4cm(w) x 15cm(h) 4.5m sample to detector (6m sample to detector)

HYSPEC HYSPEC is a time of flight spectrometer  Measure on a surface in (Q,E) space  “Interrogate” (Q,E) space by moving the surface around  Needs high intensity to sample many (Q,E) surfaces (160 detectors – 20 x 8-pack of LPSD’s)

HYSPEC HYSPEC is :-  high intensity (hence focusing mono)  medium resolution ΔE/E ~ 5%  “thermal” energy range ~5 < E < ~100meV [G. Granroth & D. Abernathy, ICANS-XVI]

HYSPEC L MC L CS L SD Moderator Disk choppers Focusing crystals Sample Detectors τMτM Δt C Resolution (qualitative – not M.C.) Spreading of pulse from chopper to sample Secondary resolution governed by ratio of burst time Δt C to distance L SD Secondary spectrometer Primary spectrometer  Low E I – τ M dominates  High E I – Δt C dominates τ M – source (moderator) pulse width for E I Δt C – burst time for disk choppers

HYSPEC Dashed lines: Inside: L MC =25m, L CS =2.45m, L SD =4.5m, Δt C =50μs Solid lines: Outside: L MC =37m, L CS =3.20m, L SD =4.5m, Δt C =50μs

HYSPEC T0 chopper Frame overlap chopper (T1a) m=3 guide Order suppressor chopper (T1b) Counter rotating disk choppers (T2) Drum shield Focusing crystals (Focusing “monochromator”) Sample stage + floor Detector vessel INSIDE OUTSIDE

HYSPEC T0 chopper  Located just outside SNS biological shield at ~6.3m  Remove (reduce) fast neutron (MeV, keV, eV) flux  Horizontal axis rotors – 20cm of Inconel running at 60 (or 30) Hz  Inside: 2 counter rotating choppers - Total of 40cm of Inconel - Straight view of moderator - Drum shield thickness  Outside: 1 chopper - Effect of curved guide - Out of line of sight - Drum shield material/size  Both cases: reduce nos. of windows - Would like (want) to integrate vacuum with guide & frame overlap chopper

HYSPEC Frame overlap chopper  Just after the T0 chopper (both inside & outside)  25m (inside) frame overlap on a “cold” source is a problem  60Hz disk chopper  B-loaded so that we can remove “hot” as well as cold neutrons if required  Integrated vacuum with guide & T0 chopper (windowless)

HYSPEC Measuring in the same frame Measuring in the next frame

HYSPEC m=3 Guide Inside: straight guide Outside: curve to get out of line of sight followed by 4m straight

HYSPEC T0 chopper Frame overlap chopper (T1a) m=3 guide Order suppressor chopper (T1b) Counter rotating disk choppers (T2) Drum shield Focusing crystals (Focusing “monochromator”) Sample stage + floor Detector vessel INSIDE OUTSIDE

HYSPEC Counter-rotating disk choppers  Disks at 300Hz (ΔT C ~50μs)  Diameter ~ 700mm  Gd coated  Want to integrate vacuum with guide  Picture above has external motors  Picture left has internal motors

HYSPEC Order suppressor chopper  Counter rotating disk 300Hz  Opens 5 times per frame  Need to block 4 out of 5 “pulses”  Order suppressor 60Hz  B-loaded disk chopper (as for frame overlap & other SNS disk choppers)  Integrated vacuum with guide & other choppers (windowless) Example: Counter rotating 300Hz, L MC =25m

HYSPEC Focusing (monochromator) crystals Non-polarizing – HOPG(002)Polarizing – Heusler(111) [Picture is of double focusing mono for MACS at NIST] [Picture is of “double” focusing Heusler mono for IN20 at ILL]

HYSPEC “Monochromator” drum shield  Needs to “stop” the beam  Inside – direct view of source, needs to be more substantial. I.D. ~ 0.4m, O.D. ~ 2.8m  Outside – curved guide, out of line of sight, can be smaller. I.D. ~ 0.6m, O.D. ~ 1.8M  Using HFIR drum (see right) as a starting point.

HYSPEC T0 chopper Frame overlap chopper (T1a) m=3 guide Order suppressor chopper (T1b) Counter rotating disk choppers (T2) Drum shield Focusing crystals (Focusing “monochromator”) Sample stage + floor Detector vessel INSIDE OUTSIDE

HYSPEC Relationship: disk choppers & drum shield INSIDE OUTSIDE Disk choppers  Inside: choppers must be inside drum shield  Outside: - drum shield is smaller (larger I.D., smaller O.D) - choppers can be further from sample for same resolution

HYSPEC

HYSPEC T0 chopper Frame overlap chopper (T1a) m=3 guide Order suppressor chopper (T1b) Counter rotating disk choppers (T2) Drum shield Focusing crystals (Focusing “monochromator”) Sample stage + floor Detector vessel INSIDE OUTSIDE

HYSPEC Fermi chopper – high resolution mode L SD Moderator Disk choppers Focusing crystals Sample Detectors

HYSPEC T0 chopper Frame overlap chopper (T1a) m=3 guide Order suppressor chopper (T1b) Counter rotating disk choppers (T2) Drum shield Focusing crystals (Focusing “monochromator”) Sample stage + floor Detector vessel INSIDE OUTSIDE

HYSPEC Sample stage – dance floor & airpads [ Picture is IN20 triple axis spectrometer at the ILL, Grenoble ] o Sample stage o Dance floor (granite tiles) o Airpads

HYSPEC Detector vessel Angular range: 60° (horz), 15° (vert) Sample detector dist: 4.5m, (6m) Detectors: 20x 8-pack LPSD’s (1.2m long for L SD =4.5m) “Copies” of ARCS/SEQUOIA Atmosphere: Argon (LPSD’s won’t work in He) Electronics/DAE: As per ARCS/SEQUOIA Front window: Permanent “rough” collim inside the detector Outside vessel: Radial collimator (remove SE scattering) Polarization analyzers

HYSPEC