1. Hardware Progress Doug Abernathy ARCS Instrument Scientist ARCS IDT Meeting Lujan Center, LANL September 30, 2002 SNS Instrument SystemsArgonne/Oak Ridge

2. SNS Instrument SystemsArgonne/Oak Ridge ARCS Test Chamber Detector Mounting Tests – Holds up to 16 tubes to test  Electronics in Vacuum  Module Handling Vacuum Tests – “Crispy Mix” Mounting and Vacuum Effects – Installation Issues

3. SNS Instrument SystemsArgonne/Oak Ridge Shielding calculations Concentrating on: Beamstop design Crosstalk between instruments Background due to proton transport line and choppers

4. SNS Instrument SystemsArgonne/Oak Ridge A brief report on the ARCS/MERLIN Workshop Doug Abernathy ARCS IDT Meeting Lujan Center, LANL September 30, 2002 SNS Instrument SystemsArgonne/Oak Ridge Agenda: Thursday 9/26/02 ISIS Morning: Introductions and instrument concepts Afternoon: Primary spectrometer Moderator; guides; choppers; polarizing filters; tour Friday 9/27/02 Morning: Secondary spectrometer Tank; detectors; shielding; beamstop; sample environment & manipulation; software Afternoon: General discussion and future plans

5. SNS Instrument SystemsArgonne/Oak Ridge MERLIN concept Original- High count rate, medium resolution chopper spectrometer as an upgrade to HET; complementary to MAPS; designed with guides and radial collimator Sample-detector distance = 2.5m Moderator-sample distance = 13.8m Angular coverage =  steradians Moderator: ambient water N9 (HET position) New ideas- Moderator: ambient water S4 (blocks S5), choice of poison depth Moderator-sample distance = 11.6m Detectors: cylindrical array of 3m long LPSDs (no Al windows) Choppers: Gd based Fermi (needs disk chopper to stop >200meV neutrons)

6. SNS Instrument SystemsArgonne/Oak Ridge Moderator Similar conclusions: Use ambient water Poison depths should be increased to >20mm but not eliminated due to large tails Different conclusions: None Future actions: Exchange source files for modeling ARCS – model performance for ARCS and SEQUOIA to determine final poison depth

7. SNS Instrument SystemsArgonne/Oak Ridge Guides Similar conclusions: Taper guides continuously from source to sample (no nose section) Use adjustable apertures and Soller collimators Guide in shutter Different conclusions: MERLIN - use only m=3 guide; sollers on movable stage between T0 and Fermi choppers; use guide after Fermi chopper Future actions: MERLIN – test guide glass in HET; Soller with guide ARCS – continue modeling (compare m values; guide just before sample; how apertures, Sollers and guide work together)

8. SNS Instrument SystemsArgonne/Oak Ridge Choppers Similar conclusions: May need disk chopper Need higher speed T0 chopper Different conclusions: MERLIN – disk chopper for Gd based Fermi chopper ARCS – disk chopper for multiple pulse and background suppression; vertical axis T0 chopper could combine disk and standard T0 chopper functions Future actions: MERLIN – test Gd slit package; continue development of 100Hz T0 ARCS – preliminary neutronic and engineering design of vertical axis T0; decide which type of T0 to pursue

9. SNS Instrument SystemsArgonne/Oak Ridge Polarizing filters Similar conclusions: Leave position in beamline for future development of filters Different conclusions: None Future actions: Monitor filter performance in other instruments

10. SNS Instrument SystemsArgonne/Oak Ridge Tank/detectors Similar conclusions: Get rid of large Al windows Avoid shadowing of all pixels in detector array Different conclusions: MERLIN – Use cylinderical array of 3m long tubes sealed at each end; 4x8 detectors mounted on a panel; tank is designed so that panels are necessary supports; use relatively short baffles that take the equivalent of one tube (~0.5m) ARCS – Put electronics in vacuum along with detectors; minimal tank feedthroughs; use a gate valve to isolate sample area for changeout Future actions: MERLIN – tests of long tubes in MAPS; vacuum tests of seals ARCS – detector module tests in vacuum; continue design work on gate valve and sample manipulation

11. SNS Instrument SystemsArgonne/Oak Ridge Shielding/beamstop Similar conclusions: Try to use standards Different conclusions: MERLIN – Standard ISIS shielding OK ARCS – No true standards for SNS; need to use non-flammable materials or encapsulation Future actions: MERLIN – provide results of dose rate vs He detector measurements ARCS – continue shielding calculations and determination of best alternative shielding materials; pursue Teflon binder for “crispy mix”

12. SNS Instrument SystemsArgonne/Oak Ridge Sample environment & manipulation Similar conclusions: Need single crystal manipulation capability Need easy and fast changeout of samples Different conclusions: MERLIN – pursue manipulation inside sample environment; use top loading CCR with rotation ARCS – pursue design of spectrometer mounted manipulation Future actions: MERLIN – sample manipulation stage development program for MARI and MAPS ARCS – continue to explore design of both types; build prototype for sample environment to test on PHAROS

13. SNS Instrument SystemsArgonne/Oak Ridge Software Similar conclusions: Need better software to handle current and future data Need standards for data files that cross all facilities Different conclusions: MERLIN – use Matlab and Fortran because of current expertise; involved in grid based computing initiative in the UK ARCS – use Python and C++ Future actions: Common ground should be explored and at the minimum standards for data storage and instrument description need to be adopted