How Can We Get More Neutrons? Upgrade Paths for the EDM Geoff Greene

1. How Can We Get More Neutrons? Upgrade Paths for the EDM Geoff Greene University of Tennessee /Oak Ridge National Laboratory Oct 2006

2. Why is the Fundamental Neutron Beamline at the SNS designed the way it is? • Introduction to Sources & Neutronics Power, Moderators, Monochromators, and Guides • Possible Upgrade Paths Current SNS Target Station w/o monochromator SNS Long Wavelength Target Station NIST CNRF Upgrade Project

3. Observations/Conclusions • There are other FNPB customers besides EDM. • The guide and monochromators are optimized to accommodate all users. • For a number of practical and political reasons, the EDM guide won’t change until EDM demonstrates that it is rate-limited*. • By the time that EDM demonstrates that it is rate limited, there will likely be several possible upgrade paths. *This represent my personal opinion and does not necessarily represent the opinions of the EDM Executive Committee, ORNL Physics Division, SNS management, DOE Office of Science, or Pete Domenici.

4. User Group (including representation from the EDM) recommended that FNPB be designed to allow parallel operation of Cold n and UCN Expts.

5. The First Round of FNPB Proposals Have Been Received and Reviewed FNPB Beamline Characterization and Commissioning Approved UCN Beam (SNS, ORNL, LANL, IUCF, NCSU,…) Determination of τn Lifetime Using Magnetically Trapped UCN Conditional Approval (Harvard, NIST, NC State) Measurement of “a” & “b” Correlations in Neutron Beta Decay Deferred (U of Va., ORNL, LANL, Indiana, UNH,…) Measurement of “a,b,B,A” Correlations in Neutron Beta Decay Deferred (LANL, Indiana, Michigan, NIST, ORNL, UNH,…) Measurement of “A+B” Correlation in Neutron Beta Decay Deferred (Michigan, Indiana, NIST, ORNL, UNH,…) Measurement of Parity Violation in n-p Capture Conditional Approval (LANL, Indiana, Manitoba, NIST, Berkeley, ORNL,…) Measurement of Parity Violation in n-d Capture Further study (LANL, Indiana, Manitoba, NIST, Berkeley, ORNL,…) Precise Measurement of Neutron Spin Rotation in H2 and He Conditional Approval (Indiana, Washington, NIST, NC State, Indiana, ORNL,…) New Search for an Electric Dipole Moment Approved UCN Beam (LANL, Caltech, Berkeley, ORNL, NC State, …)

6. Neutrons “On Target” Depends on Several Factors • Accelerator Power Neutron production is approximately linear in beam Power for 600 Mev ≤ Eproton ≤ 3 GeV • Moderator efficiency (brightness @ 8.9Å) Moderation depends upon temperature, size, and composition of moderator, as well as adjacent materials. At 8.9Å, at the same power, there can be a significant difference between the brightness of “decoupled” and “fully-coupled” moderators. Selection of moderator is a trade-off between intensity and pulse width. • Efficiency of monchromator (reflectivity AND divergence) Reflectivity of graphite is ~80%. “Mosaic” crystal increases divergence which can reduce neutron guide transport efficiency. • Neutron guide transport Guide efficiency depends on details of “supermirror coating” (“m” value) as well as guide geometry (straight or ballistic)

7. A “Totally Coupled” moderator provides a higher time averaged production of cold neutrons due to longer moderation times SNS Target/moderator(s) ILL Core/moderator

8. Current EDM Beamline Design • Accelerator Power SNS scheduled for 1.4 MW operation when EDM begins operation • Moderator efficiency (brightness @ 8.9Å) FP13 is on cold moderator that is not fully optimized for maximum integrated long wavelength flux. • Efficiency of monchromator (reflectivity AND divergence) FNPB baseline calls for double crystal monochromator. This leads to a loss of ~x2 from reflectivity and ~x3.5 due to vertical divergence. • Neutron guide transport Ballistic guide design is fully optimized for 8.9Å transport. Use this performance as baseline

9. FP14a Cold Beam with 6° Bend Current Beam Line

10. Upgrade Path #1: Direct Path from FNPB “Cold Guide” to EDM Building • Accelerator Power GAIN x1 • Moderator efficiency (brightness @ 8.9Å) GAIN x1 • No monchromator, chopper used to select 8.9Å GAIN x6 • Neutron guide transport GAIN x1 TOTAL GAIN x6

11. SNS Upgrade Plan The SNS is designed to allow operations with two target stations • Phase 1 – Power Upgrade • 3-4 MW • Completion FY10 • Phase 2 - Long Wavelength Target Station (LWTS)* • 1.0 MW @ 20Hz • Long Pulse ? (3MW @ 60Hz, p+) • Fully Coupled Moderators • VCN source ? • Completion FY13 ? *Details of final configuration is still under discussion.

12. Upgrade Path #2: 2nd Target Station Assumptions: Power 1 MW (possibly Long Pulse with higher power) Fully coupled VCN Source ? • Accelerator Power GAIN x0.7 • Moderator efficiency (brightness @ 8.9Å) 1 GAIN x4 – x8 • No monchromator, chopper used to select 8.9Å GAIN x7 • Neutron guide transport GAIN x1 – x1.5 (can start ballistic guide sooner) 2 TOTAL GAIN x20 – x50 1 Phil Fergusson, SNS 2 Paul Huffman, NCSU

13. Upgrade Path #3: NIST Upgrade NIST has proposed a major upgrade that would include a new liquid D2 moderator as well as new system of guides. If : • The existing nuclear physics beamline (~60m, straight 58Ni coated, 15x6cm2) were replaced with a ballistic guide fully optimized to match our EDM experiment, AND • There was enough space in the reconfigured NIST guide hall, AND • A monochromator is not needed to reduce background, there would be a TOTAL GAIN x 10* * J. Cook, NIST

14. Conclusions • For a number of practical and political reasons, the EDM guide won’t change until EDM demonstrates that it is rate-limited. • By the time that EDM demonstrates that it is rate limited, there will likely be several possible upgrade paths.

15. End of Presentation