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How Can We Get More Neutrons?

Upgrade Paths for the EDM

Geoff Greene University of Tennessee /Oak Ridge National Laboratory

Oct 2006

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Why is the Fundamental Neutron Beamline at the SNS designed the way it is?

Introduction to Sources & NeutronicsPower, Moderators, Monochromators, and Guides

Possible Upgrade PathsCurrent SNS Target Station w/o monochromatorSNS Long Wavelength Target StationNIST CNRF Upgrade Project

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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.

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

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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, …)

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Neutrons “On Target” Depends on Several Factors

Accelerator PowerNeutron 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 transportGuide efficiency depends on details of “supermirror coating” (“m” value)

as well as guide geometry (straight or ballistic)

7ILL Core/moderator SNS Target/moderator(s)

A “Totally Coupled” moderator provides a higher time averaged production of cold neutrons due to longer

moderation times

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Current EDM Beamline Design

Accelerator PowerSNS 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 transportBallistic guide design is fully optimized for 8.9Å transport.

Use this performance as baseline

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Current Beam LineCold Beam with 6° Bend

FP14a

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Upgrade Path #1: Direct Path from FNPB “Cold Guide” to EDM Building

Accelerator PowerGAIN x1

Moderator efficiency (brightness @ 8.9Å)GAIN x1

No monchromator, chopper used to select 8.9Å GAIN x6

Neutron guide transportGAIN x1

TOTAL GAIN x6

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SNS Upgrade Plan

• 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.

The SNS is designed to allow operations with two target stations

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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 8.9ÅGAIN x7

Neutron guide transportGAIN x1 – x1.5 (can start ballistic guide sooner) 2

TOTAL GAIN x20 – x50

1 Phil Fergusson, SNS 2 Paul Huffman, NCSU

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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 :1.The existing nuclear physics beamline (~60m, straight 58Ni

coated, 15x6cm2) were replaced with a ballistic guide fully optimized to match our EDM experiment, AND

2.There was enough space in the reconfigured NIST guide hall, AND

3.A monochromator is not needed to reduce background,

there would be a

TOTAL GAIN x 10*

* J. Cook, NIST

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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.

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End of Presentation