Prototype magnet for the splitter-polarizer design

nEDM Meeting, ASU, 2008-02-09

C. Crawford, W. Korsch

University of Kentucky

G. Greene

University of Tennessee

R. Redwine

Massachusetts Institute of Technology

Collab. Mtg., ASU, 2008-02-09 #2

Outline

review of options for neutron guide• different polarizer/splitter designs• issues determining feasibility of T/R guide

T/R magnet prototypes – design, pros/cons• external quadrupole septum• internal foil septum

schedule and budget request• pretests at UKy• common SM tests at FP12• magnet prototypes

bender/splitter revisited• more efficient design

Collab. Mtg., ASU, 2008-02-09 #3

(T)

Transmission / Reflectionpolarizer (T/R) Transmission

polarizer (T)

Reflectionpolarizer (R)

Options for neutron polarizer

all 3 designs rely on supermirror polarizers• high polarization

neutron phase space• R asymmetric bender• R, T lose 50% of flux• T/R higher divergence

construction• R standard technology• T/R, T involve R&D• T/R complicated B-field

12x14 cm2

20x30 cm2

3x4 in2

each

(T/R)

in out

(R)

Collab. Mtg., ASU, 2008-02-09 #4

Monte Carlo simulations

optimized figure-of-merit for R and T/R geometries• neutrons traced to center of 4He cell

(30% loss after the end of guide)• T/R flux depends on thickness

of Si wafers (300 mm: 775 microns)

independent simulations using three software packages all consistent:• Geant4, McStas, and Neutrack

(R) Optimization (T/R) Optimization

Collab. Mtg., ASU, 2008-02-09 #5

Cost projections

Decision decoupled from FnPB guide (first 8 m + 10 m)• bender more efficient downstream, new design in progress• if needed could insert bender upstream of 10m guide

Cost estimates for 15 m of beam guide (neutronics only)

T/R requires extra R&D, ~ $100k

Costs are comparable

Collab. Mtg., ASU, 2008-02-09 #6

Design of the T/R polarizer splitter

magnetization near vertex• effectively a quadrupole field

• current bus along top/bottom

properties of thin films – need to be measured• magnetization only along surface of film• remanent magnetization after < 1ms pulse• extension of magnetization along multilayer

300 G

N

S

S

N

Collab. Mtg., ASU, 2008-02-09 #7

Second design of polarizer splitter

current septum in guide• must be thin Al foil• wrapped around guide sections• each segment magnetized separately

pros: closer to SM

cons: closer to SM• neutron absorption• mechanical stability?

50 cm guide section

Si pol. sheet

Aluminum foil current

septum

Collab. Mtg., ASU, 2008-02-09 #8

Prototype and testing plans

SCHEDULE

Spring 2008 – UKy• test polarization reflectometry• build current pulser

Summer 2008 – LANSCE FP12• calibrate reflectometry• measure needed pulse duration• test extension of magnetization

Fall 2008 – Spring 2009 – UKy• test maximum current in foils• design and build prototypes• measure DC field gradient• measure mechanical stability

during current pulses

Summer 2009 – LANSCE FP12• test neutron polarization in

prototype, pulsed magnetization

BUDGET REQUEST

$10k – SM polarizers• 1 batch m=2 glass substrate• 1 batch m=2 Si (10x10 cm2)

$10k – magnet prototype• quadrupole, Al foils• glass SMpol support• Si wafer alignment• holding field magnets• structural support

$8k – electronics• power supply• switches• control / readout

Student support at LANSCE

Collab. Mtg., ASU, 2008-02-09 #9

New Bender Designs

double up the bender and splitter

preserve the maximum efficiencyof Liouville’s theorem rationale• 25% loss of phase space in splitter• attempt to smooth out transition• use thin channels of bender polarizer• still need to do MC simulations

endorsed by Peter Böni

design A

design B

old splitterdesign

expanderconverger

Collab. Mtg., ASU, 2008-02-09 #10

Summary

two prototypes for T/R designs• depend on unmeasured properties of SMpol coatings• test feasibility of each design at UKy and FP12

improvement of R bender polarizer in parallel• low-risk plan B

future R&D with Si wafers• design and test support structure, materials• minimization of Si thickness