Cosmicray Shield Toroid: Crew Shielding for a Manned Mars Mission

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Cosmic-ray Shield ToroidCrew Shielding for a
Manned Mars Mission

• Peter McIntyre
• Texas AM University

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Cosmic rays present a life threat to astronauts
on long space missions

• Protons from solar flares
• Ions from galactic cosmic rays
• Dose is equal from all nuclei
• Enough to kill a man if unshielded
• Must shield to 100 MeV/nucleon?
• 1 GeV/nucleon?

Z
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Existing data on radiation flux beyond the
magnetosphere
Shielding requires
The devil is in the details of particle transport
through the CST envelope, including neutrons.
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AMS Design Concept Nested Toroids
Fe
B0 Outside
Field only where it is needed minimum constraint
upon EVA safety Magnet structure independent of
crew compartment, other systems
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The Texas AM group is interested in joining your
effort to develop a Cosmic-ray Shield Toroid

• Issues that we have considered
• Optimize coil geometry for minimum mass
• pure tension D geometry?
• Optimize cryogenic cooling for cryostability
• Supercritical He?
• Optimize conductor for cryostability
• Al-stabilized, MMC-reinforced Nb3Sn?
• Optimize particle transport to maximize shielding
• He blanket to attenuate neutrons?

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What do we do?New Materials and Electromagnetics
in Superconducting Magnet Technology

• Nb3Sn block-coil dipoles to extend collider bend
  field to 16 T
• Bi-2212 coil technology for a 25 T hybrid dipole
  LHC Tripler
• Structured cable for internally cooled Nb3Sn and
  Bi-2212 coils
• Novel superconducting magnets for LHC insertions
  regions
• New process technology for extending perfornace
  of MgB2

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1) Hybrid Dipoleshow to triple the energy of LHC

• Peter McIntyre, Akhdiyor Sattarov
• Texas AM University

Presentation to CERN LHC Seminar 14/3/2005
p-mcintyre_at_physics.tamu.edu
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Discovery reach for sparticles

• Ellis et al have calculated the masses of the
  lightest 2 visible sparticles in minimum
  supersymmetric extension of the Standard Model
  (MSSM), constrained by the new results from
  astrophysics and cosmology.

observable in WIMP searches (?gt 10-8 pb)
X observable at LHC
only observable at LHC Tripler
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1a) Triple the energy of LHCHigher field
requires new superconductor, handling immense
stress loads
Nb3Sn
Nb3Sn
NbTi
Bi-2212
Bi-2212
Cost today NbTi 100/kg Nb3Sn 1,000/kg Bi-22
12 2,000/kg
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To push to higher field use high-field
superconductor, limit coil stress

• Nb3Sn 14 Tesla dipole

New result 1/2006 latest single-layer model
dipole reached gt93 short sample on 1st quench

• Maximum Coil Stress 120 MPa
• Superconductor cross section 29 cm2

• Bore field 14.1 T
• Current 12.6 kA

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Nb3Sn dipole technology at Texas AM stress
management, flux plate, bladder preload
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Stress management
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Horizontal steel flux plate redistributes flux
to suppress multipoles
0.5 T 12 T
Suppress snap-back x5, relax requirements on
filament size in Nb3Sn and Bi-2212.
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Extend to 24 TeslaBi-2212 in inner (high field)
windings, Nb3Sn in outer (low field) windings
Dual dipole (ala LHC) Bore field 24
Tesla Max stress in superconductor
130
MPa Superconductor x-section Nb3Sn 26
cm2 Bi-2212 47 cm2 Cable current 25
kA Beam tube dia. 50 mm Beam separation 194
mm
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1b) Remove 500 kw of synchrotron light!

• Synchrotron radiation power/length
• critical energy
• Use photon stop
• Instead of intercepting photons at 10 K along
  dipole beam tube, intercept between dipoles
  on room-temperature finger.
• Soft X-rays actually easier to trap that hard UV

LHC E 7 TeV P 0.22 W/m Ec 44
eV (hard UV) scatters, desorbs LHC Tripler E
20 TeV P 14 W/m Ec 1.2 keV (soft
X-ray) absorbs!
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Photon Stop

• Photoemission yields vanish for E gt 100 eV

Vertical penetration through flux return (coils
have clearance)
Effect on ltb3gt 10-5 cm-2
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Photon stop swingsclears aperture at injection
energy, collects light at collision energy
Injection Collision
150 W/stop collected _at_ 1 W/cm2 heat transfer to
Liquid Xe (160 K) Same refrigeration power for
Tripler as for LHC!
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Magnets are getting more efficient!
Bi-2212
NbTi
SuperSPS
Nb3Sn
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2) The intersection region of LHC is analogous to
the objective of a microscope

• It brings the beams into collision and focuses
  them to minimum spot size ? maximum luminosity
• Need to minimize focal length f, minimize
  chromatic aberrations df/dE, harmonic distortion
  df/dr
• Minimize chromaticity and distortion by bringing
  the objective as close to the object as possible.
  Inquire with experiments how close to go 12 m
  from crossing, 30 cm radius clear.
• Maximize gradient to minimize focal length
• Develop designs for quadrupoles, dipoles that can
  tolerate high radiation, high heat

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Optimized IR for LHC
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Q1 is in harms way, but moving closer actually
reduces losses
Q1
D1
Multiplicity f(?) e-bt Eparticle pt /? So
energy flow concentrates strongly down the beam
direction.
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Design Q1 using structured cable
6-on-1 cabling of Nb3Sn strand around thin-wall
inconel X750 spring tube Draw within a thicker
inconel 718 jacket Interior is not impregnated
only region between cables in winding Volumetric
cooling to handle volumetric heating from
particle losses
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Ironless Quadrupole for Q1
350 T/m 4-7 K supercritical cooling
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D1 levitated-pole dipole
8.7 T 4.5 K
particles from collisions
Cold iron pole piece, warm iron flux
return. Cancel Lorentz forces on coils, pole
steel.
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This approach to IR elements opens new
opportunities to optimize IR optics
Comparison to baseline IR Reduce ? Reduce of
subsidiary bunch crossings Reduce sensitivity to
error fields and placements Open space for
another doublet to fully separate corrections in
x, y.
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3) 30 T NMR using strain-tolerant Bi-2212
technology
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Stress management within Bi-2212 cable
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Structured cable for Bi-2212 manage stress
within cable, refrigerate with He flow in cable
Bi-2212 0.8 mm ? strands 300 A/strand
6-on-1 cabling of round strand around thin-wall
Inconel X750 spring tube Draw within a thicker
Inconel 718 jacket Interior is not impregnated
only region between cables in winding Volumetric
cooling to handle volumetric heating from
resistive losses.
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Fabricating the cable
Winding 6-on-1 cable onto spring tube
Drawing outer shell onto cable
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We enjoy taking on difficult challengesCST is
clearly a difficult challenge

• Optimize the trade-offs between cryostability and
  minimum mass
• Develop Nb3Sn conductor with Al stabilizer and
  internal stress management
• Develop coil system that is space-capable

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Coil Geometry

• A key challenge to minimize mass is to manage
  Lorentz stress

ITER
Straight coil segments Pure tension D
windings - forces must be supported by struts
minimum total structure mass
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Cryogenics

• Toroid windings are large, long flow paths.
• Windings must be cryostable (or close to it!)
• Operating parameters Iop current, Top
  temperature, Bop max magnetic field at
  conductor
• Choose parameters so that there is a substantial
  margin ?T
• If a local region of conductor quenches,
  the quench will heal and not
  propagate

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Example for caution the Nb3Sn outsert coil of
the 45 T NHMFL hybrid nearly failed in quench!
14 T Nb3Sn coil, cable-in-conduit Superfluid
cooled, not cryostable Quench initiated in inner
region of coil Local phase transition in
superfluid He boiled dry in quenched
zone Conductor reached temp limit for damage Lost
2 Tesla of field capability The lesson in a
long-geometry coil, it is vital to force
flow That is difficult to do without potential
failure modes in superfluid
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Simulate current transfer, heat transfer in
supercritical flow
Quench heals
Quench heals

Static modeling ignore He flow, examine the fate
of a hot zone as current bypasses through Al,
heat transfers to Al and He. The quench either
heals or propagates.
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Nb3Sn conveys advantages for cryostability, mass
reductionbut how to bond it with Al stabilizer?
3 mm
800 A
1 m dia.

• Wind Cu-stabilized Nb3Sn round strand onto
  1m-dia. spool.
• .Retract rollers, heat treat to form
  superconducting phase.
• Extend rollers, spiral strand off spool, tin with
  solder.
• Apply Al stabilizer from inside, Al MMC
  structural tape from outside.
• Flow solder in 50 cm hot zone.

Conductor never decreases radius during coil
winding never placed in tension after reaction.
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3M has developed a Nextel-Al metal-matrix
composite (MMC)

• Yield strength along fiber run is 1.6 GPa!
• 3M fabricates high-strength parts this way,
• They are about to begin developing a process line
  to make long-run lengths of continuous tape.
• A thin tape of Al MMC could be bonded to the
  outside surface of the conductor integrate
  stress management directly into every turn of the
  coils.

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Assemble and solder reacted strand, stabilizer,
and support tape and solder no strain to strand
Heat compress to solder
Quench cool
Pre-tinned Al MMC structural tape
Completed conductor
Tin strand, Al channel
Reacted Nb3Sn strand (1 m spool)
Pure Al channel (0.8 m spool)
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CST central barrel using pure tension
He supply-return
32 windings attach on inner boundary Roman arch
under symmetric compression
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Inner straight leg of one winding
Helium supply/return are manifolded through side
slots cut through extruded channels
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How much is needed for what level of
radiation shielding?
Consider neutrons reaching the crew
He
Al
Suppose we stored the inventory of liquid He in a
cylindrical layer along then inner boundary of
the toroid. He does 5 times more scattering of
fast neutrons than aluminum, relative to strong
cross-section that produces neutrons. It should
attenuate neutron flux reaching the crew by that
factor.
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What does all this mean for the mass of CST?

• We did one design exercise in which we assumed a
  field integral of 14 Tm, and imposed
  cryostability threshold corresponding to a local
  zone temperature of 15 K (very conservative)
• Mass requirements
• 6 m3 of structure, 12 m3 of stabilizer ? 52 T
• Do we need 15 K stability? Is 10 K enough? M/2
• Do we need 14 Tm bending? Is 7 Tm enough? M/2
• With those changes, total mass is 13 T.
• We need to do the many immense tasks for a
  serious conceptual design before credible mass
  estimates are possible.

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The Texas AM group would like to join AMS to
help with the development of this extension of
the AMS magnet technology for CST

• Stress analysis of coil geometries, optimization
  for minimum mass
• Conductor design for cryostable operation
• Develop fabrication of Al-stabilized,
  MMC-reinforced Nb3Sn conductor
• Heat transfer design for refrigeration
• Particle tracking, radiation dose estimation

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The people of our group

• Leadership Al McInturff
• Peter McIntyre
• Calculations simulations Dior Sattarov
• Technicians Ray Blackburn Tim Elliott
• Bill Henchel
• Andrew Jaisle
• Tool Die Maker Nick Diaczenko
• 2 graduate students, 2 undergraduates

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We have experience working with industry to
develop technology

• In 1984 we developed the worlds longest
  superconducting magnets
• 45 m long 3 T superferric dual dipoles for the
  SSC
• Development was done in partnership with General
  Dynamics.
• After 7 m prototypes in our lab, GD built 4
  full-length dipoles, shipped them San Diego-Texas
• All magnets met specs, all ahead of schedule
• In 1993 we developed the worlds first
  self-shielded high-field MR spectroscopy
  solenoid.
• Development done in partnership with Varian.
• 5 G line at edge of cryostat
• Project was on spec, on schedule.

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The Aggies may not be the last to join your
experiment!
AMS!
MARS
TO JOIN
WANTS