superconducting magnet conceptual design
DESCRIPTION
Space Radiation Superconductive Shield (SR2S) is an EU funded FP7 project which is researching new technology to protect astronauts in space from radiation. On 9th April 2014 in Torino, Italy, SR2S held their first conference to give an update on the project so far. For more information visit: www.sr2s.eu Twitter - @SR2SMarsTRANSCRIPT
Superconducting Magnet Conceptual Design
Riccardo Musenich
April 9th, 2014
Several approaches to magnetic shielding were
proposed:
Large single turn
Solenoids
Toroids
Magnetic lens
Magnetic Shielding
zHabitable Module
r
Solenoidal Shield
Br
Toroidal shield
ei RRRR
NIB <<=
20
πµ
Ideal toroid
Habitable
ModuleBr
Shielding Power of a Toroidal Magnet
i
eR
R R
RNIBdR
e
i
ln∫ ==Ξπ
µ20
Re
Ri
For an ideal toroid, the shielding power is defined as
Shielding Power of a Toroidal Magnet
Ξ=
i
e
R
R
lE
ln0
2
µ
π
−
Ξ−=ie
i
eRR
R
R
lF
11 2
0
2
lnµ
π
Quantities like the stored energy and the inward force
can be written as a function of the shielding power
It allows computing the maximum energy of the
shielded particles:
( )
+
−Ξ−−= 1
1
1
2
0
20
ϕη sincm
qcmEK
Toroidal Shield
Real toroid
Racetrack coils Tilted solenoids
(double helix)
Toroidal Shield
12
21
Toroidal Shield
1
2
21
0 2 4 6 8 10
R [m]
0 2 4 6 8 10
R [m]
Real toroidal magnets
Ripple
(period: 2π/n)
Increasing the number of coils, the amplitude of
azimuthal field oscillation decreases.
The effect of the ripple on the shielding power
is negligible if the n≥12:
( ) 010112 . minmax ≤ΞΞ−→≥n
Real toroidal magnets
To minimize both the fringe field and the
maximum field at the conductor, the magnet
must tend to an ideal toroid:
• Increasing the number of coils
• Increasing the winding aspect
ratio w/d
Shielding
Ξ = 5 Tm
Shielding
Due to the peculiar application a new kind of
conductor is proposed for the SR2S magnet
Conductor
Conductor
MgB2 conductor with welded copper strips.
www.columbussuperconductors.com
Titanium clad MgB2 conductor + aluminum strip
Cross section area = 10 mm2 (15% MgB2, 40% Ti, 45% Al)
Average mass density: 3400 Kg/m3
Operation temperature: 10-15 K
Why MgB2 ?
High stability
No helium cryogenics
Low density (~1/2 respect to YBCO CC)
Conductor
Stability:
Respect to NbTi conductors operating at 1.8 K, a MgB2
conductor operating at 10 K is more stable.
If the temperature margin is 1 K :
AMS conductor (Al stabilized Cu/NbTi)→ ΔH=420 J/m3
SR2S conductor (Al stabilized Ti/MgB2)→ ΔH=2000 J/m3
Conductor
• Winding: pancake coils
• Operative current density: Je=70 A/mm2
the operative current density is referred to the whole
conductor cross section. It is limited in order to protect the
magnet in case of quench.
• Current: I=700 A
• Total current: 46.2 106 A-turns
• Maximum field at the conductor : B=4 T
Magnet
The magnet dimensions are limited by the next heavy launchers
4 launches → Rext=6.3 m 6 launches → Rext=9.5 m
1 launch of a whole magnet → Rext=4.5 m
Launch
MAGNET MAIN PARAMETERS
Current Density
Current per cable
# of turns (per racetrack) 55
# of layers (per racetrack) 10
# of Racetracks 120
Bending Power 7.51 Tm
Bmax over conductor 3.7 T
Stored Energy 953 MJ
Inductance 3890 H
Magnetic Parameters
The magnet will operate in persistent mode
Superconducting joints between MgB2 cables already developed
Magnet sectors assembled in orbit → resisNve joints
High inductance
negligible
Decay time: 45 years
2 year mission → ΔΞ/Ξ< 0.05
Magnetic Field Stability
01
=+++
∑ nc
n
cj j I
IRIR
dt
dIL
nn
cII 1+
Inward forces
Intra-coil forces
Forces and torques
−
Ξ−=ie
i
eRR
R
R
lF
11 2
0
2
lnµ
π
Any asymmetry due to mis-positioning or non
uniform current distribution (short in case of
quench) generates forces and torques on the
coils
Forces and torques
Forces and torques
FORCES AND TORQUES PER RACETRACKS
Radial Forces on the inner bar -3.36 MN
Radial Forces on the outer bar 1.56 MN
Difference acting on the inner
cylinder
-1.80 MN
Axial Force on the outer arc 0.20 MN
Axial Force on the inner arc 0.36 MN
Axial Force on the arcs bar 0.88 MN
MAX Torque if one racetrack is
off
6.94 MNm
* referred to 120 coils , “4 launches” configuration
*
Internal structure to hold the inward forces
Mechanical Structure
Hypothesis of mechanical structure
Tie rods to hold the coil internal forces
A structure connecting the coils is required to support torques
The magnet system is weakly connected to the habitat. The tie rods have to
support only the forces due to the spacecraft acceleration.
The use of advanced materials will be studied:
Cermets (Al - Boron carbide)
Carbon fibers (tensile strength up to 1000 GPa)
Aramid fibers
Foams
Mechanical Structure: What Next?
Deep space offers favourable conditions to cryogenics
(low temperature and low pressure)
Then main heat load comes from the habitat through radiation
Absence of gravity and weak accelerations → low heat conduction
Cryocoolers can provide the required power
Solid hydrogen could be used as enthalpy reservoir
Due to the large magnet dimension, heat connections are the
most important components to be developed
Cryogenics
Quench
Comparison between the ATLAS and the SR2S barrel toroids
ATLAS SR2S
Stored energy [MJ] 1000 950
Inductance [H] 5.12 3890
Je [A/mm2] 30 70
JAl [A/mm2] 32 233
I [A] 20500 700
Conductor mass [tons] 100 36.3
E/m [kJ/kg] 10 26
Active quench protection is required
Coil subdivision can be a possible option to
improve the protection
Quench
The SR2S magnet is a modular superconducting
toroidal system based on a cutting edge conductor.
Due to the new conductor, the ligth mechanical
structure and the high energy density, the SR2S
magnet is well beyond the state of the art.
Its peculiar application demands for advanced
materials and for innovative solutions in the field of
magnet technology.
Conclusions
THE END
Slide di riserva
Magnetic flux density of an ideal toroid:
Bending power:
Lorentz forces acting on the particle:
Slide di riserva
In order to know if a particle is deflected inside the magnet, we need to find the
minimum of the trajectory along r, i.e. the radius rm corresponding to the particle
maximum penetration, imposing
In the particular case of a particle
moving on a z-r plan:
( )( ) 22 vrvmtm
≤− ϑϑ&
&
( )( ) mm
e
m
e
m rrr
r
r
r≥→≤ ϑ
ϑ&
&
lnln
Slide di riserva
Particles moving on a z-r plan are the most penetrating
Analytical solution ( ) for rm and bending power Ξ:
The bending power can be written as a function of the properties of
the incoming particle:
Cut-off energy:
( )ϕγ sin−−=Ξ 1120 cq
m
( )
+
−Ξ−−= 1
1
1
2
0
20
ϕη sincm
qcmK