e821 sc inflector and beyond wuzheng meng ([email protected]) 12 june 2008
TRANSCRIPT
I. Design Constrains – a brief history• E821 (originally) proposed a pulsed inflector . R&D was performed up to
late 1989 (g-2 note No.32).
• DC SC inflector was proposed in 1988 (g-2 note No.25), and finally approved by collaboration in late 1990 (or early 1991?).
• By that time, the design of the storage ring magnet was almost completed (cross-section and conductor type), except some controversial shimming methods.
E821 SC inflector final design had to fit this pre-defined limited space.
Down-stream –
Vertical limit: storage ring magnet gap (180 mm) Horizontal: must as close as possible to the muon storage center (77 mm)
Up-stream ---
Limited in radial direction, by storage ring outer coil cryostat
Could we make it shorter?
Could we make it curved, so that Leff could be longer?
By
S
In order to cancel 2.55 T-mFringe field from storage ring,
Bo = 1.5 T and L= 1.7 mare comfortable for a low Tc NbTi SC septum magnet
----- We did not feel comfortable about Lorentz force constrains (in the inner side)
II. Design Principle – truncated double cosθ Single cosθ distribution (R. Beth, BNL AADD-102,1966)
“Field Produced by Cylindrical Current Arrays”
K1cosθ
Double cosθ Distribution and Truncation along Vector-potential lines --- Frank Krienen (NIM A283(1989)5)
K1cosθ
-K2cosθ
Conductor -- Astromag/g2Inf
Configuration (NbTi:Cu:Al): 1: 0.9: 3.7
Processor: Co-extrusion
NbTi/Cu composite: diameter 1.6 mm (monolith)
NbTi Finament: diameter 0.02 mm
Twist pitch: 31 mmConductor dimension: 2 x 3 mm (bare); 2.3 x 3.3 mm (insulated)
Critical current density Jc > 2500 A/mm2 @ 5 T, 4.2 K
Stabilizer purl Al: 99.997%; RRR=750
NbTi area = 1.06 mm2
Prof. Akira Yamamoto (KEK)and Tokin Co.
Cold mass: 60 kgCooling power: 11 W Stored energy: ~9000 J
Inductance: 0.002 H
Conductor positions were modified to avoid technical difficulties
III. Choices of Ends –
Open-end Closed-end
Based upon following arguments, E821 chose Closed End (July 1991):
(1) Easier for fabrication, force constrains (large quench margin);
(2) Physical dimension is shorter;
(3) Smaller integral fringe field (~1/6)
Although closed-end has disadvantage –
Less muons (~ 1/1.44) are injected and stored due to Multiple scatterings through materials (11mm Al; 0.8mm NbTi; 0.8mm Cu): ---- 20 turn (x2 layer) conductors; ---- coil caps; ---- windows on the mandrel and cryostat
IV. Fringe Field Issues –Sources of fringe field: (a) continue current distribution is replaced by discrete individual conductor winding; (b) end effect (principle is based on 2d potential theroy)
Consequence of fringe field: Total integrated fringe field (~7ppm); peak field (in storage region) >200 Gauss and high gradients are beyond stable range of NMR probes. Special regional measurements introduce additional systematical errors (0.2 ppm) .
Magneto-static shimming did not work!SC shield is the solution!
Superconductivity -- (T<Tc; J< Jc; B<Bc)
(1) Zero Electric Resistivity
(2) Diamagnetism
Type I Type II κ = λ(T)/ξ(T) < 1/ κ = λ(T)/ξ(T) > 1/ Pure state (H < Hc) Mixed state (Hc1< H < Hc2) Meissner effect “Perfect conductor” Can tolerate low flux density Can tolerate high flux density No use for magnets Good for magnets and flux shields
λ(T) --- magnetic penetration depthξ(T) --- coherence length
κ ---- Ginzburg-Landau parameter
22
Type I SC Type I SCType II SC Type II SC
T = 300 K T = 300 K
T = 4 K T = 4 K
Figure from W. H. Warnes: “Principles of Superconductivity” (Red Text added by W. Meng)
B = 0
B = Ba
Ba = 0 Ba = 0
B = Ba
Multilayer SC Sheet
Nippon Steel CorporationAdvanced Technology Research Lab
Dr. Ikuo Itoh
Jc > 1200 A/mm2
@1.5 T, 4.2 K, H NbTi layer B = μ0Jc d
(d = Total thickness of NbTi layers)
Working Procedure --
Main magnet poweredFlux penetrating
Inflector stays “warm”Un-powered
Main magnet stable
Cool down inflector Main flux are trapped
by the SC shield
10 K 4.6 K 4.6 K
(1) (2) (3)
Power Inflector slowly(Io 2850 A; 2 A/sec)Main flux are trapped
Fringe flux are blockedby the SC shield
V. Possible Modification & Improvement–
Open both ends:
Prof. Akira Yamamoto & Tokin Co Contributions – 1 prototype (L=0.5 m) and 2 full length (1.7 m) SC inflectors
Prototype was tested up to 3057 A In KEK (with zero external field)
Prototype was tested up to 3000 A In BNL with Ba=1.45 T
(inside 18D72 magnet)
Figure from Tokin Technical Review No.20
March 1993 July 1994
Encouraged facts –
Open-end has been tested in the external field. SC performance was very stable.
Open-end gives additional magnetic field along beam axis.
(further detailed study is needed)
Although open-end gives more integral fringe field (x 6); peak field on inflector cold surface is estimated ~ 0.1 T.
Existing SC sheet has enough shielding capability (0.23 T).