HTS Magnets for ARIES-AT L. Bromberg J.H. Schultz MIT Plasma Science and Fusion Center ARIES Meeting March 20, 2000

HTS for ARIES AT Proposed arrangement Input for ASC Costs

HTS for ARIES AT (YBCO) For TF coils: Epitaxial techniques for depositing thick films on structural plates/shells For PF coils Epitaxial techniques for thick films on pancakes

Current density in YBCO If field is parallel to plate, the cross section utilization by HTS is very small (due to very high current density) If field is perpendicular to plate, the HTS may have to be cooled to temperatures lower than 70 K (pumped liquid nitrogen) Choices of coolant severely limited High pressure He? Cross sectional area comparable than that for Nb3Sn (without stabilizer): ~ 2-4 %

YBCO Current density (B||c)

TF and PF coil Advantageous to build coils with field parallel to tape For TF coil, build coils with shell-type structure, adopted by ARIES 2-4, ARIES 3, PULSAR and ARIES-RS For PF coils, option of either pancake or layer wound coils.

Magnet (TF or PF) construction Epitaxial YBCO films

BSCCO 2212 layered pancakes on silver (L. Bromberg, MIT, 1997)

PF construction with YBCO thick films

HTS magnets for ARIES-AT Structural considerations Cross section in ARIES-AT TF and PF magnets dominated by structure No stabilizer/quench protection, little insulation, small amounts of coolant. 85% of cross section can be structure (vs 70% for ARIES RS) For PF magnets: j ave B z R ~ 700 MPa (j ave : average current density in PF, B z vertical field in PF, R: average radius of coil) For TF magnets:  R TF ~ 0.4 B o 2 R o ln (R out /R in ) / 2  o 

HTS: strain Maximum strain in HTS is similar to that of LTS 0.2% HTS is in intimate contact with structure (as opposed as Cable-In- Conduit-Conductor, CICC) Steels have E ~ 200 GPa 0.2% strain results in only 400 MPa, as opposed to assumed stress in structure (I.e., due to strain limitations, stress in structure could be reduced by a factor of 2!) A possible solution is to manufacture HTS so that it is in compression (-0.2% strain) when cold and unloaded With 800 MPa in the structure, strain in HTS is 0.2%

BSCCO HTS BSSCO HTS superconductor has high fraction of silver Present day-cost is high, compared with LTS Silver use needs to be decreased for fusion applications Cost Activation (Layla: say something)

HTS magnet costs: YBCO epitaxial Rapid prototyping manufacturing method HTS material is inexpensive, $200/kg. Inexpensive manufacture would consist on layering HTS on structural plates with minimal winding! Largest cost of LTS magnets is cabling/insulating, winding. Superconductor volume allocation: less than 1% of structure If HTS at $1000/kg, and cost of structure is $40/kg, then cost of magnet is ~ $50/kg