Work Supported by the US Department of Energy

1. Material Material Material Operation Temp. [K] Tc [K] Tc [K] Op. Temp. [K] Theoretical Limit Eacc [MV/m] GL Parameter GL Hc [Oe] Hc1 [Oe] Hc2 [Oe] Hsh [Oe] Nb (0K) 9.2 0.78 2000 1700 2400 2400 Nb Nb 9.2 4 4 49 1 Nb3Sn (0K) 18.2 22.8 5350 520 173000 4010 Nb3Sn Nb3Sn 4 18.2 4 95 0.0195 MgB2 (4 K) 39 36.3 4290 300 220000 3210 MgB2 MgB2 39 4 4 80 0.00000217 MgB2 (20 K) 39 25.4 2780 250 100000 2090 MgB2 MgB2 20 39 20 52 0.369 Possibility of MgB2 Application to Superconducting Cavities Work Supported by the US Department of Energy Tsuyoshi Tajima, Los Alamos, NM 87545, USA Background and Summary Effect of operating temperature on the BCS resistance. Energy gap 2/kBTc = 3.5 is assumed for all the materials. The numbers in the last column are normalized by the number for Nb operated at 4 K. • Magnesium diboride (MgB2) was discovered to show a transition temperature at ~39 K in early 2001 • Studies have shown that this is a conventional BCS superconductor with absence of weak links, which makes it promising for applications to cavities • Calculations show that MgB2 has 63 % higher theoretical limit (Eacc = 80 MV/m) than Nb at 4 K and has a limit of 52 MV/m even at 20 K, and a potential for higher Q0 due to its higher Tc. • A possible method of making a MgB2 cavity using the hot isostatic press (HIP) technique is proposed Relationships between Hc, Hc1, Hc2 and GL A Concept for Making a MgB2-Layered Copper Cavity with the HIP technique Hc: Thermodynamic critical magnetic field Hc1: Lower critical magnetic field Hc2: Upper critical magnetic field Hsh: Superheating critical magnetic field GL: Ginzburg-Landau parameter, GL = L/0 L: London’s penetration depth 0: Coherence length Process • Fill the gap of two copper pipes with MgB2 powder under vacuum (10-2 Torr) • Attach this subassembly into two dies under vacuum and weld (seal) two pipes and dies at the top and bottom • Put this module in a HIP furnace and carry out a HIP in an optimum condition, e.g., at 200 MPa and 1000 °C for 200 minutes. A bulk-quality MgB2 layer is formed on copper • Remove the dies • Remove the inner copper layer with a chemical, e.g., HF, or machine it off • Weld flanges on the end pipes Critical fields for Nb, Nb3Sn and MgB2. The superheating field Hsh was calculated for Nb from Hsh = 1.2 Hc (GL ~1) and for Nb3Sn and MgB2 from Hsh = 0.75 Hc (GL >> 1) Theoretical limit of accelerating field in the case of Hpeak/Eacc= 40 Oe/(MV/m)