Work Supported by the

1
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 Londons penetration depth ?0
Coherence length
Process

1. Fill the gap of two copper pipes with MgB2 powder
   under vacuum (?10-2 Torr)
2. Attach this subassembly into two dies under
   vacuum and weld (seal) two pipes and dies at the
   top and bottom
3. 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
4. Remove the dies
5. Remove the inner copper layer with a chemical,
   e.g., HF, or machine it off
6. 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 gtgt 1)
Theoretical limit of accelerating field in the
case of Hpeak/Eacc 40 Oe/(MV/m)