1. 19./20. September 2007 Current leads for FAIR Cryogenic Expert Meeting 19./20. September 2007 Birgit Weckenmann

2. 19./20. September 2007 1. Design options for current leads 2. Current leads needed for FAIR 3. HTS leads in LHC at CERN 4. Cooling of HTS leads 5. Adaptation of CERN leads for FAIR Overview

3. 19./20. September 2007 Conventional vs. HTS leads metal LHe 4.4K He gas 300K + reduction of cryogenic losses (~2.5 W/kA in DC operation) + simple (standard) design + no quench protection + no additional instrumentation and control Resistive design HTS design metal HTS LHe 4.4K He gas 50K He gas 300K

4. 19./20. September 2007 Low-current leads Possible saving in cooling power by using HTS: 1500W => considering the large number of leads no benefit of that design MagnetsCurrent [A]Number of pairs SuperFRS dipoles~20028 SuperFRS quadrupoles~30068 Correctors/ Steerers50 ÷ 300503 Total599 Conventional leads are chosen for all low current circuits with I max ≤ 300A Resistive leads are available in optimized design for several currents and can be purchased (Mark & Wedell, American Magnetics)

5. 19./20. September 2007 High-current leads Saving in cooling power: 3700W => 87% reduction compared to resistive option => 15% of total cryogenic load of FAIR HTS leads are chosen for all high current circuits with I max ≥ 300A MagnetsCurrent [A]Number of pairs SIS300 dipoles89247 SIS300 quadrupoles783025 SIS100 dipoles6600/130007 SIS100 quadrupoles463011 Total50 Adaptation of current lead design of LHC in collaboration with A. Ballarino (CERN)

6. 19./20. September 2007 LHC current leads Resistive part: copper heat exchanger convection-cooled by forced flow of helium gas at 20K HTS part: Stacks of BSCCO-2223 tapes soldered on SS tube conduction-cooled by liquid helium bath at 4.4K 13000A type: optimized for DC current of 13000A 6000A type: covering currents ranging from 3900A to 6900A

7. 19./20. September 2007 Cooling conditions (mass flow rate in pulsed operation will probably be lower) FAIR HTS leads LHC: Cooling of resistive part with 20K Helium gas => HTS at 50K => m = 0.045 g/(s kA) FAIR: Cooling with gas at 50K results in a higher temperature of the HTS and a higher mass flow rate => HTS at 60K => m = 0.065 g/(s kA)

8. 19./20. September 2007 Adaptation of LHC design for FAIR leads Planned tests of CERN leads at ENEA (Italy) to prove the applicability of the LHC design to FAIR with 6000A type and 13000A type LHC leads provided by CERN - Redesign of the heat exchanger (diameter) - Variation of HTS stacks (number) Expected modifications: 1. Test: Stable operation under changed cooling conditions => Cooling of the resistive part with 50K gas DC operation at all currents required by FAIR magnets 2. Test: Stable operation and quench behaviour in pulsed mode => 10 triangular cycles increasing ramp rate and current step by step

9. 19./20. September 2007 SIS100/SIS300 leads One or more designs for FAIR leads? Current range SIS 100: 4600A to 6600A SIS 300: 7900A to 9000A Connection HTS to LTS SIS 100: Nuclotron conductor => adapter or change from bath to indirect cooling (???) SIS 300: Rutherford cable => CERN design => Two different designs may be reasonable

10. 19./20. September 2007