Prototyping of Superconducting Magnets for RAON ECR IS S. J. Choi Institute for Basic Science S. J. Choi Institute for Basic Science

Contents  Overview of superconducting magnet and ECR ion source  Design result of superconducting magnet for RISP ECR ion source  Analysis results  Fabrication & Experiment of Prototype hexapole magnet in Lhe

Material Design Manufacturing Cryogenics Protection Superconducting magnet Material : superconducting wire (minimum quench energy, maximum temperature when a quench occurs, etc), magnet bobbin Design : design constraint, electrical configuration, stress analysis, quench analysis Manufacturing : winding, impregnation, current lead, superconducting joint Cryogenics : stability, test in LHe, operating process Protection : detection & protection method, current lead protection, protection from x-ray head load, Technologies for Superconducting magnet

ECR Ion Source Plasma device to produce intense highly charged ion beams. Plasma is produced and heated by microwave. Plasma is confined by minimum B structure. (Solenoids + hexapole) To produce highly charged or high current ion beams need high n e (electron density) and long τ ion (ion confinement time) ➔ high ω RF ➔ high B-field 28 GHz ECRIS needs Superconducting magnets.

Design Concept B ext ~2.2B ecr B inj ~3.5B ecr G. Ciavola et al, RSI 63(1992)2881 Absorption powerResonance surface B min ~0.8B ecr B inj >3.5B ecr, B ext ~2B ecr, B r ~2B ecr, B min ~0.8B ecr  B min Effect  B inj & B ext Effect

Superconducting wire Considering the critical current, lower Cu-ratio is better! Considering the MQE, higher Cu-ratio is better! MQE : minimum quench energy The reason why the superconducting wire for ECR ion source must have more cu ratio considering the MQE  Manufacture difficulty of saddle or racetrack magnet  Heat load by wire movement  X-ray heat load Cu over SC ratio : 3  stability Wire dimension : 1.43(width)*0.98(thickness)  operating current The superconducting magnet will be designed using this wire.

Design of superconducting magnet -Racetrack type or saddle type -The saddle type has more strengths than racetrack type, but the feasibility of saddle type must be verified -We have a experiment schedule of racetrack and saddle. -With the experiment results, the hexapole type will be determined. The type of hexapole magnet

In case of saddle type, it is better than racetrack type. - Wind more turns by about 20 %. - More radial magnetic field by about 20 % with same turns. - Smaller maximum magnetic field (saddle type = 5.45 T, racetrack type = 5.74 T) Saddle type has clearly more advantages than racetrack type. However, can we realize the saddle type? Hexapole magnet

Design of superconducting magnet - Each research group has the different number of solenoid magnet. ( Riken = 6, VENUS =3) -As the number of solenoid magnet increase, more point can be controlled and better in terms of beam line. But the feasibility of superconducting magnet is decreased. -If the flat magnetic field at the middle point is the basic essential, the minimum number of solenoid magnet is 5. However, if the flat magnetic field is related with not the basic essential but efficiency, I try to reduce the number of solenoid. The number of solenoid magnet

Solenoid magnet The number of solenoid 2 : mirror magnetic field 3 : B min control 4 : B ECR length control & B min control 5 : flat magnetic field in the middle area 6 : more control point The use of more number of solenoid would allow more flexibility to modify the axial gradient in the center of the ECR zone. On the other hand, it makes the superconducting coil and the cryostat design more costly and complicated, which increases the overall risk. Training effect, by its nature, makes pre-estimating difficult. As the number of solenoid magnet increase, it is more difficult the fabrication and operation of superconducting magnet. The number of solenoidBeam line Superconducting magnet designer

Design result Solenoidsol1sol2sol3sol4hexapole Axial position of center (mm) Inner radius (mm) Depth (mm) Width (mm) Conductor size (mm)1.43*0.98 Cu/NbTi ratio33333 Turns/coil Design Current (A) Wire length (km) km/per 1coil The design is composed of 4 solenoid and racetrack hexapole magnet. This design results will be subject to the experimental results.

Design result B inj >3.5B ecr, B ext ~2B ecr, B r ~2B ecr, B min ~0.8B ecr Boundary condition : Design result : B inj = 3.61 T, B ext = 2.07 T, B r = 2.17 B ecr, B min = T

Analysis result (Magnetic shield) Magnetic shield works that the inner magnetic field increase and the outer magnetic field decrease.

Analysis result (Iron yoke) Radial magnetic field (at 75 mm from the center) Without Iron yoke = 2.17 T With Iron yoke = 2.33 T

Analysis result (Quench & protection) 0.1 s 0.3 s 1 s 3 s

Analysis result (Force analysis) ForceTorque XYZMagnitudeXYZ Solenoid 1 (injection part) Solenoid Solenoid Solenoid 4 (extraction part) Sextupole Sextupole Sextupole Sextupole Sextupole Sextupole

Prototype hexapole magnet experiment in LHe Superconducting magnet for ECR ion source -Solenoid ( axial magnetic field ) -Hexapole ( radial magnetic field ) Purpose of experiment -The hexapole magnet types can be the racetrack type or saddle type. -The hexapole magnet has more manufacture difficulty than the solenoid magnet, and then, the saddle type has more manufacture difficulty than the racetrack type. The arrangement winding of saddle type is very difficult by its characteristics. -Verification for the feasibility of saddle type superconducting magnet.

Prototype hexapole magnet experiment (saddle type) This prototype hexapole magnet is fabricated with our retained wire (1.9*1 mm), so the target current is different with the previous design results. The target current of hexapole magnet using our retained wire is 417 A after assembly full magnet.

Prototype hexapole magnet experiment (saddle type)

1 st quench : Quench current = 381 A, Total number of quench is 7. They show the “training effect”. 7 th quench : Quench current = 480 A,

Prototype hexapole magnet (saddle type) When 1 st quench occurs : Maximum magnetic field = 5.5 T Quench current(measured) = 381 A Wire Ic = 1000 A at 5.5 T Quench current/wire Ic = 38.1 % When 7 th quench occurs : Maximum magnetic field = 6.92 T Quench current(measured) = 480 A Wire Ic = 740 A at 6.92 T Quench current/wire Ic = 64.8 % Target current = 413 A at 7.6 T

Prototype hexapole magnet (saddle type) After assembly all magnet including the solenoid magnet, the maximum magnetic field is 7.6 T on the hexapole magnet By calculating from 1 st quench : Quench current(measured)/wire Ic = 38.1 % Wire Ic at 7.6 T : 610 A After assembly, Quench current (estimated) = 610*0.381 = 232 A By calculating from 7 th quench : Quench current(measured)/wire Ic = 64.8 % Wire Ic at 7.6 T : 610 A After assembly, Quench current (estimated)= 610*0.648 = 395 A Even if 7 th quench condition, the estimated quench current is below the target current 413 A. Experimental results show that saddle type is needed to make improvement.

Prototype hexapole magnet (racetrack type)

ECR ion source schedule