1.     Abstract ID : Thu-Af-Po4.01
A Study on the Sextupole Design with Iron Yoke inside Solenoids for 56 GHz ECR Ion Sources
Shaoqing Weia, Zhan Zhanga, Sangjin Leeb
aChina Three Gorges University, Hubei, China bUiduk University, Gyeongju, South Korea
(a)
Introduction
The sextupole with the short iron core has less Lorentz force at the end of the sextupole and a lower volume iron core.
Considering the Lorentz force at the sextupole ends and the characteristic of Nb3Sn, the iron yoke was added around the sextupole based on the short iron core sextupole. A design of sextupole, iron yoke sextupole inside solenoids, was presented.
The short iron yoke sextupole has larger safety margin and less coil material than the short iron core sextupole. Therefore, the sextupole with short iron yoke structure is suggested for 56 GHz ECRIS.
The Nb3Sn wire, which can generate fields in the 10–20 T range, is considered to construct the magnet coils to analyze the sextupole for 56 GHz electron cyclotron resonance ion source (ECRIS) in this study.
For 56 GHz ECRIS [1]
Presently，there are two kinds of arrangement for ECR ion source which have been operated in the world [2-3]. The parameters definition for solenoids and sextupole are shown in Fig. 1 (a), (b). According to the confinement fields, the predesigned models for the two structures were shown in Fig. 1 (c), (d).
By analysis, the maximum magnetic field Bmax in coils for the two structures was shown in Table I. Bmax in coils for solenoid-in-sextupole is beyond the capability of Nb3Sn in this study. Therefore, sextupole-in-solenoid was selected for 56 GHz ECRIS.
The gap between solenoids and sextupole has
no or little effect on the Bmax in sextupole.
Iron core was added in the center of sextupole. The length of iron core can be decided by the 2BECR surface in z direction z1 and z2 [1]. The total Lotentz force at the end of sextupole FEρ was calculated in ECRIS, as shown in Table III [4].
Air core sextupole
Long iron core sextupole
Short iron core sextupole
(b)
Table. III. Comparison of FEρ
(1)
Nb3Sn
sextupole
FEρ (kN) [-z]
FEρ (kN) [+z]
1st coil
2nd coil
2nd coil
Air core
-58.0
64.4
48.4
-42.4
Long iron core
-56.3
60.0
45.1
-41.7
Short iron core
-51.8
56.5
42.7
-38.1
Bmax
where BECR is the magnetic field in tesla for resonance, f is frequency of microwave in GHz. Binj is axial magnetic flux density at injection part, Bext is axial magnetic flux density at extraction part, Br is radial magnetic flux density at plasma chamber wall, Bmin is minimum axial magnetic flux density.
Fig. 3. Load lines for Nb3Sn sextupoles
Analysis of two Structures
Table IV. Comparison results of Nb3Sn sextupoles
Nb3Sn
sextupole
Iop
(A)
Bmax
(T)
Safety margin
(%)
Vsextupole
(×106 mm3)
Iron weight
(kg)
Air core
520
10.84
28.5
35.4
Long iron core
460
9.94
78.2
Short iron core
10.25
33.8
30.3
Long iron yoke
415
10.00
36.4
531.4
Short iron yoke
10.19
35.6
15.4
252.5
(a)
(b)
(c)
(d)
The iron yoke can provide a structure for the sextupole and can clamp down the sextupole coil. Therefore, the length of sextupole can also be decided by the 2BECR surface in z direction z1 and z2.
Fig. 1. ECR ion sources. (a) Parameters of solenoids. (b) Parameters of sextupole.
(c) Sextupole-in-solenoid structure. (d) Solenoid-in-sextupole structure.
Table I. Bmax in coils for two structures
Item
Sextupole-in-solenoid
Solenoid-in-sextupole
Location of Bmax in coil
sextupole straight part
sextupole end corner part
Bmax in sextupole
10.83 T
27.55 T
Bmax in solenoid
8.88 T
14.19 T
(a)
(b)
Long iron
yoke sextupole
Short iron
yoke sextupole z1 z2
(c)
(d)
Gap = 10 mm
Gap = 100 mm
Fig. 4. Sextupoles with iron yoke: (a) Models. (b) Effect of iron yoke. (c) Bmax in sextupole
(d) Load line analysis.
Conclusion
By the analysis of sextupole-in-solenoid structure and solenoid-in-sextupole structure for ECRIS, sextupole-in-solenoid structure was selected for 56 GHz ECRIS.
Considering the Lorentz force at the sextupole ends, the design of sextupole with short iron yoke was presented in this paper. BY comparing with several sextupoles, the design of sextupole with short iron yoke was suggested for 56 GHz ECRIS.
Fig. 2. Effect of gap for sextupole-in-solenoid structure
With the fixed confinement fields from solenoids, Bmax in the same sextupole is almost fixed with respect to the gap between the magnets. Thus, the same solenoids will be used in the sextupole design.
The values of Binj, Bmin and Bext from solenoids are equal to 7.22 T, 1.33 T, and 4.22 T, respectively.
Table II. Parameters of solenoids
Parameters
Values
ai (mm)
[ ]
ao (mm)
[ ]
bl (mm)
[ ]
bu (mm)
[ ]
Iop (A)
440
Reference
[1] Claude M. Lyneis, D. Leitner, D. S. Todd, G. Sabbi, S. Prestemon, S. Caspi, and P. Ferracin, “Fourth generation electron cyclotron resonance ion sources,” Review of scientific instrument, Vol. 79, 2008.
[2] C. Lyneis, D. Leitner, M. Leitner, C. Taylor, and S. Abbott, “The third generation superconducting 28 GHz electron cyclotron resonance ion source VENUS,” Rev. Sc.i Instrum., Vol.81, 2010.
[3] W. Lu, X. Z. Zhang , H. W. Zhao et al., “Operation status of SECRAL at IMP,” Proceedings of IPAC2011, San Sebastián, Spain
[4] Shaoqing Wei, Zhan Zhang, Sangjin Lee, and Sukjin Choi, “A study on the design of hexapole in an 18-GHz ECR ion source for heavy ion accelerators,” Progress in Superconductivity and Cryogenics Vol.18, No.2, pp. 25~29, 2016.
Design of Sextupole