1. 2014-8-13The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China1 Study of Beam Properties at SECRAL and The Solenoid Pre-focusing LEBT Youjin Yuan Institute of Modern Physics, CAS

2. 2014-8-13The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China2Outline 1.Introduction to SECRAL 2.Test Experiment and analysis 3.Simulations and possible solutions 4.Conclusion

3. 2014-8-13The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China3 The magnetic confinement fields are typically achieved by the superposition of an axial mirror field and a radial sextupole field. Achieved axial field: 3.7 T, 2.2 T Sextupole at the wall: 2.0 T Solenoids-inside-sextupole SECRAL schematic view and the axial magnetic field distribution. SECRAL Superconducting magnet structure. Superconducting ECRis at Lanzhou (SECRAL) Magnetic confinement configuration: S-Forward

4. 2014-8-13The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China4 Asymmetric plasma distribution at extraction.  Inhomogeneous ion density distribution across the extraction aperture. Particles are extracted and accelerated in a strong descending axial magnetic field.  Transversal coupled beam. Sputter marks at the inner side of the plasma electrode Layout of the multi-component ion beam transport line. Expected Beam Properties From SECRAL Analyzing beam line

5. 2014-8-13The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China5 Testing Condition Beam: 209 Xe 29+ ; Extraction voltage: 25 kV; Load current: I 0 =0.95 emA; Beam current: I 29+ ~19 e  A To study beam properties neglecting space charge effects: Minimizing the total beam current in the mixing beam transmission line. Using a low beam current. Relatively high extraction voltage. High transmission efficiency before emittance measurement

6. 2014-8-13The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China6 Transversal Coupling Property Measured beam rms emittances by changing the focusing strength of the solenoid. (“H” horizontal, “V” vertical; “F” forward, “R” reverse.) Product of projection emittances for different solenoid currents and polarities.  The difference of projection emittances product mean that the ion beam extracted from the ECR ion source is transverse coupled!  And the extracted beam is not a “round beam”! (same phase space distribution)  When the product of projection emittances reaches minimum value, equal to the determinant of the 4D sigma matrix, the beam can be considered as “decoupled”. Assume decoupled

7. 2014-8-13The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China7 Simulated projections of phase space distribution of beam from ECR at the location before the beam line solenoid. Back-tracking from measured beam parameters under Is= -180 A, assuming no coupling. Beam emittances from forward beam-tracking simulation by using the 4-D phase space distribution as the initial beam condition. Projections of 4-D Phase Space (No SC effect) xx yy At SECRAL Exit After Analyzing Measurements after Analyzing Back-tracking

8. 2014-8-13The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China8 Transfer Matrix of Solenoid RotationFocusing When  x,y plane exchange One solenoid is not sufficient to provide required strengths for both focusing and coupling! Symmetry for both x and y plane.

9. 2014-8-13The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China9 The coupled beam from ECR ion source is decoupled periodically by the solenoid lens! Simulation using the coupled beam as the initial beam. The ion beam transmits only through the solenoid lens, but not the analyzing magnet.  the beam emittance values are somewhat larger. -180A -2870Gs 450A 7160Gs Periodic Property of The Coupling Exchange of transverse emittances B  s =0.0479 Tm Sol-L=0.15 m 450 A+180 A ~1T*0.15 m

10. 2014-8-13The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China10 Layout of LEBT of SFC (Spiral Focusing Cyclotron) Solenoids Deficiency: 3 focusing solenoids used, but coupling effects are not considered!

11. 2014-8-13The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China11 Possible Solution to Overcome the Deficiency For 1st solenoid section, 1.S 1  S 1 + F + D, or 2.S 1  to decouple the phase space and provide required focusing For 2nd and 3rd solenoid sections, make the solenoids with different field direction but similar focusing strength SBBSB 

12. 2014-8-13The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China12 Test Experiment for Upgrading of the LEBT The first S section: The strength is larger than required for decoupling The rear part is modified: Without consideration of SFC efficiency, LEBT efficiency can easily reach ~100%

13. 2014-8-13The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China13 Efficiency Increase of SFC Overall efficiency of SFC is almost doubled, and for LEBT increased by ~20%. After analyzing Before injectionExtracted

14. 2014-8-13The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China14 Space Charge Induced Emittance Increasing S.Y. Lee z x Is not for beam with skewed ellipse cross section! For a symmetry “round” beam, space charge effect can be taken as defocusing lens, will keep emittance!

15. 2014-8-13The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China15 Space Charge Induced Emittance Increasing xx yy  Transfer of high intensity beam with coupled phase space will increase the emittances  The space charge effect is strong before analyzing at LEBT

16. 2014-8-13The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China16 Other Information about Efficiency of SFC In addition to the solenoids mentioned above, the final solenoid-train and the spiral inflector before injection into SFC will be considered later The voltage of pre-buncher is insufficient, it’s increase will be beneficial to efficiency of SFC. I (e  A) Voltage of pre-buncher (V) r300mm r700mm extraction

17. 2014-8-13The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China17Conclusion The beam with coupled transversal phase space and solenoid focusing makes transfer study complicated To fully utilize the powerful SECRAL, careful and deep study of LEBT and matching to SFC is necessary The modification of LEBT is easy and will contribute to dramatic increasing of SFC efficiency

18. 2014-8-13The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China18 Thanks for Your Attention!