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

The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China Outline Introduction to SECRAL Test Experiment and analysis Simulations and possible solutions Conclusion 2014-8-13 The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China

Superconducting ECRis at Lanzhou (SECRAL) Magnetic confinement configuration: SECRAL Superconducting magnet structure. Solenoids-inside-sextupole 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 S-Forward SECRAL schematic view and the axial magnetic field distribution. 2014-8-13 The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China

Expected Beam Properties From SECRAL 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 Analyzing beam line Layout of the multi-component ion beam transport line. 2014-8-13 The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China

The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China Testing Condition Beam: 209Xe29+; Extraction voltage: 25 kV; Load current: I0=0.95 emA; Beam current: I29+~19 emA 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 2014-8-13 The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China

Transversal Coupling Property Measured beam rms emittances by changing the focusing strength of the solenoid. (“H” horizontal, “V” vertical; “F” forward, “R” reverse.) 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 Product of projection emittances for different solenoid currents and polarities. 2014-8-13 The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China

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

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

Periodic Property of The Coupling 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 Exchange of transverse emittances The coupled beam from ECR ion source is decoupled periodically by the solenoid lens! Brs=0.0479 Tm Sol-L=0.15 m 450 A+180 A ~1T*0.15 m 2014-8-13 The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China

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

Possible Solution to Overcome the Deficiency For 1st solenoid section, S1  S1 + F + D, or S1  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  2014-8-13 The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China

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% 2014-8-13 The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China

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

Space Charge Induced Emittance Increasing 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! S.Y. Lee 2014-8-13 The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China

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

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 (emA) Voltage of pre-buncher (V) r300mm r700mm extraction 2014-8-13 The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China

The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China Conclusion 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 2014-8-13 The 12th Symposium on Accelerator Physics, Yuzhong, Gansu, China

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