Studies of beam quality preservation during recirculation * have been extended to generate a design of a compact arc providing bunch compression with positive momentum compaction ** and control of both incoherent and coherent synchrotron radiation (ISR and CSR) effects using the optics balance methods of diMitri et al.***. In addition, the arc/compressor generates very little micro-bunching gain. We detail the beam dynamical basis for the design, discuss the design process, give an example solution, and provide simulations of ISR and CSR effects. Reference will be made to a complete analysis of micro-bunching effects ****

-Y. Tsai, C.

Akers, E., (Ed.)

Benson, S. V.

Douglas, D. R.

Henderson, S., (Ed.)

Krafft, Geoffrey A.

Li, R.

Roblin, Y.

Satogata, T., (Ed.)

Schaa, V. R.W., (Ed.)

Tennant, C. D.

Terzić, Balŝa

English

Old Dominion University

Old Dominion University ODU Digital Commons Physics Faculty Publications Physics 2015 Control of Synchrotron Radiation Effects During Recirculation With Bunch Compression D. R. Douglas S. V. Benson R. Li Y. Roblin C. D. Tennant See next page for additional authors Follow this and additional works at: https://digitalcommons.odu.edu/physics_fac_pubs  Part of the Engineering Physics Commons, and the Nuclear Commons Original Publication Citation Douglas, D., Benson, S. V., Krafft, G. A., Li, R., Tennant, C., Terzić, B., & Tsai, C.-Y. (2015). Control of synchrotron radiation effects during recirculation with bunch compression. In S. Henderson, E. Akers, T. Satogata, & V.R.W. Schaa (Eds.), Proceedings of the 6th International Particle Accelerator Conference (pp. 1910-1912). JACoW. https://doi.org/10.18429/JACoW-IPAC2015-TUPMA034 This Conference Paper is brought to you for free and open access by the Physics at ODU Digital Commons. It has been accepted for inclusion in Physics Faculty Publications by an authorized administrator of ODU Digital Commons. For more information, please contact digitalcommons@odu.edu. Authors D. R. Douglas, S. V. Benson, R. Li, Y. Roblin, C. D. Tennant, Geoffrey A. Krafft, Balŝa Terzić, C. -Y. Tsai, S. Henderson (Ed.), E. Akers (Ed.), T. Satogata (Ed.), and V. R.W. Schaa (Ed.) This conference paper is available at ODU Digital Commons: https://digitalcommons.odu.edu/physics_fac_pubs/778 CONTROL OF SYNCHROTRON RADIATION EFFECTS DURING RECIRCULATION WITH BUNCH COMPRESSION* D.R. Douglas#, S.V. Benson, R. Li, Y. Roblin, C.D. Tennant, Thomas Jefferson National Accelerator Facility, Newport News, VA 23606, USA, G.A. Krafft, B. Terzic, Old Dominion University, Norfolk, VA, 23529, USA C.-Y. Tsai, Virginia Polytechnic Institute and State University, Blacksburg, VA, 24061, USA Abstract Studies of beam quality during recirculation [1] have been extended to an arc providing bunch compression with positive momentum compaction [2]. It controls both incoherent and coherent synchrotron radiation (ISR and CSR) using methods including optics balance [3] and generates little microbunching gain. We detail the dynamical basis for the design, discuss the design process, give an example, and provide simulations of ISR and CSR effects. Reference will be made to a complete analysis of microbunching effects [4]. METHODS FOR CSR/ISR CONTROL Recirculation and energy recovery are established means of cost-performance optimization. Their use for FEL drivers can be challenging because of the impact of CSR on beam quality, and the desirability of limiting machine size and complexity. Here, we describe a method providing bunch length compression and recirculation in a modest footprint (~10 m diameter at ~1 GeV) while limiting beam quality degradation due to CSR. The method is scalable to higher energy (by increasing bend radius and machine diameter).  “Conventional” Compressor Design A FODO-based recirculation arc can be used as a compressor; as M56>0, an incident bunch with an appropriate energy chirp will be compressed with advantages discussed elsewhere [5]. When employed as a means of final bunch compression, the impact of CSR is however dramatic and detrimental. Using a simple 1-D CSR model in DIMAD [6], we studied compression of a 150 pC, 0.5 m-rad normalized emittance beam to ~70 fsec x 0.1% p/p while bending through 180o at 0.71 GeV in an arc comprising eight quarter-integer FODO cells with bend radius of 2 m. The beam emittance increases as a consequence of phase space redistribution driven by the CSR interaction, but effects can be mitigated as follows:   1. Chromatically correct the lattice and compensate lattice and CSR-induced curvature in the longitudinal phase space, i.e., set T566. Here, this is assumed to have been done in upstream transport so as to allow compression of small relative momentum spreads while avoiding use of strong nonlinearities. We model it with a quadratic phase-energy correlation in the incoming beam (a T655 term). 2. Introduce lattice perturbations to suppress linear x-p/p and x’-p/p correlations in the beam by introducing perturbative dispersion trims. 3. Trim chromatic corrections to suppress CSR-induced nonlinear phase space distortions [7]. 4. Optimize the betatron match by varying beam input parameters to minimize output emittance.  After optimization, the output emittance was ~2 mm-mrad, representing a factor of four growth in the input. The cause of the phase space redistribution is clear: as the bunch compresses, energy modulation across the bunch due to CSR increase dramatically. As a result, the compensation described by Di Mitri et al. [8] breaks down despite the presence of desirable betatron phase and amplitude relationships inherent to the achromat. Small shifts introduced when the bunch is long are inadequate to offset the larger shifts induced when the bunch is short. Excitation-Modulated Compressor Design Breakdown in emittance compensation can be mitigated by redistribution of bending along the beamline and optimization as described above. The method is simple: increase the angle of bending in initial FODO cells – thereby enhancing the impact of CSR early in the beam line while the bunch is long – and decrease the bending angle in the final FODO cells, reducing the effect of CSR while the bunch is short. Initial simulation of such an excitation-modulated system shows immediate benefit. An optimized linearly declining bend (using dipoles of 40o, 35o, 30o,… 10o, 5o) presented less emittance degradation than a conventional arc. Guided by the concepts of optics balance [9] and magnifying achromats [10] (in both, upstream and downstream perturbations are balanced by the choice of the intervening lattice optics), we added a dispersion generator to provide additional control of the beam and lattice,  and manually adjusted the bending pattern to  minimize output emittance. Care in selection of bend angles further reduced emittance dilution; choice of bend radius managed ISR effects. As in the conventional arc, the degraded output phase space presented correlated distortions that could be compensated by perturbing the beam line optics as described above, limiting growth of normalized emittance from 0.5 to 1 m-rad, a factor of two lower than in the  ___________________________________________  * This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177. #douglas@jlab.org  6th International Particle Accelerator Conference IPAC2015, Richmond, VA, USA JACoW PublishingISBN: 978-3-95450-168-7 doi:10.18429/JACoW-IPAC2015-TUPMA034TUPMA0341910ContentfromthisworkmaybeusedunderthetermsoftheCCBY3.0licence(©2015).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOI.2: Photon Sources and Electron AcceleratorsA06 - Free Electron Lasersconventional system. Longitudinal emittance is controlled by both arcs. Further improvement in performance might be given by using more robust optimization methods [11]. Table 1 summarizes key parameters. Figure 1 shows beamline layouts for both example systems; Figures 2 and 3 illustrate optimized Twiss parameters for each case. Figures 4 and 5 give delivered 104 particle phase spaces for the uniform FODO and modulated compressor.     Figure 1: Conventional FO0DO and excitation-modulated compressor layouts. Quadrupoles and beam line in black; conventional line bends in brown, modulated line in blue.    Figure 2: Twiss functions for FODO compressor.    Figure 3: Twiss functions for modulated compressor.    Figure 4: Bend plane (left) and longitudinal (right) phase space output from FODO arc compressor.    Figure 5: Bend plane (left) and longitudinal (right) phase space output from excitation-modulated compressor. Table 1: Compressor Arc Parameters  FODO Modulated Diameter 9.78 m 8.95 m # bends 8 9 cell tune x,y=90o x,y=90o phase advance x,y=2,2 x,y=2.4,2.5M56 0.63 m 1.56 m xN in/out 0.5/1.86 m-rad 0.5/0.72 m-rad LN in/out 50/55 keV-psec 50/59 keV-psec DETAILED ANALYSIS The excitation-modulated compressor was simulated using elegant [12]. Even with a detailed physics model and a million-particle simulation, emittance growth remained modest, with growth from 0.5 to 1.0 m-rad. The simulation found significant impact from the interaction of the forward-propagating CSR field with the bunch downstream of the bends (“csrdrift” elements in elegant), the effects of which had not been a part of the initial optimization. This effect increased the final emittance to 1.45 m-rad. Of greater interest is that the compressor is insensitive to microbunching. Figures 6 and 7 present the output phase space with and without edge effects, and Figure 8 gives emittance evolution through the system; though emittance growth is greater with “csrdrifts”, the phase space remains regular and no evidence of the BI is apparent.   Figure 6: Horizontal phase space without (left) and with (right) CSR edge effects; 106 particles.   Figure 7: Longitudinal phase space without (left) and with (right) CSR edge effects; 106 particles  6th International Particle Accelerator Conference IPAC2015, Richmond, VA, USA JACoW PublishingISBN: 978-3-95450-168-7 doi:10.18429/JACoW-IPAC2015-TUPMA0342: Photon Sources and Electron AcceleratorsA06 - Free Electron LasersTUPMA0341911ContentfromthisworkmaybeusedunderthetermsoftheCCBY3.0licence(©2015).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOI.-11 -2 -3 " 20 15 - btt,_.(ml 10 - IM11_y(ml - 10•111_111 (m) 10 12 " 16 _, " § i d 20 15 - bet1_x(m) 10 - betl_y(m) 'o 'o - 1o•et1_k(ml ~ ~ ·x § ·x ! 10 12 14 16 " _J 9 § § 9 9 5•1 Q-3 0 5•1 Q·!I •5K1 o•~ 0 5• 1 Q·!I 300 x (m) x(m ) 200 0.4 1J 1(J(l l o.2 "' 3 0 a. 0.0 •x ·100 ~ --0 .2 -200 -0.4 -300 - 400 -200 0 200 400 600 -1-0 -0.5 00 0.5 1.0 X (µm) t (ps) § § ~ ~ 300 ,.._ =-,.._ =-200 0.4 ~ ~ S- ,oo ~ 0.2 "' 2- 0 "- 0.0 •x ·100 C. -0.2 ~ ~ -200 <] -300 -0.4 - 4 00 -200 0 200 400 60< -1.0 -0.5 0.0 0.5 1.0 •2 •1Q•U 0 2•10·1> .. 2., 0-1.l 0 2 •10-1 .> X (µm) t (ps) l (p s ) l (p s)  Figure 8: Emittance evolution through line without and with CSR edge effects.  A careful analysis of BI effects confirms this observation [13]; instability gain is extremely low. Figure 9 gives the microbunching gain, and Figure 10 the spectrum, for a compressor of this type operated at 0.75 GeV with a beam of 0.75 m-rad emittance and 70 pC. Initial bunch length was ~4 psec, uncorrelated p/p was 1.13x10-5, and the  compression factor was ~53.   Figure 9: Microbunching gain through compressor.  Figure 10: Gain spectrum for modulated compressor. FUTURE DIRECTIONS This discussion is only a demonstration of the method; the example is not fully optimized with regard to distribution of bending, choice of betatron match, edge radiation, FODO cell length, or lattice parameters. Future work will invoke such optimization, and will seek to suppress the effects of interaction of the forward-propagating CSR field with the bunch.  This method can in principle be extended to higher energy and is therefore of use in proposed short-wavelength FEL drivers [14]. CONCLUSIONS We find that positive compaction (M56>0) compression is an effective and advantageous parametric choice, as it may avoid both parasitic compressions [15] and microbunching. Optics balance can provide emittance compensation during compression (just as in well-designed chicane compressors). Wake signatures on longitudinal phase space can be managed in same way as RF curvature and lattice aberrations, by using nonlinear magnetic compensation.  ACKNOWLEDGMENT The authors are most grateful to Dr. Simone Di Mitri and Dr. Max Cornacchia for useful and supportive discussions on both CSR control and arc compressor design. We note that they have independently developed a meticulously detailed quantitative description of CSR effects in, and an excellent design for, an arc compressor providing effective control of CSR effects [16]. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177. The U.S. Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce this manuscript for U.S. Government purposes. REFERENCES [1] D. Douglas et al., “Control of Synchrotron Radiation Effects During Recirculation”, these proceedings. [2] S. Benson et al., “A Bunch Compression Method for Free Electron Lasers that Avoids Parasitic Compressions”, these proceedings, TUPMA033, IPAC’15, Richmond, VA USA (2015). [3] S. Di Mitri et al., Phys. Rev. Lett. 110, 014801, 2 January 2013. [4] C.-Y. Tsai et al., "CSR Induced Microbunching Gain Estimation Including Transients in Transport and Recirculation Arcs”, these proceedings, MOPMA025, IPAC’15, Richmond, VA USA (2015). [5] S. Benson et al., op. cit. [6] D. Douglas, “Suppression and Enhancement of CSR-Driven Emittance Degradation in the IR-FEL Driver”, JLAB-TN-98-012, 24 March 1998. [7] D. Dowell, “Compensation of Bend-Plane Emittance Growth In a 180 Degree Bend”, PAC’97, Vancouver, May 1997, p. 1888 (1997); http://www.jacow.org [8] S. Di Mitri et al., op. cit. [9] ibid. [10] K.L. Brown and R.V. Servranckx, NIM-A 203, pp.73-9 (1982)[11] A. Hofler et al., Phys. Rev. ST Accel. Beams 16, 010101 (2013). [12] M. Borland, “elegant: A Flexible SDDS-Compliant Program for Accelerator Simulation,” APS Light Source Note LS-287, September 2000. [13] C.-Y. Tsai, et al., op. cit. [14] R. York, Phys. Rev. ST Accel. Beams 18, 010705 (2014). [15] S. Benson et al., op. cit. [16] S. Di Mitri and M. Cornacchia, Eur. Phys. Lett., 109, 62002 (2015). . 6th International Particle Accelerator Conference IPAC2015, Richmond, VA, USA JACoW PublishingISBN: 978-3-95450-168-7 doi:10.18429/JACoW-IPAC2015-TUPMA034TUPMA0341912ContentfromthisworkmaybeusedunderthetermsoftheCCBY3.0licence(©2015).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOI.2: Photon Sources and Electron AcceleratorsA06 - Free Electron Lasersno csrdrift 1.4 r csrdrift I-/ 1.2 'o' e! E 1.0 E .s ,J 0.8 0.6 0 5 1 0 1 5 s(m) - ,._ = 0.Smm -), = 3 mm 2 -,. =10mm -;;;- • ELEGANT tracking c5' 1 5 - 1st order iteration -2nd order iteration • ELEGANT tracking 4000 6000 )..(um) 8000 10000 

Control of Synchrotron Radiation Effects During Recirculation With Bunch Compression

https://digitalcommons.odu.edu/cgi/viewcontent.cgi?article=1780&context=physics_fac_pubs

Control of Synchrotron Radiation Effects During Recirculation With Bunch Compression

Abstract

Similar works

Full text

Available Versions

Old Dominion University