A compact Compton light source using an electron linear accelerator is in design at the Center for Accelerator Science at Old Dominion University and Jefferson Lab. We report on the current design, including beam properties through the entire system based on a full end-to-end simulation, compare current specifications to design goals, and target areas for improvement

Deitrick, K.

Delayen, J. R.

Gamage, B.R.P.

Krafft, Geoffrey A.

Satogata, T.

English

Old Dominion University

Old Dominion UniversityODU Digital CommonsPhysics Faculty Publications Physics2015Progress on a Compact Accelerator Design for aCompton Light SourceK. DeitrickOld Dominion UniversityJ. R. DelayenOld Dominion University, jdelayen@odu.eduB.R.P. GamageOld Dominion UniversityGeoffrey A. KrafftOld Dominion University, gkrafft@odu.eduT. SatogataOld Dominion UniversityFollow this and additional works at: https://digitalcommons.odu.edu/physics_fac_pubsPart of the Engineering Physics Commons, and the Plasma and Beam Physics CommonsThis Conference Paper is brought to you for free and open access by the Physics at ODU Digital Commons. It has been accepted for inclusion inPhysics Faculty Publications by an authorized administrator of ODU Digital Commons. For more information, please contactdigitalcommons@odu.edu.Repository CitationDeitrick, K.; Delayen, J. R.; Gamage, B.R.P.; Krafft, Geoffrey A.; and Satogata, T., "Progress on a Compact Accelerator Design for aCompton Light Source" (2015). Physics Faculty Publications. 283.https://digitalcommons.odu.edu/physics_fac_pubs/283Original Publication CitationDeitrick, K., Satogata, T., Krafft, G., Gamage, B. R., & Delayen, J. (2015). Progress on a compact accelerator design for a compton lightsource. In Proceedings of the 6th International Particle Accelerator Conference, Richmond, VA, May 3-8, 2015 (pp. 1706-1708).http://accelconf.web.cern.ch/AccelConf/IPAC2015/papers/tupje041.pdfPROGRESS ON A COMPACT ACCELERATOR DESIGN FOR ACOMPTON LIGHT SOURCE∗K. Deitrick1† , J.R. Delayen1,2, B.R.P. Gamage1, G.A. Krafft1,2, T. Satogata1,21 Center for Accelerator Science, Old Dominion University, Norfolk VA, 23529, USA2 Thomas Jefferson National Accelerator Facility, Newport News VA, 23606, USAAbstractA compact Compton light source using an electron lin-ear accelerator is in design at the Center for AcceleratorScience at Old Dominion University and Jefferson Lab.We report on the current design, including beam proper-ties through the entire system based on a full end-to-endsimulation, compare current specifications to design goals,and target areas for improvement.INTRODUCTIONCompton Light SourceAt present, there is a high level of interest in an inverseCompton light source with a compact floor plan due to thewide variety of applications such a system could facilitate.To this end, a preliminary design was developed and pre-sented, with the necessary electron beam and resulting x-ray beam properties shown in Table 1 [1].Table 1: Electron Beam Parameters at Collision, ComptonSource ParametersParameter Value UnitsEnergy 25 MeVBunch charge 10 pCRepetition Rate 100 MHzAverage current 1 mANormalized εrms 0.1 mm-mradβx,y 5 mmFWHM bunch length 3.0 (0.9) psec (mm)RMS energy spread 7.5 keVX-ray energy Up to 12 keVPhotons/crossing 1.6 × 106Flux 1.6 × 1014 photon/secAverage brilliance 1.5 × 1015 photons/(sec-mm2-mrad2-0.1% BW)Simulation ToolsA number of accelerator codes were used to develop anend-to-end simulation. CST Microwave Studio c© (CST) isan electromagnetic (EM) field solver [2]. SUPERFISH isalso an EM field solver, provided the geometry is cylindri-cally symmetic, developed by Los Alamos [3]. The track-ing through the accelerating section was performed by AS-TRA (A Space-charge TRacking Algorithm), which tracks∗Partially authored by Jefferson Science Associates, LLC under U.S.DOE contract NO. DE-AC05-6OR23177.† kdeit001@odu.eduparticles through user-defined external fields [4]. Spacecharge was taken into account throughout, and the imagecharge due to the cathode was included within the gun.After emerging from the linac, the beam dynamics werecalculated by elegant [5]. Translating the final bunchproduced by ASTRA into the SDDS format required byelegant was done by a specific function provided withinthe package for that purpose.ACCELERATIONElectron GunThe electron gun is a 500 MHz superconducting RF(SRF) quarter-wave design, originally based on the shapeproposed by Harris et al. [6]. The design is highly reentrantin order to mitigate the growth of the transverse normalizedemittance due to space charge. In order to remove a surfacetangential discontinuity near the cathode, the design wasslightly altered. The RF properties of the altered design arepresented in Table 2 [7].Table 2: RF Properties of the 500 MHz Quarter Wave Elec-tron gun at Eacc = 1 MV/mParameter Value UnitsFrequency ofaccelerating mode 499.3 MHzλ/4 150 mmDesign β 0.95Stored energy 44 mJQRs 83.5 ΩR/Q 154 ΩPeak electricsurface field (EP ) 3.67 MV/mPeak magneticsurface field (BP ) 6.64 mTEP /BP 1.81 mT/(MV/m)In order to study the beam dynamics of a bunch, the EMfields of the gun calculate by SUPERFISH were exportedand translated into the format required by ASTRA. A 10 pCbunch consisting of 2000 electrons with a plateau longitu-dinal distribution of length 24 ps, σr of 0.5 mm, and neg-ligible initial emittance or transverse momentum was gen-erated and tracked by ASTRA through the gun. Both thespace charge of the bunch and the mirror-image contribu-tion of the cathode were included in this simulation. Theproperties of the beam after the exit of the gun (15 cm fromTUPJE041 Proceedings of IPAC2015, Richmond, VA, USAISBN 978-3-95450-168-71706Copyright©2015CC-BY-3.0andbytherespectiveauthors2: Photon Sources and Electron AcceleratorsA24 - Other Linac-Based Photon Sourcesthe surface of the cathode) are shown in the top section ofTable 3.Table 3: Beam Properties After Exiting Gun (top) and theLinac (bottom), as Simulated by ASTRAParameter Value UnitsEkin 1.55 MeVEnergy spread 0.526 keVσx,y 0.477, 0.477 mmNormalizedRMS εx,y 0.12, 0.12 mm-mradE 25.02 MeVRMS Energy spread 31.09 keVσz 2.1 (7.0) mm (psec)σx,y 0.511, 0.482 mmNormalizedRMS εx,y 0.16, 0.15 mm-mradαx,y 2.34, -0.591βx,y 82.1, 75.5 mLinear AcceleratorAs before, the linear accelerator (linac) consists of four500 MHz double-spoke high-velocity accelerating cavitiesto bring the beam up to the required energy. The EM fieldswere calculated by CST, before being translated into theformat required by ASTRA. The bunch previously pro-duced by ASTRA after traversing the gun was then trackedby ASTRA through the linac, continuing to take spacecharge into account.In order to produce the roundest possible beam, the de-sign takes advantage of the quadrupole-like effects of thespoke cavities [8]. This means as the bunch travels downthe beam line after exiting the gun, the first spoke of eachcavity that the bunch traverses is orthogonal to its prede-cessor. In essence, the first four spokes (in two cavities)are oriented as follows: (horizontal, vertical) (vertical, hor-izontal).In order to chirp the bunch for compression, the last twocavities of the linac are run off-crest at 6.5◦ each. The prop-erties of the beam emerging from the linac are shown in thebottom section of Table 3, with the transverse phase spacesshown in the top row of Fig. 1.MATCHINGWhile the beam properties are fairly reasonable, thetransverse phase spaces resemble bowties more than el-lipses. In order to correct this, a solenoid was placed af-ter the linac. The resulting phase spaces are the bottomrow in Fig. 1. While this does benefit the phase space, itincreases the magnitude of x′ and y′  x′ ≡ pxpwith asimilar definition of y′. As the emittance increases as themaximum magnetic field of the solenoid does, the strengthof the solenoid is balanced between the increase in emit-tance and the decrease of bowtie resemblance.Figure 1: Transverse phase spaces after the linac (top) andthe solenoid (bottom).In order to make αx = αy , a quadrupole was placeddownstream of the solenoid after a drift. The beam prop-erties after both the solenoid and the quadrupole are in Ta-ble 4.Table 4: Beam Parameters After (1) the Solenoid and (2)the Quadrupole, as Simulated by elegantParameter (1) (2) UnitsNormalizedRMS εx,y 0.19, 0.18 0.19, 0.18 mm-mradσx,y 0.50, 0.47 0.38, 0.39 mmβx,y 65, 61 38, 39 mαx,y 15, 12 10, 10BUNCH COMPRESSIONAs has been previously reported, there exist two possibledesigns for a bunch compressor. Both are four dipole s-chicanes, with a symmetric set of three quadrupoles in thecenter of the dipoles and a final focusing section after thedipoles. One has a net phase advance of 3π, while the otherhas a net phase advance of 4π [9]. The parameters for bothbunch compressors are presented in Table 5. Given that thesign of the M56 values are opposite for the two designs, thenecessary chirp is in different directions for each, thoughthe magnitude of the chirp is the same.Demonstrating the ability to tune the M56 of these de-signs is shown by adjusting the bend angles for the innerpair of dipoles. The bunch has been tracked through al-tered lattices where only the inner dipole bend angles havebeen adjusted. A comparison of the resulting compressionfor both the 3π and 4π compressor are shown in Fig. 2.Proceedings of IPAC2015, Richmond, VA, USA TUPJE0412: Photon Sources and Electron AcceleratorsA24 - Other Linac-Based Photon SourcesISBN 978-3-95450-168-71707 Copyright©2015CC-BY-3.0andbytherespectiveauthors0.08. 0.06 0.04 "o' O.o2 "' s ..=, 0 "k -0.02 -0.04 -0.00 0.25 0.2 0.1 5 "o' OJ "' 0.05 :,j 0 5 -0.05 "k -0.1 -0.15 -0.2 -0.25 -1 -0-5 0 0..5 1 -1 -0..5 0 0..5 1 x(mm) y(mm) Figure 2: Comparison of M56 due to bend angle of inner dipole pair and the resulting compression for 3π (top) and 4π(bottom) compressors. Longitudinal density is shown by histogram.Table 5: Bunch Compressor Parameters for the 3π and 4πDesignsParameter Value UnitsFinal βx,y 5, 3 mmM56 -1.53 mDipole lengths 0.8, 0.8, 0.8, 0.8 mDipole bend angles 60, -105, -105, 60 ◦Final βx,y 4, 8 mmM56 1.60 mDipole lengths 0.35, 1.1, 1.1, 0.35 mDipole bend angles 40, -170, 170, -40 ◦FURTHER WORKGiven the results previously presented and the parame-ter goals initially stated in Table 1, we believe that a fea-sible design is possible. It should be emphasized that wehave not applied emiitance compensation yet in the gun re-gion, and still achieve beam parameters close to those re-quired. At present, the two parameters of most concernare the transverse normalized emittance and the RMS en-ergy spread. As the transverse emittance comes out of thegun already higher than the desired value, it needs to be im-proved by another optimization of the gun. In order to meetthe desired energy spread, it may be necessary to decreasethe bunch length off of the cathode. As this adjustment willcertainly have an impact on the space charge fields withinthe gun, and thus the emittance, careful calculation and op-timization of the beam dynamics will be needed.REFERENCES[1] T. Satogata et al., “Compact Accelerator Design for a Comp-ton Light Source”, WEPWA078, Proc. of IPAC 2013, Shang-hai, China (2013).[2] Computer Simulation Technology website,http://www.cst.com.[3] Poisson Superfish, http://laacg1.lanl.gov/laacg/services/download sf.phtml (2011).[4] K. Flottman, “A Space-Charge Tracking Alogorithm”, DESY,http://www.desy.de/~mpyflo (2000).[5] M. Borland, “elegant: A Flexible SDDS-Compliant Code forAccelerator Simulation”, Advanced Photon Source LS-287,Spetember 2000.[6] J.R. Harris et al., “Design and Opertaion of a Supercon-ducting Quarter-Wave Electron Gun”, PRST:AB 14, 053501(2011).[7] T. Satogata et al., “The ODU CAS In-verse Compton Source Design”, available athttp://toddsatogata.net/Papers/2013-09-03-ComptonSource-2up.pdf (2013).[8] C. Hopper, K. Deitrick, and J.R. Delayen, “Geometry Ef-fects on Multipole Components and Beam Emittance in High-velocity Multi-Spoke Cavities”, WEPAC42, Proc. of NA-PAC 2013, Pasadena, CA USA (2013).[9] B.R.P. Gamage and T. Satogata, “Magnetic Bunch Compres-sion for a Compact Inverse Compton Source”, THPHO21,Proc. of NA-PAC2013, Pasadena, CA USA (2013).TUPJE041 Proceedings of IPAC2015, Richmond, VA, USAISBN 978-3-95450-168-71708Copyright©2015CC-BY-3.0andbytherespectiveauthors2: Photon Sources and Electron AcceleratorsA24 - Other Linac-Based Photon Sources50 -105° 32.7 -95° M 56 =-U3 m 27.25 ~ 49.95 M.56 = -0.661 m a, 'o' m 499 21.8 0... > 0 a, a, 6 49.85 16J5 t,.D ro -a P-, a, 49.8 109 0 .... a, 49.75 5.45 P-, 49.7 0 50 32.7 49.95 27.25 ~ a, 'o' m 499 21.8 0... > 0 ., a, 6 49 . .85 16.35 t,.D M5,6,= l.02 m M56 = 1.60 m M 56 = 2.02m ro ..... P-, i::: a, 49 .. S 10 .. 9 0 .... 49.75 ± 165° ± 170°' ± 175° 5.45 a, P-, 49.7 0 0 5 10 15 20 25 30 0 j 10 15 20 25 30 0 5 10 15 20 25 30 t(ps) t(ps) t (ps) 

Progress on a Compact Accelerator Design for a Compton Light Source

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Progress on a Compact Accelerator Design for a Compton Light Source

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