There exists an increasing demand for compact Inverse Compton Light Sources (ICLS) capable of producing substantial fluxes of narrow-band X-rays. While multiple design proposals have been made, compared to typical bremsstrahlung sources, most of these have comparable fluxes and improve on the brilliance within a 0.1% bandwidth by only a few orders of magnitude. By applying cw superconducting rf beam acceleration and rf focusing to produce a beam of small emittance and magnetic focusing to produce a small spot size on the order of a few microns at collision, the source presented here provides a 12 keV X-ray beam which outperforms other compact designs and bremsstrahlung sources. Compared to a bremsstrahlung source, the flux is improved by at least an order of magnitude and the average brilliance by six orders of magnitude. Surpassing other compact ICLS designs, the source presented here is attractive to a wide variety of potential users

Deitrick, K.

Delayen, J. R.

Krafft, G. A.

English

Old Dominion University

Old Dominion UniversityODU Digital CommonsPhysics Faculty Publications Physics2017High Average Brilliance Compact InverseCompton Light SourceK. DeitrickOld Dominion UniversityJ. R. DelayenOld Dominion UniversityG. A. KrafftOld 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.; and Krafft, G. A., "High Average Brilliance Compact Inverse Compton Light Source" (2017). PhysicsFaculty Publications. 327.https://digitalcommons.odu.edu/physics_fac_pubs/327Original Publication CitationDeitrick, K., Delayen, J., & Krafft, G. (2017). High average brilliance compact inverse compton light source. Paper presented at the 8thInternational Particle Accelerator Conference, Copenhagen, Denmark. https://doi.org/10.18429/JACoW-IPAC2017-MOPVA036HIGH AVERAGE BRILLIANCE COMPACTINVERSE COMPTON LIGHT SOURCE∗K. Deitrick , J.R. Delayen , G.A. Krafft ,† 1 1Center for Accelerator Science, Old Dominion University, Norfolk VA, 23529, USA1 also at Thomas Jefferson National Accelerator Facility, Newport News VA, 23606, USAAbstractThere exists an increasing demand for compact InverseCompton Light Sources (ICLS) capable of producing sub-stantial fluxes of narrow-band X-rays. While multipledesign proposals have been made, compared to typicalbremsstrahlung sources, most of these have comparablefluxes and improve on the brilliance within a 0.1% band-width by only a few orders of magnitude. By applyingcw superconducting rf beam acceleration and rf focusing toproduce a beam of small emittance and magnetic focusingto produce a small spot size on the order of a few micronsat collision, the source presented here provides a 12 keVX-ray beam which outperforms other compact designs andbremsstrahlung sources. Compared to a bremsstrahlungsource, the flux is improved by at least an order of mag-nitude and the average brilliance by six orders of magni-tude. Surpassing other compact ICLS designs, the sourcepresented here is attractive to a wide variety of potentialusers.INTRODUCTIONInverse Compton Light SourceAn Inverse Compton Light Source uses inverse Comp-ton scattering to produce X-rays (or γ-rays, at higher ener-gies), by colliding a relativistic electron beam and an inci-dent laser. For a head-on collision between the two beamsin the Thomson regime, the X-rays scattered in the forwarddirection (in the same direction as the electron beam) havethe highest energy. The energy of these X-rays is given byEX−ray = 4γ2Elaser (1)where γ is the relativistic Lorentz factor of the electronbeam and Elaser is the energy of the incident laser. Thetotal number of the scattered photons is given byNγ = σTNeNlaser2π(σ2e + σ2laser)(2)where σT is the Thomson cross section 8πr2e/3, re is theclassical electron radius, Ne is the number of electrons inthe bunch,Nlaser is the number of photons in the laser, σe isthe spot size of the electron beam, and σlaser is the numberof photons in the laser pulse. For a high repetition ratesource, the full flux of the X-ray beam is given by F =∗Partially authored by Jefferson Science Associates, LLC under U.S.DOE contract NO. DE-AC05-6OR23177.† kdeit001@odu.edufNγ , with f being the repetition rate. The flux into a 0.1%bandwidth is given byF0.1% = 1.5× 10−3fNγ . (3)For the source presented, and others also in the non-diffraction limited mode of operation, the average bril-liance of the X-ray beam is given byB =γ2F0.1%4π2ǫNx,rmsǫNy,rms(4)where γ is the relativistic factor of the electron beam andǫNx,rms and ǫNy,rms are the appropriate transverse normalizedrms emittances of the electron beam [1].Design ConsiderationsWhen designing a compact ICLS, three factors are criti-cal. The machine should be small - one suggested limit wasoccupying a footprint of less than 100 m2 [2]. The cost topurchase and operate the light source should be reasonablefor smaller facilities. Finally, the parameters of the X-raybeam should demonstrate a significant improvement overtraditional bremsstrahlung sources [3]. The parameters forthis design were inspired by [4].Accordingly, the frequency of the superconducting rf(srf) components which comprise the accelerator have beenchosen to have a frequency of 500 MHz. This frequencyallows for the machine to operate at 4 K, significantly re-ducing the cryogenic costs associated with operating thelight source. In order to limit the size of the machine,every effort was made to develop a compact design with-out sacrificing the quality of the X-ray beam. Finally, theanticipated X-ray beam of this design far exceeds typicalbremsstrahlung sources and shows improvement over othercompact ICLS designs. The design presented here consistsof an srf reentrant gun, four srf double-spoke cavities whichmake up the linac, and three quadrupoles to make up the fo-cusing section [3].Simulation ToolsThis light source design was developed through exten-sive start-to-end simulation work. The electromagnetic(EM) fields of the srf reentrant gun were calculated usingSuperfish [5], while the EM fields of the srf double-spokecavities in the linac were calculated using CST MicrowaveStudio [6]. Using IMPACT-T [7], 100,000 macroparticleswere tracked through the accelerator, before being trackedthrough the focusing section by elegant [8].MOPVA036 Proceedings of IPAC2017, Copenhagen, DenmarkISBN 978-3-95450-182-3932Copyright©2017CC-BY-3.0andbytherespectiveauthors02 Photon Sources and Electron AcceleratorsA23 Other Linac-based Photon SourcesFigure 1: A cross section of the srf gun (left) and the srfdouble-spoke accelerating cavity (right).ICLS DESIGNSrf Reentrant GunThe concept for a reentrant srf gun was introduced over20 years ago [9]. In the last decade, the Naval Postgradu-ate School, Brookhaven National Lab, and the Universityof Wisconsin have commissioned reentrant srf guns [10].For the design presented here, the gun needed to producean electron bunch with extremely small transverse normal-ized rms emittances. This goal was achieved by alter-ing the geometry of the gun, shown at the left in Fig.1,specifically around the nose-cone containing the cathodeassembly. The geometry alteration resulted in radial elec-tric fields within the gun, which provided focusing to thebunch in order to provide emittance compensation for thespace charge effects [11]. Other srf reentrant gun designsuse a solenoid for emittance compensation, instead of therf focusing used here [10].Srf LinacUntil recently, accelerating electrons near the speed oflight has not been attempted with multispoke cavities,largely due to the well-established and successful perfor-mance of TM-type cavities. However, they are familiaroptions for accelerating ions and provide the capability tooperate at 4 K through a low-frequency accelerator. Thedouble-spoke cavity which makes up the linac, seen at theright in Fig.1, was designed by Christopher Hopper duringhis PhD research at Old Dominion University [12, 13].The linac contains four of these double-spoke cavities.Due to the multipole effects of these cavities, some consid-eration was necessary to produce a nearly round electronbeam at the linac exit. The multipole effects of the cavi-ties can be approximated as “quadrupole-like”, focusing inone transverse direction while defocusing in the other. Inorder to produce a nearly round beam, the center two cav-ities within the linac were rotated 180◦ around the y-axis.While the produced beam is not perfectly round, it is closeenough to make focusing the beam easier [11].Table 1: Properties of Electron Bunch at the Collision PointParameter Quantity Unitskinetic energy 25 MeVbunch charge 10 pCrms energy spread 3.44 keVǫNx,rms 0.10 mm-mradǫNy,rms 0.13 mm-mradσx 3.4 µmσy 3.8 µmFWHM bunch length 3 psecσz 0.58 mmFigure 2: The beam spot (upper left), longitudinal phasespace (upper right), horizontal phase space (lower left), andvertical phase space (lower right) of the electron bunch atthe collision point.FocusingAfter the bunch exits the linac, it passes through threequadrupoles. The collision between the electron beam andthe laser, known as the interaction point, occurs 29 cm pastthe exit of the last quadrupole. Due to an appropriate choicein bunch length off the cathode, no bunch compression isnecessary, which significantly simplifies the design. Theproperties of the electron bunch at the interaction point aregiven in Table 1. The entire length from the surface of thecathode to the interaction point is less 6 m. The electronbunch distribution, which has been tracked from the cath-ode surface to the collision point, is shown in Fig. 2 [11].X-RAY YIELDThe intended incident laser for this project is one with1 MW of circulating power, a spot size of 3.2 µm, and awavelength of 1 µm. Using the formulae presented at theProceedings of IPAC2017, Copenhagen, Denmark MOPVA03602 Photon Sources and Electron AcceleratorsA23 Other Linac-based Photon SourcesISBN 978-3-95450-182-3933 Copyright©2017CC-BY-3.0andbytherespectiveauthors:-]-49.916 ~-~-~-~-~~ 30 49.912 ~ 0. 49.908 -30 49.904 -60 ~-~--~-~--J -60 -30 30 60 x (microns) time (ps) -I -I -2 ~--~--~--~--J -2 ~--~--~--~-~ -60 -30 30 60 -60 -30 30 60 x(microns) y(microns) Table 2: X-ray Source Properties, Using FormulaeParameter Quantity UnitsEx 12 keVF 1.4× 1014 ph/secF0.1% 2.1× 1011 ph/(s-0.1%BW)B 1.0× 1015 ph/(s-mm2-mrad2-0.1%BW)beginning of this paper, the anticipated X-ray propertiescan be calculated; these results are given in Table 2 [11].However, these formulae were developed under the as-sumption that the electron beam distribution is Gaussian,which is not the case here [1,11]. A recent work ( [3]) pro-vides the means to calculate the scattered photon spectrumfor specific electron distributions, such as those providedby a start-to-end simulation. Using this method, the antici-pated brilliance for this design is ∼ 9.4× 1014 ph/(s-mm2-mrad2-0.1%BW), which is close to the brilliance given bythe formulae [3, 11].It is important to give some perspective to these num-bers. The best rotating anodes currently in use have a fluxof ∼109 ph/s and a brilliance on the order of 109 ph/(s-mm2-mrad2-0.1%BW) [22]. On the other hand, an X-raybeam that might typically be found at a large synchrotronor free-electron laser (FEL) facility may have a flux of∼1011 − 1013 ph/s [23] with a brilliance of ∼1019 ph/(s-mm2-mrad2-0.1%BW) [24]. Table 3 contains anticipatedX-ray properties of various compact ICLS projects.Table 3: Comparison of X-ray Beam Parameters for Differ-ent ICLS Compact DesignsPh/(s-mrad2Project Ex (keV) Ph/s -mm2-0.1%BW)Lyncean [1, 14, 15] 10-20 1011 1011TTX [16] 20-80 1012 1010LEXG [17] 33 1013 1011ThomX [18] 20-90 1013 1011KEK QB [19] 35 1013 1011KEK ERL [20] 67 1013 1011NESTOR [21] 30-500 1013 1012MIT [22] 12 1013 1012ODU 12 10141015While all the projects listed in Table 3 produce X-raysbeams with a flux comparable to what may be found atlarge facilities, the anticipated brilliance falls signficantlyshort. The reason that the large facilities have such a highbrilliance is because the electrons are high energy. Othercompact projects do improve on brilliance when comparedto a traditional X-ray source; the design presented here hasa greater brilliance by orders of magnitude then the nextmost brilliant proposal. Furthermore, there is nothing tostop this design from being further optimized to producean even more impressive X-ray beam.CONCLUSIONThe compact Inverse Compton Light Source presentedhere is a world-class X-ray source, anticipating a bril-liance unmatched by traditional sources or other compactICLS designs. This brilliance is achieved by an extremelysmall transverse normalized rms emittance, which has beenachieved by a srf reentrant gun. This gun also demon-strates how rf focusing by altering the gun geometry maybe a substitute for traditional emittance compensation us-ing solenoids. Overall, this project represents a significantmilestone in the development of sources capable of produc-ing substantial fluxes of narrow-band X-rays with a highbrilliance.ACKNOWLEDGMENTSTravel to IPAC’17 supported by the Division of Physicsof the United States National Science Foundation (Acceler-ator Science Program) and the Division of Beam Physics ofthe American Physical Society. This paper is authored byJefferson Science Associates, LLC under U.S. Departmentof Energy (DOE) Contract No. DE-AC05-06OR23177.Additional support was provided by DOEOffice of NuclearPhysics Award No. DE-SC004094 and Basic Energy Sci-ences Award No. JLAB-BES11-01. K.D. and J.R.D. weresupported at ODU by DO Contract No. DE-SC00004094.This research used resources of the National Energy Re-search Scientific Center, which is supported by the Officeof Science of the U.S. DOE under Contract No. DE-AC02-05CH11231.REFERENCES[1] G. A. Krafft and G. Priebe, Rev. Accel. Sci. Technol. 3, 147(2010).[2] M. Jacquet, Nucl. Instrum. Methods Phys. Res., Sect. B 331,1 (2014).[3] G. A. Krafft, E. Johnson, K. Deitrick, B. Terzic´, R. Kelmar,T. Hodges, W. Melnitchouk, and J. R. Delayen, Phys. Rev.Accel. Beams 19, 121302 (2016).[4] W. S. Graves, W. Brown, F. X. Kaertner, and D. E. Moncton,MIT inverse Compton source concept, Nucl. Instrum. Meth-ods Phys. Res., Sect. A 608, S103 (2009).[5] Poisson superfish, http://laacg1.lanl.gov/laacg/services/download\_sf.phtml.[6] Computer simulation technology website, http://www.cst.com.[7] J. Qiang, IMPACT-T User Document Beta Version1.7, http://amac.lbl.gov/~jiqiang/IMPACT-T/documents/ImpactTv1_7.pdf.[8] M. Borland, elegant: A Flexible SDDS-Compliant Code forAccelerator Simulation, Advanced Photon Source LS-287,September 2000.MOPVA036 Proceedings of IPAC2017, Copenhagen, DenmarkISBN 978-3-95450-182-3934Copyright©2017CC-BY-3.0andbytherespectiveauthors02 Photon Sources and Electron AcceleratorsA23 Other Linac-based Photon Sources[9] A. Michalke, Ph.D. thesis, Bergische Universita¨tGesamthochschule Wuppertal (1993).[10] A. Arnold and J. Teichert, Phys. Rev. ST Accel. Beams 14,024801 (2011).[11] K. Deitrick, Ph.D. thesis, Old Dominion University, 2017.[12] C. S. Hopper, Ph.D. thesis, Old Dominion University, 2015.[13] C. S. Hopper and J. R. Delayen, Phys. Rev. ST Accel. Beams16, 102001 (2013).[14] M. Bech, O. Bunk, C. David, R. Ruth, J. Rifkin, R. Loewen,R. Feidenhans’l, and F. Pfeiffer, J. Synchrotron Rad. 16, 43(2009).[15] Lyncean Technologies, Inc. - Synchrotron lightand the Lyncean Compact Light Source http://www.lynceantech.com/technology.html.[16] P. Yu and W. Huang, Nucl. Instrum. Methods Phys. Res.,Sect. A 592, 1 (2008).[17] E. G. Bessonov, M. V. Gorbunkov, P. V. Kostryukov,Yu. Ya. Maslova, V. G. Tunkin, A. A. Postnov,A. A. Mikhailichenko, V. I. Shvedunov, B. S. Ishkhanov, andA. V. Vinogradov, J. Instrum. 4 P07017 (2009).[18] A. Variola (ThomX Collaboration), in Proceedings of the2nd International Particle Acclerator Conference, San Se-bastia´n, Spain (IPAC’11/EPS-AG, 2011), p. 1903.[19] J. Urakawa, Nucl. Instrum. Methods Phys. Res., Sect. A637, S47 (2011).[20] R. Hajima, N. Kikuzawa, N. Nishimori, T. Hayakawa,T. Shizuma, K. Kawase, M. Kando, E. Minehara,H. Toyokawa, and H. Ohgaki, Nucl. Instrum. Methods Phys.Res., Sect. A 608, S57 (2009).[21] E. Bulyak et al., Nucl. Instrum. Methods Phys. Res., Sect.A 487, 241 (2002).[22] W. S. Graves et al., Phys. Rev. ST Accel. Beams 17, 120707(2014).[23] Beamlines Directory — Advanced Photon Source, http://www.aps.anl.gov/Beamlines/Directory/.[24] S. Benson et al., Nucl. Instrum. Methods Phys. Res., Sect.A 637, 1 (2011).Proceedings of IPAC2017, Copenhagen, Denmark MOPVA03602 Photon Sources and Electron AcceleratorsA23 Other Linac-based Photon SourcesISBN 978-3-95450-182-3935 Copyright©2017CC-BY-3.0andbytherespectiveauthors

High Average Brilliance Compact Inverse Compton Light Source

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High Average Brilliance Compact Inverse Compton Light Source

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