The Helmholtz Zentrum Berlin and the Max Planck Society are going to build a new dedicated X ray beam line at the synchrotron light source BESSY II which will be used for analyzing materials for renewable energy generation. The new large scale project has been dubbed EMIL. In this document we present the modifications to the machine optics and to what extent these changes affect the  performance of BESSY I

Bahrdt, J.

Birke, T.

Follath, R.

Kuske, P.

Schmid, P.

Simmering, D.

Wüstefeld, G.

HZB Repository

MODIFICATIONS TO THE MACHINE OPTICS OF BESSY IINECESSITATED BY THE EMIL PROJECTP. Schmid∗, J. Bahrdt, T. Birke, R. Follath, P. Kuske, D. Simmering, G. Wu¨stefeldHelmholtz-Zentrum Berlin fu¨r Materialien und Energie GmbH, Berlin, GermanyAbstractThe Helmholtz Zentrum Berlin and the Max Planck So-ciety are going to build a new dedicated X-ray beam line atthe synchrotron light source BESSY II which will be usedfor analyzing materials for renewable energy generation.The new large scale project has been dubbed EMIL.In this document we present the modifications to the ma-chine optics and to what extent these changes affect theperformance of BESSY II.PROJECT DESCRIPTIONThe Helmholtz Zentrum Berlin (HZB) and the Max-Planck Society (MPG) are going to implement EMIL, theEnergy Material in situ Lab at the BESSY II synchrotronlight source.The EMIL-facility is dedicated to in-situ and in-systemX-ray analysis of materials and devices for photovoltaicapplications and for (photo-) catalytic processes. EMILis subdivided into SISSY@EMIL for the investigation ofphotovoltaic materials and processes and CAT@EMIL forambient-pressure spectroscopies at catalytic materials. Thelarge variety of available methods (PES, PEEM, HAXPES,XES, XAS, XRF, XRD) will enable the investigation ofsample structures with information depths ranging from afew nanometer up to the micron scale.The X-ray light source for these stations will consistof two canted insertion devices, a variably polarizing AP-PLE II undulator for soft X-rays (80 eV- 2.2 keV), and aplanar cryogenic undulator for hard X-rays up to 10 keV.The end stations can either be operated with both beamssimultaneously in a common focus or use alternatively ei-ther the soft- or the hard X-ray radiation. Two beamlinesare attached to the undulators and disperse and distributethe radiation to the various end stations. A double crystalmonochromator is used for the hard X-ray branch, while acollimated plane grating monochromator with variable de-flection angle is planned for the soft X-ray branch.EMIL includes two undulators. The undulator U16 isforeseen as a cryogenic in vacuum undulator with a periodlength of 16.25mm and a peak field on axis of 1.16T at anominal gap of about 5mm. The second undulator, gener-ating predominantly soft X-rays, is of APPLE II type andhas a period length of 48mm. To mitigate deleterious ef-fects of the undulator on the performance of the storagering and to avoid beam scraping the β-functions along theundulators have to be kept sufficiently small.∗ peter.schmid@helmholtz-berlin.deREQUIREMENTS FOR THE MACHINEOPTICSTo separate the beam cones generated by the two undu-lators, the undulators have to be canted; i.e. there has to besome deflection between those undulators. The undulatorswill be installed in a triplet section of the BESSY II storagering [1].In the following, we show that the vertical beam waistcan be shifted by about a meter from the center of thestraight at the planned location of the cryogenic undula-tor keeping the original value of the vertical β-function atβyo = 1.2m at the beam waist.Finally, a refined machine optics is presented which en-hances the performance of the undulators by optimizingthe vertical β-function locally and minimizing the pertur-bations in the rest of ring.THE MACHINE TESTThe modifications to wirings of the magnets in the sec-tion T6 are shown in [1].At BESSY II all elements of the quadrupole familiesQ3,Q4 and Q5 are wired in pairs connected along the straight.Each pair in a straight is powered by a single power sup-ply. Only for this test a facility was provided to power thequadrupoles in a single section asymmetrically.Since power supplies providing the full current for thenew circuits were not available, equipping the ring withpower supplies and the required large cross section cablesand the cuts through the shielding would have required along shutdown (postponing the test by at least a year), theadditional power feeds required for the EMIL optics areprovided by floating power supplies, capable of providingoffsets of ±40A (four quadrant power supplies).The requirements for the test are: Keeping the proper-ties of the users’ optics intact while shifting the vertical β-function in one of the short straight sections (T6) by 0.8mdownstream utilizing no new optical elements. The min-imum of the β-function at the beam waist should remainat 1.2m and the tune has to remain the same [1]. The re-sult of optics simulation with the help of MAD8 [2] for thestraight T6 in comparison to the original optics is shown inFig. 1.The β-functions for the entire BESSY II storage ring af-ter the modification is presented in Fig. 2. The area shadedin yellow indicates the modified section T6.With the help of LOCO [3, 4] and the Matlab MiddleLayer (MML) [5], we were able to dial in the machine op-tics within two iterations. The resulting optics obtained fol-TUPPP007 Proceedings of IPAC2012, New Orleans, Louisiana, USAISBN 978-3-95450-115-11614Copyrightc ○2012byIEEE–ccCreativeCommonsAttribution3.0(CCBY3.0)—ccCreativeCommonsAttribution3.0(CCBY3.0)02 Synchrotron Light Sources and FELsA05 Synchrotron Radiation FacilitiesFigure 1: β-functions in the straight T6. Blue lines indicatethe original optics, green lines the optics modified for theproject EMIL.Figure 2: Design optics for EMIL after modifying sectionT6.lowing a LOCO analysis is presented in Fig. 3.A comparison between the design optics and the mea-sured one predicted by LOCO is shown in Fig. 4 convinc-ingly demonstrating that the vertical beam waist can beshifted to the appropriate location.The required and the achieved figures for the shift of thevertical beam waist ∆s0 and the vertical β-function βy0 atthis location are compiled in Table 1.Table 1: Comparison of design and measured figures forthe shift of the vertical beam waist ∆s0 and the verticalβ-function βy0 at the vertical beam waist.design measured∆s0 0.856m 0.923mβy0 1.194m 1.212mAfter optimizing the settings of the sextupoles in sectionT6 while keeping the settings of the remaining sextupolesFigure 3: Measurement: LOCO-Analysis of the opticsmodified for the EMIL project.at their usual values, the lifetime at a current of 300mA canbe restored to 10 h, somewhat less than the typical 12 h forthe original optics. The injection efficiency did not changeappreciably from the values obtained for the standard op-tics.Figure 4: Comparison of the β-functions of the design op-tics and the actual optics measured by LOCO.RECENT DEVELOPMENTSCombining the center dipole of the straight with aquadrupole is beneficial in two aspects: i) in the current op-tics design the minimum vertical betatron function is 1.2m.Decreasing this value permits a smaller magnetic gap ofthe cryogenic undulator without sacrificing beam aperture(lifetime reduction). This permits a reduction of the periodlength which enhances the flux in the hard X-ray regime;ii) The large betatron function at the UE48 downstreamend is reduced avoiding a beam scraping with the undulatorchamber. Reducing the gap of the cryogenic undulator toless than about 5mm, increases the photon flux by a factorof two for hard X-rays.Furthermore, photon beam calculations suggest that thecanting angle can be lowered to 2mrad.We estimate that the vertical β-function at the locationProceedings of IPAC2012, New Orleans, Louisiana, USA TUPPP00702 Synchrotron Light Sources and FELsA05 Synchrotron Radiation FacilitiesISBN 978-3-95450-115-11615 Copyrightc ○2012byIEEE–ccCreativeCommonsAttribution3.0(CCBY3.0)—ccCreativeCommonsAttribution3.0(CCBY3.0)of the downstream end of the undulator UE48 has to bekept smaller than originally thought requiring an additionalquadrupole modeled as a gradient on top of the deflectingdipole in the center of the straight if the beam waist at thecenter of the cryogenic undulator is further decreased.Utilizing the well-known formula for the propagation ofa β-function in a drift [6], the value of the β-function∆s =3.37m distant from the waist is calculated to 13.5m for aβ-function β0 = 0.9m at the location of the waist.Since a β-function of this size equates to a vertical aper-ture of 6.6mm given BESSY II’s vertical acceptance of3.2 × 10−6mrad leading to beam scraping and thus areduction in life time, an additional focusing element ismandatory.The detailed requirements for the refined optics are: Avertical β-function at the beam waist in the center of thecryogenic undulator of 0.9m, a shift of the vertical beamwaist by 1.125m and a βy-function at the downstream faceof the undulator U48 of less than 6.4m. A machine opticsfor the cell including T6 which fulfills the requirements andminimizes the optics perturbations caused by the EMIL op-tics is shown in Fig. 5. The beam cross sections and theemittances remain at almost the same values as those forthe user optics.To maximize space available for undulators, the extradeflection can be provided by reducing the main dipolesdeflection by 1mrad compensating the bending angle ofthe additional dipole at the center of the straight T6. Fur-thermore, a gradient on this dipole provides focusing in thesimulation, minimizing the vertical β function at the down-stream end of the undulator U48 (drawn in red in Fig. 5).The location of the cryogenic undulator is indicated in blue.We are confident that a value of βy0 = 0.9m for thevertical β-function at the center of the cryogenic undulatorwould allow a full gap of 5mm and thus the undulators canprovide the requested flux and brightness.The resulting optics for the entire BESSY II storage ringis presented in Fig. 6.Figure 5: Simulation of the refined unit cell for EMIL.Figure 6: Simulation of the β-functions for BESSY II in-cluding the refined unit cell modified for the project EMIL.CONCLUSIONSThe Project EMIL necessitates modifications toBESSY II’s machine optics. The vertical beam waist instraight T6 has to be shifted. We successfully demonstratedthat during an experiment a shift by the required amountkeeping the original value of the vertical β-function atthe beam waist is indeed possible without hampering theperformance and the beam parameters of the BESSY IIstorage ring.If smaller values of the vertical β-function at the beamwaist are required for optimizing the performance of theundulators, this quantity can be lowered to 0.9m withoutsubstantially altering the beam properties of BESSY II.ACKNOWLEDGMENTThe excellent support by BESSY’s engineering depart-ment is gratefully acknowledged. Support by G. Rei-chardt and K. Lips of EMIL’s project management and byA. Jankowiak is gratefully appreciated.REFERENCES[1] J. Bahrdt et al., "Modification of the BESSY II optics forthe implementation of a small gap undulator, Proceedingsof the 2nd International Particle Accelerator Conference(IPAC 11), pp. 3251–3253, San Sebastian, Spain, September2011.[2] H. Grote and F. C. Iselin, The MAD program (methodi-cal accelerator design) version 8.4: User’s reference manual,CERN, 1991.CERN-SL-90-13-AP-REV.2,[3] J. Safranek, Nucl. Inst. Meth. A 388 (1997) 27.[4] J. Safranek, G. Portmann, A. Terebilo, and C. Steier, Matlab-based LOCO,  Proceedings of the 2002 European Par-ticle Accelerator  Conference  (EPAC 02),  pp. 1184–1186,Paris, France, June 2002.[5] J. Corbett et al., Accelerator control middle layer,Proceedings of the 2003 Particle Accelerator Conference(PAC 03), pp. 2369–2371, Portland, May 2003.[6] H. Wiedemann, Particle Accelerator Physics ISpringer, 2003., p. 154,TUPPP007 Proceedings of IPAC2012, New Orleans, Louisiana, USAISBN 978-3-95450-115-11616Copyrightc ○2012byIEEE–ccCreativeCommonsAttribution3.0(CCBY3.0)—ccCreativeCommonsAttribution3.0(CCBY3.0)02 Synchrotron Light Sources and FELsA05 Synchrotron Radiation Facilities

Modifications to the Machine Optics of BESSY II  Necessitated by the EMIL Project

Modifications to the Machine Optics of BESSY II Necessitated by the EMIL Project

http://www.helmholtz-berlin.de/pubbin/oai_publication?VT=1&ID=72096

Modifications to the Machine Optics of BESSY II Necessitated by the EMIL Project

Abstract

Similar works

Full text

Available Versions

HZB Repository

HZB Repository