Marquardt, N

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Particle Accelerators, 1990, Vol. 33, pp. 27-32Reprints available directly from the publisherPhotocopying permitted by license only© 1990 Gordon and Breach, Science Publishers, Inc.Printed in the United States of AmericaTHE DORTMUND ELECTRON TEST ACCELERATOR • 0 E L T A •A NEW LOW-EMITTANCE STORAGE RING OF 1.5 GeVNIELS MARQUARDT*DELTA GroupInstitute of Physics, University of Dortmund,P.O.Box 500 500, 4600 Dortmund 50, GermanyAbstract A new low-emittance electron storage ring has been designedat the University of Dortmund, the construction of which starts now. Theintention of this facility is to provide test possibilities for acceleratorresearch and synchrotron-radiation instrumentation and to foster thedevelopment of compact high-brightness photon sources, of acceleratorcomponents, and of various insertion devices. Of particular interest is thedevelopment of FEL's in the UV and VUV range (A. < 20 nm). To alimited extent DELTA will be used as a light source for short-termsingle-user experiments exploiting very special beam qualities, i.e.a particular time structure, high-current single-bunch operation orlow-beta focusing for micro-undulator operation. The facility consists ofa 100 MeV LINAC, a booster synchrotron BODO which can operate also as astorage ring, and the main storage ring DELTA. The large flexibility of theDELTA lattice with two 20 m long dispersion-free straight sections allowsto run with different beam optics and is optimized for FEL operation.INTRODUCTIONThe Dortmund ELectron Test Accelerator DELTA (1,2) currently underconstruction at this University is a third-generation synchrotron light sourceof maximum energy of 1.5 GeV covering different ranges of photonenergies. It is aiming at improving the spectral brilliance by several ordersof magnitude by optimizing the storage ring magnetic lattice for low emittanceand very high circulating currents and by extensive use of magnetic-insertionand free-electron-laser devices. For such experiments one can chooseoptics with emittances as low as € = 4'10-9 m rad at 1 GeV. However, oneof the design goals of the DELTA lattice is its large flexibility whichalso provides normal operation with standard optics of emittances of€' = 2.10-8 m rad and emittance values as large as ~ 10-7 m rad.* B. Baasner, C. Biermann, F. Brinker, S. Brinkmann, J. Friedl, R. Heisterhagen,N. Marquardt, M. Michel, M. Negrazus, D. Nolle, M. Schiirmann, K.Wille,V. Ziemann[1717]/2728/[1718] N.MARQUARDTBesides its low emittance the DELTA lattice with its triplet focusingstructure and strong bending fields guarantees also short synchrotron dampingtimes and, due to an effective sextupole arrangement, a reasonably largeenergy acceptance of at least ~p/p = 2%.The new facility uses a 100 MeV electron LINAC and a 1.5 GeV slowlyramped booster synchrotron, called BODO (BOoster DOrtmund), forfull-energy injection into the 1.5 GeV storage ring DELTA (see Figure 1).This main machine with a circumference of 115.2 m consists of twohalf-circular arcs separated by two 20 m long, straight sections withoutdispersion, providing space for extremely long undulators. A ratherconventional stainless-steel (316 LN) vacuum chamber of small cross-sectionhas been designed with one antechamber at its inner circumference forcontinuously pumping with a combination of integrated DIP's and NEG pumps.A few lumped ion pumps at selected locations and turbo-molecular pumpsfor roughing are also part of the system. An average vacuum pressurewith circulating beam of at least 10-9 mbar is foreseen and should providebeam lifetimes of 10-20 h. This ultra-low pressure and the smallimpedance of the designed beam chamber are providing the necessaryhigh-current operation. The RF frequency is 500 MHz to utilize DESYcavities in the beginning of the operation of DELTA. Routine machineruns and first experiments are expected to start late in 1993.PURPOSE OF THE DELTA FACILITYThe basic design goals of DELTA described above were chosen to providea test-accelerator facility which also meets the stringent requirementsnecessary to serve as a powerful driver for different FEL experiments.Since test measurements and FEL operation of the storage ring imply ratherfrequent changes of machine optics, operational conditions and evenbeam-line modifications and have a severe influence on the beam qualities,DELTA will not be a typical light source for long-term experiments of~nchrotron-Radiation ( SR ) users and industrial production services.Although clearly available for preparation and test runs of such SRapplications, the main purpose of DELTA is different. The intention of thistest accelerator facility is threefold, namely :(1) investigation of accelerator physics in general,(2) FEL experiments from the visible to the XUV regime,(3) Single-user experiments utilizing very special beam qualities.Concerning point (1) an intense program ofR &D of mode-damped single-and multi-cell cavities and an investigation of cavity modes and of theinfluence of higher-order-mode losses on beam quality are planned. Thedevelopment of various accelerator components, SR instrumentation, feedbacksystems, beam-position and emittance monitors as well as of differentinsertion devices will also be performed. A special program for investigatingthe unsolved problems of low-energy injection and beam instability dueto the generation of ions will be attacked, in particular, by using the booster.THE DORTMUND ELECTRON TEST ACCELERATOR [1719]/29Secondly, the main goal of DELTA is FEL research with the aim of pushingthis technology from the visible regime to the XUV, in particUlar, to wave-length clearly below 20 nm. There is a three-phase FEL project planned at theDELTA laboratory for joint FEL-storage-ring operation (2,3). Startingwith an inexpensive and flexible optical klystron, FELICITA I J the mainpart of which is a simple electromagnetical undulator of 16 identical,25 em long periods (4m total length), the second step will be the 14 m longhybrid-magnet undulator, FELICITA II , of ~230 periods of 6 em length each.In the beginning experiments with FELICITA I will be performed in thevisible with the DELTA storage ring running at low energies (== 500 MeV).Since this device can simply be split into two undulators and a dispersivesection by differently powering the various coils, FELICITA I can operatein an optical-klystron mode of about 10 % gain and lower output or in thenormal FEL mode with lower gain (=4%) and higher output. With astorage-ring energy of 1 GeV FELICITA I should reach the oscillatorthreshold also at intermediate wavelengths of the order of 100 nm, sinceat higher electron energies twice the peak current (180 A) is expected.The next step is the high-gain FEL , FELICITA II , operating near100 nm with DELTA running at 500 MeV and peak currents of 150 A. With theexperience gained so far and operating DELTA at even larger peak currentsand energies around 1 GeV, it should be possible to generate radiationat wavelength as low as 20 nm. This will be possible, however, only if suitablemulti -layer mirrors of reasonably high reflectivity for these wavelengthregime will then be available. If the severe mirror problems can not besolved in time, construction of a single-pass FEL with very high gain(750 periods of 2 crn length, few mm gap height) operating in a pulsedmode is envisaged as phase III of the Dortmund FEL development program.Finally, the DELTA facility will also be available for short-termsingle-user research work either with the demand for testing theirinstrumentation or for very special beam qualities, like a particular timestructure by single- or multi-bunch operation, high electron currents,optimized emittance and spectral brilliance, or particularly stable beams.LATTICE AND MACHINE PARAMETERS OF STORAGE RING AND BOOSTERMany features of the DELTA lattice and its optical functions are dictatedby the requirement of using the storage ring as an efficient FEL driver.As mentioned already, these are- low emittance- short damping time- high peak currents- high flexibility of the optics- long beam life time- large energy acceptance- high beam stability- about 20 m long straight sections with zerodispersion and slOWly varying betafunctions- sophisticated accelerator-control and diagnostic system.30/[1720] N. MARQUARDTTo fulfill all these conditions and, moreover, to provide sufficient space inbetween the iuany bending and focussing lilagnets, the original closelypacked FOOD lattice has been modified to a triplet structure. The fourfoldsymmetry has been preserved but with much more ample space between allmagnets and a short straight section in each arc for injection andacceleration cavity, respectively. Different versions of the opticscontaining either the optical klystron, FELICITA I, in one of the long straightsections or a by-pass in the other one, have been calculated togetherwith preliminary versions of two transfer channels for ejection of theelectrons from the booster. A layout of the new lattice exhibiting all thesefeatures simultaneously is shown in Figure 1.DELTAEjectionBY-PASSFIGURE 1 General layout of the lattices of the DELTA storage ring withoptical klystron and by-pass (different version) and of thebooster synchrotron BODO with two ejection lines and LINAC.Figure 2 shows the dimensions of the new triplet focussing structure and theoptical functions of the new lattice design for one full quadrant of DELTAtogether with the FELICITA I undulator as insertion in one of the straight sec-tions. The unit cell has slightly been modified compared with the previousdesign (2). Each cell consists now of two short (20 em) defocussing and one long(40 em) focussing quadrupoles mounted between two dipoles of 115 em length,20 0 deflection angle, and 1.52 Tesla field strength at maximum energy of1.5 GeV. Low emittance has been obtained, as for the original design, due to therelatively small and flat beta and dispersion functions. Dispersion matchingTHE DORTMUND ELECTRON TEST ACCELERATOR [1721]/31QrQDBQDIDELTA Triplet CelliFIGURE 2 Dispersion D(s) (top) andhorizontal and verticalbeta functions (3x,z(s) (middle) for onequadrant of DELTA and FELICITA Iinsertion included. - The lower partshows the layout ofa single triplet cell.Qr~.The injection system ofDELTA consists of a 100 MeVLINAC and the synchrotronBODO which can be rampedslOWly to the full injectionenergy of DELTA of 1.5 GeV. Besides functioning as a standard synchrotron,BODO can also be operated in a storage-ring mode with low-energy currentaccumulation, but shorter life times. To reduce costs the same dipoles of 1.15 mlength and the short 0.20 m quadrupole magnets as for DELTA are also used forBODO. The design of the various DELTA magnets was determined by thesmall cross-section of the vacuum chamber and the necessary field strengthsand, therefore, also by arguments of cost reduction. The specificationswith the long straight sections has been accomplished by splittingthose four (of a total of 18) bending magnets adjacent to the driftsections into 8 bendings of half the length. In the case of the insertion ofFELICITA I only 7 0 deflection10-1 D instead of 10 0 are generated101 Px.Pz X_\~~~~o~~=~~~~F=~=~=~~M~a~f=~~T~A~U~Q~~~·~~~~~~~~~bY the short matching dipoles.\ 1\ 6.0 Another four quadrupoles are3.00 \ ',! "............ necessary at both sides of5.0\ 1 I fJz the long straight section to\ D(s) " r \ 4.0 properly match the optical2.00 . \~.1\ .. /\ .. /\ ..I\ .r..}........... 3.0 functions at the centralI \ ! \ I i\ ! \ II ,t", 2.0 symmetry point in the center ofI \ l\! I ~ '"I J V V I \ ,.~ 1.0 this drift section. By two.('7"7\. . ./ >:-<:~.__ _0.0 additional weak 3 0 bendingsI \ ,---\ r--' r--' / 1.0 the electron beam is deflectedI/ -2.0 into the undulator and 10 0deflection is obtained again.In this way, electron beam andlaser beam are sufficientlyseparated near the mirrors inthe optical cavity by E:20 em.Similar lattice calculationshave been done with an extraby-pass at the opposite side-t~~~: -,,-,8.~.' "W'-"-"-"-"-"-'~8'e... "-"- ~~~. - ~G~:~:2:+:~~~:~~:n~:~~~;ue· e· ~ ~ e· eee· bysextupolar-fleldcomponents~ integrated in the quads (2).115 .~335 c.... _ Table 1 summarizes all para-meters of the standard versionof the· linear beam optics ofDELTA and the correspondingparameters of the booster BODO.32/[1722] N.MARQUARDTTABLE 1 MACHINE PARAMETERS OF DELTA Be BODO( at 1.5 GeV )Circumference L [m] 115.2 50.4Number of Dipoles nd 22 20short (0.575m) 6 4long (I.15m) 16 16Bending Radius &end [m] 3.43 3.43Number of Quadrupoles nq 73 24short (0.2m) 55 24long (O.4m) 18Tunes Qz 9.285 3.197Q% 2.613 3.225Natural Emittances:0% coupling £r [nt.rad] 1.1 · 10-8 3.8. 10-11% coupling Ez [m.rad] 1.1 · 10-8 3.8.10-7~% [m.rad] 1.1 · 10-10 3.8.10-9100% coupling ~:r,% [m.rad] 0.55.10-8Momentum Compaction a 4.48.10-3 9.0.10-2Natural Chromaticity ex -20.95 -5.36ez -6.17 -5.43Damping Times:horizontal Tr [msec] 8.67 4.7vertical Tz [msee] 8.46 3.7Synchotron Damping Time T~ [msee] 4.18 1.6Revolution Frequency In (kHz] 2602.37 5952.38Energy Spread 6.E/E 7.02. 10-4 6.7.10-4Energy Loss / Thm dE (keV] 136.24 136.0Accelerating Frequency fRF [MHz] 500 500Hannonic Number q 192 84Max. Av. Current ( 1 blmch ) I,na% [rnA] 100Max. Av. Current ( 10 bunches) [max [rnA] 500Number of Cavities nc 1 1RI Power for I = 500mA RRF (kW] 80 60of the bending magnets with 50 mm gap height and of the quadrupoleswith 70 mm inner aperture were only slightly changed compared with theformer ones (2). First designs of the accelerator hall (on ground level),laboratories and radiation-shielding walls were performed.REFERENCES(1) K. Wille, Nnc!. Instr. Meth. Phys. Res. A272(1988)59; DELTA Report (1986)and Status Report (1988), University of Dortmund, unpublished.(2) N. Marquardt, Proc. 1989 Particle Accelerator Conf., Chicago, to bepublished in IEEE Conf. Record.(3) M. Negrazus, Contribution to this Conference.

The Dortmund Electron Test Accelerator Delta: A New low-emittance Storage ring Of 1.5-gev

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