Projects of SR sources including research and development for insertion devices in the USSR

Nuclear Instruments and Methods in Physics Research A303 (1991) 435-447 North-Holland

435

Projects of SR sources including research and development for insertion devices in the USSR G.N. Kulipanov Institute of Nuclear Physics,

630090 Novosibirsk, USSR

In this article the technical status and the properties of the already existing electron-positron storage ring synchrotron radiation (SR) sources and those under construction at the Institute of Nuclear Physics (Novosibirsk) are reviewed. The prospects of developing SR sources and the possibilities of new projects, in particular Siberia-3 (based upon the 10 GeV storage ring) and Siberia-4 (based upon the 2.4 GeV storage ring with 6 T superconducting magnets), are discussed. Also considered are various wigglers and undulators (electromagnetic devices, superconducting devices, and devices based on permanent magnets) designed for the INP storage ring . Possible schemes for the arrangement of insertion devices at SR sources and in the FEL optical klystron, which were invented and designed at our Institute, are shown. 1. Introduction The major characteristic that determines the practical value of any SR source is the spectral brightness (Ba ). It is equal to the number of photons (NPh ) emitted within a given spectral range (OX/X) per unit time (At) and per unit area of source (OS) into a unit solid angle (OS2): B

approximately by an additional order of magnitude. Third generation SR sources having even still lower emittance and higher energy, make it possible to employ undulators as sources of X-ray radiation. Owing to the interference of radiation from all undulator poles these devices generate quasimonochromatic radiation with monochromaticity OX/X a 1/n and spectral brightness n2 times higher than radiation from bending magnets.

Nph

(AX/X) Ot OS012'

Brightness defines the duration of a great variety of experiments and technological procedures [1]. Fig. 1 shows a now well known diagram of the history, current state-of-the-art and prospects for increasing the brightness of X-ray sources. Since the invention of the first X-ray tubes, i.e . in the past 60 years, their brightness has been improved by a factor of about 100. The use of electron synchrotrons and then electron-positron storage rings as X-ray synchrotron radiation sources has enabled the SR community around the world to increase the brightness of SR sources in a revolutionary way since the 1970s. Changing over from synchrotrons to storage rings increased the brightness about 10 2-10 3 times. Further increase was due to the usage of multipole wigglers for X-radiation generation . These devices establish a sign-variable magnetic field on a rather long section of the orbit, thereby concentrating the radiation to a beam with a n-fold increase of its intensity (n = 10 1-102 is the number of wiggler poles) . Dedicated storage rings - second generation SR sources - have offered the possibility of reducing the emittance of electron (positron) beams and, hence, decreasing the area of SR sources, and thus increasing the brightness

20 16 V) d

û á A

16

14

ó

12

. L.

10

a on

8

6 1900 1920

1940

1960

1980 2000

Fig. 1 . Spectral brightness of the existing, constructed or planned X-ray sources .

0168-9002/91/$03 .50 © 1991 - Elsevier Science Publishers B.V . (North-Holland)

II . SR FACILITIES

43 6

G.N . Kulipanov / SR source projects

Bearing in mind the fact that undulators with n = 102 are now in use and that in the nearest future undulators with n = 103- 10 ° are expected to be employed, we may surely predict an increase of the brightness of SR sources by a factor of 10 3-104 in the next decade, as is shown in fig. 1 . This diagram also illustrates the brightness of the SR sources that are currently in use, or are being designed and constructed at the Institute of Nuclear Physics (Novosibirsk) .

/ ,ra/~ZSWRVAWM W.1

6

-2M E=650 Me 1=100 mA r=1-6 h U,=10 cm f=16 .7 MH

Î ~Í~r1

2. The use of INP storage rings as SR sources For thirty years, the Novosibirsk Institute of Nuclear Physics has created a family of electron and positron storage rings (VEP-1, VEPP-2, VEPP-3, VEPP-2M, VEPP-4, BEP) for research in elementary particle physics using colliding beams. The Siberian SR Center was founded on the basis of VEPP-2M, VEPP-3 and VEPP-4 [2]. Table 1 lists the basic parameters of the storage rings and the arrangement of the experimental stations is depicted in figs . 2-4. A list of experimental stations and the teams involved in SR research at these stations are given in table 2. At present there are over 100 teams from institutes and institutions in the Soviet Union (Novosibirsk, Moscow, Leningrad, Vladivostok, Krasnoyarks, Yerevan, etc.) and abroad (Germany, Czechoslovakia, Bulgaria, Poland, England, India, China) [3,4]. Since 1974 the electron-positron storage ring VEPP2M has been used as a source of UV and soft X-ray radiation in the parasitic operational mode with colliding beam experiments . To generate undulator radiation with X = 300-100 Á, a helical electromagnetic undulator with a 2.4 cm period [5] was installed at this storage

2 3

a

G

ring ; in 1983 it was replaced by a superconducting undulator [6]. For a long time it was the only source of undulator radiation having circular polarization in the world. A five-pole superconducting wiggler with an 8 T field has been in successful operation at the storage ring since 1984 [7]. It has facilitated SR research with X = 3-10 A. The installation of this wiggler at the 0.65 GeV storage ring has instigated the solution of a number of acceleration problems. In recent years, the VEPP-2M was reconstructed in order to improve its experimental possibilities . The storage ring VEPP-3 has been used as a SR source since 1973 . Since 1979, one of its long straight sections has been used for work with wigglers and undulators . The world's first practical 3.3 T superconducting 20-pole wiggler, mounted at VEPP-3 in 1979, has enabled the brightness of the X-ray SR beam to be increased by a factor of 200 in the 1 .4 range [8].

VEPP-2M

VEPP-3

VEPP-4

operational 2.0 290 2.3

reconstructed 6.0 270 0.3

120 120 2 240 10

250 220 60 72 25

60 20 78 181 15

2-6 e-, e+ 9 3 (W+2U)

6-20 e , e+ 19 6 (4W+2U)

operational 0.7 205 18-BM, 4.5-W

1-6

a

X-ray lithography SXR-spectroscopy y UV-time resolved spectroscopy 4. VUV-spectroscopy 5 SXR-microscopy 6,7. X-ray lithography 1. 2. 3

Fig. 2. Accommodation of experimental stations on VEPP-2M SR beams.

Table 1 Main parameters of VEPP-2M, VEPP-3 and VEPP-4 Name Status Energy [GeV] Emittance [nmrad] Critical wavelength [,k] a Stored current [mA] Total Single bunch SR power [kW] Rf frequency [MHz] Bunch length 2as [cm] Lifetime [h] Touschek Vacuum Type of filling Number of beam lines Insertion devices number

0

e-, e+ 9 2 (W + U)

BM : bending magnet ; W: wiggler; U : undulator .

43 7

G. N. Kuhpanoo / SR source projects

a EXPERIMENTAL AREA

SR

BYPASS FOR FEL

E=2 GeV 1=200 1nA T=2-6 h

---

b

Fig. 3. (a) Layout of the VEPP-3 storage ring. (b) Accommodation of experimental stations on VEPP-3 SR beams: 2a - Lane diffractometry, 2b - anomalous scattering, 3 - SPXRFA ; 4 - angiography; 5a - X-ray microscopy and microtomography; 5b - time resolved diffractometry ; 5c - macromolecular crystallography; 5d - small-angle diffractometry; 6 - time-resolved spectroscopy ; 7 X-ray topography ; 8 - EXAFS ; 10 - X-ray lithography.

Fig. 4. Plane view of the new SR experimental hall near the VEPP-4 tunnel .

Since 1979 the VEPP-3 storage ring has also been employed in work with the optical klystron - a modification of the free electron laser [9]. In 1979-1985, modifications of undulators (constructed with permanent magnets) OK-1, OK-2 and OK-3 were positioned at the storage ring (see table 6) . In 1987 a dedicated straight section, a DC bypass parallel to the major straight section, was installed for work with the optical klystron (see fig. 3) . The bypass can be used only if the electron beam energy is less than 500 MeV . Accordingly, the magnetic elements of the bypass are considerably shorter than those of the major straight section of VEPP-3, designed for an energy of 2.2 GeV. This gave an 8 m long free space at the bypass which is available for the OK system : electromagnetic undulators (each 3.5 m long) and a buncher. Generation of radiation in the 6900-2400 Á range was obtained at the bypass VEPP-3 OK in 1988 . It is the first FEL which is able to operate in the UV range [10] . II . SR FACILITIES

G.N. Kuhpanou / SR source projects

43 8

Table 2 List of experimental stations in Siberian Synchrotron Radiation Centre

X-ray lithography X-ray lithography Photoelectron spectroscopy Photochemistry Time resolved luminescence X-ray photoemission spectroscopy VUV spectroscopy SXR spectroscopy Optical klystron Compton back scattering Laue diffractometry Anomalous scattering X-ray fluorescence elemental analysis Digital subtraction angiography X-ray microscopy and microtomography Time resolved powder diffractometry Macromolecular crystallography Time resolved X-ray luminescence Small angle anomalous scattering Topography and diffractometry EXAFS spectroscopy Total

Number of groups 4

1 2 2 5 1 6 5 2

4

1

4

14 3 3

31 2 5 2

8

31

139

For further research on X-ray holography using undulator radiation, the scheme of mutually coherent radiation generation from two undulators separated by an achromatic bend is of interest. This scheme was realized on the VEPP-3 bypass [11] .

At present, VEPP-3 is involved in OK experiments, in X-ray synchrotron radiation experiments [2-4], in nuclear spectroscopy experiments on the internal target [12], and in photonuclear experiments using the beam of gamma quanta produced by backward Compton scattering [13] . Between 1979 and 1985 the storage ring VEPP-4 was used in experiments with hard X-ray synchrotron radiation in parasitic mode coupled with colliding beam experiments . Updating VEPP-4, which envisages a special straight section in middle half-rings for wigglers and undulators, is being completed. Not far from the VEPP-4 tunnel, the construction of a shielded bunker (of about 1200 m2 total area) is under way. About 20 experimental stations and special laboratory rooms for users (see fig. 4) will be installed.

3. Development and construction of dedicated SR sources for other regions of the USSR At the Institute work is in progress on the creation of dedicated and very efficient SR sources - the storage rings Siberia-1 [14] and Siberia-2 [15] . The small Siberia-1 is used as a source of VUV and soft X-ray radiation, while the large Siberia-2 is intended for research studies in the hard X-ray range. Note that Siberia-1 serves as a booster for injection into Siberia-2. Siberia-1 was built at the INP and operation began at the Kurchatov Institute in 1983. The storage ring is schematically shown in fig. 5, and table 3 gives its basic parameters. The facility has a weakly-focusing magnetic lattice, its maximum energy amounts to 450 MeV, and

Fig. 5. Schematic diagram for the installation of Siberia-1 components.

G. N. Kuhpanov / SR source projects

439

Table 3 Parameters of the dedicated SR sources Siberia-1, Zelenograd and Siberia-2 Name

Siberia-1

Zelenograd

Siberia-2

Status Energy [GeV] Emittance [nmrad]

Operates 0.45 880 61-BM, 21-W

Conctr. 1991 1 .5 27 8-BM

Constr . 1991 2.5 78 1.75-BM

360

Critical wavelength [tl] Stored current [mA] Total Single bunch SR power [kW] Rf frequency [MHz] Bunch length 2a, [cm] Lifetime [h] Touschek Vacuum Type of filling Number of beamlines Insertion devices number

360 4 34 .5 60

300

100 -30 181.3 4

300 100 200 181.4 4

5

10

10

e7

e39

e39

1 (W)

2 (SCW) 5 (W) 2 (U)

7 (2W+5U) 2 (SCW)

the injection is performed at 35-60 MeV. Despite the relatively low injection energy, Siberia-1 is able to multiply accumulated electrons up to a current of 360 mA

with an injection current of no more than 20 mA .

Several seconds is sufficient for the beam to be accel-

erated from injection to maximum energy. A three-pole 4.3 T wiggler was specially designed for Siberia-1 (see

table 5) . Siberia-1 can accommodate ten SR beam lines from bending magnets with X = 61 Á and one beam line from the wiggler with A = 21

A.

Since 1985, experi-

~ - UNDULATOR - SUPERCONDUCTING WIGGLER o - CONVENTIONAL WIGGLER

Fig. 6. Layout of the Siberia-2 storage ring. II . SR FACILITIES

44 0

G. N. Kulipanou / SR source projects

Table 4 Parameters of undulators and wigglers created for Zelenograd and Siberia-2

a

Parameters

Wl (SC)

W2 (SC)

W3 (SC)

W4 (EM)

W5 (EM)

W6 (REC)

W7 (SC)

Penod [cm] Total length [cm] Number of periods Field amplitude [T] Minimum gap [cm] Wavelength [ .4] Critical Fundamental

-45 -100 1 10 4

-40 80 1 8 3 .5

11 130 12 < 0 .65 3 .2

24 110-210 4-8 1 3 .2

20 180 8 0.15 3 .2

5 -260 50 0.4 2 .5

10 -260 25 3 2 .5

a

0 .3

--1

100-1500

8 .3

800

10-40

=1

SC : superconducting magnets ; EM : conventional electromagnet ; REC : permanent magnets .

ments with the SR generated by Siberia-1 have been carried out at five experimental stations . The storage ring Siberia-1 is a booster storage ring of the facility, including an injector (a linac at 80-100 MeV), two transport lines for electron beams, and the large storage ring Siberia-2 with a maximum energy of 2.5 GeV). Siberia-2 (fig. 6) is planned to have about 40 SR beam lines from bending magnets and from wigglers and undulators positioned in nine straight sections, each being about 3 m long . The other three straight sections will accommodate the injection system for electrons and rf cavities . Table 3 presents the basic parameters of the storage ring, and in table 4 the parameters of insertion devices which are planned to be employed at Siberia-2 in the Kurchatov Institute are listed . All the Siberia-2 systems are scheduled for completion in mid-1991, and the work on beam injection to the storage ring will be initiated in late 1991 . An additional project using the 1 .2-1 .5 GeV electron storage ring (the dedicated SR source for technological purposes in microelectronics) was reported at the SRI-82 conference [161 . The project has envisaged an integrated solution to the following problems in submicron technologies and materials science : - Commercial and cheap fabrication of devices having submicron structures (0 .7-0 .1 Wm) using X-ray lithography . To do this, bright beams of soft X-ray radiation within 4-40 A from bending magnets and dedicated lithographic wigglers are required . - Implementation of dry, low-temperature deposition and etching of various oxide and metal films with the aid of photoinduction processes in gaseous phase (CVD process) . The latter are realized using high-power radiation beams from undulators in the 2500-100 A range. - Express analyses of both the used materials and the technological processes for the creation of submicron electronic devices . The plan is to use bright SR beams (A = 0.5-4 ~k) from 7 T superconducting wigglers for this analyses. Research and development for the project were initiated in 1986 . A construction site was found in

Zelenograd, 30 km away from Moscow . This town is the Soviet analogue of Silicon Valley. The building is expected to be constructed by the end of 1990 ; the equipment is to be installed in 1991 . The linac-injector, the booster and the large storage ring are to be commissioned by the end of 1991 . The project incorporates the basic elements of the magnetic system and lattice of Siberia-2 . The same injection system is used . The parameters of the storage ring Zelenograd are listed in table 3, and those of the wigglers and undulators in table 4 .

4 . Some peculiarities of INP electron-positron storage rings Electron-positron storage rings, that were designed and built at the Institute over the past 30 years (VEP-1, VEPP-2, VEPP-3, VEPP-2M, VEPP-4, Siberia-2, Zelenograd) are undoubtedly different both in their parameters and their design. However, they have some common features, distinguishing them from the facilities traditionally utilized outside the USSR . These features do not always imply better operation. First of all there are certain characteristics determined by the engineering and technological potential of our Institute, its traditions and its long history of practical work with storage rings . Let us dwell upon these peculiarities : a) As injectors for major storage rings, use is made of booster-storage rings rather than boosters-synchrotrons (VEPP-2, and then BEP for VEPP-2M, VEPP-3 for VEPP-4, Siberia-1 for Siberia-2). Booster-storage rings are intended to preliminarily store electrons or positrons in order to obtain the necessary number of bunches and increase their energy up to the required value. Due to radiation damping in booster-storage rings, the injected electron and positron beams have a small phase volume, thus enabling the aperture in the major storage rings to be determined depending only on lifetime requirements without infection ones. In addition to lowering the cost major storage rings, this also

G. N. Kulipanov / SR source projects

441

Table 5 Parameters of superconducting wigglers and undulators created at the INP (Novosibirsk)

Wiggler (VEPP-3) Undulator (VEPP-2M) Wiggler (VEPP-2M) Wiggler (Siberia-1)

Year

E [GeV]

1979 1984 1984 1985

2.1 0.65 0.65 0.45

[kG]

a~ [?+]

P [kW]

Jt o [cm]

Np

L [cm]

34 4.7 80 58

1 .3 63 6 21

1 0.6 0 .07

9 2 .4 -

20 16 5 3

90 25 60 35

Bmax

gives the possibility of installing small-aperture wigglers and undulators. (For example, the helical undulator vacuum chamber at VEPP-2M has an 18 mm inner diameter) . Both the relatively slow increase of energy in booster-storage rings and the low rate of injection cycles are compensated by the high storage current obtained . b) Bending magnets of the major storage rings are usually made from nonlaminated magnetosoft ARMCO-type steel . At maximum energies, the magnetic fields in bending magnets are fairly high : B = 1 .9 T at VEPP2M, B = 2 .1 T at BEP, and B = 1 .7 T at Siberia-2 . As a rule, in the case of low-energy injection, the working fields in storage rings change over a wide range (for VEPP-3 Bmax/B ,i = 8, for Siberia-1 Bm~/B ,i = 10) . c) A special correction of the pole-shape in the quadrupole lenses and a set of weak sextupoles are used for chromaticity control (VEPP-3, BEP) . d) Sets of octupole lenses are employed to control the value and sign of the cubic nonlinearty of betatron oscillation frequencies (VEP-1, VEPP-3, VEPP-4, Siberia-1) . e) To suppress the high current, coherent instabilities of betatron oscillations, not only the values of the chromaticity and cubic nonlinearity are corrected, but also their required signs are given (VEPP-3, Siberia-1, VEPP-3 bypass) [17,18] . This enables the mode of fast damping of coherent betatron oscillations to be reached during injection which, in turn, provides for example particle accumulation at Siberia-1 with a frequency of 0.5 Hz at 2-5 s radiation damping time. Table 6 Parameters of undulators created at the INP (Novosibirsk) for work with an OK

Period [cm] Total length [cm] Number of periods Field amplitude [kG] Gap [cm] Length of OK [m] Wavelength [gym] Years

OK-1

OK-2

OK-3

SmCO 10 30 3 3 1 .1 1 .1 0 .63 1979-1980

SmCo 6.5 30 4.5 7 1 .1 1 .1 0.63 1981-1982

Smco 6 .9 80 11 6 .4 1 .3 2.0 0 .63 1984-1985

f) The INP storage rings are mainly comprised of long wave rf cavities (f = 180 MHz) . Although this provides no possibility for the generation of the shortest bunch lengths, it does readily facilitate the single-bunch mode of operation at 100 mA/bunch current. g) In order to be able to use the full length of the straight sections, the power coil connections to the bending magnets and the quadrupole lenses are made at the centre of the elements rather than at their ends . For the same reason, all the joints in the vacuum chamber are welded, and there are no flange connections . h) The power coils for the bending magnets at Siberia-2 and Zelenograd have a special shape [19] . With the fixed gap between the poles, this provides at the end of the magnet a section whose field is 4-' of the maximum field . It is thus possible to separate radiation from bending magnets and from undulators positioned in straight sections, as well as to reduce the heat flux from the end of the magnets to the straight sections containing superconducting devices .

5. Research and development on insertion devices at the INP Since 1978 the Institute has designed and constructed a fairly great number of insertion devices . Various technologies for the fabrication of these devices on the basis of i) superconducting magnets (table 5), ii) permanent magnets (table 6), and iii) conventional electromagnets (table 7), were developed . The choice of both the design of wigglers and undulators and of the type of magnetic lattice was, on the one hand, based on user's requirements for wigglers and undulators as optical sources and, on the other hand, on the acceleration requirements for insertion devices as the elements of the storage ring magnetic lattice. This choice was influenced by other factors such as the cost, materials, traditions, etc . 5.1 . Peculiarities in the design of superconducting wigglers and undulators a) Utilization of iron magnetic cores and yoke . This allows us to increase the wiggler field by 1 .5-1 .8 T, to 11. SR FACILITIES

442

G. N. Kuhpanov / SR source projects

Table 7 Parameters of electromagnetic undulators and wigglers created at the INP (Novosibirsk)

Helical undulator VEPP-2M Wiggler VEPP-4 Wiggler VEPP-3 Undulator OK VEPP-3

Year

E [GeV]

B_ [kG]

1980 1985 1986 1987

0 .7 5 .5 2.0 0 .34

2 .1 16 22 5 .6

reduce the stray field, and to decrease the magnitude of the energy stored in a wiggler. b) Employment of segmented, series coils in strongfield wigglers. Large diameter wire is used for an inner coil, thus allowing a reduction of the current density in turns being in a maximum magnetic field . c) Use of vacuum chambers at nitrogen temperature . Owing to this some sections of the wiggler being at helium temperature are thereby shielded from the beam, and the possibilities of heating these sections by the SR beam or the coherent energy losses of the beam are eliminated . On the other hand, the pole gap may be made smaller than in the case of a warm vacuum chamber due to the absence of additional nitrogen screens . d) Utilization of an alcohol solution cooling agent for SR absorbers with a freezing temperature lower than that of water . e) Simultaneous utilization of radiation from wigglers by a large number of experimental stations (for example, nine stations at the VEPP-3 wiggler) . To do this on strong-field wigglers-shifters (VEPP-2M, Siberia-1, Zelenograd) the problem of a "second" source had to be solved, i .e . it was necessary to avoid simultaneous arrival of radiation from two sections of a wiggler at any experimental station . This necessitated in collimation at VEPP-2M by means of additional beam stoppers despite the fact that such a collimation limits the number of experimental stations . For Zelenograd, a special wiggler construction is used . The long edge poles of this wiggler produce a magnetic field equal to 100 of the field in the central pole. In this case, radiation from the "second" source is considerably softer and is readily absorbed by Be foils . 5 .2 . Peculiarities in the design of undulators on the basis of permanent magnets [20,21] a) Iron in undulators OK-1, OK-2 and OK-3 is utilized to reduce the stray magnetic fields . b) The idea of longitudinal concentration of the magnetic flux with the aid of iron poles was first realized in the design of OK-2 (1981) . Known as "hybrid", these undulators have found wide use not only in the generation of undulator radiation, but also in the

[f1] 100 0 .4 2 .1 2400 7200

Àu

[cm]

S [cm]

Nu

lu

2 .5 22 15+30+15 10

1 .8 2 .2 3 2.2

10 5 3 68

25 110 70 680

[cm]

FEL magnetic systems . It should be noted that the design of OK-2 has fixed thin poles being at zero potential . The presence of such poles in the OK-2 design permits one to independently change the gap between the major poles on any section of the undulator without changing the field in the remaining sections (see fig. 7) . c) In the OK-3 design (1984), the major and neutral poles are wedge-like . This shape makes it possible to reduce the stray fields and to optimally utilize the magnetic material. 5.3. Peculiarities of undulator designs on the basis of conventional electromagnets. a) The third harmonic of the field in the long undulators of the VEPP-3 bypass is suppressed to less than 3% . This minimizes the contribution of undulators to the cubic nonlinearity .

PM a) OK-1 unducator

Tunung Stud

r,ll~lr r~rr lui/rr~

loi il!

ts (CS EM) Gap 9

ÎIIiIIÎ

rrOrM

.al.!aM 6) OK-2

undu2ator

rr

MEN 1

..rfr~r1

p.C e

110

~13á~ )Mr%rr

Îi Zero poten

... 1

c) OK-3

undu2at,or

Fig. 7 . Vertical cross section of undulators OK-1, OK-2 and OK-3 designed at the INP for work with the optical klystron .

G. N. Kulipanov / SR source projects

b) To induce the field in undulators of the VEPP-3 bypass, there are eight, periodically curved copper buses with holes for water . Commutation is performed at the end faces, thus offering the possibility of using a highcurrent power supply and a design which is both cheap in construction and simple in service . 5 .4. Minimization of the effect of insertion devices on the beam in a storage ring The installation of strong-field wigglers and long undulators exerts a significant effect on particle motion in a storage ring . The most noticeable effects are : - shift in vertical betatron tunes due to the edge-focusing effect (Ax,, = 0 .12 for the VEPP-2M wiggler and Ov~ = 0 .23 for undulators at the VEPP-3 bypass) ; - shift in the horizontal betatron tune due to both the finite dimension of the magnetic field in a wiggler in the horizontal direction and the appearance of the field . = 1/15 for gradient on the orbit in a wiggler (Op,/w the VEPP-3 wiggler) ; - there appears a dependence of the betatron oscillation frequencies on the amplitude (ap./aa 2 = 5 .4 x 10 -z cm -2 for undulators of the VEPP-3 bypass) and an appropriate decrease of the dynamic aperture . a) To weaken these effects in storage rings, it is necessary to consider insertion devices as the usual elements of the magnetic lattice which have to be matched in the standard way. For this purpose, either each quadrupole lens of the periodicity element has an individual power supply, as for example the VEPP-3 bypass, or independent strong-field stirring coils are used in quadrupole lenses, as at VEPP-2M . To minimize the influence of strong-field wigglers, straight sections with small f3-function are usually required (B, = 5 cm for VEPP-2M, 8, = 50 cm for Siberia-2). b) Sets of octupole lenses are needed to compensate for the dependence of betatron oscillation frequencies on the amplitude. It was impossible to have small beam sizes in the bypass VEPP-3 without such a compensation since strong third- and fourth-order resonances with large islands were observed in a wide range of betatron oscillations frequencies. c) A horizontal displacement of the centers of the wiggler poles is applied either to redistribute the magnitudes of the betatron oscillation shifts, as for example at Siberia-1, or to match Op. t o zero at the ultimate fields as at VEPP-2 [7].

6 . Development of compact SR sources for technological purposes Commercial production of submicron devices for microelectronics makes it necessary to implement the X-ray lithographic technology and a great number of

443

Table 8 Parameters of the BEP and Siberia-SM storage rings Name

Siberia-SM

BEP

Status Energy [GeV] Emittance [nmrad] Critical wavelength [ .~] Stored current [mA] Total Single bunch SR power [kW] Rf frequency [MHz] Bunch length gas [cm] Lifetime [h] Touschek Vacuum Type of filling Number of beamlines Insertion devices

constructed

commissioned

300

760

0.6 85 8.6

10

30 16

0.8 41 13.6

29 26 .83 15

4

4

e-

e-

no

no

28

12

comparatively compact and reliable sources of X-ray radiation with X . = 10 A. The BEP storage ring, the recently built facility with standard warm magnets, may be considered as a prototype of a compact SR source for X-ray lithography [22] . The parameters of the storage ring are listed in table 8, and its layout may be found in fig. 8 . The distinct feature of this storage ring lies in the fact that it utilizes magnets whose poles are made as concentrators with large chamfers in transverse cross section . The resulting field equals 2 .1 T, such that 850 MeV electrons have a

BEP E=800~leV

Fig . 8. Installation of the BEP storage ring components . II . SR FACILITIES

G. N. Kuhpanoo / SR source projects

44 4 superconducting magnet

0

2m

Fig. 9. Installation of the Siberia-SM components .

total orbit circumference of 22 .3 m. The BEP magnetic system comprises 12 periods, each representing a FODO cell . Synchrotron radiation can be readily extracted from each bending magnet . A 200 MeV synchrotron is now being designed and is to be placed inside the BEP ring as the injector . Such a storage ring would be able to compete, in compactness, with storage rings utilizing superconducting magnets . A project for such a compact, superconducting storage ring Siberia-SM is being developed at the INP in cooperation with NPO Vacuummashpribor (Moscow) . The Siberia-SM [23] is designed for a 600 MeV electron beam with a 10 m orbit circumference containing 8 superconducting rectangular magnets at a field of 6 T . The general view of the storage ring is demonstrated in fig . 9 and the basic parameters are listed in table 8 . A superconducting rectangular magnet is the most complex component of the storage ring. Such a magnet has low energy capacity, no stray fields and a high-quality field at the injection energy (at a level of 0 .6 T) . The wedge-like winding utilizing iron makes it possible to obtain a 6 T field in the gap by using simple tools because of the low level of field at the superconducting windings (no higher than 4 .5 T) and the insignificant forces acting on the windings. The first tests of this magnet were performed in a special cryostat . A magnetic field of 6.25 T was reached the first time the current was increased . After 20 test cycles the maximum field in the gap was 6 .74 T. After the test of two prototypes, the manufacturing of the first real devices was started in March of 1990 . Detailed magnetic measurements on these samples are expected to be completed by the end of 1990. Their aim is to evaluate the quality of the magnets from the

accelerating point of view . Superconducting magnets for two storage rings of the Siberia-SM facility are scheduled to be ready for use in 1991 . The remaining components of the storage rings (rf cavity, quadrupole lenses and others) are made warm ; some are already ready and the others are being fabricated . Siberia-SM is planned to be put into operation in 1992 . Superconducting rectangular magnets are designed in such a way that they are suitable for use in high energy storage rings. For example, a compact 600 MeV storage ring for submicron X-ray lithography may be composed of eight magnets ; a compact storage ring at 900 MeV energy for X-ray lithography for micromechanics [24] may be composed of 12 magnets, and finally, a 1 .8 GeV storage ring for angiography may be composed of 24 magnets . At the INP, a small-scale electron synchrotron at an energy of 200 MeV [25] and a superconducting linear accelerator at an energy of 50 MeV [26] are being fabricated as injectors for compact storage ring SR sources utilized for technological purposes . The small synchrotron (fig. 8) is a compact device with overall dimensions of 2 x 2 mZ and a weight of 3 tons . The synchrotron magnetic system includes four 90 ° magnets, each having a homogeneous field of 1 .5 T, and four independently powered quadrupoles . The straight sections between magnets are 0 .6 m ; the synchrotron circumference is 5 .1 m ; and the magnet aperture along the vertical and the horizontal directions amount roughly to ± 2 cm . The magnets are supplied by pulsed current, exponentially increasing with a time constant of about 0.5 ms . The energy stored in a capacitor employed for pulsing the magnets is about 10 kJ, and the mean power is roughly equal to 10 kW with a pulse repetition frequency of 1 Hz . The acceleration time amounts to about 1 .5 ms . The vacuum chamber is made from stainless steel of 0 .2-0 .3 mm thick. With the law of field increase chosen, the chamber practically does not distort the topography of the magnetic field in the aperture . The accelerating rf cavity power is supplied by a power amplifier which provides a pulsed power of about 30 kW . A small 8 MeV microtron serves as the injector for the synchrotron . The microtron is positioned under the center of the synchrotron .

Table 9 Parameters of the superconducting linac Energy [MeV] Electron pulse current [mA] Duration of pulse [ns] Repetition frequency [Hz] Rf frequency [MHz] Acceleration gradient [MeV/m] Liquid helium consumption [1/h]

50 20 20 0.5 2450 25 3.5

G. N. Kulipanoo / SR source projects

445

The utilization of superconducting magnets in the Siberia-SM facility, coupled with cryogenic equipment, makes it natural to use a superconducting injector . A superconducting pulsed linear accelerator is being designed at the INP [26] . Its parameters are given in table 9. The linac accelerating structure is a niobium round waveguide with a diaphragm . The structure operates in travelling wave mode and its operation is accompanied by the recirculation of the electromagnetic wave . The linac is comprised of two section, each 1 m long. The overall length of the linac, including the injector, buncher and the cryostat is 4 m. The linac is powered by a 5 MW klystron at an anode voltage of 50 kV . 7 . Projects of new SR storage rings; third-generation SR sources in the USSR The third generation of dedicated X-ray SR sources which is now being planned in Europe, USA and Japan (ESRF, APS, SPring-8), will produce beams of X-ray undulator radiation whose spectral brightness is limited only by diffraction effects . The Institute of Nuclear Physics, in cooperation with the JINR (Dubna), is planning a similar 10 GeV storage ring with the name Siberia-3 . The preliminary parameters and layout of the storage ring may be found in table 10 and fig. 10 respectively. Besides the generation of synchrotron and undulator radiation beams, this project also envisages opening new possibilities due to an increase in energy to 10 GeV [27] : a) Photon (polarized) generation with record intensity and brightness in a wide spectral interval : 100 eV to 100 keV using undulators ; 100 keV to 3 MeV using superconducting wigglers ; 3 to 30 MeV using backward Compton scattering by far infrared laser intracavity Table 10 Design parameters of the Siberia-3 storage ring, the third-generation dedicated SR source Name

Siberia-3

Energy Circumference Horizontal emittance Magnetic field strength Number of cells Number of straight sections Number of insertion devices Critical energy from BM Energy loss per turn Positron current Number of bunches Bunch length Rf power

10 GeV 1452 m 6X10-9 m rad 7 kG 10 30 27 46 .6 keV 18 .7 MeV 100 mA 10-100 1 cm 2-3 MW

Fig. 10. Layout of the Sibena-3 storage ring - the 10 GeV third-generation dedicated SR source.

photons (without the knocking out electrons from the beam) ; 30 MeV to 3 GeV using backward Compton scattering by laser photons, with the energy of secondary-photons determined by measuring the energy of a knocked-out electron ; 3 to 10 GeV using backward Compton scattering by photons of undulator radiation (c = 5-50 eV), mirror-reflected from the preceding bunch and with an energy of the secondary-photons determined by measuring the energy of a knocked-out electron . Of particular interest are the beams of full energy photons having a monochromaticity of - 10-2 when using the primary photons of undulator radiation with an energy greater than 50 eV . b) Utilization of the beams of gamma quanta (e, _ 1 .7-2 MeV) from a superconducting wiggler in order to obtain powerful pulsed fluxes of neutrons via photonuclear reactions . The use of beryllium, having the lowest threshold for photonuclear reactions (1 .66 MeV), as the target gives the possibility of obtaining an intense, pulsed flux of neutrons without any moderation (energy range 10 3 -10 5 eV, number of neutrons per pulse 10 9, repetition rate 2 X 10 5, and pulse duration 10 -9 s) . For experiments which use time of flight monochromatization the energy resolution is better than 10 -3 and is already achievable on 10 m bases . c) Generation of pulsed beams of slow, bright positrons from electron-positron pair production by a beam of gamma quanta (e y = 1 .2-1 .5 MeV) from a superconducting wiggler . At present, the highest efficiency for the production of slow positrons using linear electron accelerators is [28] : K(e -.

+ eSiow )

_ 10-6 II. S R FACILITIES

G.N. Kulipanoo / SR source projects (in es',.W/200 MeV electrons). This provides a flux of slow positions of 10 6 (es;,/pulses) for a pulse ranging from 10 to 3 ns duration and a 300 Hz repetition rate . For gamma quanta beams of synchrotron radiation, the achievable efficiency for production of slow positrons is as follows: K(-y-esóW )-3x10 -5

(in esów,/1.5 MeV -y-photons) . For a given power in the primary beams of either electrons or gamma quanta (10 kW), the flux of positions will be 10 ° times larger when using gamma quanta. Correspondingly, 107 (e;'+OW/ pulses) is attained at a 1 ns pulse with a repetition rate of 2 x 10 5 Hz. The proposed project for the Siberia-3 storage ring can also open other interesting experimental possibilities [27]. This project has a need for physicists who are eager to take advantage of these possibilities and who are able to formulate adequate problems . The Siberia-3 project will become a reality only if it finds the support of physicists of various specialities from JINR (Dubna). Another and not so expensive project for a dedicated third generation SR source, the storage ring Siberia-4, is planned for construction at the Siberian Synchrotron Radiation Centre in Novosibirsk. The project is based on the use of superconducting bending magnets with a field of 6 T that are similar to those intended for the storage ring Siberia-SM. In addition, the electron energy is assumed to be about 2.4 GeV, corresponding to the maximum admissible quantity for 6 T superconducting bending magnets . This energy is determined by the fact that due to the growth of energy spread in the beam (Sz.(cE 3B) the lifetime of the electron beam reduces because the tails of the Gaussian energy distribution lie outside the ultimately permissible limit (SE/E)max, which is determined either by the size of an

Table 11 Design parameters of the superconducting storage ring Siberia4 Name Energy [GeV] Circumference [m] Emittance [nmrad] Magnetic field strength [T] Critical wavelength [A] Energy loss per turn [MeV] Stored current [mA] Total Single bunch Rf frequency [MHz] Type of filling Insertion devices

Siberia-4 2.4 72 21 6 0.55 2.03

300 100 180 enone

Fig. 11 . Layout of Siberia-4 (1 2.4 GeV storage ring) with superconducting magnets.

rf bucket or the dynamic aperture. It is usually equal to SE/E = 2.5-1%. It is easy to show that Emax (GeV) B.r < 103(SE/E)max

Setting B = 6 T and SE/E = 1.25% we therefore obtain E,ax a 2.5 GeV. The Siberia-4 magnetic lattice has been chosen to be symmetrical relative to the centre of the bending magnets, thus providing a minimum of betatron functions inside the magnets and a considerably smaller emittance of the electron beam as compared with the lattices consisting the achromatic bends. In this case, only the radiation from bending magnets is planned for utilization. Possibly, there will be two long straight sections for undulators . The basic parameters of the storage ring Siberia-4 are listed in table 11, and the layout of the storage ring is depicted in fig. 11 . This type of storage ring may be employed as a commercial SR source for angiography as well . In this case, by analogy with the name of a Japanese SR source SPring-8 the storage ring for angiography may be referred to as SUMMER-2 .4 (Superconducting Universal Medical Middle Energy Ring). 8. Conclusion The presented survey does not include compact SR sources based on pulsed synchrotrons which are being fabricated in the USSR. This survey is not concerned with the previously suggested projects for electron storage rings in Yerevan and Kharkov since the financing

G. N. Kuhpanoo / SR source projects for these projects still remains open . Related information for these may be found in a previous survey [29] .

Acknowledgements I would like to acknowledge the help of my col-

leagues,

V.N .

Korchuganov,

N.A .

Mezentsev,

A.N .

Skrinsky and N.A . Vinokurov in writing this survey . I

also thank T. Golubnichaya, E.B . Levichev, S.B . Lee and L.G . Morgunov for their contributions to the preparation of this survey for publication.

References [1] G.N . Kulipanov and A.N. Skrinsky, Sov . Phys . - Uspekhi 20 (1977) 559 . [2] Siberian SR Centre, Preprint INP N 90-90 (Novosibirsk, 1990) p. 55 . [3] G.N . Kulipanov (ed.), Proc. 7th USSR Nat. Conf. on Synchrotron Radiation Utilization (SR 86), Nucl . Instr. and Meth . A261 (1987) 1-338. [4] G.N . Kulipanov and E.S . Glushkin (eds .), Proc. 8th USSR Nat. Conf. on Synchrotron Radiation Utilization (SR 87) A282 (1989) 369-768. G.L . Kezerashwili, A.P. Lysenko, V.M . Khorev et al., Proc . Nat. Conf on Synchrotron Radiation Utilization (SR 82), Preprint INP (Novosibirsk, 1982) p. 109. [6] V.V . Anashin, G. Kezerashwili, A.P. Lysenko et al ., Preprint INP 84-111 (Novosibirsk, 1984). [7] V.V. Anashin, I.B . Vasserman, A.M . Vlasov et al ., Preprint INP 84-123 (Novosibirsk, 1984). [8] A.S. Artamonov, L.M . Barkov, V.B . Baryshev, N.S . Bashtovoy, N.A . Vmokov, E.S . Glukin, G.A . Korniukhm, V.A . Kochubei, G.N . Kulipanov, N.A. Mezenksev, V.F . Pindiurin, A.N . Skrinsky and V.M . Khorev, Nucl . Instr. and Meth . 177 (1980) 239. N.A . Vinokurov and A.N . Sknnsky, Preprint INP 77-59 (1977). IN . Drobuazko, G.N . Kulipanov, V.N . Litvinenko, IN Pmayev, V.M. Popik, I. G. Silvestrov, A.N . Skrinsky, A.S . Sokolov and N .A ., Vinokurov, Free Electron Lasers, ed . Y. Petroff-Bellingham, Proc. SPIE (Int . Soc. Opt. Eng. (USA) 1133 (1989) 2. [111 N.G . Gavrilov, G.N . Kulipanov, V.N . Litvinenko et al ., Preprint INP N90-13 (Novosibirsk, 1991).

44 7

[12] S.G . Popov, Proc. Topical Conf. on Electronuclear Physics with Internal Target, ed . R.G . Arnold (World Scientific, Singapore, 1989) p. 37. [13] G.L . Kezerashwili, Preprint INP, N 262-90 (Novosibirsk, 1990). [14] V.V. Anashm et al., Preprint INP, N 82-116 (Novosibirsk, 1982). [15] V.V. Anashin, A.G . Valentinov, V.G . Veshcherevich et al., Proc. 8th, USSR Nat. Conf. on Synchrotron Radiation Utilization (SR 88), Nucl. Instr. and Meth . A282 (2989) 369. [16] V.N . Korchuganov, G.N . Kulipanov, N.A . Mezentsev, A.N . Skrinsky and N.A . Vinokurov, Proc. Int. Conf. on X-ray and VUV Synchrotron Radiation Instrumentation, Nucl . Instr. and Meth . 208 (1983) 11 .

[17] N.A. Vmokurov, E.A. Perevedentsev et al ., Preprint INP N 76-88 (Novosibirsk, 1988). [18] N.A. Vinokurov, V.N . Korchuganov, G.N . Kulipanov et al ., Preprint INP N 76-87 (Novosibirsk, 1987). [19] A.G . Valentinov, P.D . Vobly, S.F . Mikhailov et al ., Preprint INP N 89-174 (Novosibirsk, 1989). [20] G.A. Kornyukhin, G.N . Kulipanov, V.N . Litvinenko, N.A. Vinokurov and P.D . Vobly, Proc Int . Conf . on X-ray and VUV Synchrotron Radiation Instrumentation, Nucl. Instr. and Meth . 208 (1983) 189. [21] N.A . Vinokurov, Proc . Int. Conf. on X-ray and VUV Synchrotron Radiation Instrumentation, Nucl . Instr. and Meth . A246 (1986) 105. [22] V.V . Anaslnn et al ., Preprint INP N 84-114 (Novosibirsk, 1984). [23] V.V . Anashin, V.S . Arbusov, G.A. Blinov et a] ., Proc. 8th USSR Nat. Conf. on Synchrotron Radiation Utilization (SR 88), Nucl . Instr. and Meth . A282 (1989) 386. [24] W. Ehrheld, P. Bley, F. G6tz, J. Mohr, D. Miinchmeyer, W. Sehelb, H.J. Baving and D. Beets, J. Vac. Sci. Technol. B6 (1988) 178. [25] 1.1 . Averbukh, T.A . Vsevolo,Iskala et al ., Preprint INP N90-116 (Novosibirsk, 1990) . [26] S.I . Bibko, V.G. Vescherevich et al ., Preprint INP N90-117 (Novosibirsk, 1990) . [27] G.N . Kulipanov, Proc . 3rd Int. Conf. on Synchrotron

Radiation Instrumentation, Rev. Sci. Instr. 60 (1989) 1406 . [28] J. Dahm, R. Ley and K.D. Niebling, Proc. Symp. on Antimatter '87, Kernforschungszentrum Karlsruhe (KfK), eds. P. Poth and A. Wolf (Baltzer, 1988) p. 151 . [29] G.N . Kulipanov, Proc. 7th USSR Nat. Conf. on Synchrotron Radiation Utilization (SR 86), Nucl . Instr. and Meth . A261 (1987) 1.

II . SR FACILITIES