Nuclear Instruments and Methods in Physics Research A 347 (1994) 9-13North-Holland

Taizo Sasaki

1. Introduction

This article is primarily intended to celebrate the30th anniversary of the first successful demonstrationof the potential capability of synchrotron radiation byR.P . Madden and K. Codling at the National Bureauof Standards in 1963, and the 25th anniversary of thecommissioning of Tantalus I, the first electron storagering made available as the dedicated synchrotron sourceof the University of Wisconsin, 1968 .

Since those early days we have witnessed dramaticprogress in synchrotron radiation research, a tremen-dous expansion of the users' community as well asfields of exploitation, the advent of a number of newdisciplines and novel research opportunities coming onone after another, upgraded instrumentation and tech-nical standards, and so on .

The scene of synchrotron radiation research we seenow is totally different from what we saw 30 years ago.We have reached a world which was merely a fantasythen . Anybody who dreamed of a great future forsynchrotron radiation research could perhaps not an-ticipate, nor predict, the presently realized benefit andthe variety of its progress as an entity . The spectaclecurrently in front of us lies far beyond the horizon ofthose early days .

One may well doubt then if it is worthwhile toattempt a retrospective glance of the way throughwhich we have come up to the present status .

What I would like to emphasize in this retrospectivereview is not this and that individual scene of the olddays, but to envisage what kind of motivations andincentives guided us to this new world, and what kindof difficulties had to be overcome through the last 30years. Then it will become clear that the nature ofenergy actuating our ceaseless effort has essentiallyremained the same since 30 years ago.

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2. State of the art around 1963

NUCLEARINSTRUMENTS&METHODSIN PHYSICSRESEARCH

Section A

The international development of synchrotron radiation research -a view from Japan

Spring-8 Project Team, and KEY, National Laboratory for High Energy Physics, 1-1 Oho, Ibaraki-ken, Tsukuba 305, Japan

A sketch of the early phase of synchrotron radiation research is attempted. The initial efforts undertaken worldwide towardsutilization of synchrotron radiation for spectroscopy are reviewed, and the historical significance of the first achievements by NBSscientists and the commissioning of the first dedicated storage ring source, Tantalus I, is emphasized. Early developments in Japanand U.S.-Japan interactions and a history of the collaboration are also reviewed .

Studies on the nature of light and the interaction oflight with matter have played a key role in humanunderstanding of nature . Electromagnetic theory, thetheory of relativity, and quantum mechanics were allcreated on the basis of a long term human quest intheories and experiments on optical phenomena.

Developments in optical sciences have obviouslybeen tied to the availability of artificial light sources.Various light sources with different wavelength rangeswere made available by the mid-20th century but therewere a few important dark gaps in the electromagneticspectrum left . Above all the most significant gap was aregion extending from ultraviolet through X-rays, whichwas considered serious for the entire scientific activi-ties as it is just the region of the most intensiveinteraction of light with matter .

Synchrotron radiation emerged to fill this importantgap of the spectrum and made possible many opticalexperiments previously unexplored .

In 1963, when the NBS scientists achieved their firstsuccessful results with synchrotron radiation, aJapanese users' group, INS-SOR, had just started aset-up of a soft X-ray beam line . The author was thenengaged in vacuum ultraviolet spectroscopy by using aspark discharge of Weissler's type . Fig. 1 shows atypical record of the spectral lines from the dischargesource, emitted from ions in a low pressure He-N2mixture. As seen from this record, no lines adequate asa practical source for photometry are observed above20 eV .

The Tanaka lamp, another practical source of thatday, provided a continuum extended beyond 10 eV, butnothing above 20 eV.

It was hopeless then to attempt any spectroscopicalstudies beyond it, as 20 eV lies at the end of valence

I. HISTORICAL MILESTONES

10

T. Sasaki /Nucl. Instr. and Meth

electron excitation for most materials, and the oscilla-tor strength of the shell is nearly exhausted by thisenergy .

As a consequence studies on electronic excitationsin atoms, molecules and solids in the 1950s and 1960swere basically limited to those associated with valencestates, and the fundamental concepts of valence stateshave been established by the end of the 60s. Dramaticprogress had been witnessed in solid state spectroscopyand the main features of spectral behavior of thedielectric function were successfully interpreted interms of electronic band structures .

However, a major part of inner-shell phenomenawere left entirely unexplored due to the lack of asource . More exactly, even shallow inner-shells wellbelow 20 eV were also left unknown before the adventof synchrotron radiation, a typical example being spec-tral behaviors of shallow p-shells of K, Rb, and Cs inalkali halides .

In these circumstances, structure studies with anovel spectroscopic means such as XANES and XAFS,and X-ray crystallography were far beyond our scope.

The great potential capability of synchrotron radia-tion as a light source covering ultraviolet through X-rayswas anticipated by a number of physicists and chemistssince the early 1950s when an intensive characteriza-tion experiment in soft X-rays by Tomboulian's groupat Cornell resulted in excellent agreement withSchwinger's theoretical prediction in every respect,namely, spectral behavior, angular distribution, andpolarizing character [1]. Similar efforts in characteriza-tion had also been reported from Moscow, Frascati,Sendai [2] and from the USA, all concluding in agree-ment with theory . All these results were quite encour-

to Phys Res . A 347 (1994) 9-13

aging and it was natural that people tried to proceed tothe next phase, the actual exploitation of the radiationas a source for soft X-ray spectroscopy . Such initialtrials in the 1950s have been reported by D. Tombou-lian himself, U. Timm at the Bonn Synchrotron, andF.A. Korolev at Lebedev Institute, Moscow . Unfortu-nately, however, most attempts in the 1950s eventuallyfailed to achieve promising results in spite of big ef-forts given by all these pioneering workers. Thingswere not so easy as the beautiful theory suggests . Thesignificance of the Madden-Codling experiments [31deserves particular emphasis under the unfavorablecircumstances around 1963 in that it demonstrated forthe first time the great power of synchrotron radiationas well as the technical feasibility of SR spectroscopy .It was indeed a great encouragement to all those tryinghard to cope with the severe conditions of the experi-ments.

The impact of this experiment was also tremendousin its scientific achievement . This was the full demon-stration of autoionizing phenomena produced by theconfiguration interaction between two degeneratequantum states, and envisaged a previously unknowncomplexity and beauty of inner-shell excitations andelectron correlation phenomena.

It was also a beautiful example of the interplaybetween theory and experiment as all the unusualspectral features observed in absorption bands havereadily been interpreted by a comprehensive theoryalready worked out by U. Fano shortly prior to theexperiment [4] . In fact Fano also was fully aware of thepotential capability of synchrotron radiation, and gavegreat encouragement in carrying out this particularexperiment . Experimental circumstances for NBS spec-

Fig . 1 . A photoelectric record of emission lines from a spark discharge

in a low pressure mixed gas (N 2 /He) . Wavelengthsindicated on each line are given in t-\ .

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troscopists were also more favorable than those forother synchrotron radiation users of that time, as theywere privileged to use a big fraction of the operatingtime of the machine.

Most of the users at the other facilities had to workmostly as the parasite, namely, they were not allowedto manage the operational schedule, and access to theexperimental area was regulated under security con-trol . Furthermore, electron synchrotrons are in generalunstable . Electrons are injected at low energy and thenramped up to a predetermined maximum energy, andfinally the beam is converted to y-rays by hitting atarget placed inside the orbit and totally lost ; thenanother injection starts . Electron numbers captured inthe orbit may differ with every injection so that theintensity fluctuates . During a cycle of acceleration, thephoton spectrum varies according to the electron en-ergy, and the beam position, the cross section and itsshape are also time dependent. An example is shownin Fig. 2, which is the typical behavior of the beamprofile observed with a streak camera some day at theTokyo synchrotron [5] . Although the stability of syn-chrotrons was improved later, it was obvious that stor-age rings should provide a great improvement in thisrespect. Commissioning of Tantalus I at Wisconsin 25

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T. Sasaki /Nucl. Instr. and Meth . in Phys. Res. A 347 (1994) 9-13

Fig. 2 . Cross sections of electron beam during a cycle ofacceleration observed with a streak camera. Instantaneous

values of electron energy are indicated in the figure [5].

years ago was therefore a big step towards a newconcept of the synchrotron light source, and the effectof this transition was a dramatic improvement of thequality of optical experiments . Thus the 25th anniver-sary of its commencement also deserves celebration .

3. US-Japan interactions in synchrotron radiation re-search [6]

An electron synchrotron was first made available inJapan in 1962 . It was completed at the Institute forNuclear Study (INS), Tanashi, Tokyo, as the firstJapanese facility for the production of the pion whichwas predicted by H. Yukawa, with 14 years' delaybehind the discovery of that particle in Berkeley, Cali-fornia .

The delay was related to some political background .Immediately after the 2nd World War the occupationauthorities considered activities associated with parti-cle accelerators to be nuclear power oriented and anyattempts toward building new accelerators were strictlyforbidden. Furthermore, four cyclotrons built by thattime in Tokyo, Kyoto and Osaka were destroyed andthrown into Tokyo Bay and Osaka Bay in 1945 .

American physicists paid serious attention to thesefacts, and A. Compton and E.O . Lawrence took initia-tives in advising the occupation authorities to revisethe policy . As a consequence the ban was lifted in1951, a year ahead of the US-Japan peace treatysigned in 1952 .

These developments encouraged Japanese physi-cists to establish INS, the first national collaborativeinstitution for high energy and nuclear physics equippedwith accelerators, with S. Kikuchi as the first directorin 1955 .

Construction of an electron synchrotron was startedin 1956 and completed in 1961 . Meanwhile, S. Kikuchiand S. Sawada, who was an X-ray spectroscopist, bothbeing then professors of physics in Osaka university,happened to stay in early 1950s at Cornell Universityand had contact with D.H. Tomboulian . Japanese syn-chrotron builders were interested in applications ofsynchrotron radiation through this experience from thevery earliest moment . The first beam line at INS wasmade available in early 1963 soon after a proposal wassubmitted by T. Oshio and T. Sasaki . A users' group,INS-SOR, was formed to make timely use of it . INS-SOR was assigned beam time twice a year, and onaverage, each beam time allocation was two weeks.The rest of the beam time was also open, but onlyavailable parasitically . After a year's characterizationand beam monitoring studies, INS-SOR decided tostart with photographic recording of spectra in view ofinstabilities of the source . A 1 m grazing incidentspectrograph was made available by Y. Iguchi, Institute

I . HISTORICAL MILESTONES

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T. Sasaki/Nucl. Instr. and Meth . in Phys. Res . A 347 (1994) 9-13

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Fig . 3 . A densitometer record of absorption spectrum ofhelium in the region of autoionization series obtained with a 1m spectrograph at INS in March 1965 . Electron energy was450 MeV, and a thin foil of aluminum was used to filter the

higher order components below 170 .4 [8] .

for Optics, by a courtesy of M. Seya . The first success-ful absorption measurements with this instrument wereachieved in March 1965 .

Published results included a few inner-shell absorp-tion spectra of metals and alkali halides in solid states[7] . Specimen were thin evaporated films supported onorganic foils . We also tried to record rare gas spectraas a confirmation of the NBS results . An example ofour densitometer trace of the autoionization series ofhelium is shown in Fig. 3.

The result of our analysis was in excellent agree-ment with the NBS result and we were convinced ofthe optical quality of our experimental setup.

This figure was not published as there was nothingnew, but it was included later in a review article byNakamura [8] . Fig. 4 is another reproduction of a filmrecording the well-known Rydberg series of heliumwhich also was not published. However, it was veryuseful as a wavelength standard for analyzing the restof the spectra. It was indeed an enjoyable experiencefor me to discuss these exciting results with colleaguesin NBS and NRL in Washington DC, R.P . Madden, K.

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Codling, J.W . Cooper, U. Fano and W.R . Hunter, inthe period following my visit in 1965 of the UnitedStates . During a subsequent period INS-SOR and F-41,DESY were active in building new beam lines forexpanding activities, while SURF-I, NBS was forcedinto a rather extended shut-down due to the move toMaryland .

Meanwhile the Japanese SR community was able toorganize a US-Japan seminar at the Institute for SolidState Physics (ISSP) a Roppongi, Tokyo, as a satellitemeeting to the International Congress for Optics heldin Tokyo, in summer 1964 . Main American participantof that meeting were D.H . Tomboulian and P.L . Hart-man. It was intended to discuss matters of mutualinterest on synchrotron radiation experiments, but thegreatest benefit of the discussion was of course thetransfer of the abundant experiences of the Cornellgroup to the Japanese novice workers. Tombouliangave a 2-hour lecture, twice as much the request,talked about every detail of the Cornell experiment,and gave a very strong impact to all who attended . Itwas extremely unfortunate that we lost him at the endof that year .

US-Japan interactions and collaborations have con-tinued in subsequent years at an ever growing rate . Anumber of Japanese scientists enjoyed participating inactivities in major American SR facilities such as Wis-consin, Stanford, Brookhaven, and others . A counter-part of this stream, the number of visitors from the USto Japan, is also growing nowadays, in particular to thePhoton Factory. Advice given from US experts toJapanese researchers, particularly in the constructionphases have to be gratefully acknowledged : for in-stance, Ed Rowe for advice and encouragement givenduring the construction of SOR-RING, the first pur-pose-built storage ring as a source, H. Winick foradvice on beam line design and ideas of permanentmagnet undulators at the Photon Factory, and all thosevaluable favors which should be given high credit fortheir contribution to the progress in Japan. The US-Japan one-week seminar held in Honolulu, Hawaii, inNovember 1979 was also an extremely fruitful andpleasant opportunity for discussing forthcoming con-structions i.e., NSLS, Brookhaven, and Photon Factory,Tsukuba [9] . Collaborations between the presently run-

2T n

Fig . 4. A reproduction of a film recording the absorption spectrum of Rydberg series of helium [8] .

ning facilities, the next-generation projects, as well asthose based on personal communications have alwaysproved fruitful and will certainly continue into thefuture .

4. Summary

Synchrotron radiation research has evolved in thepast 30 years as follows:

1st generation : parasitic use of synchrotron radia-tion ; parasitic use of storage ring ; symbiotic use ofstorage ring.

2nd generation : dedicated use of storage ring radia-tion ; storage ring built as dedicated light source .

3rd generation : insertion devices; optimized sourceoptics .

4th generation : coherent production of X-rays ; freeelectron lasers .

Evolution from the first to the third generation hasbeen driven by the demand for higher brightness andhigher stability. However, these two objectives are notnecessarily compatible to each other, and one alwayshas to consider what will be the most appropriatetrade-off.

Nevertheless the average product of brightness andstability (assuming this can be defined has increaseddramatically.

Technical difficulties associated with early sourceswere such that present day users would never tolerate,

T. Sasaki /Nucl. Instr. and Meth . an Phys. Res. A 347 (1994) 9-13 13

but they were finally overcome with the great enthusi-asm of pioneers of that day, based on the convictionthat there was no other way to go .

Now we are at the entrance to the third generationof synchrotron radiation research, where the technicaldifficulties and other problems to be solved are form-idable and unprecendented . In this respect our presentstate-of-the-art seems just the same as what we en-countered 30 years ago, when people challenged thefuture because it is the only way to go.

References

[1] D.H . Tomboulian and P.L. Hartman, Phys . Rev. 102 (1956)1423 .

[2] M. Kimura et al., Sci . Rept. Tohoku Univ. I, Vol. XL(1957) 233 .

[3] R.P . Madden and K. Codling, Phys. Rev. Lett . 10 (1963)516.

[4] U . Fano, Phys . Rev. 124 (1961) 1866 .[5] M. Otsuka and K. Sato, private communication .[6] 20 years of INS, Institute for Nuclear Study, Univ . of

Tokyo (1975) in Japanese .[7] T. Sagawa et al ., J . Phys. Soc. Jpn. 2 1 (1966) 2587, 2602 .[8] M. Nakamura, Jasco Report 4 (2) (1967) 1, m Japanese .[9] Proc . Japanese/USA Seminar on Synchrotron Radiation

Facilities, Honolulu, 1979, ed . M.R . Howells, Nucl . Instr .and Meth . 177 (1980) 1-272.

I . HISTORICAL MILESTONES