SLAC BEAM LINEIt ain't the things we don't know thathurt us. It's the things we do know thatain't so. -Artemus Ward

Volume 14, Number 5 May 1983

MOCKUP OF THE LINEAR COLLIDER ARCSThis model shows a section of one of the two underground arcs which will guide the electrons andpositrons from the SLAC linac to the collision point. Four of these bending magnets are mountedon a large steel girder to form one of the 250 modules needed in the SLC. This mockup, which isbehind the PEP offices, was first used in studying PEP designs and is slightly larger than the SLC

tunnel. (Photo by Joe Faust)

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On March 22, Secretary of Energy Donald Hodelvisited SLAC as a part of a several-day trip to the westcoast. Other members of the visiting party includedBarbara Hodel, his wife, and Rebecca Mullin, his prin-cipal aide.

They were accompanied by Joseph LaGrone, theManager of DOE' s San Francisco Operations Office, andby William Gough, head of the DOE office at SLAC.

Members of the SLAC Directorate who met with theSecretary and his group included Pief Panofsky, SidDrell, Burt Richter, John Rees and Gene Rickansrud.

The visit lasted only about three hours, so there wasa great deal to try to cover in not very much time.The history and major accomplishments of SLAC werereviewed, followed by a tour of the site that includedstops at the Visitor's Gallery along the linac, the SLCdamping ring vault, the control room and IR-6 at PEP,and SSRL.

There was a wide ranging discussion of SLAC's_i1 _ a it ._ P __ 1 u , -T _ s . I-~11 A_

plans ior mte Iuture inciuaing tne SLAC Linear olllMaerproject and the prospects for the exciting physics thatwill be done with this new facility.

CONGRESSMAN MINETACongressman Norman Y. Mineta

(Democrat, San Jose) toured SLAC

on March 30. The visit included ameeting with Director Pief Panofsky,general discussion of the SLC project,and a tour of the site includingthe Stanford Synchrotron RadiationLaboratory SSRL.

The photograph at left was takenduring the tour at the overlook be-hind End Station A with (from left)Representative Mineta, his Washingtonaide Gene Frankel, and Burt Richter.

(Photos by Joe Faust.)

Editorial Staff: Bill Ash, Jan Adamson SLAC Beam Line, Bin 80

Dorothy Edminster, Bob Gex, Herb Weidner Stanford Linear Accelerator Center

Photography: Joe Faust, Walter Zawojski Stanford University

Illustrations: Publications Department Stanford, CA 94305I_ - ------- - -- - ------ --- - - - - -- "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

SLAC Beam Line, May 19832

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SLA Bea Lie Ma 198 3

JOHN EHRMAN LEAVES SLACJohn came to SLAG in February, 1966 from the

University of Illinois where he received his degree inphysics and his first exposure to computing. Johnhas been an outstanding contributor to computing atSLAC. As SHARE Fortran project leader, he helped con-vince IBM to re-do vs Fortran to suit our needs. Herewrote the Fortran error traceback, revised the JCLcataloged procedures, and wrote many subroutines.His 'WYLBUR Tutorial' is a shining example of gooddocumentation. Much of his effort was directed towardaltering the computer system so people could use it withless 'expert' help. From teaching Computer Sciencecourses at Stanford to chastising those of us who violatethe rules of good programming practice, he has been avalued friend to all of us who use computers.

Those of us who know him personally value hisdedication to SLAG and his concern for people. We aresad to see him go but are pleased that John will beworking for IBM on the development of future program-ming languages. (I am sure this will benefit SLAC.) Wethank John for his years of dedication to SLAC and wishhim well on his new adventure.

-Chuck Dickens

JOHN EHRMAN listens to one of more than a dozentoasts at a party given by his colleagues at the SLACcafeteria on March 15. Some twenty light-hearted giftswere presented including a do-it-yourself personal com-puter kit consisting of a spindly tree hung with randombits of hardware.

Sandwiched in with the jokes and banter was theconstant theme of how much John had done for mak-

ing computing useful for physics at SLAC. He set theexample of clarity and accuracy and then developed astaff with the same principles.

The last gift reflected John's interest and ability inmusic: the Alleuia chorus sung by his many friends here.

-(photo by Tom Nakashima)

ROGER CHAFFEE MOVES ONRoger Chaffee joined the Computation Research

Group in 1972 on a one-year appointment with thePresidential Internship Program.Eleven years later (afterserving the group as aMathematician for tenyears), Roger decidedhe needed to branchout and so has leftthe group to join anew company, MetaphorComputer Systems. Roger'sfirst interest has alwaysbeen making computers

-_- , , 1 ^ .- _ . -i ± - -easy ior people co use.He put this theme to use immediately by upgradingthe SLAC version of Kiowa to a sophisticated systemdesigned to make full use of SLAC's 360/91 system.

This was soon followed by Graphic Kiowa and Sage.The coming of the Triplex Computer gave Roger evengreater scope for his abilities and resulted in such in-novations as Topdrawer, Tidy, Hist-l&2, Goodgnus,Loadgnus and TD3D. After VM arrived, conversionswere made for the above programs and Roger was in-spired to even greater heights with Aid, Mortran-VM,Tapeit, Diskit and Blockit. Probably the biggest chal-lenge of all was bringing up Tex on the VM system.

Roger's departure is a great loss to the ComputationResearch Group, the physics community which uses somany of his programs, the scs Group, the many Texusers, and the summer students who have each yearrelied on Roger's Programming Course to guide themthrough the intricacies of the SLAC Computing System.I'm sure everyone at SLAG joins us in wishing Roger thegreatest success and happiness with Metaphor.

-Harriet Canfield

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4 SLA Bea Line Ma 18

MEL MELONIJulio 'Mel' Meloni died

on April 20. He was 59but he accomplished morein that time than mostpeople could in 159 years.

Mel was born onNovember 6, 1923. A na-tive of San Francisco, heserved in the South Pacificduring World War I. Afterthe war he worked in thelocal tube industry un-til 1949. Then for thenext 30 years, interruptedby a two year stint in

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industry, ne worKeu atStanford University.

From 1949 to 1956 he was at the Hansen Labs, wherehe helped construct the MKIIand MKIII accelerators,and later medical accelerators for the Stanford MedicalSchool (then in San Francisco), the University ofChicago and Michael Reese Hospital in Chicago. Heworked on the early accelerator klystrons and guns andwas also involved with other klystrons and travellingwave tubes built at the Microwave Laboratory. The twoyear off-campus stint was at Eimac, mainly to shortenhis commute. However, in 1958 he returned to Stanfordwhere he joined SLAC to work in the Klystron Group.He was involved in the construction, testing and instal-lation of the SLAC-made klystrons. He also workedon klystron window construction and testing, vacuumproblems and many other parts of the accelerator.

In 1968 he returned to the Hansen Labs. Hiswork there and in the Physics Department, in areasof accelerator physics, led to part-time work with thestudents and faculty in the Solid State ElectronicsLaboratory and ultimately to his full employment inthat lab in January of 1983. He joined SSEL at atime when several accelerators were being obtained andreworked for use in the study of ion implantation forthe fabrication of high frequency devices and advancedmaterials. His work at SSEL, even in the short periodof time that he was employed there, showed the charac-teristics of Mel's work everywhere: enthusiasm, energy,and a great concern for his fellow workers, especiallythe problems of struggling PhD students.

Mel was a man of great energy. He combined thiswith a strong desire to know how things work, howthey are built and how to repair them. Those whoworked with him will remember his willingness to helpand his good humor. If you told him you felt behind in

returning a favor, he would say "who's counting?" Hehad a vast store of knowledge and experience and waswilling and able to share it with others. He was eagerto tackle any problem and usually found a solution.Several generations of accelerators owe a great deal toMel. He was a wonderful, warm human being, and a'gentle man.' All who knew him will miss him.

This tribute to Mel Meloni is from several of his friendsand fellow workers. -HAW

ROMY CASTRO'S CITIZENSHIPRomy Castro enjoys a glass of champagne at a

celebration staged by his co-workers in the PlantEngineering Office. Romy, an Electrical Designer,and his wife, Carmelita, became United States citizenson March 29, 1983. Romy hails from the PhilippineIslands where he graduated from the Mapua Institute ofTechnology in 1960. He subsequently worked for severalyears for the US Navy at Clarke Air Base. He im-migrated to the United States in 1976 and joined SLACin December of that year.

SLAC Beam Line, May 19834

SLAC Beam Line, Ma9 1983 5

GORDON BABCOCK RETIRESCordon ,. Rabhoek.

electronic engineer in theRadiation Physics group,retired on March 31, 1983,after almost 20 years atSLAC. Sometimes it'sdifficult to capture thespirit of a co-worker anda friend in a few shortsentences, and in Gordon'scase, it may be impos-sible because he is unique.He is one of the genuinesquare pegs in a round-

A!la ..nr.l -a .rn..;-In or._uLlue wrIIu, a creltiAt per-

son not only in the fieldof electronics but in all histhinking.

this learning opened new territories for his intellect, butnever curbed his creative imagination.

Gordon is a perfectionist, a teacher, a man who feelshe can do much more than he was ever given freedom orscope to do either here at SLAC or elsewhere, and a loverof words who has left us with some abiding expressions(eg., when he came to SLAC, he knew only 'hollow-state-electronics'; when interviewing someone, he 'calibratedtheir souls,' an instantaneous process even though hisinterviews were legendary in length)-and we'll misshearing them.

As to the future, I'm not sure what Gordon will doin retirement; perhaps write (he is a frequent letter-to-the-editor contributor), perhaps just let his imaginationroam unfettered at last. Mostly, I think it will be thelatter and I, for one, look forward to seeing the fruitsof these labors as much, perhaps, as he does.

-Ted Jenkins

When I first worked with Gordon, he was in charge ofa small group of technicians maintaining the electronicsof a silicon-growing plant. In May of 1963 he followedme to SLAC to join the old Health Physics group. Whenthat group split, he went to Radiation Physics where heremained for the rest of his SLAC career designing andmaintaining radiation detection equipment.

You may have bumped your head on one of thoselemon-colored cylinders with the meter in it on the wallsin the Research areas. Those are Beam Shut-Off IonChambers, designed by Gordon in the mid-60's and stillgoing strong after 18 years of sunshine and rain. Andthough you don't usually see them, there are small hutsaround the SLAC periphery which house the equipmentfor monitoring radiation at the site boundary. Thenthere's the equipment which we never see but whichreads out our radiation dosimeters once a year. Theelectronics on this is Gordon's.

These examples of Gordon's designs are symbolic ofhis output: equipment that is designed perfectly, willlast far beyond normal expectations, and will be almosttrouble-free during its entire lifetime.

In those early years, Gordon demonstrated hiselectronic green thumb. He could almost instan-taneously give the value of a resistor or capacitor, theircombination, or exact location in a circuit to betteraccuracy than our slide rules and calculators. Later,after participating in the Master's Program at Stanfordand taking graduate courses, he fertilized his greenthumb with complex variables, imaginary numbers, andLaplace transforms, and then spent his time workingin the computerized electronic garden called Spice. All

CHARLIE XUEREB RETIRES/£1arnie11 % C uar1 e x1(. 1 Utereu

ended his work careerwith SLAC at noon onApril 20. This wasa time and date of specialsignificance for Charlie,a native of Malta, since itmarked precisely 34 yearsfrom the start of his firstjob in the United States.

Charlie started with SLACin the mechanical fabrica-tion group under DickMessimer. After severalyears there, he moved tothe accelerator operationsgroup.

There he took data on performance of the klystronstations and worked with Joe Spranza on acceleratoralignment. He next moved to the klystron depart-ment where he tested klystrons, looked after the ac-celerator vacuum system and installed klystrons on theaccelerator.

A human dynamo in compact size, Charlie findsCalifornia too crowded and has purchased a home inGrants Pass, Oregon. Oregon will never be the sameand neither will SLAC; Charlie leaves a big gap in theklystron department. We all wish him the best of luck.

- Ted Johnston

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6 STGR- in, ~ 12

SUNDAY FLICKSo Mem Aud at 7:00pm and 9:30pm. $1.50o May 15 All that Jazzo May 22 The Spy Who Loved Meo May 29 An Officer and a Gentlemano June 5 The Graduate

MUSIC AT STANFORDo Fri. May 20 and Sun. May 22, Verdi Requiem,Stanford Chorus and Orchestra, Dinkelspiel Aud,8:00pm. $4.00

BAY TO BREAKERSo Join more than 50,000 people at 8:00am, Sunday, May15th in a 12 km run from I side of San Francisco to theother (the SLAC Accelepede will be a featured entry)

RECENT RETIREMENTS

Al James, who beganworking at SLAC in 1969,retired this month. Heserved as a Senior S and Etechnician with the gallerymaintenance group. --

Joseph Miceli, a ComputerOperator Leader with theSLAC Machine OperationsGroupannounced his retire-ment last month.

COMPUTER USER SERVICESRill lThnc nn hio'h onororvL-a 11 J"IL113U)l j J.6 xb LLxUaU1 t

physicist with Group B, hasbeen appointed Head, UserServices of SLAC Computingreplacing John Ehrman.The User Services Grouphelps users understand theirrequirements, develops andmaintains general purposesoftware, and provides educa-tion through classes, con-sulting and documentation.

SLAC'S MOST SENIOR EMPLOYEE

Blanche Shoemake, SLAC's most senior employeeat age 78, celebrated her birthday with her colleaguesin the Technical Publications Dept. Blanche has beenemployed at SLAC since November 1979.

PANOFSKY STEPPING DOWN IN 1984

Professor W.K.H. Panofsky has announced that hewill step down as director of SLAC effective August 30,1984, a little more than a year from now. The decisionis part of an informal policy at SLAC by which topadministrators relinquish these posts at age 65. Theannouncement was received as the Beam Line went topress. Details will be carried in the June issue.

THEORETICAL SOFTBALL

The annual softball game between experimentalistsand theorists has been scheduled for Sunday afternoon,May 22nd at SLAC. The theorists, who, after 18 years,finally proved their superiority last year, fear that theexperimentalists will not even show up this year.

DONATE BLOOD ON JUNE 9

The Stanford Blood Center will be returning to SLACon Thursday, June 9, from 8:30 a.m. through noon.Donations can be credited to the SLAC Donor Club,to Kaiser accounts, or to individuals as requested. Atrophy will be awarded to the group with the highestproportionate number of donors. Flyers will be arrivingin the mail-send in your name and extension, or callNina Adelman at 3113. Give the gift of life.

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6 SLAC Beam Line, May 1983

SLAC BEAM LINESpecial Issue Number 3 May 1983

-AN INFORMAL HISTORY OF SLAG

PART TWO: THE EVOLUTION OF SLAG AND ITS PROGRAMby W.K.H. Panofsky

THE CONSTRUCTION OF SLAC MARCH 1965

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THE EVOLUTION OF SLAG AND ITS PROGRAM

W.K.H. Panofsky

The history of electron accelerators at StanfordUniversity started with the brilliant contributions ofW.W. Hansen. There has rarely been a physicist likeHansen who combined physical insight with superbanalytical power and mechanical skills. The resultingsequence of early accelerators made great contributionsto physics; in particular the work of Hofstadter and col-laborators established the electromagnetic dimensionsof the proton and the neutron and also of heavier nuclei.Moreover, inelastic electron scattering and various testsof the electromagnetic behavior of muons and pionsset the stage for things to come. In consequence theproposal to construct the 'Monster' was well receivedand eventually led to approval in 1962 to proceed withthe construction of SLAC at Stanford University underthe auspices of the Atomic Energy Commission.

The new machine was very much larger than any oneprevious undertaking of Stanford, and in fact it was aproject larger than any which had then been carriedout under the aegis of a single university. The Mark IIIaccelerator, constructed under the leadership of EdwardL. Ginzton, was 300 feet in length-30 times smallerthan the SLAC linac. Thus the actual creation of SLACwas a very large leap and required the answers to manyproblems-human, administrative, technical and, aboveall, questions in physics.

Organizing

All prior projects of Stanford University, includ-ing the construction of the earlier electron linear ac-celerators, were carried out within the framework ofthe regular departmental structure of the Unversity.Although the W.W. Hansen Laboratories of Physicsformed the umbrella laboratory under which the Markn and Mark III electron accelerators were built, theindividuals responsible were members of the regulardepartmental faculties of Stanford. Also, the Mark IIand Mark III accelerators were designed to be researchtools intended for use of Stanford faculty, staff, andstudents; the participation of outside visiting scientistswas incidental. It became clear from the outset thata machine costing above 100 million dollars (at a timewhen a million dollars really was a million dollars!)would have to be a national facility; that is, it should beaccessible to any scientist on the basis of the quality ofthe proposed research, without preference for Stanfordpeople.

At the same time we were also fully aware of thefact that the SLAC machine was a maverick in the thenprevalent pattern of US high-energy physics . At the

time of the SLAC proposal in 1957, and even at thetime of groundbreaking in 1962, the main thrust ofAmerican high-energy physics depended on proton ac-celerators, primarily the Bevatron at Berkeley and theCosmotron and the Alternating Gradient Synchrotronat Brookhaven. Only a small number of physicistswithin the international community shared Stanford'senthusiasm for electron machines. At that time,however, competition for funds was not extremely in-tense. Therefore, although few physicists intended touse SLAC at that time, there was general acquiescence,even if not outright support, by the entire scientific com-munity for the construction of the Stanford accelerator.

One can speculate whether SLAC would ever havebeen built had the current financial climate prevailed inthe 1960's. Had SLAC not been approved, one can onlysurmise what insights in physics would have been lost,or at least greatly delayed. Since initially it was doubt-ful that many non-Stanford physicists would be willingto commit large fractions of their scientific careers inplanning for physics use of the new machine, we hadto take the initial responsibility for planning for physicsresearch with the machine when it was completed, andthen make it nationally accessible.

There was another important difference in the re-search planning for SLAC and the national pattern

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centered around proton machines: the technical na-ture of doing physics with a high-intensity, low duty-cycle electron accelerator required that most of theexperimental program be facility-centered. Elaboratedevices would have to be constructed for a successionof scientific experiments. In contrast, a large number ofexcellent experiments then being done with proton ac-celerators were more of the building block type. Theparticipating physicists constructed experiments withrelatively small components such as counters with as-sociated electronics, shielding blocks, and small mag-nets. A central elaborate facility was not needed.

There are two technical reasons for this difference.First, the poor duty cycle of the linac (the small fractionof the time in which the beam is concentrated) makes itvery difficult to do experiments where time coincidenceis a primary signature identifying the event. Whenmany counters look directly at a target exposed to an in-tense but low duty-cycle beam, almost all events appearto be in coincidence as seen by the different counters;some presorting of the events is necessary. The secondproblem comes from the nature of electromagnetic inter-actions. The cross sections for producing the particlesof interest are small while at the same time an intense'shower' of electrons, positrons, and x-rays is producedin a narrow cone in the forward direction. This veryintense cone must be isolated from the devices whichdetect the particles of interest.

Translated into human terms, it soon appeared thatthe SLAC linac could only become a tool for excel-lent particle physics immediately after turnon if wecreated a very strong in-house research staff. This groupwould have to put a large part of its scientific skillsand careers on the line to design the major facilitieswhich were needed to exploit the electron beam onceit became a reality. In turn, this required that theleaders of this research staff be regular members ofthe Stanford University faculty because attracting thenecessary talent would only be possible if the leadershipwas composed of 'first class citizens' on campus. Thisnew faculty was set up as a separate structure in ordernot to produce a major imbalance in the professorialmix within the Stanford Physics Department. At thesame time we assured the outside physics community offull and equitable access to the SLAC facilities, and weset up the necessary advisory committees and other ad-ministrative machinery to make sure that this assurancecorresponded to reality.

A further problem which had to be faced was toconvince the Stanford community that the 'Monster'was not a threat to traditional academic values. Wedesigned the link between SLAC and the balance of

the Stanford community to be intellectually tight;but administratively SLAC would be entirely separateand would thus not drown the existing administrativemachinery of the University. SLAC would operate un-der general policy set by the University, but its actualoperation would be almost autonomous. This methodhas worked out well.

We then negotiated a contract between StanfordUniversity and the Atomic Energy Commission (now theUS Department of Energy). This negotiation resultedin a contract which fully preserved academic values andpolicies and which totally delegated to the Universitythe responsibility for managing the SLAC program.

Building the Linac

The most essential step in building the SLAClaboratory was, of course, the construction of the two-mile linear accelerator itself. The job was directed byProfessor Richard B. Neal and he deserves the primarycredit for the construction being finished on schedule,within budget, and to performance standards exceedingthe original goals set by the proposal. The detailedstory of the construction of the two-mile machine isdocumented in the well-known 'Blue Book'* in whichthe many contributors to the subsystems of the machinedescribe the technical characteristics and history intheir respective areas.

Dick Neal established a systematic method of chart-ing the progress in design and construction of the ac-celerator using critical-path networks. He met regularlywith each of the individuals responsible for the varioussubsystems so that progress and costs of everythingcould be charted and no surprises would occur later inthe game. Interestingly enough, the contingency whichwas contained in the budget for the unexpected was notused on the basic two-mile machine at all, but was al-most entirely spent on the target area and the beamswitchyard which distributed the beam to the varioususers. The construction of the accelerator did not turnup many surprises and went pretty much according toplan.

Since the extrapolation by a factor of 30 above exist-ing machines appeared large, assurance was needed thattechnical problems would be tractable. Nevertheless,one of the first decisions made during the constructionproject was that building a separate prototype for thebasic accelerator was not necessary. We used the factthat a linear accelerator is in fact linear-a small sectionof it can function while the larger part of it is still underconstruction. We therefore awarded contracts for the

* The Stanford Two-Mile Accelerator, R.B. Neal, editor,W.A. Benjamin, New York (1968).

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first 800 feet of the machine separately and managedto obtain a beam from this section while the rest ofthe machine (and in particular the experimental targetareas) was far from completed. This saved the moneywhich a separate prototype would have cost and it alsoraised our confidence that no fundamental design errorshad been made.

From the point of view of the electron the extrapola-tion by a factor of 30 in energy and accelerator lengthis actually minor: the relativistically contracted lengthas observed in the electron's rest frame is only 3.4times longer for the SLAC linac than for the 100 meterMark II machine. The focusing required to confine thebeam is thus moderate and alignment standards are notsevere.

In spite of these comforting facts, the matter ofstability of the machine-in earthquake country inparticular-received a great deal of internal and exter-nal attention. Thanks to the effort of many seismic ex-perts, in particular Dr. John Blume, this matter wasanalyzed in great detail since the chosen site placedthe injector only one-half mile east of the San AndreasFault. The consensus was that with careful constructionpractices the earthquake risk could be held to standardswhich assured the safety of people and which minimizedthe potential damage to the facilities.

Outside Industry and In-House TalentConstruction of the accelerator was accomplished

partially with in-house talent and partially throughindustry. The principal civil engineering for the ac-celerator was handled by an exceedingly capable out-side Architect-Engineering-Management firm managedby John Blume whose help had been crucial with earlyseismic studies. They were responsible for the design ofall accelerator housing, the beam switchyard, and thetarget areas in addition to managing the constructionitself. The photograph on the front cover was taken inthe midst of this activity.

The actual construction work was doneby a variety of individual contractors. Wewere, of course, obligated under govern-ment rules to award each item of construc-tion to the lowest bidder, unless we wereable to prove that the bidder was unableto do the work!

The klystrons must stand 25 feet above the ac-celerator to allow earth shielding. This causedmore difficulty during tests on campus than inthe actual construction.

Let me illustrate this problem with just one example.We had received bids for a major electrical job. Ourconstruction manager, a 75-year-old gentleman work-ing with our management firm said "Don't award thejob to the lowest bidder." I asked why and he said"Because he's a son-of-a-bitch." The AEC manager, thelate Larry Mohr, replied "That doesn't disqualify himin the eyes of the AEC." So the job was awarded tothe low bidder, and indeed our 75-year-old constructionmanager turned out to be correct.

The accelerator itself, of course, involved an enor-mous amount of engineering and construction ofprototypes for separate components and subsystems.Feeding power from the klystrons to the accelerator re-quired very complex waveguide plumbing. We decidedto mock up a prototype consisting of a single klystronfeeding an accelerator section through the actualwaveguide system. To provide for adequate shieldingfrom the linac, the klystrons must be 25 feet abovethe machine in the actual installation. Therefore, thismockup had to be constructed as a tower which con-tained the klystron and its supplies while the acceleratorsection was placed at ground level. The easiest wayto install the waveguide feeds from the upper story ofthe tower down to the accelerator was by helicopter (amethod later used in the actual accelerator construc-tion). As it happened, this mockup tower was next tothe Stanford football stadium, and it also happened thatthe lowering of the waveguide by helicopter was madeon the Friday before a critical game. The Stanford foot-ball coach was practicing some very secret formationsin the stadium at the time and thought the helicopterwas part of a spy operation by Saturday's opponent! Hecancelled the practice, and when informed of the actualsituation sent a strong letter of protest to SLAG.

4' .

/CROSS'SECTIOROF WAV~dUIDE,COOLING TUBESAND THE4WALINSULATION

OF KLYSTRON,

LNS AND

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Building an accelerator on a university campus hasits singular difficulties.

Our experience with industry was mixed, rangingfrom absolutely superb performance to some disappoint-ments, not only in connection with civil constructionbut also with the highly technical items. For example,we placed a contract for research and development ona prototype for the modulator which supplies pulsedpower to the klystrons. Half a million dollars later wewere left with a very unsatisfactory and poorly per-forming design. We then built our own prototypesfor the modulator at SLAC under the direction of CarlOlsen, and procured the 245 modulators as a straightfabrication job with the industry simply following ourdesign. This saved a great deal of money and resultedin modulators which gave excellent performance.

Klystrons

The performance of the klystrons is absolutely cru-cial to the success of the SLAC accelerator. Our earlyexperience with making our own klystrons at the MarkIII accelerator was mixed. At times our tubes performedwell, but there were periods when the yield of in-housetubes slumped and the physics program almost came toa halt while we studied the problem.

We decided to play it safe and build up both an in-

ternal capacity to produce klystrons (under the direc-tion of Dr. John Lebacqz) and also to contract with twodifferent industrial firms. The first two outside contrac-tors were unable to perform to the required standards,and two new contractors bid for the job. As a result,our initial inventory of klystron tubes was varied.

Having an in-house capacity for klystron productionturned out to be a wise move for a number of reasons.During the early days when the first contractors haddifficulties, one of them apparently let his problemsbe known to Congress. I was asked as a witness dur-ing Congressional testimony whether it was true theklystron specifications which we required industry tomeet were physically impossible. I replied that we metthese specifications with our own tubes, and that endedthe dialogue. Having a 'yardstick' operation in-housewas the most powerful lever we had to assure good per-formance.

As time went on the mean lifetime of the tubes grewto over 20,000 hours and the total replacement ratedropped to only 5 tubes per month. This was insufficientto be economically attractive to industry, so by mutualagreement we phased out the industrial suppliers. Allklystron tubes at SLAC are now homemade. The in-house capacity has also served us since in supplying thelower power klystrons in the drive chain and the large

The first SLAC klystrons were made both by industry and within the lab. The photo shows fouroutside versions and one made by SLAC. Eventually all tubes were produced in-house.

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tubes used in the storage rings.

As this example shows, an essential element in build-ing up SLAC was a balance between internal and in-dustrial support. In our case the balance turned outto be somewhat further in the direction of buildingup an in-house capability than in customary at otherUS laboratories. This applied not only to the case ofklystrons and modulators but also to such diverse itemsas magnets, detectors, and electronic components. Thiscontinues to be a delicate issue, but SLAC history clearlyindicates that this laboratory would have been in veryserious trouble indeed, and may not have survived at all,if we had not had the opportunity to pitch in with ourown forces to construct vital components when neces-sary.

The Linac Structure

The linear accelerator itself is the two-mile evacuatedtube in which the electrons gain energy from themicrowave power provided by the klystrons. This re-quired both choosing a design for the accelerating struc-ture itself and then deciding how to build it.

The basic design consists of a long series of connectedcavities as shown in the figure.

Such a cylindrical disk-loaded waveguide permits ac-celeration of the electrons by the electromagnetic wavetraveling down the guide. Clearly the linac construc-tion is much easier if all the sections can be madeidentical. Unfortunately, there is a problem with sucha 'constant-impedance' structure since the acceleratingfield decreases along the length as the power is absorbedin the walls. This leads to poorer acceleration andelectrical breakdown properties. If, however, the dimen-sions of the successive cavities are chosen so that thegroup velocity progressively decreases, then the electricfield can be held to a constant value. This 'constantgradient' structure was the method chosen although it

was a major departure from previous practice. As itturned out, the choice was fortunate not only because itpermits larger overall acceleration (greater than 20 MeVper meter) but also because it leads to greater stabilityat high beam intensities.

The choice of fabrication method was the secondcritical item. The technique used in the Mark III was ashrinking method originally developed by Bill Hansen.This caused some trouble over the years as cold flowgradually loosened the disks. New approaches werenecessary and we developed two different techniques andkept both going for over a year as candidates for thefull-scale production. In the electroforming method, thecopper disks were separated by aluminum spacers whilea thick layer of copper was electroplated on the

Brazing the assembly of disks which form the linearaccelerator itself required a special hydrogen furnace.

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outside. The aluminum spacers were then dissolvedwith lye. The other technique was to braze disks andrings together in a special vertical hydrogen furnace.Both methods worked, but the time between discoveringpossible defects and correcting the production processwas too long in the electroforming process, and it wasdropped.

The brazing process was a novel undertaking. It wasa repetitive job which had to be done with extremelyhigh precision as mistakes could be very damaging.We started with about two million pounds of oxygen-free high-conductivity copper. The rings and spacerswere machined, annealed, finish-machined, stacked, andfinally brazed together in a hydrogen atmosphere usingthe primitive-looking furnace shown in the photograph.The work was largely done by housewives respondingto this special opportunity for steady part-time employ-ment for several years. It speaks well for the qualityof that operation that not a single one of the 200,000brazed joints of the accelerator has developed a vacuumleak in more than 15 years of steady operation.

The First BeamsCommissioning the two-mile accelerator was generally

less difficult than anticipated. In fact, ob-taining a beam in the two-mile structure wasnot significantly more difficult than in the 300-

foot Mark III. There was one unanticipated difficulty,however: the beam intensity was limited bya 'beam breakup' phenomenon. Beams of the designintensity could not be accelerated the full length ofthe linac without colliding with the walls or collimators.

We had anticipated one process which would limitcurrent. The electron beam produces a secondary waveas it travels through an accelerator section. This wavetravels backward to the front of the section and disruptsthe beam. The observed effect occurred at much lowercurrents, however, and was due to something else.

The basic physical process responsible was soon diag-nosed: if an electron bunch within the beam travelssomewhat off-axis, it produces electromagnetic fields inthe structure which deflect the following bunches evenmore. This results in an instability which grows both intime and in distance along the axis. Happily, the choiceof the non-uniform constant-gradient structure greatlymitigates this effect since only a small portion of eachsection matches another. Nevertheless, initially we werelimited to about one-third of the design beam intensity.The cure of small deformation of the structure and in-creased magnetic focusing was carried out in small stepswhich eventually brought the beam up to the predictedvalue.

In the original proposal we had conservatively

A view of the rings, disks, and brazingg material toge withh a partial assembly of a section ofthe linac. About 200,000 such pieces went into the machine.

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8 SLA Beam Lie Ma 1983 ~_predicted the energy of the machine to be between 10and 20 GeV. This caution was prompted mainly by con-cern about klystron performance. In fact, 20 GeV wasexceeded early in 1967, and the energy continued severalGeV past this as klystron power grew.

The SLAC Energy Doubler program (SLED ) beganmuch later and has raised the beam energy to over30 GeV. In this scheme a small cavity is coupled tothe waveguide which connects the klystron to the ac-celerator as shown in the figure. Microwave power fromthe klystron begins to accumulate in this cavity in-stead of the accelerator when the klystron is turned on.Partway through the pulse a slight adjustment in theklystron allows the power already stored in the cavityto flow out and add to the power from the klystron onits way to the accelerator. Thus, we have nearly twicethe power in exchange for a shorter pulse time.

Using the BeamsIn some ways the original 1957 proposal was a

more far-seeing document in respect to the constructionmethods and the human and administrative problemsthan it was in respect to the technical arrangementsneeded for physics research. Perhaps this is not surpris-ing, considering the fast pace of high-energy physicsresearch and the decentralized initiatives guiding theresearch program. SLAC research was to be facility-oriented and these facilities were designed on the basisof proposals generated largely by the laboratory staff.The proposals were reviewed extensively and publicly;the green light was then given by SLAC and the AECprovided a one-shot infusion of funds to support thefirst generation of research facilities.

These initial facilities turned out to be quite differentthan those envisaged in the 1957 proposal. Theelectron-scattering area, for example, was to consist oftwo large spectrometers each sweeping out 180 degrees.During the actual design we recognized that there waslittle need for having a single detector sweep all theway from the forward to backward region, since par-ticles scattered in the backward direction are of muchlower energy and are produced much less copiously.Accordingly, a better match would be two kinds ofinstruments: spectrometers designed for high energyand relatively small acceptance in the forward regionsand different spectrometers for low-energy particles butwith large acceptance in the backward angles. Webuilt three spectrometers, in fact, to cover the for-ward, intermediate, and backward angles in a very largeshielded building called End Station A. These instru-ments, shown in the photograph, were the work horseswhich led to establishing the pointlike substructure ofthe neutron and proton.

CAVITY I- - CAVITY 2

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A schematic of the SLED cavity which gives substantialincrease in beam energy with the same klystrons.

The 1957 proposal also envisaged that SLAC mightcopiously produce secondary particles such as the Xr

and K mesons in addition to its role of studyingthe primary interactions of the electron and photonbeams. Historically, such secondary beams had beenthe sole province of the proton accelerators; electronaccelerators had generally lower intensities and facedmuch lower basic production cross sections. SLACsucceeded in revising this tradition for two reasons.First, the intensities of the SLAC beam are ten to ahundred times larger than those previously available atelectron machines. Second, although the total produc-tion cross sections for secondary particles are indeedlower in electron beams than in proton beams, the par-ticles that are produced are thrown forward into a verynarrow cone. This phenomenon of forward concentra-tion was predicted theoretically by Sidney Drell andwas confirmed by a team of SLAC physicists led by JoeBallam in early experiments at the Cambridge ElectronAccelerator.

Thus, we could anticipate that SLAC would notonly be preeminent in high-energy electron and photonphysics, but would also be competitive in the ex-ploitation of secondary beams of unstable particles.Accordingly, the research area of SLAC was segregatedinto a complex dedicated to studies of primary (that is,

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electron and photon) interactions and another area forsecondary beams.

Not only were the secondary beams produced atSLAG competitive in terms of particle flux, but someof the beams could also be designed with characteris-tics not found at proton machines. A high-intensityx-ray beam with photons of only one energy was pos-sible, for example. This contrasts favorably with thephoton beams at proton machines which are producedby the decay of neutral pions and consequently have asmeared-out energy spectrum.

Initially, such a monochromatic photon beam wasproduced by annihilation of positrons on atomicelectrons in hydrogen. In another technique near-monochromatic x-rays were produced by electromag-netic radiation from high-energy electrons striking tar-gets composed of a single crystal.

In the present method the beam is produced by scat-tering ultraviolet-light (low energy) photons from a laseron the high-energy electron beam itself. These collidehead-on with 30 GeV electrons and are scattered backf9 Ca 0 bnf r nhTt\ ne Tlie m»ntnnrnmatie» ant] n4iari7-

violated in the weak interaction. The main bugaboowith proton machines for these purposes is the con-tamination of neutral kaon beams by neutrons whichare, of course, difficult to separate from neutral kaons.The nature of the production mechanism of neutralkaons by electrons and photons reduces this neutroncontamination so that the kaon beams can be useddirectly in many particle detectors, including bubblechambers. Thus SLAC in its early days became amajor contributor to the worldwide activity in furnish-ing quantitative values of the weak interaction decayparameters of the neutral kaon.

The Beam SwitchyardThe applications of the SLAC beams proved much

larger than anticipated in the 1957 proposal, and a com-plete re-engineering of the distribution of beams to ex-perimenters was required. This was solved by the designof a 'beam switchyard' (BSY ) carried out under thedirection of Dick Taylor.

The BSY is much more than a tool to direct beamsto a variety of experiments. It is also a 'purgatory'

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to assure that each experimenter receives electrons ofknown energy and energy spread, and that the primaryand secondary beams have known and stable opticalproperties. The requirements set by the different ex-perimental facilities for pulse delivery rate and intensitycan be very different. Bubble chambers, for example,cannot handle more than a few pulses per second tomatch the chamber's expansion rate; spectrometers, onthe other hand, can take all the pulses available. Allthese needs were met by the BSY design.

The beam first entered a pulsed magnet which coulddeflect the beam right or left on a programmed pattern.The energy of the beam could also be predetermined ona pulse-by-pulse basis by activating the required num-ber of klystrons along the length of the accelerator atthe correct pulse time while deliberately mistiming therest. As a result, each beam pulse could enter one ofthree magnetic channels set at a fixed momentum band.Two of these channels used elaborate magnetic trans-port lines. The energy was dispersed halfway along thepath to the switchyard to permit energy selection bysuccessive cooled slits. The beam was then refocusedand directed to each experimental area. Targetingprovisions within the BSY were made for the produc-tion of secondary beams, including hadron beams andspecialized x-ray sources. In general these secondarybeams could be transported to experimenters outsidethe BSY by transport channels similar to those of protonmachines.

The average beam power could be as high as amegawatt, a value unheard of in high-energy machines.As a result, the shielding and remote maintenance re-quirements were severe. Slits, collimators and beamstoppers required novel design not only to withstandthe high average power but to handle the shock stressesdue to the pulsed delivery. Radioactivity in the coolingwater had to be dealt with.

The result of all these needs was a system muchmore complex than envisaged in the original proposal.Fortunately, we could control the costs of the construc-tion of the basic accelerator and of the 'conventionalfacilities' (the beam housing, buildings, site develop-ment, and utilities) to within the original estimates.Thus, almost all the budget contingency could be dedi-cated to the beam switchyard.

Each experimenter established downstream from theswitchyard can in essence control his own accelerator,receiving beams of preselected composition, time struc-ture, energy, and resolution. Thus the technical designof the BSY was the primary factor in making the SLAGbeams available to a substantial number of simultaneous(or, more accurately, interlaced) experiments.

Bubble Chambers at SLAG

This entire story documents the fact that the re-search program at SLAC became very much broaderthan was foreseen in the original proposal. Not onlydid this increased activity lead to more experimentalresults, but at the same time it widened the horizons ofdetector technology. In particular, it turned out thatthe use of bubble chambers at SLAC, which was notat all considered in the proposal, was highly produc-tive. Proton machines produce a pulse only every fewseconds, while the linear accelerator can pulse hundredsof times per second. Generally bubble chambers registerin a single picture all charged particles produced dur-ing a pulse, and therefore only a few particles perpulse would be handled by the chamber. Note that forproton accelerators a bubble chamber can pulse morerapidly than can the accelerator, while the SLAC linearaccelerator can pulse more rapidly than a bubble cham-ber. Thus the data production rate for bubble cham-bers can be greatly enhanced if they are used at SLAC.The exploitation of these facts resulted in excellent datafrom the early work in the monoenergetic photon beam.

Luis Alvarez at Berkeley also recognized that hisfamed 72-inch bubble chamber would become verymuch more productive if it were moved across the bayto SLAC. This increase would stem from two sources.First, the data rate would increase because of the moreefficient use of pulses as discussed above. Second, SLACcould produce higher energy secondary beams thancould the Bevatron at Berkeley. As is frequently thecase, however, a great deal more was involved thansimply moving the chamber from one place to another.It was decided to make extensive modifications, includ-ing a totally different expansion system. The chamberbody was revised and the instrument changed from the'72-inch' to the '82-inch' bubble chamber.

The 82-inch chamber turned out to be the world'smost prolific producer of bubble chamber photographsfor the large community of high-energy physicists in-terested in analyzing the results of bubble chamberexposures. In fact the entry of the bubble chamberinto the SLAC program caused a major increase in thenumber of outside users here. Since both interest andfacilities connected with bubble chamber analysis wereworldwide, the outside user participation in bubblechamber physics has always exceeded that of in-housephysicists by a large factor. As many as six millionbubble chamber photographs were generated at SLACduring one year. In fact, the production of the 82-inch bubble chamber was so prolific that in a relativelysmall number of years the market for bubble cham-ber photographs became saturated. Exposures at all

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reasonable particle energies and with all available par-ticle types were made and the number of pictures wasso large that the limiting factor was the ability of theworld to analyze data rather than the rate at which itcould be produced.

The fact that secondary particles with electronmachines are produced according to a well-understoodtheoretical model means that searches for new unstableparticles become particularly useful. If no new particlesare found, one can conclude that within the limits ofavailable energy none exist. Such a search for new long-lived particles was carried out by Martin Perl in theearly days of SLAC with negative results. It is interest-

ing to note that Professor Perl and his collaborators dis-covered a third member of the lepton family of elemen-tary particles at a later date using an electron-positronstorage ring. The secondary beam fluxes were also usedextensively with other detectors. In particular, a verylarge streamer chamber was built and other, more tradi-tional, detector arrangements were put in place. Allthese devices generated important physics data com-plementary to those generated by the proton machines.

Thus the total coverage of SLAC research becamemuch broader than that envisaged in the originalproposal. On top of this increased and unforeseen scopecame another addition-the development of electron-

The 82-inch hydrogen bubble chamber with (from bottom) LuisAlvarez, Bob Watt, Joe Ballam, and Pief Panofsky.

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positron storage rings. This is a separate and excitingstory described by Burt Richter.

Conclusion

One vexing question which was raised at the timeSLAC was started and which continues to be askedtoday is "How long will SLAG live?" The answer wasthen, and still is today, "About 10 to 15 years, unlesssomebody has a good idea."

It is now indeed 20 years after beginning of construc-tion and we are again looking a decade or more ahead.As it turns out, someone always has had a good ideawhich was exploited and which has led to a new lease onlife for the laboratory. It is indeed true that full researchexploitation of most, if not all, large accelerators andcolliders takes about 10 or 15 years and thus the mottorelating to such machines has always been "Innovate orDie!"

Happily, new ideas have not been lacking in the en-vironment of Stanford University. We have moved fromthe original proposal for the SLAC linac dedicated toelectron and photon physics to the exploitation of secon-dary hadron beams, to electron-positron storage rings,and SLAG is now on its way to developing the SLAG

Linear Collider-a device aimed at bringing 50 GeVelectrons and positrons into annihilating collisions.

Worldwide we have seen a life and death cycle ofvarious accelerators as the frontier of particle energy hasadvanced and as the type of accelerators and colliders toachieve these energies has changed. The life and deathcycle of machines need not correspond to the life anddeath cycle of institutions unless the size of machinesrequired to remain at the frontier becomes so large thatthey cannot be accommodated within the boundaries ofthe laboratory. It is fortunate that Stanford Universitycould accommodate a two-mile accelerator on its ownlands; thus far the additions to that accelerator, inparticular the SPEAR and PEP storage rings and theproposed SLC collider project, also fit within the bound-aries provided by Stanford to the government under a50-year lease. What may come after is an open question.

The evolution of SLAG and its program has indeeddemonstrated again that the principal contributions tophysics of a new accelerator are rarely those envisionedin the original proposal Although those goals have beenmet, the actual program turned out to be much richerand more exciting. Let us hope that the future will beequally unpredictable in the same manner.

W.K.H. PANOFSKY

W.K.H. PANOFSKYIn a talk at the SLAG Anniversary Celebration Stanford

University President Donald Kennedy noted, "The institu-tion is the shadow of the man; in the case of Pief Panofsky,that shadow is two miles long." Since 1961 the biography ofPanofsky is very much a history of SLAG.

He received his A.B. degree in physics at Princeton in 1938and his Ph.D. from the California Institute of Technology in1942. From 1942 to 1943 he was Director of the Office ofScientific Research and Development Project at Caltech, andfrom 1943 to 1945 was consultant to the Manhattan Districtat Los Alamos.

He served on the faculty of the University of Californiaat Berkeley from 1945 to 1951, when he came to StanfordUniversity as Professor of Physics. He was Director of the HighEnergy Physics Laboratory at Stanford from 1953 to 1961, andhas been Director and Professor at SLAC since that time.

Panofsky's extensive research has been in x-rays and naturalconstants, accelerator design, nuclear research, and high-energy particle physics. His interest in international armscontrol is reflected as a Consultant to the Arms Control andDisarmament Agency since 1959 and as a member of theCommittee on International Security and Arms Control of theNational Academy of Sciences since 1981.

His many honors include the National Medal of Science in1969 and the Enrico Fermi Award in 1979.

This article was based on a talk givenby W.K.H. Panofsky at SLAC's Multi-Anniversary Celebration held on August 14and 15, 1982. Bill Ash, Editor

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