A PERIODICAL OF PARTICLE PHYSICS

SPRING 1993 VOL. 23, NUMBER 1

EditorsRENE DONALDSON, MICHAEL RIORDAN

Executive EditorBILL KIRK

Guest EditorDAVID HITLIN

Editorial Advisory BoardJAMES BJORKEN, ROBERT N. CAHN, DAVID HITLIN

STEWART C. LOKEN, RONALD RUTH

MARVIN WEINSTEIN, HERMAN WINICK

Photographic ServicesTOM NAKASHIMA

BETTE REED

IllustrationsTERRY ANDERSON, KEVIN JOHNSTON

SYLVIA MACBRIDE, JIM WAHL

DistributionCRYSTAL TILGHMAN

The Beam Line is published quarterly by the StanfordLinear Accelerator Center,P.O. Box 4349, Stanford, CA 94309.Telephone: (415) 926-2585INTERNET: BEAMLINE@SLACVM.SLAC.STANFORD.EDUBITNET: BEAMLINE@SLACVMFAX: (415) 926-4500SLAC is operated by Stanford University under contractwith the U.S. Department of Energy. The opinions of theauthors do not necessarily reflect the policy of theStanford Linear Accelerator Center.

Cover: An EGS4 computer simulation of a cancer-therapyaccelerator operating in the electron mode. An initial group of100 electrons (blue lines), each of 20 MeV, strike a scatteringfoil (dark blue and green), then pass through an ion chamber.Some x rays (yellow lines) are produced, and the beam isshaped by a succession of collimators. This simulation wascreated by Alex Bielajew and George Ding of the NationalResearch Council of Canada.

Printed on Recycled Paper 4

CONTENTS

FEATURES

2 FROM THE EDITORS' DESK

3 WHO NEEDS SCIENCE?Curiosity about the natural world,pursued for its own sake, has alwaysbeen a wellspring of innovation.

Frederick Reines

6 LITTLE LINACS FIGHT CANCERLinear electron accelerators are usedin medicine to treat millions of cancerpatients every year.

John Ford

14 DOWN TO THE WIREBuilding Fermilab's Tevatron acceleratorbrought science and industry togetherin a unique partnership.

Judy Jackson

22 TECHNOLOGY TRANSFER AT SSRLFrom its inception, the StanfordSynchrotron Radiation Laboratoryhas worked closely with industry.

Arthur Bienenstock

29 MICROWAVE TUBESFOR SCIENCE & INDUSTRY

High power microwave sources developedfor particle accelerators have potentialapplications in emerging technologies.

George Caryotakis

35 WHERE ARE THEY NOW?Six former high energy physicists who aremaking their mark in the world.

David Hitlin and Michael Riordan

42 CONTRIBUTORS

44 DATES TO REMEMBER

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Above: Charles Laverick, left, ArgonneNational Laboratory, and William Fowlerof Fermilab during a 1974 conferenceon applications of superconductivity.

Because electric current that flowsthrough superconducting wiredoesn't lose energy to resistance,magnets made with such wire useless electric power to achieve thehigh magnetic fields required by par-ticle accelerators. It does take energyto cool the magnets, however, so thenet reduction in power use is lessthan 100 percent.

Shortly after Heike KamerlinghOnnes discovered superconductiv-ity in 1911, he also discovered thebane of superconducting materials:quenching. This phenomenon occurswhen a superconducting materialreaches a certain critical current,temperature or magnetic field; it sud-denly "goes normal," that is, returnsto its nonsuperconducting state, re-leasing its stored energy-and some-times melts. His discovery of thisphenomenon also quenched Kamer-lingh Onnes's enthusiasm for thepractical uses of superconductivity.It was not until the late 1960s thatsuperconducting technology reachedthe stage where it began to interestthe builders of particle accelerators.

BETWEEN MAGICAND WITCHCRAFT

Many have credited Wilson with agenius for bringing the right people-with the right skills and knowledge-together at the right time in order toaccomplish scientific goals that were,to say the least, challenging. He neverused this talent to better effect thanin the design and building of theDoubler.

In the mid- 19 70s, when physicistsand engineers at Fermilab began try-ing to design and build super-

conducting magnets, the technologyof manufacturing superconductingwire and cable was still "exotic," asLeon Lederman, who becameDirector of Fermilab in 1978 afterWilson resigned, has written."Somewhere between magic andwitchcraft," is where University ofWisconsin metallurgist DavidLarbalestier places it.

Using his own brand of magic,Wilson brought together his avail-able sources of expertise in super-conducting technology for the taskof designing and making the wireand cable. Fermilab physicists Wil-liam Fowler, Paul Reardon and RussHuson and metallurgist Bruce Strausshad gotten their feet wet in super-conducting technology by buildingmagnets for the 15-foot bubble cham-ber. John Purcell, a physicist fromArgonne National Laboratorybrought to the project his experiencein building its 12-foot bubble cham-ber.

The Applied SuperconductivityLaboratory at the University ofWisconsin gave Fermilab anotherentree into the field of supercon-ductivity. Attracted partly by thewire-fabricating facilities designedby specialist Remsbottom, Larbales-tier had come to Wisconsin fromBritain's Rutherford Laboratory,where he had worked on supercon-ducting materials in the effort tounderstand how they work at amicroscopic and molecular level."Larbalestier was our mentor insuperconductivity," says retiredFermilab Associate Director J.Ritchie Orr. "He made it his businessto understand how it really worked. "

Sixty years after KamerlinghOnnes's disheartening discovery,

16 SPRING 1993

Engineer Willard Hanson andmetallurgist Bruce Strauss test

an early superconducting magnet.

quenching still caused problems formagnet builders at Fermilab, explainsphysicist Alvin Tollestrup, who,along with Orr and Fermilab physi-cists Richard Lundy and HelenEdwards, received the 1989 NationalMedal of Technology for their con-tributions to the Tevatron. A super-conducting magnet uses coils of cablemade of strands of superconductingwire to induce a magnetic field. Theperformance of a magnet made ofsuch wire-its ability to reach andmaintain a prescribed magnetic fieldwithout quenching-depends onmany factors but fundamentally onthe critical current of the supercon-ductor, that is, on the amount ofcurrent the wire can conduct, at itsoperating temperature and field,without quenching. Thus, saysTollestrup, the object of making su-perconducting wire is to achieveworkable wire-that bends easily,for example, and has precise dimen-sions-with a high critical current.

IT'S NOT SO EASY

The would-be wire maker must com-bine the right alloy of the right su-perconducting materials in the rightconfiguration with a conventionalconductor, such as copper; then findthe right methods of heating anddrawing the materials into wire, inorder to achieve the requisite criticalcurrent and mechanical propertiesthat will allow the wire to be formedinto cables. Finally, those materialsand methods must be adapted formass-production of wire of uniformquality. The problem to solve in ca-bling the wire is to find the rightnumber of strands of wire, in the

right configuration, with the rightmaterials on the surface of the strandsand on the cable itself to achieve thehighest critical current and appro-priate mechanical properties so thatit can be wound into magnet coils.

What kind of cable works best insuperconducting magnets? Particleaccelerators have lived and died bythe answer to that question. Foryears, magnet builders at BrookhavenNational Laboratory struggled tobuild superconducting magnets forthe ISABELLE collider using not flatcable but a braid of superconductingwire. Many point to this choice ofbraided cable as a fatal flaw that ledto ISABELLE's demise when the De-partment of Energy withdrew fund-ing for the project in 1983.

These were problems thatmembers of Wilson's Doubler grouptook on in the early 1970s. "When itcomes to making superconductingmagnets," says metallurgist Strauss,"a let's-try-it" approach works betterthan a theoretical one based oncalculations alone. If you think aboutsuperconductivity too long, you'llrealize it won't work. " By early 1975,Fermilab's highly systematic andtightly organized "let's-try-it"

approach had made enough progressto fix important wire and cable speci-fications. The cable would be a 23-strand, flat, twisted "Rutherfordcable." The superconductor itselfwould be an alloy of 53.5 percentniobium and 46.5 percent titanium,proportions chosen to be non-proprietary and in the middle of therange of proprietary alloys of thevarious wire vendors. (Later researchwould show that the exact ratio ofniobium to titanium was not criticalin wire performance.) The work ofFermilab physicists Fowler, Reardonand Donald Edwards, metallurgistStrauss, technical consultant Rems-bottom, and others ultimately pro-duced not simply a set of speci-fications for superconducting wirebut a sort of "build-by-numbers"wire-making assembly, the so-calledFermilab Kit.

BY THE TON?

As the needs of the magnet-development program increased,Fermilab researchers began lookingfor manufacturers who could workwith them to supply large quantities

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Above left: Each wire strand contained2100 filaments of superconductor. TheNew England Electric Wire Companywove the wire into 23-strand, flatRutherford cable which was wrappedin Kapton insulating material. Aboveright: Paul Reardon, right, at a 1974conference in Illinois. Opposite left:The "Fermilab Kit" for makingsuperconducting wire comprised acopper can filled with 2100 niobium-titanium rods in hexagonal coppertubes (foreground), capped with atailpiece and a nose piece. Employeesof Intermagnetics General Corporationassemble the kit. Opposite right: AFermilab machinist winds supercon-ducting cable to form the outer shell ofa Doubler magnet coil.

of superconducting wire and cablethat would meet the specificationsof the evolving magnet design.Having previously served asFermilab's business manager,Reardon played a central role inputting together the collaborationbetween the laboratory and themanufacturers of superconductingalloy, of wire and of cable to producethe materials the project required.Orr sees Reardon as another ofWilson's strategic choices, anotherperson with the right skills at theright time, a man with "organiza-tional brilliance and guts. He didn'tmind gambling a little with thetaxpayers' money when he believedit would mean substantial benefitsin the end." Reardon's gamblesusually paid off for Fermilab.

Niobium-titanium is an alloyformed at high temperatures bymelting in a vacuum with an electronbeam. In 1974, when Fermilab firstwent looking for superconductingalloy, the Teledyne Wah ChangAlbany Corporation in Oregon wasthe major supplier of niobium-titanium in the United States-andthe Laboratory was virtually the onlybuyer. Strauss and Reardon onceconstructed a bar chart showing thatFermilab had bought 95 percent ofall the niobium-titanium ever

produced since the beginning of time.Niobium is mined in only a fewplaces on earth-Brazil, Canada andChina. In the 1970s China was not apractical source, and the ores withthe highest concentration came fromBrazil. Most of Fermilab's niobiumalloy came from Brazilian ores untilclimbing export taxes sent WahChang to Canadian sources.

In the spring of 1974, Reardon,Strauss and contracts manager Ed-ward West made a trip, legendary inFermilab lore, to the Northwest tobuy niobium-titanium from WahChang. "How much is it by the ton? "Reardon is supposed to have asked.Strauss remembers him explaining,"If we order it by the pound, they'llnever learn how to make it in quan-tity." That early decision to buy alarge amount of niobium (an initialorder of about 15,000 pounds) provedsignificant in defining the relation-ships Fermilab established with thecompanies that made the alloy intosuperconducting wire.

FROM MINE TO MAGNET

Fermilab requested delivery of thealloy from Wah Chang as straight 24-inch rods, an eighth of an inch indiameter. The rods were the firstpiece of the Fermilab Kit, which con-sisted of a "billet" of 2100 niobium-titanium rods inserted into hexago-nal oxygen-free, high-conductivitycopper tubes with round bores, allpacked into a 10-inch diameter cop-per "can." Nose and tail pieces werewelded onto the can. The niobium-titanium rods came from Wah Chang.The Small Tubes Products Companymade the hexagonal copper tubes.

18 SPRING 1993

The Phelps-Dodge Company fur-nished copper for the cans, whichwere made by the Janney Manufac-turing Company.

Fermilab bought all these kitmaterials for delivery to the wiremanufacturers, whose task was topush and pull each 10-inch billet ofcopper-tubed niobium-titanium intoa strand of superconducting wire 27thousandths of an inch in diameter.Each strand would thus contain 2100filaments of copper-coated niobium-titanium superconductor. Theoreti-cally, each billet would produce220,000 feet of superconducting wire.In practice, Fermilab paid a premiumfor any usable lengths over 210,000feet that met specifications.

After the wire had been tested fordimension and superconductingproperties, it went to the New En-gland Electric Wire Company, whereit was formed into flat 23-strandRutherford cable. Fermilab magnetbuilders worked with the cablemanufacturer to develop tooling andmethods to "keystone" the cable,slightly changing its shape to fit thecurve required by magnet design. Tothe finished cable they added a wrap

of the insulating material Kapton.Tollestrup had discovered that wrap-ping with Kapton not only elimi-nated short circuits in the cable butinsulated the superconductor againstthermal transference that led toquenching. Both Fermilab inven-tions-keystoning and the Kaptonwrap-played significant parts in thesuccess of the Doubler magnets.

New England Electric Wire deliv-ered the cable to Fermilab's MagnetFabrication Facility for winding intocoils for magnets. Each magnet used110,400 feet of wire, twisted into4,800 feet of cable. The 796 dipolemagnets and 224 quadrupoles in theDoubler used enough wire to circlethe earth 2.3 times, says contractsmanager Lawrence Vonasch. In ad-dition, prototype and experimentalmagnets used millions more feet ofwire.

"We had learned very early," saysLarbalestier, "that the properties ofthe conductor determined theproperties of the magnet." Theprocess of making 10-inch billets into0.027-inch wire takes many steps,including an initial extrusion intotwo-inch diameter rods, various heat

treatments, and "cold-working,"drawing the wire into ever-finerdiameters. No single step is morecrucial in determining the criticalcurrent than the heat treatment thewire receives. How hot should thewire be heated? For how long? Atwhat wire diameter should the heattreatment occur? Each wire companyhad its own proprietary recipe.

Fermilab dealt with four manu-facturers of superconducting wire-Magnet Corporation of America,Supercon, Airco and IntermagneticsGeneral Corporation (IGC). The firstorders gave only a few billets to amanufacturer to make into wire.Fermilab would test it, rejecting wirebelow a certain level of performance.The vendors' early efforts yieldedwildly erratic results. As a company'sperformance improved and the needsof the magnet program increased,Fermilab furnished more billets. Bythe project's end in 1982, IGC-theremaining wire vendor-was process-ing 150-billet orders into highly uni-form wire.

Close communication betweenFermilab and the manufacturersinfluenced the success of the

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Im.f

H

Above: Billets at Intermagnetics GeneralCorporation (IGC), manufacturer of mostof the wire for the Energy Doubler. Each10 inch billet yielded about 200,000 feetof 0.027 inch superconducting wire, onspools in background. Opposite: IGCemployee winds superconducting wireonto a spool.

Laboratory-industry collaborations,says physicist Lundy, who puttogether and ran its mass-productionassembly line for superconductingmagnets. Wisconsin's Remsbottom,a skilled hands-on veteran in thesuperconducting field who, saysLundy, "knew as much about how tomake superconducting wire asanyone in the world," spent most ofhis time on the road, traveling fromWah Chang to IGC to New EnglandElectric Wire and back again. "If youwere a Fermilab vendor, you knewthat every two weeks or so, Bob wouldshow up." Often Lundy, who washimself a practical and inventiveengineer as well as a high-energyphysicist, accompanied him on thesetrips. "They let me in because I waswith Bob," he says. These personalvisits provided a direct channel forthe back-and-forth flow of informa-tion that helped improve the qualityof the wire.

ASSUMING THE RISKS-AND CUTTING THE PROFIT

Fermilab's decisions not only topurchase the raw materials for thesuperconducting wire but to requirethe wire manufacturers to use theFermilab Kit were key factors indetermining the nature of the

working relationships that evolved.These decisions had important andcontroversial consequences, worthexamining for their effect on thesuccess and the limitations-ofFermilab's major procurement ofsuperconducting wire in creating andencouraging the superconductingwire industry in the United States.

The greatest cost component inproducing superconducting wire isthe cost of the alloy. It wasexpensive-about $100,000 a tonwhen Fermilab began buying it in1974. For large corporations withdeep enough pockets to assume thelevel of financial risk required to buylarge quantities of alloy, the Doublerrepresented a relatively limitedmarket that did not justify thenecessary investment in research andretooling. They just weren'tinterested. Smaller, specializedcompanies that did find the Doublermarket worth pursuing lacked thefinancial resources to buy largequantities of alloy. From Fermilab'spoint of view, the Laboratory'spurchase of alloy helped the fledglingindustry by assuming one of themajor financial risks for these smallmanufacturers, that operated, recallsOrr, "on the ragged edge of nothing."

"Sure they took away some of therisk," says Carl Rosner, president ofIGC, the manufacturer that ulti-mately supplied most of the wire."They also took away most of theprofit. By refusing to allow us to buythe alloy ourselves, to our own speci-fications, and mark it up, they tookaway our major opportunity to makeany money on the contract."

"It's true we didn't have the cashon hand to buy niobium," he adds"but with an order from Fermilab we

20 SPRING 1993

could have gone to the bank for aloan. That's how it's supposed towork. "

By furnishing kits to the wiremanufacturers, Fermilab eliminatedmany technical variables in an en-terprise in which systematic controlof the parameters of superconduct-ing magnets was absolutely crucialto success. But the kits also tookaway most of the opportunities forvendors to use their own proprietarymaterials and methods-and thuseven more of the opportunities toprofit.

"Fermilab helped us enor-mously, " says Rosner. "They forcedus to accelerate our learning curve insuperconducting technology. But ourexperience making wire for the Dou-bler should have positioned us as aworld leader in superconductingtechnology." Instead, he believes,Fermilab's refusal to allow vendorsto profit left U.S. superconductormanufacturers like IGC ill equippedto compete in the world market thattook off in the 1980s with the adventof magnetic resonance imaging.

Maybe so, says Bruce Chrisman,Fermilab's Associate Director. "Butif we had let those guys mark up theniobium, it would have sent the costof the Doubler up so high that DOEwould have told us to forget it. TheDoubler would never have been built,and there wouldn't be any market totalk about today."

WHY IT WORKED

Another thorny issue in this rockymarriage between science andcommerce concerned who wouldhave custody of the information that

the partnership engendered. Whattradition is more hallowed in sciencethan the free dissemination of theresults of scientific investigation?What commodity is more preciousto a technology-based company thanhard-won technical secrets? ToFermilab scientists, it seemed onlynatural and ethical to share whatthey learned about superconductingwire with the world. To the wiremakers, it seemed like giving awaythe farm. From their point of view,the scientific community simplyhanded foreign firms a state-of-theart recipe for making supercon-ducting wire, effectively eliminatingthe leg up that U.S. companies hadgained from their fast and arduousscramble up the learning curve.

If "The Case of the Superconduct-ing Wire" raises difficult questions,it also shows that science and indus-try can find common ground whereboth can thrive. Although it didn'twork perfectly, the collaborationbetween Fermilab and the supercon-ducting technology industry did in-deed work.

Asked why, Wisconsin's DavidLarbalestier says, "I think it camedown to honesty-good old-fashioned intellectual honesty. In allthe organizations, there were peoplewho could focus on the things thatwere real. It's all too easy in this

business to get egos into play. Butthe question is, 'Will the game beplayed in an honest fashion?' "It'snot a trivial thing-simply to under-stand," he adds, "In the long run inthis country, we need a long-termcommitment to understanding."

Successful companies in the col-laboration had the motivation to in-novate and experiment and investresources to supply the materials tobuild the world's highest-energy par-ticle accelerator, and in doing so theybuilt a new industry. High-energyphysics did not invent MRI, but it didpush superconducting technologyout of the nest so that when MRIcame along, the industry was readyto fly. For the future, we can't predictthe exact flight plan, but we can besure that superconducting technol-ogy has just begun to soar. In thewords of the late Robert Marsh, ofTeledyne Wah Chang, still theworld's largest supplier of supercon-ducting alloys, "Every program insuperconductivity that there is to-day owes itself in some measure tothe fact that Fermilab built theTevatron and it worked."

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