Fall 1991 Vol

CONTENTS ^aiWee

FALL 1991 VOL. 21, NUMBER 3 FEATURES Editors RENE DONALDSON, BILL KIRK WHITE DWARFS Contributing Editor Going Gentle Into that Good Night MICHAEL RIORDAN A review of what we know and don't know about these planet-sized stars. Editorial Advisory Board Virginia Trimble JAMES BJORKEN, ROBERT N. CAHN, DAVID HITLIN, STEWART C. LOKEN, JOHN REES, RONALD RUTH 7 PARTICLE PHYSICISTS, TEACHERS MARVIN WEINSTEIN & SCIENCE EDUCATION REFORM Photographic Services Particlephysicists are teaming with teachers TOM NAKASHIMA to improve the quality of pre-college BETTE REED science teaching in the United States. Marjorie Bardeen Illustrations TERRY ANDERSON, KEVIN JOHNSTON 12 WORKSHOPS TARGET THE NEXT SYLVIA MACBRIDE, JIM WAHL LINEAR COLLIDER Distribution A review of recent linear collider conferences CRYSTAL TILGHMAN by two participants. David Burke and Ewan Paterson

The Beam Line is published quarterly by the Stanford Linear Accelerator Center, P.O. Box 4349, Stanford, CA 94309. DEPARTMENTS Telephone: (415) 926-2585 BITNET: BEAMLINE@SLACVM FAX: (415) 926-4500 SLAC is operated by Stanford University under 17 DATES TO REMEMBER contract with the U.S. Department of Energy. The opinions of the authors do not necessarily 18 TOWARD THE NEXT LINEAR COLLIDER: reflect the policy of the Stanford Linear Accelerator Center. THE ACCELERATOR TEST FACILITY AT KEK Koji Takata

FROM THE EDITORS' DESK Cover: A photograph ofa planetarynebula in Aquarius, 21 taken with the 200-in. telescope on Mt. Palomar. Planetary nebulae are the ejected outer layers of dying 22 LETTERS TO THE EDITORS stars of relatively low mass. The relic cores become the white dwarfs discussed in Virginia Trimble's article in this issue. Photo courtesy of California Institute of 23 CONTRIBUTORS Technology. »^4 WE HAVE MADE several attempts during the past two years to secure a spectrum of the companion of Sirius. .. .The great mass of the star, equal to of Sirius, and its low luminosity, one one- hundredth part of that of the Sun and one ten-thousandth part of that of Sirius, make the character of its spectrum a matter of exceptional interest.... The line spectrum of the companion is identical with that of Sirius in all respects so far as can be judged from a close comparison of the spectra.... Direct photographs taken by Dr. van Maanen with and without the use of a yellow color screen agree with the spectrographic results in indicating that the companion of Sirius has a color index not appreciably different from that of the principal star. valter Adams Alvan Clark "The Spectrum of the Companion of Sirius," Walter S. Adams, Publications of the Astronomical Society of the Pacific 27, 236-237 (1915) reproduced in A Source Book in Astronomy and Astrophysics, 1900-1975, Lang and Gingerich, Editors, Harvard, 1979. I Only a very few stars that begin (PV = nRT) thermal-gas pressure in (hence temperatures), and lumi- their lives with more than six to stars like the sun, but by electron nosities were nearly always strongly eight times the mass of our sun will degeneracy pressure in white dwarfs. correlated. The properties of Sirius end spectacularly. In other words, if B, reported in 1914 by Walter S. you allowed every star a vote , * then Adams at Mt. Wilson Observatory, white dwarfs would win, hands HISTORY defied the correlations. The star was down, but supernovae seem to have Friedrich Bessel (as in functions) blue (hot) and yet faint. A handful of much better public relations. advocated massive, dark companions additional white dwarfs joined in the Admittedly, they are easier to make as the cause of wiggles in the motion defiance over the next decades. sound exciting, being responsible for of Sirius and Procyon that he had Theoretical understanding began the production of heavy elements seen in data from a couple of decades with R.H. Fowler's development of like uranium and thorium (and the up to 1844. The companion of Sirius (non-relativistic) quantum statistics distribution of most of the rest), for advanced from dark to dim in 1862 in 1926 and was essentially com- accelerating cosmic rays, leaving through the intervention of Alvan plete when S. Chandrasekhar pre- pulsars behind, and (perhaps) trig- G. Clark, arguably the last optical sented the exact equation of state for gering new generations of star for- astronomer to make a fundamental relativistically degenerate electrons mation. Still, numbers should count discovery with a telescope he had and the properties of stars dominated for something, and white dwarfs have designed and built himself. * * Turn- by that degeneracy between 1930 the additional, parochial attraction ing a newly-ground 18.5-inch lens and 1935. His contemporaries were of showing us what our sun will toward the brightest star in the sky, slow to understand the correctness eventually become-unfortunately he saw separately the 0.01% of the and importance of what he had done, not in time to prevent the next round photons that come from the com- but I think this belongs more to the of presidential primaries, but only panion, 10 arc-sec away from the after five or six billion years. glare of Sirius A. Procyon B turned Briefly, a white dwarf contains up as a separate point of light in "Of course, if stars are allowed to vote, a 1894. then they should also pay taxes. One the mass of a star, crammed into dollar per star in our Milky Way galaxy volume the size of a planet, and has White dwarfs counted as a would just about take care of this year's therefore a density larger than that of problem, however, only after the on- budget deficit (which I decline abso- set of serious classification of stellar lutely to describe as "astronomical.") terrestrial substances by a factor of a " A point which may not be totally million. The force of gravity holding spectra and the recognition that irrelevant to recently revealed problems stars together is balanced by ordinary absorption line patterns, stellar colors in optical telescope design.

2 FALL 1991 realm of sociology than to history of and a good many others. Enough science. Incidentally, 20 years be- astronomers earn a living studying tween recognition of an astronomi- CVs to permit gatherings of a hundred cal problem and arrival at a solution or two every few years. that then holds up for much longer is Very occasionally, mass transfer a fairly typical time scale. or merging in white dwarf pairs may 0 gd0) trigger explosive burning of the car- t- bon and oxygen core material up to THINGS WE UNDERSTAND iron. The stars are blown to About one white dwarf per year smithereens called Type I superno- C) forms somewhere in our galaxy, a vae. (Massive stars make type II, com- Subrahmanhan Chandrasekhar number arrived at independently by moner but less bright.) counting the young (hot, relatively bright) ones, by counting prospective progenitors, and by counting the nebulae ejected in the intermediate The Great Scheme of Things "thin shell" phase (called planetary nebulae, and if you want to know AT LEAST BY THE STANDARDS OF ASTROPHYSICS, stellar structure and why, you must read a real astronomy evolution are in pretty good shape-meaning we can marshall a set of coupled, book). Ten percent or more of a non-linear differential equations and their solutions to support what is said in the next few paragraphs. complete stellar inventory consists Stars are, by definition, stable objects deriving their energy from nuclear of white dwarfs, just sitting there, reactions. A gas cloud of standard composition (about 3/4 hydrogen, 1/4 helium, radiating away the thermal (kinetic) and 2% everything else) and mass = 0.085-100 solar masses [one solar mass 33 energy of their carbon and oxygen (M0 ) = 2x10 g] will contract to form such a star. Smaller masses do not get hot nuclei from underneath very thin enough for any fusion reactions; bigger ones are unstable. All stars spend 90 skins of hydrogen and helium. percent or more of their lives fusing hydrogen to helium. The time to exhaust They 2 will continue this uneventful course hydrogen fuel is, very crudely, t = [10 yr/(M/M) ], that is, millions of years for big stars, billions for little ones, including the sun. until the universe recontracts, their Masses less than about 0.4 Me leave their helium cinders so degenerate that baryons decay, or they collapse to no further contraction, heating, or fusion can occur. The universe is not yet old black holes by barrier penetration. * enough for this to have happened to any isolated star. But stripping of outer layers Half or so of all stars have can occur among close stellar pairs, leaving low-mass helium cores in shorter companions close enough for gas to times. There exist low-mass white dwarf binaries where the stars are tearing each flow from one to the other. Material other apart viciously enough that the layers accessible to spectroscopy confirm the transferred to a white dwarf falls into mostly-helium composition predicted for these cores. Larger masses all heat a deep potential well, hence radiating to at least 108 K at their centers and so fuse helium to carbon and oxygen, in roughly equal amounts, first in their cores and then in thin copiously as it goes, and exploding shells. A combination of radiation pressure and pulsational instability in this "thin- from time to time, when it piles up shell" phase ejects much of the hydrogen-rich envelope. Thus initial masses up to to fusion temperatures and densities. 6 or 8 M0 are stripped down to carbon-oxygen cores of 0.4-1.4 M0 . These Collectively such systems are called degenerate C-O cores are much the commonest kind of stellar relic. cataclysmic variables, botanically Only higher masses still go on to fuse carbon and oxygen to heavier elements divided among novae, dwarf novae, and eventually make supernovae. Afew on the ragged edge may burn out en route, leaving degenerate cores of oxygen, neon, and magnesium, a third category of white dwarf. The C-0 and O-Ne-Mg compositions are confirmed spectroscopically in nova explosions that eject some material from white dwarfs in more massive *Likely time scales for these three outcomes close pairs. are 1014, 1033, and 101076(years for the first two and for the third one it doesn't matter).

BEAM LINE 3 I I

.2 .F I ( n (1 :2 2s0 -3pl

C/) w JL : i~~~~~~I I . . c6 3600 4600 5600 6600 < (A) Rudolph Minkowski

Observed spectrum and line identifications AND THINGS WE DONIT of coupling. But we cannot currently in the magnetic white dwarf PG 1031+234 Why are white dwarfs such slow describe the process well in words, (greatly simplified from G.D. Schmidt 1987, rotators? Why do a few have enor- let alone in differential equations. inA.G.D. Philip et al., Eds. IAU Colloq. 95, mously strong magnetic fields and MAGNETIC FIELDS. For the majority the Second Conference on Faint Blue Stars, of white dwarfs, absence of quadratic L. Davis Press, p. 377). The most very little? Why are there so Schenectady: shift tells us that surface wiggly line is observed flux vs. wavelength. few faint white dwarfs? Where are Zeeman Long vertical lines are placed at the wave- the Type I supernova progenitors? fields are ' 105 G (10 Tesla*). Conser- lengths of the indicated transitions for There are lots of others, but these are vation of flux from a 1-10 G solar magnetic fields of 200-300 MG; arrows and my favorites and will do to get on dipole through the contraction pro- shorter vertical lines indicate the range of with. cess brings us within this limit. But wavelengths of absorption in those ROTATION. A spinning white dwarf a few percent of single degenerate transitions for somewhat stronger fields. The dwarfs and 10-20% of the close bi- are those that reach begins to break up only for rotation lines you expect to see nary ones have fields between 1 and turning points or asymptotes, so that periods shorter than a few seconds. wavelength changes only slowly with field Conservation of angular momentum 1000 MG. Wavelengths of atomic strength in the 100 MG range. Remember in layers as stars evolve from initial transitions are so distorted by such that, for hydrogen in the absence of a hydrogen burners to degenerate cores fields that absorption lines in mag- magnetic field, all components of 2-3 should lead to rotation periods of netic white dwarfs remained uni- A, (called H a or Balmer a) are at 6562.8 minutes to hours. In most cases, we dentified for some 40 years after and all components of 2-4 (called H f or know only limits to rotation speeds Rudolph Minkowski recorded the Balmer f) are at 4861.3 A. The strong field first spectrogram of one in 1939. Early of the transitions as (from absence of Doppler blurring of breaks the degeneracy came from well as shifting absorption wavelengths. spectral lines) and periods (from ab- field determinations thus sence of changing surface magnetic measurements of circular polariza- field patterns). The limits range from tion. Recognition that the random- hours upward to years. looking features were just the shifted Neutron stars left by supernovae Balmer lines of hydrogen came gradu- exhibit the same phenomenon. Most ally and from close interplay of of them are not born spinning nearly theory, observations, and laboratory as rapidly as stability permits or as experiments. The largest stellar field angular momentum conservation in layers predicts. Evidently stars are *White dwarfs seem to be the only objects good at transporting angular momen- in the universe for which the Tesla is a tum outward, through turbulence, reasonable-size unit, which is magnetic fields, or some other form undoubtedly why we never use it.

4 FALL 1991 -2

-3

.E c a Z I 0- c 0 -4 a c |c/ c -5 .E Oc -5 cf

Jesse Greenstein

-o 0 -1 - 2 -3 -4 -5 -6

Log L/L o

for which deconvolution has been than expected unless (a)some serious Observed vs. expected numbers of achieved approaches 300 MG (work physics has been left out of the white dwarfs in the solar neighborhood in progress by Jesse L. Greenstein at parentheses a couple of sentences as a function of luminosity in solar units. Caltech on G 240-72). back or (b) the galactic disk is not Dots are observed numbers per cubic parsec per decade in L (from J. Liebert, It is permitted to attribute the very old. Notice that if more stars C. Dahn and D.G. Monet, 1989, Astro- range of fields to exact flux conserva- formed in the past, the problem gets physical Journal 332, 891). Dashed tion from main sequence progeni- worse. curve is the simplest possible model, tors with l-3x104 G dipole fields. Blaming everything on the sec- with constant birthrate and constant This does not explain the excess of ond cause yields a disk much younger ratio of surface to central temperature, strong fields in binary white dwarfs than the galactic halo stars (globular roughly normalized to the intermediate or the difference from neutron stars, clusters), and we have learned some- points. Solid curve is a model with constant birthrate but much better all of which start with 1012-13 G thing about galaxy formation and treatment of radiative transfer and other fields, though their progenitors pre- evolution. Active researchers are physics (from F. D'Antona and sumably have a wide range. In any about equally divided on whether or I. Mazzitelli 1989, Astrophysical Journal case, the genesis of stellar magnetic not a young disk is required by white 347, 934). Both clearly predict too many fields in general is not understood, so dwarf statistics; the rest of us are faint stars. The observed cutoff below one is merely pushing the problem sitting on the side lines, attempting Log L /Lo = -4 can be achieved by back a step in time. to make encouraging noises. having the faint stars cool very suddenly or by imposing an upper limit to ages of FAINT WHITE DWARFS. Start with the PROGENITORS OF TYPE 1 SUPERNOVAE. 6-8x109 yr (vs. 12-17x109 yr for the halo plausible assumptions that white Having confidently told you that we stars in our galaxy). dwarfs have formed at a constant know these nuclear explosions come rate since the galactic disk has been from binary white dwarfs, I must around and cooled as black body now back off and confess that there radiators ever since, drawing on their are no known examples of the most internal kinetic energy supply. Then, promising sort of system. To get the after a lot of hard work (occasioned requisite explosion, pairs must be (a) by crystalization of the core, radiative close enough for angular momentum transfer through partly degenerate loss in gravitational radiation to bring gas, and so forth) you can predict the stars together in the age of the what the current distribution of universe and (b) massive enough that white dwarf brightnesses should be. the merged pair will comfortably You generally get the wrong answer. exceed the Chandrasekhar limit to We see far fewer faint white dwarfs masses supported by electron

BEAM LINE 5 degeneracy (about 1.4 Mo). But the These same radial velocity data known close pairs are all low mass, produced the 105 G limit on magnetic and the known massive ones are too fields for typical white dwarfs wide to merge. There the problem mentioned above and were the source sits, and has sat through about five of the first list of candidate massive years of increasingly serious searches double degenerate stars, none of for massive close pairs. which have actually turned out to be likely SN Ia progenitors. In April 1991, I submitted a proposal to look F YOU HAVE STAYED with us this for coronal x rays from single, cool far, I will try your patience a mo- magnetic white dwarfs using the ment longer and explain my own ROSAT satellite in collaboration with involvement with white dwarfs over Keith Arnaud of Goddard Space Flight the years. All Caltech graduate stu- Center. dents in astronomy were (and are) o required to complete a test research project before settling on a PhD dis- sertation topic. The one assigned to me in 1965 was measurement of radial velocities of about 60 white dwarfs, based on 200-in. telescope prime focus spectrograms obtained by Jesse L. Greenstein in the 50s and 60s. In retrospect, I think this may have been partly because the task was thought to be impossible, and female graduate students were new, at least to Caltech, in those days. The task turned out to be difficult (pressure broadening makes the spectral lines of white dwarfs remarkably broad) but not impossible. The measurements led to an estimate of the amount of gravitational redshift and so to values for masses of single white dwarfs, not otherwise available. Our average value, 0.75 Mo, was slightly larger than the modern average, 0.6 Mo, as found from pressure effects on the shape of the stars' spectral continua. Deep down, I still believe the larger value, and, after all, every scientist is entitled to be cranky about one or two points.

6 FALL 1991 s, Teachersi i:L : ;cience Edt Ition Reform

by MARJORIEfi:.11... BA EN

Particle are teaming with teP, nprove the *escience teachil ite

,,BSHOCKED AMERICAN 1S:0<:000v0040:~ :-:and ought scientie ,ii ed"ueators and t....teache ther to revan thie wag cience and math 'Ihe ahabtft soutp" igcurri n id Chem Study at the high ( vei SCIS a

F.support U.eduniv ersity -b asedAt e4ac he e n h an e n t t ied some of the best teachers in s assrooms.In 1983, A Nation at Risk, the first in series of reports critical of contemporary American ecollege education, produced similar results. Again search scientists joined with educators to give teachers d(theirstutdfents an opportunity to discover the true tof the wor;ld of science.

:MLINE Particle physicists have been lead- Contemporary Physics Education education programs in response to ers in this effort since 1979 when Project based at LBL and SLAC. This Secretary of Energy James D. Leon M. Lederman, director of group of 20 educators and scientists Watkins' aggressive education policy Fermilab, started Saturday Morning has created the first physics opening laboratory doors to schools. Physics for high school students. At equivalent of the Periodic Table of For example, at Bates Linear the time Fermilab funds could not be the Elements. The Particle Chart is Accelerator in Massachusetts, Ernest spent on precollege education pro- the centerpiece of a package of J. Moniz has inaugurated a program grams, so Lederman encouraged the teaching materials (above) that to augment high school teachers' establishment of Friends of Fermilab, includes interactive HyperCard knowledge about nuclear and particle a not-for-profit corporation dedicated software for the Macintosh com- physics. Three high school teachers to supporting Fermilab precollege puter. A student book and a teacher's worked with local staff mentors to programs. Since its incorporation in packet are being developed under produce a draft resource manual that 1983, Friends of Fermilab has raised the leadership of R. Michael Barnett, will be used in a fall lecture series for over $2,600,000 from public and pri- Lawrence Berkeley Laboratory, and high school teachers. The course will vate sources including DOE, NSF, Helen R. Quinn, SLAC. Workshops be team taught by the teachers and the state of Illinois, and various pri- for teachers are an essential aspect of faculty members from MIT, Boston vate foundations. the project-SLAC held a one-week University, and Northeastern Uni- The Conference on the Teaching workshop this summer, and The versity. Under the leadership of of Modern Physics was held at Modern Physics Institute, held at Beverly Hartline, a partnership be- Fermilab in 1986. Organized by the Westminster College, New Wil- tween the Continuous Electron Beam American Association of Physics mington, Pennsylvania, has close ties Facility (CEBAF) in Virginia and the Teachers and Fermilab, the Confer- to the Project. Workshops have also Newport News Public Schools offers ence brought high school teachers been presented in conjunction with a program for fifth and sixth graders and college professors together to professional meetings. called Becoming EnthusiasticAbout develop ways of translating the Math and Science (BEAMS). BEAMS excitement of modern physics to brings regular classes and their introductory physics classrooms. An INCE 1989 OTHER PARTICLE teachers to the Laboratory for week- important collaboration to emerge physics laboratories funded by long visits. The classes follow their from the Conference was the DOE have initiated precollege normal curriculum augmented by

8 FALL 1991 special activities conductedby CEBAF scientists, engineers and technicians. A parent open house is held one evening during the week. The Superconducting Super Collider Laboratory (SSCL) has developed a program, Adopt a Magnet, to help students in kindergarten through fifth grade understand the purpose and function of the SSC. The younger students are introduced to the SSC through songs and games. Older students do various electronic projects. Upon completion of the program, participating schools "adopt" one of the more than 10,000 SSC magnets. Schools receive an adoption certificate, and the school's name is placed on the adopted magnet. Particle physicists based at universities also participate in school reform. For example, Howard through their own hands-on exper- Physicist Jim Strait listens intently S. Goldberg leads a team of scientists iments. Resource centers for teachers to Zelda Tetebaum during the Summer and mathematicians from the will be established across the state. Science Project at Fermi National University of Illinois at Chicago The new extended community of Accelerator Laboratory. which is developing a K-8 curri- teachers, faculty, and researchers culum, Teaching Integrated created by this program will ensure Mathematics and Science (TIMS). that every classroom teacher has This initiative, based on under- state-of-the-art advice and assistance standing fundamental concepts and available every day. processes, integrates the teaching of Other particle physicists are in- science and mathematics while volved with hands-on science muse- remaining faithful to the spirit of ums modeled after the Exploratorium both disciplines. The conceptual in San Francisco, California, founded framework for TIMS experiments by Frank Oppenheimer. MICRO- includes a four-step format that con- COSM is a new science museum at tains the essence of the scientific CERN. Hannu I. Miettinen is a method allowing students to define founder and former director of the two primary variables, measure Heureka, the Finnish Science Cen- the responding variable after having tre. SciTech, a science museum in set up an appropriate experiment and Aurora, Illinois, was founded by analyze the results. Ernest Malamud. Kenneth G. Wilson participates in The Ohio Mathematics/Science Discovery Project, led jointly by the AT FERMILAB THE OLDEST Ohio board of Regents, the Ohio State continuing collaboration be- University and Miami University. tween particle physicists and Initially, the project is aimed at educators is responsible for the 35 improving the way science and precollege education programs mathematics are taught to fifth- offered in 1990 for over 10,000 through ninth-graders by enabling students and 2100 teachers. The them to recreate some of the most following description of those fundamental discoveries in science Fermilab programs focused directly

BEAM LINE 9 Physicist Steven Delchamps, left, explains the process of superconducting magnet making to teachers during the Summer Science Project at Fermi National Accelerator Laboratory.

expertise of scientists and mathematicians who give seminars on current research topics with the expertise of master teachers who lead laboratory sessions that present the topics at a high school level. One of the most effective spin- offs of the Summer Institute is Physics West, a teacher support network. Teachers meet on a month- ly basis during the school year to on particle physics serves as an share successful teaching strategies example of what a research facility and instructional materials. A corps can offer. of dedicated teachers keeps the HIGH SCHOOL PROGRAMS. Fermilab's network alive, and Fermilab supports high school programs include re- the newsletter. search participation, institutes and Topics in Modern Physics is a workshops, classes, support net- collection of instructional materials works, instructional materials, and developed from Saturday Morning Public Information Office guided Physics, the Summer Institute and tours. the 1986 Conference. Included are a Fermilab has offered summer re- three-volume teacher resource search appointments to teachers manual, a series of 15 videotapes since 1983. A first-hand experience from the Fermilab archives and sev- in the laboratory can translate into eral posters. Fermilab provides the enhanced teaching strategies and new materials at cost, and the six physics instructional materials for teachers teachers who prepared the collec- who may never have worked in a tion give presentations and work- research environment. Current ap- shops at professional meetings and pointments are supported in part by on request. the DOE Teacher Research Associ- Three sessions of SaturdayMorn- ates Program (TRAC). ing Physics are offered annually for Institutes and workshops offer high school students. The class, opportunities to enhance teachers' which meets for three hours on ten backgrounds in basic science, model Saturdays, includes a lecture by a successful teaching strategies, and senior scientist and small discussion present new instructional materials. groups and tours of the Laboratory Middle: California high school physics Fermilab has offered the Summer with postdoctoral students. teachers Richard Taylor, left, and Earl Institute for Science and Mathe- Research experiences are offered Boynton review material during SLAC's matics Teachers (Summer Institute) to high school students who have week-long Teacher Workshop. Above. since 1983. Today, the Summer Insti- the background to join either an in Aurora, Illinois, Visitors to SciTech a technical group. Two enjoy the three-armed Chaotic Pendu- tute is sponsored jointly by Fermilab experiment or lum, one of over 130 hands-on exhibits. and Chicago State University and is programs, the DOE High School Scitech, an interactive science and hosted at the university primarily Honors Research program and technology center, had over 62,000 for Chicago public high school Target: Science and Engineering, visitors its first year. teachers. The program combines the enhance the research experience with

10 FALL 1991 seminars or classroom work on a related science project. MIDDLE/ELEMENTARY SCHOOL PROGRAMS. Fermilab makes research appointments to middle school teachers in the TRAC Program, offers institutes and workshops, supports a middle school teacher network, and provides instructional materials. Students may visit the Laboratory and partici- In 1983 it was not at all clear that Above left. High school teachers from pate in a variety of science experi- a research facility was an appropri- Massachusetts engage Professor ences. Two particle physics programs ate setting for a major science reform Jerome I. Friedman, right, one of last are described below. initiative. Teachers and students year's Physics Nobel Laureates, in Beauty and Charm: an Introduc- have given us the answer: "Yes!" discussion after his talk to the group. tion to ParticlePhysics includes an Precollege education programs work The program is supported by Bates Linear Accelerator Center and the instructional unit, a tour, and a at DOE national laboratories because National Science Foundation. The teacher training workshop. The pur- it is not business as usual. Teachers come to a world class high energy "mentors" helping the teachers are pose of the unit is to provide an physics research laboratory for a supported by the Department of Energy, experience in science to broaden and unique opportunity to witness sci- an example of collaboration among enrich attitudes and to develop an ence conducted at the frontiers of funding agencies to improve the quality appreciation for physics. Students human understanding and to learn of pre-college science education. Above who study the unit at school may right. Students in CEBAF's BEAMS from leading research scientists. Stu- tour the Laboratory and meet program compete in a "slow" bicycle with a dents have an experience in science physicist. race, computing their average velocity that broadens and enriches their at- by measuring their time and distance. The Summer Science Project is a titudes and develops their apprecia- summer institute for middle school tion for science. Students see, per- teachers who receive training as lead haps for the first time, what the world teachers. During the institute par- of science is really like, and they like ticipants develop a dissemination what they see. project to implement during the fol- 0 lowing school year. The curriculum includes seminars on basic science, training sessions on effective science instruction and inservice techniques, laboratory sessions where participants try out hands-on classroom activities, and tours.

BEAM LINE 11 1V„~~~~or~~~~~ 1

A review of recent linear collider conferences in Lapland and Protvino by two participants.

by DAVID BURKE and EWAN PATERSON

WO WORKSHOPS CONVERGED THIS FALL to focus and sharpen the goals and development of future electron- positron linear colliders. These two meetings, one centered around the particle physics of e +e - collisions, and the other around the accelerator physics and technology of linear colliders, were attended by a total of nearly 250 physicists from all parts of the globe. Together they marked the first opportunity for such a broad representation of particle and accelerator physicists to meet for serious discussions aimed at the realization of the next high-energy electron-positron linear collider.

12 FALL 1991 The First International Workshop electroweak interactions. Displayed constitute a major test of our on Physics and Experiments with throughout the plenary talks that understanding of the origin of mass. Linear Colliders was held at ended the conference, this consen- Scan of the tt threshold region Saariselka in Finnish Lapland the sus of the participants was succinctly will allow measurement of the mass second week in September and was put forth by Bj6rn Wiik (DESY) in his of the top quark to better than followed a week later by the gather- final summary: "The physics 0.5 GeV. This is an interesting mea- ing of accelerator physicists in programme of a 300-500 GeV e+e- surement in itself, and, when com- Protvino, USSR, for the Third Inter- collider with luminosity 10 fb-1 per bined with expected improvements national Workshop on the Accelera- year has unique features and is in measurements of the W mass at tor Physics and Technology of Lin- complementary to the physics CDF and LEP II, will constrain the ear Colliders. These meetings were programme at the hadron colliders Higgs mass with accuracies of 20- spawned by recommendations from LHC and SSC." 30%. This would comprise the ulti- the International Committee on Fu- It is remarkable that the mass of mate test of radiative corrections to ture Accelerators (ICFA) and were the top quark is (apparently) greater the Standard Model. These same data organized by the Finnish Institute than that of the electroweak gauge will pin down the strong coupling for High Energy Physics (SEFT) and bosons, and furthermore, approaches constant as(2mt) to within 5%- by the Branch of the Institute for the vacuum expectation value of the comparable to measurements made Nuclear Physics at Protvino (BINP). Higgs field. Understanding the role at the ZO with LEP, and with studies The tightly coupled sequence of two of this particle in the hierarchy of of QCD at center of mass energies meetings created a most effective nature is an important goal for the above the tt threshold [Siegfried format. future. The analysis techniques and Bethke (Heidelberg) and Valery Khoze Burton Richter (SLAC) opened the machine parameters required for ex- (St. Petersburg)]. Saariselka meeting with a report on perimental investigation of the top Many new and beautiful studies the recent performance of the SLC quark were extensively discussed and of the physics of gauge boson and an overview of progress in the considerably sharpened at Saariselka interactions were reported at the advancement from the SLC to the [Peter Zerwas (DESY) and Keisuke workshop [Kaoru Hagiwara (KEK) and next linear collider. Gus Voss (DESY) Fujii (KEK)]. Helicity analyses of the Timothy Barklow (SLAC)]. The introduced the audience to the vari- production and decay of top quarks fundamental structure of the massive ety of work and problems being ad- will provide constraints of a few per W and ZO boson states and their self dressed by accelerator physicists cent on the static moments of the interactions remain an important un- around the world, and Michael top quantum state and similar con- tested sector of the Standard Model. Peskin (SLAC) outlined the particle straints on unexpected components The static magnetic dipole and physics issues to be confronted by in its charged electroweak coupling electric quadrupole moments of the the workshop participants. (e.g., a right-handed current). These charged W bosons can be measured The opening session was followed analyses are significantly enhanced with accuracies of 1-2% by careful by extensive parallel meetings in by the ability to control the spin of analysis of the helicity structure of which various studies and results the incident electrons to project out the WW final state produced at 400- were presented and critically com- different polarization states of the 500 GeV center of mass. This elegant pared. A unique and compelling pro- produced tt pairs. technique is fully able to resolve the gram of physics to be addressed by a The top quark may also be a source differing couplings of the photon and collider capable of reaching 300-500 of new particles. It will be particularly ZO boson to the W from a single data GeV emerged in the synthesis of work important to look for decays such as set; the improvement in accuracy of reported by European, Japanese, So- t -9 bH+ or t - ty. Some of these may more than an order of magnitude viet, and American scientists. De- occur with significant branching over similar measurements to be tailed studies of the production and fractions, and are easily isolated at made at LEP II is attributable to the decay of top quarks, studies of the an electron-positron collider. With rapid growth with center-of-mass interactions of electroweak gauge sufficient luminosity (30-50 fb-1) it energy of the production of longi- bosons, and exhaustive searches for will be possible to measure the cross tudinal gauge bosons-the remnants scalar particles comprise the heart of section for production of the ZOtt of the Higgs fields that are essential the physics program for the next lin- final state, which allows a deter- to the Standard Model. Confirmation ear collider. These investigations will mination of the Higgs Yukawa that the interactions of these new directly and decisively probe the most coupling of the top quark. This first massive polarization states are puzzling of the outstanding prob- probe of the Yukawa piece of the described correctly by the Standard lems of the Standard Model of Standard Model Lagrangian will Model is essential, and no other

BEAM LINE 13 technique will provide the precision These limits exceed the grasp of squarks and gluinos are copiously and discrimination offered by an LEP II but are well within the reach produced at hadron colliders, it will collider. of the next linear collider. The SUSY require successful experiments with electron-positron - Production of multiple gauge theory working group concluded e+e colliders to find and sort the charg- bosons will allow further investi- [Fabio Zwirner (CERN)] that a linear spectra of colorless sleptons, gation of the three-boson coupling collider with center-of-mass energy inos, and Higgsinos. prescribed by the Standard Model, of 500 GeV is guaranteed either to and samples of tagged W-pairs as find at least one Higgs (and most the large as 105 can be accumulated and probably three neutral states and the T HE PARTICIPANTS LEFT used to search for anomalous W- charged states), or the Minimal autumn colors of Saariselka (300 decays. Beam energies of 200-250 Supersymmetric Standard Model is kilometers north of the Arctic Circle) of GeV yield the largest cross sections ruled out. These new states gener- with a crisp view of the future and best detection efficiencies for ally appear in the intermediate mass electron-positron physics and look- in these studies. At considerably higher region where discovery and investi- ing forward to the next workshop energies and luminosities it will gation at hadron colliders are diffi- this series to be held on the balmy of begin to be possible to study W-W cult tasks. shores of Hawaii in the spring to scattering processes [Ken-Ichi Hikasa Initial studies of more subtle, but 1993. For many, however, the road Soviet (KEK)]. Unfortunately, in the absence equally important, aspects of Higgs Hawaii passed through the of TeV-scale resonant structures, the physics were also reported- searches Union, where the Third International 1) event rates for such process are for non-dominant decay modes were Workshop on Linear Colliders (LC9 extremely low, and it will require among the most interesting. The was held in Protvino, 100 kilometers machines with TeV center-of-mass exciting prospect of measuring the south of Moscow. Nearly 100 scien- U.S., energies and luminosities approach- coupling of the Higgs to two photons tists from Europe, Japan, the of ing 1035cm-2s - 1 to resolve differing was explored in some detail. Photon- and the USSR met for ten days is- models of strong WL interactions. photon collisions, created by back- discussion and review of current This clearly awaits a future genera- scattering laser beams from the in- sues in the development of future tion collider. coming electrons and positrons just linear colliders. A centerpiece of experimental par- prior to the interaction point, pro- A report from the Saariselka work- ticle physics for the foreseeable fu- vide a rich variety of final states for shop [David Burke (SLAC)] set the sessions ture is the systematic search for sca- study [Valery Telnov (Novosibirsk)]. stage for two days of plenary heard from lar particles that can play the role of Production of Higgs particles by this in which updates were to Higgs fields. It is essential that no mechanism occurs with good rate in each of the laboratories working encour- possible avenue of escape be left for most cases and is easily detected. develop linear colliders. The during these states and that we fully under- The H°y coupling is attributable to aging performance of the SLC that stand the spectrum of such particles triangle graphs and receives contri- the past year, and the lessons it, were re- and their interactions. Extensive butions from all particles that carry have been learned from analyses reported at the conference electric charge and whose mass is viewed by Stan Ecklund (SLAC). Af- [Howard Haber (Santa Cruz) and generated by the Higgs mechanism. ter considerable upgrading of the in- Sachio Komamiya (Tokyo)] made This is true regardless of the mass of frastructure of the accelerator and clear that data samples well below the particle in the loop (!), and it with maturation of the control and the performance expectations of vari- endows this measurement with a feedback systems, the luminosity and ous accelerator designs will be suffi- spectacularly large discovery reach. efficiency of accelerator operations cient to illuminate even the most Historically electron-positron have shown dramatic improvement; complex Higgs spectra. As with LEP, colliders have been ideal hunting the SLC met all of its luminosity these studies are limited only by the grounds for new particle states, and a goals for this past year's run. The energy of the accelerator; masses up wide variety of search goals and strat- SLD detector was rolled onto the to 70% or so of the nominal center of egies were presented at the work- beam line, and was able to success- mass are accessible. Of particular shop. These ranged from exotic lep- fully complete an engineering test interest is the fact that recent calcu- tonic states like heavy Majorana neu- run. Further improvements are ex- lations of loop corrections increase trinos [Wilfred Buchmiiller (DESY)] pected in the next year, and with the the upper limit on Higgs masses that to the familiar spectra of particles polarized gun also being installed can be tolerated within the param- predicted to exist in models of super- and debugged, the SLD group is an- eter space of the Minimal Supersym- symmetry [Jean-Francois Grivaz ticipating a fruitful run for particle metric Standard Model (MSSM). (LAL)]. While colored objects such as physics in 1992 and 1993.

14 FALL 1991 Linear colliders can be broadly categorized by the method used to generate and utilize rf power and the structure of the main accelerator. The DESY/Darmstadt Collaboration [Thomas Weiland (THD)] has made considerable progress toward understanding the limits of machine designs based on existing S-band (2.8 GHz) klystrons for rf generation. Meanwhile KEK [Koji Takata] and SLAC [Ron Ruth] are pressing klystron technologies toward higher frequency (X-band at 11.4 GHz) where higher accelerating gradients are expected to be achievable. The SLC provides the experimental tool required for further development of S-band accelerators, but stand-alone facilities are needed to test new X-band technologies. Both SLAC and KEK are planning such test beds. Klystrons suitable for incorporation into these facilities are under development at SLAC and are expected to The advent of superconducting Robert Palmer's original Guide to Linear be available soon. High-power tests linacs offers another approach to Collider Design (in white). As noted on of rf pulse-compression techniques linear collider design that is being page 17, the three topics shown at the modeled after the SLED cavities used studied by the TESLA Collaboration top of the figure are recent additions to the design matrix. at SLAC will be completed within [Dieter Proch (DESY)]. Very long the year. Success with these tests (msec) low-frequency (1.5 GHz) rf will allow completion of the neces- pulses are generated by conventional sary engineering and the start of klystrons, stored in superconducting construction of full-scale sections structures, and used to accelerate a of X-band accelerators with gradi- large number (-1000) of electron or ents of 50-100 MeV/m. positron bunches. Spot sizes of a few A slightly higher frequency tenths of a micron can then be used (14 GHz) is being pursued by the to reach the required luminosity. group from Protvino working on the The large spacing between bunches VLEPP Project [Vladimir Balakin and the small luminosity per bunch (BINP)]. The VLEPP rf system uses a crossing that are inherent to this novel coaxial long pulse charge-stor- technique eliminate many of the age network that is discharged to problems created by the high- drive 14 GHz klystron tubes. Key brightness beam-beam interactions elements in the klystron are a incorporated into other design multicell gridded cathode used philosophies. Unfortunately, these to control the current and a per- machines require extensive refriger- manent magnet focusing system. ation plants, and much of the length One of the highlights of the work- of the linac is consumed by cryostats shop was a tour of the 20-meter- and other plumbing. The challenge long test facility, presently un- to this collaboration is to arrive at a der construction in the labora- cost-effective design. tory at Protvino, that will be used Progress is continuing at CERN to test these systems later next on development of a two-beam linac year. for CLIC [Wolfgang Schnell (CERN)].

BEAM LINE 15 problem already at These accelerators differ rather problem that received much damage is a are several designs for fundamentally from existing accel- attention in this group. New 40 MW. There windows that look erators in that generation of rf power approaches to positron production large area is not done in klystron tubes but is using wigglers or channeling crystals attractive. examination of calcula- created by a low-energy high-current were discussed, and the use of pre- Careful wakefields created by in- beam of electrons that is transported damping or collector rings with large tions of in detuned or damped alongside the high-energy low- acceptance was reviewed. tense bunches structures led to opti- current beam that is being accel- A group chaired by Gilbert accelerating complexity of adding erated. Radio-frequency power is Guignard (CERN) worked on prob- mism that the can be avoided and periodically extracted from this lems of beam dynamics and control damping slots structures will provide secondary beam and fed to the during acceleration in various that detuned of these wakefields accelerating structure of the main structures. The main topics were adequate control bunches to be ac- linac. The energy is replaced using single and multibunch beam stability to allow multiple each rf pulse. There also low frequency (353 MHz) supercon- and alignment and trajectory celerated on on manufac- ducting cavities. The secondary beam correction techniques. Much of the was useful discussion for accelerator and its transport structure are in discussion centered on beam-based turing techniques and in particular, the ad- essence a single multi-port klystron alignment techniques that have structures, and disadvantages of cell- that operates at very high frequency worked well at the SLC. It is vantages tuning strategies and the prob- (30 GHz in the CLIC design). Tests of important that the ultimate accuracy by-cell of maintaining preci- structures are underway, and a test of these procedures and the instru- lems and costs fabrication. facility is expected to be operating in mentation required to make them sion during (SLAC) organized a about a year. successful be fully understood. More John Irwin to concentrate on The opening plenary sessions were work remains to be done. Strategies fourth group particular to the final-focus concluded with summary talks on for controlling multibunch insta- problems region. This group the recent improvements in the bilities using tuned accelerating and interaction topics including modeling of the interactions of high- structures were discussed at some covered several problems associated energy, high-intensity beams [Kaoru length. Here, too, more work is optics designs, the beam-beam interaction, Yokoya (KEK)], and a status report waiting to be done. Optimization of with backgrounds, and instru- from the Final Focus Test Beam Col- BNS damping and linac focusing to detector mentation. There was an interesting laboration (FFTB) [Alexander maintain control over emittance of wide-bandwidth optics Mikhailichenko (Novosibirsk and growth generated by single-bunch discussion designs [Reinhard Brinkman (DESY)], BINP)]. The FFTB is well underway. wakes was also discussed. This is, by particular, evaluation of Approximately one half of the mag- now, a well established technique and in and electrical tolerances nets fabricated at Novosibirsk have that is incorporated into nearly every mechanical to make them work. Also been delivered to SLAC for installa- machine design. needed was a new concern that tion, and the remaining magnets are A large group organized by discussed resistance of the metal in expected to be completed and in- Seishi Takeda (KEK) reviewed the finite pipe of the final quadrupole stalled by spring of next year. It is problems in the development of high- the beam destroy the emittance of anticipated that the beam line will power rf sources and accelerating lens might beam. This was found not to be a begin operations at the beginning of structures. Everyone was interested the but it did place a limit on 1993. in the VLEPP 14 GHz klystron. problem, of the final lenses used The participants separated into Inefficiencies in beam transmission the aperture the interaction point. This limit four working groups and continued have prevented these tubes from near to be incorporated into more detailed discussions of the reaching full voltage, but the Protvino will have designs. problems confronting the building group is optimistic that additional future Experience with the SLC has made blocks of linear colliders. A group design changes will alleviate this that the experimental chaired by Jean-Pierre Delahaye problem. SLAC and KEK are making it clear are an integral part of the (CERN) reviewed the preparation of steady progress with tube detectors and control of non-physics low-energy, low-emittance beams. development at X-band. The latest machine, is a challenge for Integration of the properties of tubes in this series have generated backgrounds and particle physicists electron guns and bunching systems, microsecond pulses with 40 MW of accelerator Problems in beam collimation positron sources, damping rings, and delivered power; 50 MW is the initial alike. detector shielding are being bunch compressors to achieve goal. Everybody is experimenting and by a growing number of optimum performance is an intricate with high-power output windows as attacked

16 FALL 1991 accelerator and particle physicists, and much work has gone forward in the calculation of the backgrounds that can be produced in the interactions of small intense beams. The peripheral photon flux that accompanies the electron beams grows with increasing energy, and can become a troublesome source of background if the luminosity produced by the collider within the resolving time of the detector becomes too large. This ultimately will constrain machine designs to favor higher repetition rates and lower luminosities per bunch crossing. Of particular interest at the workshop were new calculations of hadronic photon-photon processes [Manual Drees (DESY)] that may pose further limitations on machine and detector designs. It remains for future work to sharpen these issues, but it is apparent that Robert Palmer's Guide to Linear Collider Design on page 15 is more complex than one might have imagined!

N VIEW OF THE VERY difficult and uncertain conditions in the host country, the Workshop at Protvino was organized and conducted in a remarkably gracious at- mosphere well-suited to intellectual exchange and growth. The conference fulfilled an important function for the international community, and served as a useful professional experience for all who attended. As the pace of work on linear colliders ac- celerates, so too will the need for physicists and engineers to gather to discuss and redirect their efforts. The next in this series of workshops (LC92) will be held next Summer in Garmisch Partenkirchen, Germany. 0

BEAM LINE 17 TOWA10 THI3 NEXT 2INEAR CO LIER

The Accelerator Test Facility at KEK

KOJI TAKATA

HE ACCELERATOR TEST FACILITY (ATF) was created to promote TeV linear collider re- i search at KEK, the National Laboratory for High Energy Physics in Tsukuba, Japan. The Japanese high energy physics community has been investigating the feasibility of next generation TeV electron-positron linear colliders -imilr .1 n h+-r\'NT,---- T i .n-r -11-A-,i,, /NTT r\ Oll1lC1111 LU L I -,INVLAL -llldal l UlllULUCi I1 L k. under study in the United States. We call our collider the Japan Linear Collider or JLC. Studies for the JLC were initiated as early as 1982, when construction of the 30 GeV TRISTAN storage ring, the first high energy electron-positron collider in Japan, was at its height. We have been examining the realistic possibilities that would enable us to reach a luminosity greater than 103 3cm-2 s-l at center-of-mass energy around 1 TeV. In a linear collider there are two identical main linacs that accelerate beams from a few GeV to several hundred GeV facing each other-one for electrons and the other for positrons. We decided that the main linac should use the well-established technology of conventional linacs. The acceleration gradient should be 100 MV/m or more so that the linacs are not too long, and the wall plug power should be less than 200 MW, the maximum available at KEK. Those considerations have led us to the following JLC design parameters: (1) the main linacs are at X-band frequency (11.4 GHz, four times the SLAC S- band frequency of 2856 MHz); (2) these linacs accelerate ten beam bunches and have a repetition rate of 150 Hz; and (3) the beam size at the collision point would be about 5 nm high by 600 nm wide.

18 FALL 1991 ONVENTIONAL S-BAND LINACS still play important roles in high energy linear colliders as injectors and positron production linacs because of their capability of accelerating high currents. Therefore, although research for the X-band linac is key, S-band technology is still being pursued intensively. A 2.5 GeV S-band linac has been in operation at KEK since 1982 as the injector for the Photon Factory and later on for the TRISTAN Accumu- lation Ring. Such a busy machine is not useful for experimental accelerator studies, and when we founded the ATF in 1987 we started to build a test S-band linac. We wanted this linac to accelerate the very short, high current bunches required by the JLC design and to have an accel- in high energy physics. We designed The high gradient test setup at the ATF. erating gradient higher than the the test linac to use these powerful Using this 66.5 cm long S-band struc- conventional 10 MV/m so we could tubes. It has a bunching section with ture an average gradient of 92 MV/m gain experience with high gradient subharmonic cavities to capture the was attained with an input power of more than 160 MW. operation. We plan to test a 1.5 GeV beam and a short SLAC-type struc- Beside the structure damping ring (also an important part Helmholtz coils are shown that are part ture to accelerate it to 40 MeV. The of the test S-band of a linear collider complex), linac being and the regular part of the linac has 3 m long constructed at the A TF. linac was to be extended to the damp- SLAC-type structures with a gradi- ing ring injection energy if enough ent of 40 MeV/m. The peak rf power space was available. required is high, and the SLED sys- Even at S-band the rf source was a tem is used to compress the klystron central issue. The most powerful S- output power. Using the 5045 tubes band klystron then available in Ja- and the SLED system, only six klys- pan was a 30 MW tube that was not trons will be needed to get to 1.5 GeV. reliable partly due to the old design This should be compared with more of the electron gun. Therefore, we than 40 klystrons for the KEK 2.5 GeV were grateful to SLAC when several linac. 5045 tubes, the state-of-the-art klys- We have set-up the linac on the tron used for the SLC, were shipped 25 m by 25 m floor of an unused to KEK in 1987 and 1988 according to TRISTAN experimental hall, where the US/Japan Cooperative Agreement radiation safety regulations can be

BEAM LINE 19 at the JLC is 1 to easily satisfied. We prepared an area tubes have enabled us to test a longer emittance required smaller than surrounded by shielding blocks for structure by driving it directly with 2 orders of magnitude operating storage the injection section and one or two sufficiently long, rectangular rf that of presently way to achieve regular structures in addition. We pulses. A peak power of 200 MW rings. A promising to use wiggler magnets. The have used precision beds to easily with a 1 gis duration is possible if we this is are complicated, and place linac components to a preci- combine outputs from two klystrons. wiggler fields to study the beam dynamics sion of a few tens of microns. The We fabricated a SLAC-type structure we want reaching low emittance injection section has been completed, 66.5 cm long with a high shunt im- and verify This is the reason, and a couple of regular structures are pedance to try to reach 100 MV/m experimentally. consider a strong one, that being manufactured. Outside the with this rf pulse. which we construct a test damping shield we set up four rf systems, each We began rf processing the struc- we wish to will have a racetrack consisting of a modulator, klystron ture mid-1989, and after 900 inte- ring. The ring 60 m long by 30 m wide. and evacuated waveguides, capable grated hours of processing at 25 Hz shape about problems associated with of delivering a peak power of 100 MW we reached 92 MV/m. Beam accel- One of has been finding a space with 1 tus duration. eration was tested with these fields. this plan for the linac and ring. The test linac construction is not We were particularly concerned by large enough it, we are clearing a building the only activity at the ATF. The rf field-emitted dark currents, since To solve been used to assemble systems have been very useful for they are a crucial factor in operating that had cavities. Substantial civil other R&D including having big at such high gradients. Currents in- TRISTAN rf is needed to reinforce modulators for developing X-band creased drastically as the gradient construction to hold shielding and to klystrons and developing low power approached 100 MV/m. Their behav- the floor radiation safety regulations. We rf components and control circuits ior was in good agreement with that meet that the construction of the to meet the stringent specifications observed in experiments at SLAC. hope linac and ring complex will be com- of the JLC. The energy spectra had a low-energy component due to local discharges pleted by the end of 1994. and a broader one that was the result Although the main activity is the S-band linac, we HE MOST IMPORTANT research of acceleration over the structure. construction of R&D for the JLC. at the ATF has been high gradi- This structure was fabricated by a are pursuing other X-band klystron and structure ent tests with S-band structures. Japanese firm in the same way con- The important issues and Without high power X-band klys- ventional linacs for medical use were. are particularly great deal of fundamental trons, such tests are usually done at We are now testing a second one that need a If we are fortunate in carrying S-band. Information obtained is valu- has the same geometrical shape but study. this work, we will set up a short able for estimating the performance was fabricated more carefully with out of the X-band linac beside of X-band structures at 100 MV/m. less surface contamination. The pro- section ring and accelerate When the 30 MW klystron was our cessing time seems much shorter as the damping emittance beams extracted only high power source, we tested a expected. small it. At that point it will be pos- short structure using a special wave- from judge whether technologies guide system to boost the rf power. sible to matured enough to construct The rise time of the power pulse was A S MENTIONED ABOVE one goal have top short, but we of the ATF is to construct a the JLC. long and the flat O reached 100 MV/m anyway. The 5045 1.5 GeV damping ring. The beam

20 FALL 1991 FROM THE EDITORS' DESK

THIS IS THE SIXTH ISSUE of the new version of the Beam Line, which may be a time for us to pause briefly to take stock. Our masthead says "A Periodical of Particle Physics," and particle physics has in fact been the subject of most of the articles that have appeared since our first issue in the summer of 1990. But the niche we are trying to carve for the Beam Line might better be described as "A periodical of particle physics and other a things that the particle physics community is likely to be interested in." (Not a very elegant masthead.) Thus in the present issue we have articles on white dwarfs and science education, and in earlier issues there have been | nie.ces on onsmnlnov and sociPnrPc nnlirv ...... - V.L.. . CL...... L -,'1 · tL-cwin IVI.IV/cvllan, 1907/-1991 This is all to the good. We hope to continue this mix of high-energy physics (HEP) and related fields, of the factual and the speculative, of the specific and the general. We have articles in train on possible new accelerators, on detectors for the SSC and for gravity waves, and on computation developments in particle physics. We continue to be very interested in soliciting articles and ideas for articles. We have a special interest in speculative or opinion pieces about where the field of HEP is going, or should be going. Give us a call, electronic mail, or FAX and let's talk about it. WE TAKE NOTE OF THE RECENT DEATH of Edwin M. McMillan, one of the great names in our field of physics. A particularly warm and interesting tribute to McMillan, written by J. David Jackson, appeared in Nature 353, 602 (1991). We also take note of the devastating fire in mid-October that destroyed several thousand homes in the hills above Oakland and Berkeley, California. We know of ten of our particle-physics colleagues and 45 others from Lawrence Berkeley Laboratory who lost their homes in this inferno. And this rather hard upon the heels of the large earthquake almost two years earlier. Our sincere sympathies to those affected.

BEAM LINE 21 LETTERS TO THE EDITORS

Why SSC? concepts in accelerator design. We think presentations of those ideas and the the ideas were represented well. discussions about them were, to me, PAC's of the 1980s. In most cases I write letters to the editor It is true that new concepts are lost in highlights of the a large fraction of the out of anguish, to protest some thing or the ocean of engineering work being done They were never were among the most the other. This time it is praise. I find the on accelerators. One factor which both- papers, but they article on "Why SSC" (for short) by ers me is the lack of accelerator engineer- interesting. changed, and advanced Riordan to be excellent. Probably the ing programs at universities. The tech- Times have physics has matured. Some best I read on the subject so far. I urge you nology is stable enough and the applica- accelerator explored and found to be to try to give it wider circulation by tions are growing to the point where ideas were were found suffi- sending it to other journals. Would the businesses are buying accelerators for wanting. Others that they have CERN Courier take it? production work. The search for new ciently interesting of the mainstream of DRASKO JOVANOVIC methods of building accelerators should become part the Fermilab be a much smaller group than the im- acceleratorphysics. I missed proved engineering design of applications ferment at the 1991 PAC and my addressed to that. I We give our permission to anyone who already in place. comment was ideas for reaching wishes to reprint Riordan's article I don't think there is an absence of didn't hear new using recent advances in "Why Are We Building the SSC?" pro- advanced accelerator concepts. There is 1 GeV/m, for for accelerators,etc. viding they acknowledge the Beam so much room for improvement of all the laser technology realities are too hard, or Line. We do not know what the CERN old concepts that it just swamps out the Maybe the are in a consolidationphase Courier'sreaction would be to reprint- new ideas by volume. Once a new idea is maybe we flurry. ing the article; however, we would be shown to work it becomes an old one and following a creative Whatever the cause for my percep- happy to publish an article on the LHC. more people work on improving it. With 1991 PAC, I value The Beam Line has a distribution the number of accelerators on line in the tion about the acceleratorwork and was of about 4500. If you would like to world for specific purposes it's hard to advanced Beam Line article to express receive it, send electronic mail to see where there is time for pure accelera- using the my concern for it. It needs resources BEAMLINE@SLACVM or regularmail to the tor research. and people, and here I am in complete Beam Line Editors, SLAC, P.O. Box The AWA mission is higher gradients, with Dr. Rosing. 4349, Stanford, CA 94309 USA. an "advanced accelerator activity." We agreement are very lucky to be able to focus on research without having to worry about users. I agree with Siemann that more 91 PAC groups similar to the AWA should exist, EGS but I doubt that they will ever seem to be in numbers compared In our Beam Line article, "EGS-A Tech- It's not that letter writing is a lost art, "well represented" accelerator work now nology Spinoff to Medicine," we ne- mail] is just a lot easier. to all the other this [electronic glected to mention the important contri- In the Summer 1991 issue, in a re- taking place. ROSING butions made by Hideo Hirayama of KEK view of the '91 Particle Accelerator Con- MIKE National Laboratory and Ray Cowan of MIT. In particular, the Robert Siemann said "The sec- Argonne ference, cover photograph was produced by means ond absence is disturbing: Advanced ac- Siemann replies: About ten of the SHOWGRAF graphics package de- celerator concepts were not well repre- Robert ago was a time of ferment in veloped for EGS by Dr. Cowan. sented." I hope this was in reference to years accelerators. Plasma-based RALPH NELSON, SLAC the number of papers and not to their advanced grating accelerators, ALEX BIELAJEW, NRC, Ottawa, Canada content. The AWA (Argonne Wakefield accelerators, free electron lasers, two-beam Accelerator) group had a few papers at inverse accelerators, collective implosion We are indebted to Ray Cowan for the the conference, and we had a few col- wakefield accelerators, cover of the Spring 1991 issue of the laborators at SLAC who also used some accelerators, were actively discussed. The Beam Line. "advanced techniques" to measure new ....

22 FALL 1991 CONTRIB UTORS

VIRGINIA TRIMBLE oscillates at a frequency of 63.4 nHz between the Physics Department of the University of California, Irvine (where she has tenure) and the Astronomy Department of the University of Maryland, College Park (where her husband, physicist Joseph Weber, is Professor Emeritus). Her degrees come from UCLA (B.A.), California Institute of Technology (M.S., Ph.D.), and Cambridge University (M.A.). She was the 1986 recipient of the U. S. National Academy of Sciences Award for scientific reviewing and currently serves as editor of Comments on Astrophysics and associate editor of the Astrophysical Journal. Virginia is interested in stars and galaxies and other structures that require relatively little maintenance.

MARJORIE G. BARDEEN is Program Director of the Fermi National Accelera- tor Laboratory (Fermilab) Education Office and is the Vice President of Friends of Fermilab, a not-for-profit corporation whose sole purpose is to develop and conduct precollege education programs at Fermilab in Batavia, Illinois. She is also an elected member of the Board of Trustees, College of DuPage, in Glen Ellyn, Illinois, and is currently the Chairman. Marge holds a B.A. in Mathematics from the University of Minnesota and an Educational Certificate (Mathematics) from Elmhurst College, Elmhurst, Illinois. Under her leadership numerous needs assesment workshops with teachers, school administrators, and community leaders have been conducted to develop science education programs, and 40 such programs currently make a wealth of resources available to elementary and secondary teachers and students at Fermilab.

DAVID BURKE. a regular contributor to the Beam Line. is head of Exnerimen- tal Group I, established as part of SLAC's effort on the accelerator physics and technology of the Next Linear Collider (NLC), in addition to playing a major role in the construction and instrumentation of the Final Focus Test Beam (Vol. 20, No. 2, 1990). David came to SLAC in 1978 and distinguished himself in the commissioning of the Stanford Linear Collider and as a key member of the Mark II Collaboration. He served on the Organizing Committee of the Saariselka conference and organized the NLC study efforts at previous Snowmass (Colorado) meetings. i

BEAM LINE 23 EWAN PATERSON is a Professor at SLAC and is Assistant Director for Accelerator Systems. He has been at SLAC for almost 20 years and has been involved in the commissioning, development, and construction of all the accelerators on the site. He is interested in many areas of advanced accelerator development from next-generation linear colliders to next-generation synchrotron light sources.

KojI TAKATA is head of KEK's TRISTAN accelerator department. He came to KEK in 1972 and became engaged in developing fast kicker magnets for the 12 GeV proton synchrotron. In 1977 he became responsible for design, construction, and operation of the rf system of the Photon Factory 2.5 GeV electron storage ring, and then in 1980 also of the TRISTAN 30 GeV electron- positron storage ring. Since 1982 he has been supervising R&D work at KEK for TeV linear collider technologies.

24 FALL 1991 I~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~