The a to Z of Accelerators

present explanation for this behav The long timescale needed to terparts. But superconductivity iour is that superconductivity exists produce acceptable conductors of above 77K provides a powerful in many discrete regions within niobium-tin (10-12 years) following stimulant to solve the technological the sample but only weak coupling its discovery in 1962 inevitably problems of dealing with brittle exists between these regions. This comes to mind in assessing the materials. The next few months weak coupling is strongly dimin potential timeîscales for developing could give us many more surprises ished by an external field. Electro high field magnets with the new in an area where none were sus magnetic and structural character materials. These new oxides, like pected only a few months ago. izations of these compounds are niobium-tin and the other A15 The discovery of Bednorz and proceeding furiously and we may compounds are inherently brittle Muller has given a profound new soon expect to know whether this and this is bound to affect their stimulus to superconductivity and percolative nature of the supercon application in magnets, just as the last discovery has surely not ductivity is inherent in the material large scale construction of niobium- yet been made. or results from the way present tin magnets has lagged behind samples are being prepared. their ductile niobium-titanium coun

The A to Z of accelerators

With great skill, the organizers physics but this information was 1965. The attendance of over of the 1987 Particle Accelerator surpassed in volume by reports 1100 was another reflection of Conference arranged a vast pro from the many other areas where the wealth of activity in the field. gramme to run through nearly 700 accelerators now play a key role. papers from Session A to Session Synchrotron light sources are The debate on the big machines Z. They took in en route the latest now illuminating the world in al on construction and plans for the most thirty Laboratories. Free elec high energy machines for particle tron lasers are confirming their Since the hot topic appeared in promise for the creation of un Session Z, not many people left US Superconducting Super Collider Central dreamed of fluxes of electromag the Conference early. In the wake Design Group leader Maury Tigner — aiming at the highest possible energies. netic radiation. 'Star wars' ma chines are now openly discussed. Reports on other actual or potential applications in medicine, food pro cessing, fusion, etc., underlined how the seemingly esoteric tech nology developed for the study of particles has continued to ripple into everyday life. (Already many people sit in front of a particle ac celerator for several hours every evening!) The Conference was held in Washington from 16-19 March and was the 12th in the North American series which began in

Giorgio Brianti — pushing for a hadron collider in the tunnel now being completed at CERN for the LEP electron-positron collider. ^

CERN Courier, May 1987 7 Leon Lederman — international collaboration on future accelerators. of President Reagan's endorsement 1989. Congressional hearings for of the Superconducting Super Col budget authorization were immi lider and of the CERN Committee nent at the time of the Conference. of Council's promotion of the Large Tigner quoted Abdus Salam on Hadron Collider, there was no hid the importance of aiming at the ing the potential overlap between highest possible energy and re the two projects. It would clearly peated the statement that partici not make sense to build two sim pation from other countries could ilar machines of such size and cost be envisaged with the machine (unless perhaps the lower energy ultimately open to qualified scien machine could be completed much tists from all countries. faster or one machine had signifi While the Conference was in cant capabilities inaccessible to progress, a meeting of the Amer the other). ican Physical Society in New York Maury Tigner, who leads the was in ecstasies about the newly Central Design Group on the SSC, discovered high temperature super gave the first talk, followed by conductors (see page 3). Tigner Giorgio Brianti, deeply involved in brilliantly fielded a question about LEP is not in operation (and the the LHC work at CERN. Accom the possible impact of these new CERN machines are busy with anti- panying both proposals are invita materials on the magnet design protons) and would not necessarily tions to other world regions to join for the SSC. As known at present, interfere with completion of LEP in the construction and exploitation their current densities are a factor to its 100 GeV per beam design of the huge machines. Leon Leder of 1000 down on those needed energy. The estimated earliest man had a more delicate task than for the SSC; mechanical properties, timescale for LHC is 1995. The he could reasonably have antici feasibility of volume production, CERN Committee of Council (see pated when he accepted the title production costs are all unknown. April issue, page 1) has proposed of The status and outlook for in From past experience, moving scientific and technical cooperation ternational collaboration on future from this situation to the demand with non-Member States. accelerators' for the concluding ing environment of storage ring Lederman recalled the history talk. magnets is likely to take a very of the moves towards greater in Tigner outlined the main para long time. ternational collaboration since the meters of the SSC — 20 TeV per Brianti cited the LHC parameters World Laboratory/Very Big Accel beam, luminosity of 1033, six inter — about 8 TeV per beam, luminos erator (VBA) was first discussed action regions, 6.6 T magnets, ity of over 1033, magnet fields up in 1975. Following the formation 85 km circumference, $ 4.4 billion to 10 T in 'two-in-one' magnets, of the International Committee for cost (R and D, machine, detectors, located over the electron-positron Future Accelerators (ICFA) a year computers), 8 Vi year construction ring in the 27 km circumference later, which initially had the VBA time. Preparations are going well LEP tunnel now being completed as a potential mission, at every and, in particular, the dipole bend at CERN. point in time one or other region ing magnets, which are the most The attractions of the LHC stem was, to use Pief Panofsky's costly of the technical compo from its much lower cost because phrase, 'pregnant with a new ma nents, are comfortably exceeding of the existing tunnel and injectors, chine'. What has happened in the design specification in the recent and from the unique physics poten intervening years has followed the prototypes which have been tial of proton-proton, proton-elec 'leapfrog model' rather than full tested. tron, and even ion collisions. The collaboration. ICFA has had to Beginning in April, the site se final touches are now being made content itself with promoting inter lection procedure is scheduled to to the conceptual design and a national collaboration in exploita filter out a small set of favoured cost estimate will be detailed at tion of machines and in developing sites by July 1988. The final the same time. accelerator technology. choice is planned for end 1988 so Construction could proceed dur An alternative route has emerged that digging could begin early ing the six months per year when in recent years and has become

8 CERN Courier, May 1987 Installation work for the LEP electron-positron collider at CERN is well underway. This shows the pit to house the L3 experiment, with the tunnel opening in the background. At the Washington meeting Gunther Plass described LEP progress.

(Photo CERN 446.3.87) known as the HERA model since it has been crucial to the building of that electron-proton collider at DESY. It involves the core of the responsibilities and costs remaining with the host country but with very extensive bilateral agreements for machine component construction and financing worked out for other countries. Lederman recognized that the SSC proposal itself, when it first emerged, 'was a blow to hopes of a World Laboratory'. (In fact at that time it caused considerable dismay in ICFA since it was pro moted without prior consultation or consensus amongst the different regions. The latest LHC proposal has been promoted in the same way.) Lederman concluded with his personal thoughts on the present situation. He is concerned about the adequacy of the LHC to cope with the needs of all regions, par ticularly when constrained by LEP X/;:; exploitation in the same tunnel. The SSC is likely to be at least double the cost but for double the energy (the European contention is that the interesting energy region example, the tiny beam spot size Gunther Plass talked about the would be reached at LHC). at the crossing point has been other Z°, and eventually W, facto A strong case can be made for relaxed to 2.8 compared to 1.6 ry-LEP at CERN. The first ele going in either the SSC or LHC microns, the pulse rate is reduced ments of the injection system have direction. Both regions are pro to 120 rather than 180 Hz, initial all reached or exceeded specifica moting their candidate with con energy is likely to be 47 GeV and tion and the next stage will occur viction, just as they have always so on). in July when electrons go into the done in the past. There are some problems in the SPS; the first transfer to LEP will damping rings causing bunch be a year later. LEP operation is lengthening which will require at scheduled for mid-89 and comple The present front-line machines tention to the vacuum chamber tion of the machine to its full and the pulsed magnets. In the design energy of approaching John Rees reported imminent linac the 'heroic efforts' on the r.f. 100 GeV could follow soon after operation of the Stanford Linear klystrons have produced excellent wards with the use of supercon Collider (see page 31), to provide results and there are now 200 of ducting cavities. 50 GeV per beam electron-positron the 67 MW klystrons available. In The newcomer to the particle collisions via arcs at the end of June, Stanford hopes to attack physics scene, the electron-posi the Stanford linac. Initial perfor the physics of the Z° (93 GeV), tron collider, TRISTAN, at KEK in mance aims have been reduced the neutral carrier of the weak Japan, was greeted with particular compared to the design values (for force, discovered at CERN in 1983. appreciation when G. Horikoshi

CERN Courier, May 1987 11 A newcomer. The TRISTAN electron- positron collider at the Japanese KEK Laboratory operates at 25 GeV per beam, aiming soon for 28 GeV.

(Photo KEK)

them will be installed in the elec tron ring. Colliding beams are scheduled for 1990. Roland Johnson reported on operation of the world's first su perconduction collider —the Teva- tron at Fermilab where proton- antiproton collisions have been achieved at an energy of 900 GeV per beam, the highest ever achieved. The antiproton source is now working excellently, stack ing at the rate of up to 1010 anti- protons per hour, and has ex ceeded the performance of the CERN Antiproton Accumulator (though not of the improved source at CERN which will come into action later this year). However it has proved difficult to profit from these healthy antiproton fluxes because a high pro portion of the beam is lost prior to full energy interactions. Trans mission through the conventional magnet ring is troublesome follow ing a major revamp last year, in cluding the construction of a seven metre-high by-pass to take beams over the Collider Detector Facility, CDF. The superconducting ring is gave his talk. They are now oper Prototype superconducting magnet for the sensitive to ramp history which proton ring of the PETRA electron-proton ating with 32 r.f. cavities, giving collider now being built at DESY, Hamburg. introduces difficult operational a peak energy of 25 GeV per Tests give promising results. problems. The CDF is, neverthe beam. From July it is intended to less, taking data at the highest (Photo DESY) nudge this to 28 GeV with more proton-antiproton collision ener cavities, and vacuum improve gies, with luminosities steadily ments should extend the beam challenge since it incorporates su improving. lifetime. perconducting magnets. Five pro At the CERN SPS proton-antipro R. Kose reported on another totype 9 m dipoles have exceeded ton collider, preparations are well Laboratory happy with electrons, design field with good field quality. underway to cope with the in DESY, where the new synchrotron, In fact the performance is so good creased intensities from the new DESY II, is performing well. It is that they could sustain a beam antiproton source. Lynn Evans one of the injection elements for energy of over 1 TeV; conventional described the manoeuvres of beam the electron ring of HERA which magnets in the ring limit the pos separation all round the collider, is under construction to collide sible peak energy to 1 TeV. Simi and an additional 100 MHz r.f. 30 GeV electrons with 820 GeV larly the energy of the electron ring system. An interesting experiment protons. The HERA tunnel is three may be taken higher by the use of will be the use of stochastic cool quarters complete and the four r.f. superconducting cavities. If ing in the SPS itself with an optical halls are finished. prototype cavities work well in link across the ring. The proton ring is the greatest tests on the PETRA ring, eight of (continued on page 15) ^

12 CERN Courier, May 1987 ^ (from page 12)

Construction of the 3 TeV proton fixed target and, eventually, collid European Particle Accelerator Conference ing beam machine, UNK, at Ser pukhov in the Soviet Union aims The North American series of The need for a local outlet, for first full energy beams in 1992. particle accelerator conferences particularly for the younger Civil engineering is well underway has been successful for a variety scientists in accelerator technol and the remaining major decision of reasons. By comparison with ogy, has been felt in Europe for concerns the choice of supercon the International series, now some time. It has therefore been ducting magnet design. Up to now, held once every three years, it decided, particularly on the ini development has concentrated on allows a very much broader tiatives of the European Physical warm-iron versions and prototypes coverage of topics with con Society and the European Com have achieved good quality field siderable emphasis on practical mittee for Future Accelerators, at 6 T (in excess of the 5 T needed applications. It also provides a to initiate a European series for 3 TeV beams). Heat loss is still forum for younger accelerator (though with US participation uncomfortably high. Cold-iron ver physicists and engineers who in the organizing committee). sions like the HERA design are have limited outlet in the rarified The first European Particle being studied and the decision will spheres of the international Accelerator Conference will be be taken by the end of the year. meetings. Geography and the held in Rome from 7-11 June The magnet test facility is being related travel expense also play 1988. It will follow the success installed. a role, sihce the international ful US model closely with em For UNK, a colliding beam Conference passes through a phasis on applications and, scheme had been envisaged be particular region only once every probably, an exhibition of related tween the 3 TeV superconducting nine to twelve years. industrial products. ring and the 600 GeV conventional magnet ring acting as injector. However this is falling increasingly under the shadow of a higher ener gy collider project using a third ring. With big hadron colliders beams of high current at energies Tests have been carried out in the being pushed in Western Europe of a few GeV. CEBAF, via a CESR machine at Cornell. Site and the US, Soviet physicists point 0.5 GeV recirculating linac, aims clearing at Newport News started to the usefulness of a fixed target to provide such beams with 200 in February (see April issue, programme in the 1990s at energy microamp current and energies page 30). Full project authorization beyond the present Fermilab from 0.5 to 4 GeV. Superconduct is still sought at a project cost of Tevatron. ing linacs would be used and Grun $ 255 million over a construction der paid tribute to the aid of many time of six years. other Laboratories in mastering Mark Barton reported on the The big nuclear physics machines this thechnology. So well is this next in line in nuclear physics prio work going that 6 GeV peak ener rities in the USA —the Relativistic Turning to major projects where gy may be feasible within the pre Heavy Ion Collider, RHIC, proposed machine parameters are selected sently foreseen scope of the pro at Brookhaven to make use of ions for other areas of physics, partic ject. Four companies have built accelerated in the Alternating Gra ularly nuclear physics, we reach acceptable cavities and placing dient Synchrotron and collide them the enthusiastic talk at the Confer contracts in industry is therefore at up to 100 GeV per nucléon (for ence given by Hermann Grunder no problem. gold on gold) in superconducting on the Continuous Electron Beam The beam physics has received magnet rings installed in the tunnel Accelerator Facility, CEBAF. a lot of attention to avert the dan built for the abandoned ISABELLE Studies of the quark-gluon sys ger of beam break-up, which has project. The project is being ap tem call for continous electron proved to be a problem in the past. proached progressively with ions

CERN Courier, May 1987 15 in the AGS from tandems and the intensity proton synchrotron has volved in longer term development addition of a booster to achieve been in action for just over a year options which include an additional ions across the periodic table. Four and is now feeding six neutron target station and the rebuilding dipole prototypes for RHIC have beam instruments (four more are of the linac —the least reliable ele been tested with results above the under development). Muon spin ment of the machine at present. 3.45 T design field. rotation work and a neutrino ex Kaon factories (high intensity periment should start soon. The proton synchrotrons of several machine intensity has reached 50 Forthcoming attractions tens of GeV for copious production microamps and the operating ener of kaons and other particles) were gy is 550 MeV. This will be in This first report from the reviewed by Mike Craddock. Four creased to 100 microamps and Washington Conference concen such machines are at present on 750 MeV in the near future. (An trates on news from particle/nu the table in Canada, Europe, Japan interesting implication of dealing clear physics machines. In our next and USA but none has yet received with such high intensities in the issue we will cover some of the construction authorization (see neutron source is that ISIS is one accelerator news at the meeting April issue, page 23). of the few machines in the world from other fields. Graham Rees reported on the where the operators are keen to operation of the ISIS intense neu increase the beam emittance!) Eu By Brian Southworth tron source at the UK Rutherford ropean co-operation (France, Ger Appleton Laboratory. The high many, Italy and Sweden) is in

With the CELLO experiment retired in the background, the beam pipe of the Around the Laboratories substantially modified PETRA ring is now encased in concrete blocks. In the foreground is a superconducting cavity test installation.

(Photo DESY)

DESY PETRA

After the successful start for the new DESY II electron synchrotron at the German DESY Laboratory in Hamburg (see April issue, page 14), the PETRA ring restarted operations on 8 March as PETRA II. Both these second generation rings will be used to handle parti cles destined for the HERA elec tron-proton collider now under construction. PETRA II is a substantial modi fication of the ring used from 1978 to 3 November last year (see Jan uary/February issue, page 23) for electron-positron collision physics.

CERN Courier, May 1987 17