The changing face of DESY

A full-length 6 metre prototype superconducting magnet for the proposed HERA ring at DESY. The fixed cryostat used for testing these magnets is in a pit in the floor.

(Photo DESY)

In more ways than one, the proposed In addition, cold iron (Brookhaven HERA electron-proton collider looms type) dipole magnet design is being large over future plans at the Federal developed by industry. Quadrupole German DESY Laboratory. Once final magnet design is being worked on at approval is obtained, a vast pro­ Saclay, and a scheme is being inves­ gramme of civil engineering work tigated at NIKHEF, Amsterdam, to and equipment construction would mount correction coils inside the be launched. To accommodate main magnets. HERA most of the existing DESY It is hoped that a final decision on machines would be modified, and by the magnet design will be taken at 1990, when the new machine is the end of next year, leading to full planned to come into operation, production in 1986. The project DESY would have undergone an al­ would also require the biggest helium most total facelift. refrigeration plant in Europe and two In the 6.5 km underground HERA designs are under study. ring, extending far beyond the boun­ HERA civil engineering presents no daries of the DESY site, protons apparent problems. The legal as­ would be accelerated up to 820 GeV pects of the project have been tied and electrons up to 30 GeV. Inter­ up to the satisfaction of all con­ national involvement in the project is cerned, and there is wide experience being cultivated, with a 'shopping of tunnelling for other large civil engi­ list' of requirements which could be neering projects in the Hamburg supplied by other countries. area. To develop the superconducting Less clear at the moment are the magnets for the HERA proton ring, a plans for experiments at HERA at the big effort has been mounted. Using four proposed intersection regions. the cold bore/warm iron (Fermilab- Working groups have been set up, Existing machines type) approach, a number of 1 metre and periodic workshops have been dipole magnets have been built and held (see page 256) to examine the measured extensively. These tests physics attractions of HERA. At the existing PETRA electron- are continuing. However initial trials Colliding high energy protons with positron ring, the push towards high­ were encouraging enough for full- lower energy electrons is highly er energy continues, undeterred by length 6 metre magnets to be built, asymmetrical, with the overall developments elsewhere. Thanks to and these too are undergoing strin­ centre-of-mass very much on the the installation of additional r.f. gent tests. Much was gained from proton side. However the proton's equipment, the total collision energy the initial Fermilab experience with component quarks can carry much is being nudged higher in 15MeV this type of magnet. less momentum, and important phy­ steps in a careful scan for new The present HERA warm iron de­ sics should also be seen in the central thresholds. At each new energy sign uses interlocking aluminium region around the collision point in step, a stipulated number of colli­ segments to form a rigid collar which the laboratory. sions are logged before the energy is grips the superconductor assembly Extensions of existing detectors increased once more. and withstands the tremendous could be attractive, and this is being At the end of the summer shut­ forces involved. Rather than being studied by one working group. down in July, the total energy welded, these collars are closed by Another group looks at new pur­ reached 43 GeV. After installation of tie rods, so that the magnets are rela­ pose-built detectors. Rather than the maximum possible number of tively easy to take apart. seeking general-purpose designs, conventional r.f. cavities, the subse­ The tooling for winding, com­ the mix of detectors finally adopted quent run will push up to the 45 GeV pressing and assembling these mag­ could be complementary. As for LEP, ceiling. The quest for higher energy nets has been developed to the much of the cost of the experiments in PETRA has dominated over lumi­ stage where it could be taken over by would have to be carried by the par­ nosity (number of collisions). With industry. ticipating institutes. finally some 200 metres of cavity in

254 CERN Courier, September 1983 place, there are strong interactions ing a limited lifetime. The four detec­ mulating data at 100 times the rate at on the beam which limit its current. tors currently installed (TASSO, which upsilon events were seen at The subsequent running conditions Mark-J, CELLO and JADE) each have DORIS I back in 1978. After sitting at in PETRA have yet to be decided. their own plans for natural develop­ the narrow 2S upsilon, the plan is to Even if nothing is found at the peak ment and improvement to extend the move up to the wide 4S state to look PETRA energies, the new r.f. cavities already impressive list of physics at the B mesons which are produced. represent money well spent as the achievements. No major changes in Between them, the Crystal Ball and surplus cavities could be taken out the experimental lineup are foreseen. Argus experiments hope to amass a (thus restoring lost luminosity) and The PLUTO detector is now out of wealth of data on upsilon spectro­ used for the HERA electron ring. the ring for good and is currently scopy and on decay processes. PETRA is also the scene of valua­ being used in a passive study to look Crystal Ball contributed significantly ble tests with new superconducting for signs of double beta decay. to knowledge of charmonium r.f. accelerating cavities (see May Also with HERA in mind, the ven­ spectroscopy at the SPEAR ring at issue, page 129). Both DESY and erable 7.5 GeV electron synchrotron SLAC, and is now covering the same CERN have a stake in this work, (DESY I), in service since 1964, is to ground for the heavier quark-anti- CERN's effort being geared to boost­ be replaced by DESY II, a new 9 GeV quark bound states. The present DO­ ing the energy available from its new electron machine to be built in the RIS II experiments are foreseen as LEP ring. For DESY, superconducting same tunnel. Installation is foreseen continuing for several more years. r.f. could provide a way of maintain­ for winter 1984-85, with tests in If HERA construction goes ahead, ing PETRA at high energies without 1985 and final connections in winter it is possible that for some time be­ spoiling beam quality, and at less 1985-86. DESY I would then be fore the big machine comes into ac­ expense. transformed into the proton injector tion there will be few experiments Because PETRA would be needed for HERA. running at DESY. DORIS II will still be as the injector for HERA, the present The rebuilt DORIS II ring is now there, and PETRA could be made physics programme is seen as hav­ working in the upsilon region, accu­ available at lower energy, except for a period of some three months. But there will be a lot to do, with a big new machine to be commissioned and the experiments for it to be con­ structed and tested. With such an ambitious programme, DESY will continue to be in the forefront of the international particle physics scene.

(Report by Gordon Fraser.)

The CELLO experiment at the PETRA electron-positron collider at DESY. At the rear of the hall, the PLUTO detector can just be seen. After sterling service at both the DORIS and PETRA rings, PLUTO is now being used in a passive search for double beta decay.

(Photo DESY)

CERN Courier, September 1983 255