Fascinating research Physics

In t h e Me c h a n i c s De p a r t m e n t o f t h e Ma x Pl a n c k In s t i t u t e f o r Ph y s i c s in Mu n i c h , t h e t e c h n i c i a n s c r e a t e i n n o v a t i v e s o l u t i o n s f o r scientific e x p e r im e n t s

The truss of the (2) c s MAGIC telescopes: i h y s

The space truss P supports the mirrors f o r

of the telescopes. : MPI h o t o s P

Tinkering in Uncharted Technological Territory

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Physicists will lower the GERDA Experiment in the mountain: The water tank in the laboratory In the Machinery Pool: Thomas Haubold heads the Mechanics detectors in rows into liquid argon. below the Gran Sasso massif harbors the GERDA experiment. Department, which also encompasses a mechanics workshop. yet unknown rest mass of these ‘ghost’ particles. t is just as well The germanium detectors will hang I that border con- in a tank in the underground labora- trols have all but tory in Gran Sasso. This tank has disappeared in Eu- roughly the circumference of a brew- rope. Otherwise, the ing vat, but is twice as high and filled scientists at the Max with about 70 cubic meters of liquid Planck Institute for Physics would argon. The tank is crowned with a have to put up with unpleasant ques- system of locks from which protrude tions time and again in the coming two tubes, each measuring four me- months when they drive to the un- ters long; the germanium detectors derground laboratory in Gran Sasso, are transported through the lock into Italy: “Why do you have two pres- the argon tank, which rests in a wa- sure cookers strapped into the child ter tank the size of a feed silo. seats? What are those connectors The details of the construction and fittings doing on the pots?” The were thought up by the staff of the physicists would be able to quickly Mechanics Department – in contin- placate the customs officers – with a uous dialog with the scientists: document that declares the pressure “Since the project started in 2004, cookers to be tested transport con- we have been getting together one tainers; each contains about two ki- morning a week to discuss technical lograms of germanium and is filled problems,” says Thomas Haubold, with the noble gas argon. who heads the Mechanics Depart- It was Karlheinz Ackermann’s idea ment at the institute in Munich. In to put the germanium into pressure those days, the only specification cookers. He is an engineer, and one was that the 14 germanium detec- of eight design engineers at the Max tors should be positioned as close Planck Institute for Physics. They together as possible, yet still develop instruments for complicated equipped with the necessary mea- physics experiments that go by such suring instruments, and suspended c s i

names as Gerda, MAGIC, ATLAS, h y s in an argon tank – “from sky P

CRESST and HEGRA, based on the f o r hooks.” scientists’ specifications. The work of : MPI Su s p e n di n g Six e s c h these design engineers is all in the i h o t o Ki l o g r a m s o f Ge r m a n i u m r P name of research, but it is also a sci- G x e l a n d

c i : A ence in itself and frequently leads h The design engineers use the term p r a h o t o

them into uncharted technological G sky hooks when scientists want to P territory – and not always via the fix something in thin air so that it shortest route. Prototypes and models of some de- Fourteen of these crystals form the floats as freely as possible. The sci- is indistinguishable from the rare only copper, Kapton and Teflon, The engineers’ laboratory stretches tails can also be seen. The originals core of GERDA, the GERmanium De- entists have their reasons, of course: events that are so important to the which release radon in even smaller across the entire Mechanics Depart- of some of these pieces fill rooms the tector Array, which the physicists most materials in an engineer’s tool- physicists. Even minute traces of ra- doses than other materials. So Karl- ment of the institute in Munich, but size of a sports hall. want to use to detect an extremely box, and in our environment, con- don become a problem for the GER- heinz Ackermann spent six months the engineers produce their designs The researchers use many of the rare nuclear decay event in the crys- tinuously emit the radioactive noble DA experiment: a concentration of tinkering with filigree supports, try- in an open-plan office with chest- instruments to investigate exotic tals. Such events are caused by neu- gas radon. There are about ten mil- 500 radon nuclei per cubic meter in ing to support the crystals with high cabinets for dividers, and walls species from the particle menagerie trinos, and the researchers expect lion radon nuclei per cubic meter of the apparatus is sufficient to render three nylon threads, or with steel that are covered with structural of physics. The germanium crystals there to be less than one nuclear de- air in a building, which presents no the measurement useless. wires for one or more detectors on drawings and photographs from lots in the pressure cookers, which are cay event per year in one kilogram risk to health. But in the Gran Sasso This means that most plastics, trays. Ackermann keeps the result of of projects and devices that have used as detectors in the GERDA ex- of germanium. The results will main- detector, the nuclear decay of the ra- metals and glasses are ruled out as his exercises in suspension in a been dreamt up and realized here. periment, serve this same purpose. ly serve to gain insight into the as don nuclei can produce a signal that possible materials. Physicists accept plastic dish next to his PC: more

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Working in a dust-free atmosphere: The muon detectors for the ATLAS experiment The brains behind this plan. After the detectors for ATLAS have been manufactured, at the Large Hadron Collider were assembled in a clean room at the institute. Thomas Haubold also checks whether they have been installed correctly. could recognize at a glance that this piece of copper, which looks like a hexagonal stamp the size of your palm with an impractically shaped and perforated handle, is complicated to produce. Markus Eichenlaub has already ti- dily arranged five of these contact plates side by side on his workbench. Each one requires 26 production steps and more than a day’s work. They are produced on a programma- ble CNC machine that Eichenlaub taught when and where to mill away copper and where to drill holes.

Ru s t a n d Di r t Th r e a t e n GERDA’s Li f e

The end results of this protracted work are supports, tracks and skids. Assembling these parts into a fin- ished device sometimes requires a screwdriver, sometimes a welding torch. As we speak, Marco Wehr- meister is working with a welding torch in the metals workshop. He is welding together a stainless steel housing the size of a milk carton: “It will hold a small cable drum,” says Wehrmeister, pulling down the visor on his helmet, only to discover that he cannot work with the pistol- shaped welding electrode inside the

housing. He needs to shorten the (2) e s c h i

electrode. r G

After a small adjustment, Wehr- x e l

meister holds a wire to the open edge : A h o t o s

of the housing and strikes the arc, P which, when viewed through the vi- c s than a dozen of these parts together shop, a precision mechanics work- scene in the workshop. The devices i sor of his helmet, shines about as effort here, because rust and dirt are treatment, the weld gleams again in h y s

weigh a mere 34 grams, but they shop, and one where plastics are required for GERDA present a chal- P brightly as the flame of a cigarette life-threatening to GERDA. steel-gray. In the future, the fin- can support more than six kilo- processed. Reinhard Hofmann is the lenge not only for Karlheinz Acker- f o r lighter. He briskly moves it along the “We have specially procured a ished cable box will hold a cable to

grams. Since the components of the master craftsman in the production mann, the engineer, but also for : MPI joint, leaving behind a small blue- device to remove the oxides,” ex- a measuring device that will be h o t o

supports cannot be bought, either engineering section and organizes the technicians – even when we are P black bead. Not only does this look plains Wehrmeister, bringing a lowered into the argon tank togeth- individually or as a set, the staff of the work of 18 staff members, in- talking about such an unassuming sloppy, it also points to the presence transformer on a kind of trolley er with the germanium detectors. the Mechanics Department must cluding those in the metals and the item as a contact plate: the germa- of oxides, which act as a breeding closer to his workbench. He rubs an The crystals themselves are sus- manufacture them themselves. The plastics workshops. nium detectors are suspended from ground for rust. Wehrmeister would oily liquid onto the weld and moves pended from ten-meter-long chains institute has its own workshops for The light green paint of more it, and it also serves to provide an usually remove these discolorations an electrode the width of two fin- along which the cables for the de- this kind of precision work: a car- than a dozen drills, milling ma- electrical contact to the detectors. with a wire brush and sandpaper, but gers along it. The liquid foams and tectors also run – a custom-made penter’s workshop, a metals work- chines and lathes dominates the Probably only a precision engineer the scientists have demanded more becomes brown. Following this construction. “The physicists would

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It fits! A member of the institute checks whether the clusters A lightweight at 65 tons: A number of tricks have been employed in the of the MAGIC camera can be inserted without a problem. construction of the MAGIC telescopes to make them extremely mobile. c s i h y s P f o r : MPI h o t o P

have liked to have the detectors row of detectors from the scaffold to tors into and out of position next to suspended from a nylon thread, but a depth of about seven meters and each other. nylon stretches over time,” says test the support. “When we have installed GERDA in Sven Vogt, who developed the sup- Gran Sasso, everything has to work,” Wo o d e n Mi n i a t u r e port. A wire is also unsuitable, be- says head engineer Thomas Haubold. o f a Te l e s c o p e cause it twists. And even on two This applies to all the devices he and ropes, the detectors still moved too In the room below the platform, the his people have built, so they put a much. Wires dangling from a hook technicians are also experimenting lot of work into models and test as- five meters above the floor in a re- with the assembly of GERDA. They semblies. One such model immediate- c s mote corner of a workshop are a re- have laid a square plate on several ly catches the eye in the engineers’ i ing Cherenkov telescope. The second using both its telescopes, the research- when a black hole devours a particu- h y s

minder of the most recent attempts head-high supports. Underneath the open-plan office: the wooden minia- P of these telescopes was commissioned ers will one day be able to determine larly massive star. in this direction. plate, 20 or so short pieces of track ture version of a telescope. It stands f o r in September on La Palma in the Ca- the direction from which the gamma In order to be able to investigate

Even the chains must first prove have been arranged in a group to act on a filing cabinet next to Peter : MPI nary Islands, where it detects Cheren- rays have come and how the cascade the source of the gamma-ray bursts h o t o

that they do what Vogt expects of as a switchyard for the germanium Sawallisch’s desk and is so large that P kov radiation. This ultraviolet light is in the air is formed. This will reveal a more closely, MAGIC must roll its them. That is why a member of the detectors. Using a piece of track the engineer could just barely carry it produced when gamma rays impact great deal about the sources of the ra- eyes pretty quickly because these mechanics workshop is increasing some two meters long as a feeder, alone. Peter Sawallisch tested the me- on the atmosphere, generating a cas- diation: star explosions, black holes mysterious bursts usually last no the height of the scaffolding that sits and a chain running around the plate chanical principle of both MAGIC cade of particles and light. The physi- that gobble up matter, and huge gam- longer than a few minutes. A MAGIC on a floor-to-ceiling platform in the as a distributor, the engineers and telescopes on this three-dimensional cists use the visible traces to recon- ma-ray bursts. The latter may be gen- telescope actually takes no more workshop and carries the guideway physicists employ several dummies model. MAGIC is an acronym for Ma- struct the properties of the gamma erated in special supernovas, when than 27 seconds to focus on any of the chain. The plan is to suspend a to test how best to move the detec- jor Atmospheric Gamma-Ray Imag- rays. Since MAGIC can see ‘in stereo’ two neutron stars fuse together, or point in the sky. This is some feat for

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specialized company milled a slight their luggage, every technician car- Obi t u a r y curvature into the mirror panels, pre- ried a pair of the arm-long clusters, Würzburgs neue Top-Location ... The project leader of the MAGIC-II cise to within fractions of a millime- each of which consists of seven pho- telescope, Florian Goebel, lost his v a t e i ter. The shining surface was then tocells arranged in a hexagon. The life as the result of an accident at r : P coated with a wafer-thin film of retina comprises 169 of these facet- work on September 10, 2008 on für Tagungen, Messen, Kultur, Feste. h o t o the Canary Island of La Palma. P quartz glass for protection. ted clusters. Just before the trip be- Fl o r i a n Go e b e l was born in Cologne, Germany, in October The lightweight construction of gan, Enrico Töpper and two of his 1972 and studied at the University of Heidelberg. He the three-dimensional truss structure colleagues from the institute’s Elec- completed his studies at the State University of New York that supports the mirror is the sole tronics Department, the sister group in Stony Brook and obtained his Ph.D. at the German reason why it weighs a ‘mere’ eight of the Mechanics Department, were Electron Synchrotron (DESY). In 2001, he was awarded tons: at the suggestion of a physicist, still soldering and screwing clusters

the DESY Prize for the best doctoral thesis of the year. L+D 05585 Florian Goebel had been a member of the MAGIC re- Peter Sawallisch constructed the together. search group at the Max Planck Institute for Physics in framework out of carbon fiber tubes. Stefan Horn checked every wired Munich since 2002. For the past three years, he was the The material is about as light as alu- photocell under the microscope – a project manager responsible for the development and minum and almost as rigid as steel. task that was not originally planned. construction of the second MAGIC telescope. He lost his life in a tragic accident only a few days before the of- Sawallisch thus used carbon fiber But some photocells had been ficial inauguration while carrying out some final work surfing masts to support the cameras knocked out by short circuits after on the telescope. of the four HEGRA telescopes, MAG- being mounted into the clusters. This Florian Goebel was an exceptionally friendly and enthu- IC’s predecessor. Following exhaus- happened because wire threads thin- siastic employee with many interests both within and tive load tests, a three-dimensional ner than a hair were hanging loose outside the field of physics. He was an outstanding physicist and warmhearted colleague who we will miss truss made of this material now also in the electronics; one device had very much. His c o l l e a g u e s a n d f r i e n d s supports the mirrors of the MAGIC not performed up to par during sol- telescopes, which are nearly 30 times dering. This did not become appar- as large. A structural engineering ent until the components were being an astronomical instrument whose company erected the structure on La mounted and pressed against a 17-meter diameter mirror looms as Palma. “We place orders with exter- spring. high as a five-story building. nal companies wherever possible,” Reinhard Hofmann also had to The only reason the telescope is says Thomas Haubold. This means I carry out some modifications before this agile is because it weighs rela- don’t tie up my own staff and can setting off for La Palma: he drilled tively little: 65 tons including drive, give them tasks that can be done holes into cogs to eliminate surplus which rolls on a circular rail and ro- only here at the institute.” weight. In a gear, these cogs serve to tates the instrument in any direction. increase the torque of a motor that Pa c k i n g Ph o t o c e l l s “We actually wanted to manage with opens the hatch in front of the cam- f o r a Bu s i n e s s Tr i p less weight,” says Peter Sawallisch, eras of the telescopes. “Although we so he designed the motors that push When design engineers, technicians had tested the mechanism here, it did the telescope around the circular rail and scientists work on the telescopes, not operate smoothly on La Palma,” on this basis. “Fortunately, one al- they are roped up like climbers as says Hofmann. ways leaves a little bit of leeway.” they clamber through the truss, usu- The motor had too little power. The But even 65 tons is low for tele- ally with a strong wind whistling nominal voltage of the Spanish grid scopes of this size. Sawallisch and around them. This is how they is 220 volts, just like in Germany. his colleagues achieved this light- mounted the mirrors, and how they However, whereas in Munich the grid weight construction with a few tricks lubricate the moving parts and take actually supplies 237 volts, on La – in the selection of the material, for care of small repairs, for example Palma it is only 219 volts – which do example. The four-ton mirror com- when components are destroyed by not provide the motor with enough prises square plates made from an the intense sunlight. Peter Sawallisch power. “Since we are building devic- Erlebnisräume für Ihre Events Vogel Immobilien & Marketing GmbH alloy of aluminum, magnesium and has been on La Palma 37 times in re- es that nobody has ever constructed · 2300 m² Fläche Horst Vollhardt silicon. Lasers on the movable, one- cent years. before, we always need to be flexi- · modernste Raum- und Konferenztechnik Max-Planck-Str. 7/9 meter square plates adjust the plates On one of his recent business trips, ble,” says Thomas Haubold: “But this so the light is deflected precisely he and his colleagues planted the is also the attraction of our job.” · komfortable Klimatisierung 97082 Würzburg onto a camera located at the focus. A retina into the second MAGIC eye: in Pe t e r He r g e r s b e r g · individuelle Beleuchtung und Bühnentechnik Telefon: 0931 418-2211

5 2 Ma x P l a n c k R e s e a r c h 4/2008 · 250 Parkplätze [email protected]

05585_a_vcc_maxplanck_210x280_011 1 11.07.2007 10:48:05