Page 1 of 7 Date: Annual Report 2010 1. Double Disk Chopper for KWS1 and KWS2 at FRM II in Garching, Germany Both small angle neutron scattering instruments KWS1 and KWS2 at FRM II in Garching will be driven by Forschungszentrum Jülich, Germany, resp. Institute of Solid State Research (IFF) in Jülich, Germany. (ZAT) developed, designed, and fabricated each double disk chopper for both instruments in Jülich. The diameter of the four disks is 620 mm, their rotational frequency is 200 Hz. Due to the requirement of a maintenance-free suspension of the disk, non contacting and wear-free magnetic bearings are used. After manufacturing of all parts, the coating of the discs, and the electronic installation of the choppers took place. The double disk chopper for KWS 2 has been implemented and starting at FRM II in October 2010. The double disk chopper KWS 1 will be installed and commissioned in 2011 (fig. 1, 2). Fig. 1, 2: KWS1, KWS2 housing including disk and dummy lower housing (left); view into lower housing (right)
Page 2 von 7 2. Fermi-Chopper für BRISP am ILL in Grenoble For the Philipps-University of Marburg, Germany, and the BRISP experiment at ILL in Grenoble, France, respectively the development and design of a magnetic bearing and drive system, the housing, and electronics for a non contacting, wear-free, maintenance-free driven Fermi rotor was finished. The rotor has a mass of approx. 31. kg and has to be operated horizontally. The rotor has been provided by the customer, ZAT realises the bearings, the drive, the control system, and the vacuum housing. The chopper will replace an existing older Fermi rotor. Thus, the new rotor has to fit into the enclosure of the already existing chopper. The maximum rotational frequency is 25,000 min -1, the phase stability will be better than 0.1. Fig. 3 shows the design of the BRISP Fermi chopper, fig. 4, 5 show the chopper assembly in the test rig in Jülich. Fig. 3: Design study of the horizontal driven Fermi chopper for BRISP (Source: Prof. Dr. Wolf-Christian Pilgrim, Philipps-Universiy Marburg, Germany)
Page 3 von 7 Fig. 4, 5: BRISP Fermi chopper in a test rig 3. TOPAS The first studies for the choppers for the thermal time-of-flight spectrometer TOPAS at FRM II in Garching have been started. Two Fermi choppers and one disk chopper, so called Cross Talk Chopper (CTC), will be needed. The Fermi choppers will have rotational frequencies of 166.7 and 600 Hz respectively, and windows of 60x80 mm² and 30x60 mm² respectively. The rotational frequency of the CTC will depend on the number of neutron windows in the disk. All suspensions have to be magnetic bearings, i.e. non contacting, wear-free, and maintenance-free. 4. 1.25 MHz Light Chopper for Operation at BESSY, Berlin, Germany For Max Planck Institute of Microstructure Physics in Halle, Germany, a 1.25 MHz light chopper has been developed, designed, and manufactured to be used at Helmholtz Centre Berlin for Materials and Energy Storage Ring BESSY in Berlin,
Page 4 von 7 Germany. The chopper has to select light pulses of 100 ps out of a pulse gap of 200 ps with a repetition rate of 800 ns. Fig. 6, 7: Light chopper: disc in opened housing (left); view onto the bearing and drive at closed housing (right) Fig. 8, 9: Light chopper: disc (left); slots on the circumference (right) The chopper disc is rotating with a frequency of 998.4 Hz in an ultra-high vacuum housing made of stainless steel (figures 6 to 9). The disc is positioned in such a way that the beam of the light passes the slotted circumference of the disc parallel to its
Page 5 von 7 shaft. Resulting from a design study the diameter of the disc was fixed to 340 mm with 1252 slots on its circumference. Each slot has a width of 0.15 mm with a depth of 1 mm. The thickness of the disc at the circumference is 0.5 mm. The material of the disc is a high-strength aluminium alloy. Due to the requirement of highest precision of the chopper the disc had to be manufactured with accordant accuracy not only concerning the disc itself but also the positioning of the slots on the circumference. Manufacturing the disk and first testing of the high precision drive system took place in 2009. Due to the fact that the vacuum of the beamline cannot be realised with the existing chopper, additional fittings were implemented in the chopper housing to reduce the slit of the beamline close to the disk to 2 mm. Due to a failure in the safety bearings the disk was damaged during a test run. Now the disk is being manufactured again and other safety ball bearings will be used. Installation and commissioning of the chopper is planned after some more tests in 2011. 5. 3 Disks Chopper Cascade for BioRef at Helmholtz Centre Berlin, Germany For the chopper system BioRef commissioned at Helmholtz Centre Berlin for Materials and Energy, HZB, in 2009 an additional electronics has been delivered as a spare electronics. When a failure with one of the chopper electronics occurs, the spare can be implemented by the user easily. The faulty electronics can be shipped to the manufacturer for repair. In the meantime the instrument can be used without downtime. 6. PST-Chopper / SPHERES To allow higher rotational frequencies the PST/SPHERES chopper is going to be redesigned. After an optimisation process the angular speed and the arrangement of the crystals at the circumference will be changed.
Page 6 von 7 The disk will be made of aluminium. On 215 of the circumference the crystals will be fixed. The rotational frequency will be 83 Hz, the radius will be 413 mm (middle of the crystals) While changing the diameter of the disk the housing has to be redesigned. The housing will be made of aluminium. Steel will be inserted as a shatter protection (fig. 10). Fig. 10: Housing made of aluminium, chopper disk, aluminium housing including steel inserts at the circumference and at the lid 7. European Spallation Source, ESS For the planned European Spallation Source, ESS, in Lund/Sweden some development work shall be done. Neutron choppers have been identified as critical components for instruments. The following parameters shall be investigated:
Page 7 von 7 T0-shopper, evaluation concerning the development status, potential for development. radiation level, amount of maintenance, drive and bearing concepts, novel design of choppers, materials selection, safety of housings. Fixation of Fermi packages in novel chopper designs, change of Fermi packages. Coating of high speed rotors at high radiation levels. Investigation of magnetic/electromagnetic interaction between external magnetic fields and running choppers. Requirements concerning standardisation and reduction of costs.