Paul Frings

Photon regeneration experiment for axion search using x-rays.

In this Letter we describe our novel photon regeneration experiment for the axionlike particle search using an x-ray beam with a photon energy of 50.2 and 90.7 keV, two superconducting magnets of 3 T, and a Ge detector with a high quantum efficiency. A counting rate of regenerated photons compatible with zero has been measured. The corresponding limits on the pseudoscalar axionlike particle-two-photon coupling constant is obtained as a function of the particle mass. Our setup widens the energy window of purely terrestrial experiments devoted to the axionlike particle search by coupling to two photons. It also opens a new domain of experimental investigation of photon propagation in magnetic fields.

A 30 T pulsed magnet with conical bore for synchrotron powder diffraction

We report on the design, construction, and operation of a horizontal field, 30 T magnet system with a conical bore optimized for synchrotron x-ray powder diffraction. The magnet offers ±31° optical access downstream of the sample, which allows to measure a sufficiently large number of Debye rings for an accurate crystal structure analysis. Combined with a 290 kJ generator, magnetic field pulses of 60 ms length were generated in the magnet, with a rise time of 4.1 ms and a repetition rate of 6 pulses/h at 30 T. The coil is mounted inside a liquid nitrogen bath. A liquid helium flow cryostat reaches into the coil and allows sample temperature between 5 and 250 K. The setup was used on the European Synchrotron Radiation Facility beamlines ID20 and ID06.

New Developments at the National Pulsed Field Laboratory in Toulouse

Pulsed-magnet users are requesting higher fields with longer pulse-times in larger bores. This request led logically to user facilities similar to facilities existing for continuous fields. The Laboratoire National des Champs Magnetiques Pulses (LNCMP) in Toulouse (FRANCE) has a user community from all over Europe. We report on current efforts in Toulouse to fulfill the request of users. We developed and tested coils up to 80 T and reduced the cool-down time. Moreover, we created special design installations: a transportable pulsed-field installation to be used at other large instruments and coils with optimized field profiles for optical experiments. We are currently investigating the sources of noise on our fields and have successfully tested a preliminary method to reduce this noise.

Rapid Cooling Methods for Pulsed Magnets

Pulsed magnets are generally evaluated and compared in terms of the magnetic field they can achieve in combination with a bore size. However, in practice another criterion is equally important: the waiting time for a researcher in between two consecutive shots. The cooling time of pulsed magnets can range from a few minutes up to several hours, depending on coil size and desired field. Using simulations and measurements several options to reduce the cool down time are compared in this paper. One of the discussed methods is now routinely in use at the Laboratoire National des champs magnetiques pulses (LNCMP) in Toulouse.

Copper/Stainless Steel Polyhelix Magnets

The LNCMI has been involved since many years in the research and development of copper/stainless steel (Cu/SS) macrocomposite conductors for wire wound pulsed field magnets, generating magnetic fields up to 80 Tesla. The mechanical and electrical properties are adjusted to the magnet requirements by selecting the area fraction of the stainless steel reinforcement and the work-hardening state at the end of the drawing procedure.

A 31 T split-pair pulsed magnet for single crystal x-ray diffraction at low temperature

We have developed a pulsed magnet system with panoramic access for synchrotron x-ray diffraction in magnetic fields up to 31 T and at low temperature down to 1.5 K. The apparatus consists of a split-pair magnet, a liquid nitrogen bath to cool the pulsed coil, and a helium cryostat allowing sample temperatures from 1.5 up to 250 K. Using a 1.15 MJ mobile generator, magnetic field pulses of 60 ms length were generated in the magnet, with a rise time of 16.5 ms and a repetition rate of 2 pulses/h at 31 T. The setup was validated for single crystal diffraction on the ESRF beamline ID06.

First operation of the 20 MW Nijmegen High Field Magnet Laboratory

The University of Nijmegen has realized a new installation for high magnetic field research. The user-facility has opened its doors in April 2003. The principal part is an installation for continuous magnetic fields based on a 20 MW power converter, capable of energizing resistive magnets up to 33 T. We discuss the principle of the installation, and the magnets that have been installed and are under development. In addition, there is a pulsed field installation based on 2 MJ stored energy, capable of magnetic field pulses up to 70 T with several milliseconds duration.

40-tesla pulsed-field cryomagnet for single crystal neutron diffraction

We present the first long-duration and high duty cycle 40-T pulsed-field cryomagnet addressed to single crystal neutron diffraction experiments at temperatures down to 2 K. The magnet produces a horizontal field in a bi-conical geometry, ±15° and ±30° upstream and downstream of the sample, respectively. Using a 1.15 MJ mobile generator, magnetic field pulses of 100 ms length are generated in the magnet, with a rise time of 23 ms and a repetition rate of 6-7 pulses per hour at 40 T. The setup was validated for neutron diffraction on the CEA-CRG three-axis spectrometer IN22 at the Institut Laue Langevin.

Pulsed magnetic field synchrotron X-ray powder diffraction of the Jahn-Teller distortion in TbVO4

X-ray powder diffraction experiments under pulsed magnetic fields were carried out at the DUBBLE beam line at the ESRF. A mobile generator delivered 110 kJ to the load coil, which was sufficient to generate peak fields of 30 T. A liquid He flow cryostat allowed us to vary the sample temperature accurately between 8 K and 300 K. Powder diffraction patterns of TbVO4 were recorded in a broad temperature range using 21 keV monochromatic X-rays and an on-line image plate detector. We present results on the suppression of the Jahn-Teller structural distortion in TbVO4by to the magnetic field.