Flip Coil Research Articles

Field integral correction in neutron resonance spin echo

Neutron resonance spin echo (NRSE) as a variant of neutron spin echo (NSE) has the advantage that it needs only relatively small magnetic coils. Field inhomogeneities are therefore less important than in NSE. We have built a new type of NRSE spectrometer that overcomes the main limitation of NRSE towards high-energy resolution. Our setup profits from a new longitudinal NRSE field geometry which allows to use Fresnel coils correcting for the beam divergence effect, while former NRSE setups with transversal static magnetic fields could not use Fresnel coils. We demonstrate the function of the longitudinal resonance flip coils, and show first results of spin echo test measurements performed by means of the new setup.

Classical and quantum-mechanical picture of NRSE—measuring the longitudinal Stern–Gerlach effect by means of TOF methods

If a neutron pulse passes through an NRSE flipper coil, the coherent splitting in energy of the spin-up and spin-down states leads to their macroscopic spatial separation, depending on the experimental parameters (longitudinal Stern–Gerlach effect). We furthermore present a discussion about the effects measurability and propose two possible setups.

Classical and quantum-mechanical picture of NRSE?measuring the longitudinal Stern?Gerlach effect by means of TOF methods

If a neutron pulse passes through an NRSE flipper coil, the coherent splitting in energy of the spin-up and spin-down states leads to their macroscopic spatial separation, depending on the experimental parameters (longitudinal Stern–Gerlach effect). We furthermore present a discussion about the effects measurability and propose two possible setups.

Superconducting solenoids for an international muon cooling experiment

The international muon ionization cooling experiment MICE will consist of two focusing cooling cells and a pair of uniform field solenoids used for particle identification and emittance measurements. The 2.75-meter long cooling cells have a pair of field flip coils and a coupling coil. The 0.52-meter diameter field flip coils surround an absorber that removes transverse and longitudinal momentum from the muons to be cooled. The beam in the absorber is at a minimum beta point so that scattering of the muons is minimized. The 1.7-meter diameter coupling coils are outside of conventional 201.25 MHz RF cavities that accelerate the muons putting longitudinal momentum into the muons without putting back the transverse momentum into the beam. A third set of flip coils helps the muon beam transition from and to the experimental solenoids. The 0.6-meter diameter experimental solenoids have a uniform field region (good to about 1 part in 1000) that is 1.3-meters long. The MICE experiment magnets must operate as a single unit so that the field profile will produce the maximum muon cooling.

Results of magnetic field measurements of SPring-8 magnets

Magnetic measurements have been performed for all dipoles, quadrupoles and sextupoles of the SPring-8 storage ring. The long flip coil and the rotating coil system were used for the measurements and they were good enough in measurement accuracy. Dispersion of the magnetic length and strength of the multipole fields were found to be within tolerable range for the three types of magnet. The position of the fiducial points for alignment was measured in the accuracy of better than 20 /spl mu/m for all the quadrupoles and the sextupoles.

Features and performance of an NRSE spectrometer at BENSC

Abstract Neutron Resonance Spin Echo (NRSE), also called Zero Field Spin Echo, is a spin echo technique that replaces the long high field precession coils of conventional spin echo (NSE) (1) with field free regions bounded by magnetic resonance flip coils (2,3). One advantage of the method is that it is easily adapted to use the tilted field technique first proposed by F. Mezei (1) for high resolution measurement of phonon linewidths and by R. Pynn (4) for high resolution elastic small angle scattering. The relatively small r-f flipper coils can be readily tilted through rather large angles.

Long term magnetic performance of the steel concrete dipoles in LEP

The steel-concrete cores of the LEP bending magnets were built of regularly spaced steel laminations, the spaces being filled with cement mortar. The effects of compressive stresses were studied on models and the long term behaviour has been monitored during operation of the LEP machine over a period of four years. The requirements for stability and reproducibility of the magnetic field have increased in step with the development of the accelerator and its particle detectors. After the initial ageing in the LEP tunnel, the most important parameter was the temperature coefficient. The temperatures of a number of magnet cores are therefore continuously monitored and corrections are applied to the indicated value of particle momentum as measured by NMR and a flip coil in a reference dipole connected in series with the bending magnets. This reference magnet is in turn calibrated periodically by a direct measurement of flux variations in a loop mounted in the lower poles of all bending magnets installed in the tunnel. >

A short period undulator for MAX

A hybrid undulator for generation of high brilliance synchrotron radiation in the photon energy range of 60–600 eV at the 550 MeV electron storage ring MAX in Lund, Sweden has been designed and built at the Technical Research Centre of Finland in close collaboration with MAX-lab of Lund University. At the rather modest electron energy of MAX this photon energy range can be reached only by an undulator featuring a fairly short period and the smallest possible magnetic gap. Even then, higher harmonics (up to the 13th) of the radiation spectrum must be utilized. An optimization of the magnetic design resulted in a hybrid configuration of NdFeB magnets and soft iron poles with a period of 24 mm and a minimum magnetic gap of 7–10 mm. A variable-gap vacuum chamber allows reduction of the vacuum gap from a maximum of 20 mm, needed for injection, down to 6 mm during stored beam operation. A special design of this chamber permits a magnetic gap between pole tips that is only 1 mm larger than the vacuum gap. Adequate field uniformity was ensured by calibration of magnets to equal strength at their true operating point and verification of the homogeneity of their magnetization. Magnetic measurements included Hall probe scans of the undulator field and flip coil evaluations of the field integral.

Performance of the TRISTAN main ring magnet

The main-ring magnet system of the TRISTAN accelerator has a circumference of 3 km and is composed of four arcs of 377 m average radius and four long straight sections of 194 m length. Each arc contains 68 dipole magnets and 76 normal quadrupoles; each long straight section contains 22 normal quadrupoles and 4 insertion quadrupoles. The sextupole magnet system consists of 240 laminated magnets with two different lengths. The integrated radial field profiles of the dipole were measured by a 6.5 m long flip coil at several excitation levels. The voltage induced in the coil was integrated and measured by a digital voltmeter. The excitation curve, which is a relation between magnetic strength and current, was measured by using a 6.5-m search coil with 70.053-mm width at 17 excitation currents under pulsed excitation. For the quadrupoles, the integrated transverse-field profiles and the excitation curves were measured using conventional long twin coils under pulse operation of a power supply. For the sextupole and the steering dipoles, the field qualities were measured statically using a rotating coil and a spectrum analyzer. Performance results for the dipoles, quadrupoles and sextupoles are presented and discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An improved spin-flip switching system for neutron spectral modulation

The switching circuit for a spin-flip chopper developed by Badurek and Westphal has been modified to give improved time resolution for neutron time-of-flight spectrometry. With the modified system, the switching time constants can be reduced to as short as 200 ns or less, and the thickness of the flip coil can be reduced to as thin as 2 mm or less. Thus bursts of 3 μs duration of neutrons with a wavelength of 2.47 Å can be used for the conventional flip-chop mode of TOF experiments. A substantial improvement of the time resolution can be achieved with the improved switching system when combined with the neutron spectral modulation technique, as in NSM the wavelength spread of the incident beam is decoupled from the overall time resolution of the system.

Fast inversion of neutron spin

The action of a dc-current spin-flip device is thoroughly analyzed and its optimal design for dynamic mode of operation examined. It is found that the combination of a static and a dynamic flip coil allows a reduction in size of the latter for a given beam cross-section and, therefore, a shorter switching time. To drive such a flip device with highest possible speed, flexibility and power economy a special pulsed current supply has been developed. The essential electronic details of this are described in an appendix.

H-type dipole model for future plan at KEK

For the bending magnet of the electron ring of the so-called TRISTAN project at KEK, the H-type dipole, full scale model with 4 m in length, has been investigated at first to examine the feasibility to the electron storage ring from some points such as magnet performance, accessibility for the field measurement and vacuum chamber installation, manufacturing problem and magnet cost. Here, the magnet performance is treated. To measure the magnetic field inside the air gap, the specially designed flip coils were used. Fields of 11 points at the same longitudinal positions could be measured at once by rotating probe containing 11 flip coils on its axis.

Magnetic Field Measurements in the MSU 500 MeV Superconducting Cyclotron

The measurements of the magnetic field in the superconducting cyclotron under construction at Michigan State University are reported. The 55-channel flip coil gaussmeter built at MSU for this purpose is described. Twelve field maps measured with various currents in the two sections of the main coil have been Fourier-analyzed for evaluation of magnetic imperfections and data errors and for comparison with calculated magnetic field distributions. The calculation procedure is in excellent agreement with the measured data. The imperfection harmonics are small and there is evidence in the measurements that they are partly correctable by better alignment of pole tips and coil tank at final assembly of the cyclotron.

Magnetic Field Measuring System for Remapping the ORIC Magnetic Field

The Holifield Heavy Ion Research Facility will integrate a new 25 MV tandem electrostatic accelerator into the existing cyclotron laboratory which includes the Oak Ridge Isochronous Cyclotron (ORIC). 1 Computations of ion paths for beam injection from the new tandem into ORIC require field mapping in the regions traversed by the beam. Additional field data is also desired for the higher levels (~19 kG) now used for most heavy ion beams. The magnetic field measurement system uses 39 flip coil/current integrator sets with computer controlled data scanning. The coils are spaced radially at 1 inch intervals in an arm which can be rotated azimuthally in 2 degree increments. The entire flip coil assembly can be shifted to larger radii to measure fields beyond the pole boundary. Temperature stabilization of electronic circuitry permits a measurement resolution of ±1 gauss over a dynamic range of ±25,000 gauss. The system will process a scan of 8000 points in about one hour.

Null Reading Flip-Coil Fluxmeter

Two flip coils are rotated through 180° to give a precision measurement of the ratio of separate magnetic fields. The output voltages are connected in opposition and balanced in a resistance potentiometer using a sensitive galvanometer as a null indicator. The ratio of the fields is a linear function of the potentiometer setting. In fields of several thousand gauss and using a common shaft for the coils, readings were reproducible to within 0.01%. With separate selsyn motor drives the precision was 0.02%.