Current status of BL06 beam line for VIN ROSE at J-PARC/MLF

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1 Available online at Physics Procedia 42 (2013 ) th International Workshop on Polarised Neutrons in Condensed Matter Investigations (PNCMI2012) Current status of BL06 beam line for VIN ROSE at J-PARC/MLF Masahiro Hino 1*, Tatsuro Oda 2, Masaaki Kitaguchi 1, Norifumi L Yamada 3, Hidenori Sagehashi 3, Yuji Kawabata 1 and Hideki Seto 3 1 Research Reactor Institute, Kyoto university, Kumatori,Osaka, , Japan, 2 Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto , Japan 3 Neutron Science Laboratory, High Energy Accelerator Research Organization, Shirakata, Tokai, Ibaraki, , Japan Abstract We started to construct new beam line for neutron spin echo spectrometers (VIN ROSE) at BL06 J- PARC/MLF from FY2011.The advantage of MIEZE is flexible sample environment and polarimetry analysis. The key device of NRSE is focusing mirror and high-m polarizing device. Both spectrometers are to use intensity gain of J-PARC and dedicated for small sample size. In this study, we show conceptional design of the VIN ROSE and current status of the BL06 beam line at J-PARC/MLF The Authors. Published by Elsevier B.V. Open access under CC BY-NC-ND license. Selection 2012 and Elsevier peer-review BV. under Selection responsibility and/or of peer-review the Organizing under Committee responsibility of the 9th International of the organizing Workshop on committee Polarised Neutrons for in Condensed PNCMI Matter Investigations Keywords:Supermirror; Neutron Spin Echo; MIEZE NRSE J-PARC * hino@rri.kyoto-u.ac.jp The Authors. Published by Elsevier B.V. Open access under CC BY-NC-ND license. Selection and peer-review under responsibility of the Organizing Committee of the 9th International Workshop on Polarised Neutrons in Condensed Matter Investigations doi: /j.phpro

2 Masahiro Hino et al. / Physics Procedia 42 ( 2013 ) Introduction Kyoto University and KEK started to construct a new beam line for neutron spin echo (NSE) spectrometers at BL06 at the Materials and Life Science Facility (MLF) of Japan Proton Accelerate Research Complex (J- PARC). NSE method proposed by F.Mezei [1] is very powerful tool to investigate slow dynamics. It measures directly intermediate scattering function S(q,t) with very high neutron energy resolution. In order to cover wide energy range with various sample environments, our instrument consists of two types of NSE spectrometers: NRSE (Neutron Resonance Spin Echo)[2] and MIEZE (Modulated Intensity by Zero Effort) [3]. We named these spectrometers VIN ROSE (VIllage of Neutron ResOnance Spin Echo spectrometers) to discover new things by taking lessons from the passage of time with enjoyment. As shown in Fig.1(a) for NRSE, two Resonance Spin Flippers (RSFs) and the distance replace a Larmor precession magnet in the Mezei-type NSE spectrometer. On the other hand, in Fig.1 (b) for MIEZE, there is no optical component after sample and the neutron spin state is one only (but it has two energy levels). Thus it is easy to combine MIEZE and polarimetry analysis. Furthermore MIEZE signal is scanned every neutron pulse. In other word, MIEZE measurement can be done with one neutron pulse if neutron flux is strong enough. Even in J-PARC, the neutron intensity is not enough for one pulse measurement, however, it is possible to synchronize with the sample environment, for example, pulse magnetic field and laser excitation. MIEZE has a big potential to discover new field with high neutron intensity since it is suitable for Time-Of- Flight (TOF) technique, still new spectroscopy and the sample environment is very flexible. Fig.1 Schematic view and energy diagram of (a) NRSE and (b) MIEZE spectrometer. The RSF consists of a static magnetic field and an oscillating magnetic field. The static field is proportional to the frequency of the oscillating field. We have developed RSF with iron yoke dipole magnet which creates strong static fields and solves problem of cooling and power consumption. It also reduces the material in beam line and is suitable for use of long wavelength. MIEZE and NRSE signals using the RSFs have been demonstrated with high frequency at MINE1 port at JRR3 at JAEA [4]. The energy resolution of MIEZE and NRSE spectrometer is determind by Fourier time and it is proportional to the frequency of the oscillating field, the flight path length between a pair of RSFs, the third power of incident wavelength. In NSE including NRSE and MIEZE, it is very important for high resolution measurement to use longer wavelength. In MIEZE, the Fourier time is strongly depend on sample geometry [5] and it is very difficult to measure large

138 Masahiro Hino et al. / Physics Procedia 42 ( 2013 ) 136 141 sample with high resolution since two energy levels exist at sample.

3 138 Masahiro Hino et al. / Physics Procedia 42 ( 2013 ) sample with high resolution since two energy levels exist at sample. NRSE is better to measure with higher Fourier time since there is no energy level at sample. In NSE, the Fourier time is limited by the deviation of the precession due to the inhomogeneity of the magnetic fields and the divergent beam. It is necessary to keep the neutron intensity by taking the divergent beam and the use of Fresnel coils enables the measurements [6]. The beam divergence effect can be successfully corrected with the arrangement of three Fresnel coils in the static magnetic field of NSE [7]. The neutron intensity, especially longer wavelength, is reduced by passing through the coils. Similarly, the resolution of NRSE is also limited by the effect of beam divergent. It is impossible for NRSE to use such Fresnel coil since the spin quantization axis is not parallel to neutron path. In NRSE, there is no and weak static magnetic field between a pair of RSFs and the deviation of flight path makes the deviation of the relative phase between up-and down-spin components, which is equivalent to spin precession. It is possible for high resolution NRSE measurement to keep same path length between a pair of RSFs. When we consider focal point, the flight length can be adjusted by using two dimensional (2D) elliptic focusing mirrors [8]. The numerical simulation using 2D elliptic focusing mirrors is carried out and clear spin echo signal and neutron intensity increased with the wide acceptance of beam divergence [9]. The sample size is smaller than 5mm with high resolution and it is difficult to realize ideal 2D elliptic focusing mirrors. However, recent supermirror development progress rapidly and it is effective correction device even in use of polygonal shape 2D elliptic focusing mirror [10]. It is, to our knowledge, best way to satisfy high resolution and brightness. One of big advantage of short pulsed neutron source, such as J-PARC, is very low background by using time resolving technique. On the contrary, the total neutron intensity is not special; it is same with JRR-3 reactor. When we use longer wavelength with large sample size, the advantage becomes small. Thus we determined that the design of VIN ROSE and BL06 beam line is dedicated for small sample. 2. BL06 beam line for VIN ROSE Fig. 2 Schematic top view of VIN ROSE beam line at BL06 at J-PARC/MLF. Figure 2 shows schematic top view of BL06 beam line at the cold coupled H 2 moderator of the J-PARC. Neutrons from the moderator are transported by a straight m=2 supermirror guide in which cross-section of 10 cm 10 cm in the shutter(z= m) and biological shielding (z= m), where z indicates a distance from the moderator. At the position of z=7.3 m, the neutron beam is separated into supermirror guides for MIEZE and NRSE spectrometer. The BL06 experimental space is also very limited and these curved guides role to create experimental space for two spectrometers and transport optimized neutron beam. The radius of curvature of both guides is 140 m and characteristic wavelength of MIEZE and NRSE are 2.9 and 4.9 Å, respectively. MIEZE and NRSE guides consist of two and three parts to install band-chopper and neutron optical elements, respectively. The number of band-chopper is less than two for each beam line and unneeded

4 Masahiro Hino et al. / Physics Procedia 42 ( 2013 ) Table 1. The parameter of neutron guide for MIEZE and NRSE Schematic at BL06 at J-PARC/MLF. Guide parameter NRSE MIEZE Length (a) 4.7m(z=7.3-12m),(b) 4.8m(z= m), (c) 5.4m(z= m) (a) 4.7m(z=7.3-12m), (b) 4.8m(z= m) Radius 140m 140m Supermirror m=2.5 m=3 Cross section width:30 mm, height: mm width:15 mm, height:50mm Focus (polygonal elliptic) vertical:(a),(b),(c); major axis:11.8m,minor axis:60 mm horizontal:(c);major axis:3.5 m,minor axis:25mm - long wavelength in high order frame is eliminated by frame overlap mirror which consist of m=3 supermirror on silicon wafer in thickness 0.3mm. It is important for high resolution measurement to transport longer wavelength neutrons as much as possible. In NRSE beam line, the cross section of neutron beam is large as much as possible. The all vertical component are polygonal elliptical shape and horizontal component of last guide part is also polygonal elliptical shape. The detailed parameter of each guide is shown in Table1. By using curved guide tube, unneeded fast neutrons and gamma rays from the source are stopped by an iron beam dump placed between the two guides. BL06 area should be covered with concrete walls. Each neutron guide is covered by B 4 C rubber sheet and iron block to reduce the concrete and create experimental space as large as possible. As shown in Fig.3, the dose rate and neutron background at experimental space are dramatically decreased. Numerical simulations of the beam line are done by using PHITS [11]. Neutron intensity is expected to be about n/cm 2 /s/ Å at each guide exits, and peak wavelength are 3.5 and 5.2 Å for MIEZE and NRSE respectively in case of 1MW operation [12]. Fig. 3 The top view of BL06 guide geometry (left) and the dose level (right) calculated by PHITS. Supermirror is most important key component of neutron guide tube and it is deposited on silicon substrate in thickness 3mm. All BL06 supermirrors will be fabricated by KUR-IBS machine. The total length of the guide tube is about 29 m and the size of deposition area is very important when we fabricate neutron guide tube. Ion beam sputtering (IBS) technique enables us to fabricate smooth layer structure with sharp edge and we have succeeded in fabricating m>5 supermirrors and very small d-spacing multilayer [13]. The maximum substrate area at our KUR-IBS machine was limited to 200 mm in diameter. On the other hand, the maximum substrate area at JAEA is 500 mm in diameter. It is enough large to fabricate neutron guide tube and they are producing a lot of supermirrors for J-PARC project [14]. Figure 4(a) shows photograph of new substrate holder for fabrication of the BL06 guide tube at J-PARC. The diameter of substrate holder is 460 mm and the deposition

140 Masahiro Hino et al. / Physics Procedia 42 ( 2013 ) 136 141 area is limited by the size of process vacuum chamber. Figure 4(b) shows reflectivity by NiC monolayer and m=2.

5 140 Masahiro Hino et al. / Physics Procedia 42 ( 2013 ) area is limited by the size of process vacuum chamber. Figure 4(b) shows reflectivity by NiC monolayer and m=2.5, 3 supermirror on the silicon wafer, respectively. The wafer is placed on three points, top, center, Fig. 4 The photograph of substrate holder for (a) NRSE and (b) MIEZE installed to the KUR-IBS machine, respectively. (c) Measured and theoretical reflectivity of NiC monolayer, m=2.5, 3 supermirror deposited on silicon f bottom on the substrate holder. The center means middle of circle (substrate holder), top and bottom is about 200 mm outer from the center. The measurement was carried out at Time-Of Flight (TOF) instrument installed at CN-3 beam port at KUR. These reflectivities at all points were better than theoretical values in PHITS. We succeeded in fabrication of large scale neutron supermirror with high reflectivity for real neutron guide. We will finish to fabricate all mirror and measure reflectivities of them at FY2012. We are going to install neutron guide to observe first MIEZE signal in FY2013. Acknowledgements The construction of BL06 beam line was supportted by the Neutron Scattering Program Advisory Committee of IMSS, KEK (Proposal No. 2009S07). The development of spectrometer was also supported by the interuniversity program for common use JAEA and KURRI and financially by the program of Development of System and Technology for Advanced Measurement Analysis (SENTAN), JST. The key technique of multilayer fabrication was improved by Grant-in-Aid for Scientific Research Grant Nos , of JSPS. References [1] F.Mezei, Z.Phys 255(1972)146. [2] R. Golub and R. Gähler, Z. Phys.B65(1987) 269. [3] R. Gähler, R. Golub and T. Keller, Physica B (1992) 899. [4] M.Kitaguchi, M.Hino, Y.Kawabata, S.Tasaki, H.Hayashida, R.Maruyama, T.Ebisawa,Physica B404(2009) [5] H Hayashida, M Hino, M Kitaguchi, Y Kawabata, N Achiwa, Meas. Sci. Technol. 19 (2008) [6] F. Mezei, ed., Neutron Spin Echo, Lecture Notes in Physics 128 (Springer, Heidelberg, 1980) 178, [7] M. Monkenbusch, R. Schatzler, D. Richter, Nucl. Instrum..Methods A399 (1997) 301. [8] M.Bleuel, F.Demmel, R.Gähler, R.Golub, K.Habicht, T.Keller,S.Klimko,I.Köper,S.Longeville,S.Prokudaylo, F. Mezei, C.pappas,T.Gutberlet, eds.,lecture Notes in Physics,vol.601(Springer,Berlin,2003)176.

6 Masahiro Hino et al. / Physics Procedia 42 ( 2013 ) [9] M.Kitaguchi, M.Hino, Y.Kawabata, S.Tasaki, R.Maruyama, T.Ebisawa,Physica B406(2011) [10] T.Oda, M.Hino, M.Kitaguchi, Y.Kawabata, in this conference paper. [11] H.Iwase, K.Niita and T.Nakamura. J. Nucl. Sci.Technol., 39 (2002)1142. [12] T.Oda, M.Hino, et. al., to be published in PNST. [13] M.Hino, H.Sunohara, Y.Yoshimura, R.Maruyama, S.Tasaki, H.Yoshino and Y.Kawabata., Nucl. Instrum..Methods A574 (2004)292. [14] R.Maruyama, D. Yamazai, T. Ebisawa, M. Hino, and K. Soyama, Physica B (2006)1256.

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