Figure correction of a metallic ellipsoidal neutron focusing mirror

Abstract

An increasing number of neutron focusing mirrors is being adopted in neutron scattering experiments in order to provide high fluxes at sample positions, reduce measurement time, and/or increase statistical reliability. To realize a small focusing spot and high beam intensity, mirrors with both high form accuracy and low surface roughness are required. To achieve this, we propose a new figure correction technique to fabricate a two-dimensional neutron focusing mirror made with electroless nickel-phosphorus (NiP) by effectively combining ultraprecision shaper cutting and fine polishing. An arc envelope shaper cutting method is introduced to generate high form accuracy, while a fine polishing method, in which the material is removed effectively without losing profile accuracy, is developed to reduce the surface roughness of the mirror. High form accuracy in the minor-axis and the major-axis is obtained through tool profile error compensation and corrective polishing, respectively, and low surface roughness is acquired under a low polishing load. As a result, an ellipsoidal neutron focusing mirror is successfully fabricated with high form accuracy of 0.5 μm peak-to-valley and low surface roughness of 0.2 nm root-mean-square.

A Focusing Test of a Multiple Segmented Ellipsoidal Neutron-Focusing Mirror for a Compact-Focusing SANS Instrument

“…The fabrication method of the mirror segments was the same as that proposed in our previous work [9,10,11]. To efficiently process an ellipsoidal figure, a milling process was employed before the ultra-high precision cutting (UPC) process.…”

“…It is therefore able to install them even at a place close to the neutron source, which enables focusing from the upper stream of the beam line to utilize the emitted neutrons more efficiently [7]. A metal substrate made with electroless nickel-phosphorus (NiP) plating is a good candidate for producing optical devices because of its amorphous structure, good machinability and hardness, and capability of being applicable to mostly any type of substrate material [8,9,10].…”

Precision Mechanical Design of 900 mm Long Ellipsoidal Neutron-focusing Supermirror for VIN ROSE at J-PARC/MLF

“…The polishing ends when the surface roughness fall below 5 Å rms , which is sufficiently smooth for supermirror deposition. Details on this polishing process are given in [4,13,14]. The substrates with polished ellipsoidal surfaces are then coated with supermirrors at KURRI-IBS, whose details are found in [15].…”

“…We chose this because necessary elemental techniques are already established in the earlier studies by our group. In terms of substrate preparation, the figuring and polishing methods for partial ellipsoids on surfaces coated with phosphorousrich electroless nickel (Ni-P) plating has been reported [13,14]. The plating is amorphous; thus, it provides surfaces with sub-nanometer roughness when polished, which is sufficiently smooth for supermirror deposition.…”

Profile measurement of a bent neutron mirror using an ultrahigh precision non-contact measurement system with an auto focus laser probe

“…It can also increase the signal rate and improve resolution. Some techniques have previously been reported for fabricating neutron focusing mirrors such as numerically controlled local wet etching (NC-LWE), ultraprecision shaper cutting and fine polishing, bending technique and electroformed nickel replication [6][7][8][9][10][11][12][13][14][15][16]. Compared with other methods, the bending technique is simpler and more time-efficient from the viewpoint of cost-benefit performance.…”