Prise winners list

Free-oxygen copper electroforming and electrolytic polishing are used to treat the inner surface of J-PARC's high-intensity proton accelerator

Kamigyo-ward, Kyoto Prefecture (Gifu Anpachi Factory: Anpachi-machi, Gifu Prefecture)
Asahi Metal Industry Co., Ltd.
Other award winners
Takaaki Matsuoka, Takashi Yoshida
Recommended by
Asahi Metal Industry Co., Ltd.

Tsujimoto Katsuya  (45)
Process Technology Dept., Director

Although we handled this product for the first time, we had to obtain good results in only one try and had to endure great pressure.

An elementary particle accelerator is used in the nuclear physics to resolve the mystery of universe's creation and in the substance study in nanometer level. Different from an accelerator for electrons that have small mass, for a proton accelerator, it is necessary to generate a strong magnetic field by flowing high current to accelerate heavy protons up to near the velocity of light. For the high-intensity proton accelerator constructed in the Japan Proton Accelerator Research Complex (J-PARC) Center in Tokai-mura, Ibaragi Prefecture, oxygen-free copper electroforming and electrolytic polishing have been performed to treat the inner surface of the accelerating cavity (liniac: straight section) in order to minimize the electric resistance and the heat generation. Asahi Metal Industry Co., Ltd. performed that treatment. The superior technology of this company was indispensable to manufacture J-PARC's high-intensity proton accelerator that has the top-level performance in the world.


Exploring the uncharted territory where pure copper is electroformed on the inner surface of a 3-ton accelerating tube

In nuclear physics, an accelerator is used for an experiment to accelerate the elementary particles such as electrons and protons up to near the velocity of light and collide them. In Japan, the High Energy Accelerator Research Organization and the Japan Atomic Energy Agency jointly constructed a high-intensity proton accelerator in the Japan Proton Accelerator Research Complex (J-PARC) in Tokai-mura, Ibaragi Prefecture and started test operation in 2007. The various factors influence the performance of this accelerator, but the inner surface condition of the accelerating tube is very important. 

It is necessary to flow high current into the accelerating tube and generate a strong magnetic field to accelerate heavy protons, which are different from electrons having small mass. Therefore the conductivity of the inner surface of accelerating tube must be enhanced to the maximum to minimize heat generation and the inner surface must be polished carefully just like a mirror surface to regulate the magnetic flux. This company started its test and research in 1996 and its results were highly appreciated. As a result, it received an order from the J-PARC to treat the inner surface of the accelerating cavity (liniac: straight section) in the high-intensity proton accelerator. 

Briefly speaking, "electroforming" is "thick electroplating". A subject product is submerged into a solution where metal ions are solved and electric current is flowed with the subject product used as a cathode to reduce the metal ions and lay them on the product surface. If the metal ions are laid thickly on the surface, it is electroforming, and if they are laid thinly, it is electroplating. Oxygen-free copper electroforming is electroforming of highly-pure copper, which is in the level of oxygen-free copper. 

"In usual bright copper electroforming, organic substances remain on the surface and they gasify and become impure substances when vacuumizing the interior of the accelerator cavity. In oxygen-free copper electroforming, however, no gas is generated and vacuumization can be performed easily. In addition, by using the oxygen-free copper electroforming, we have obtained the electric conductivity 1.3 times as high as that in the conventional bright copper electroforming."

Since the accelerating tube that flows high current generates heat, the cooling water is flowed through the interior and is exposed to radiation and so the wastewater must be treated properly. However, when the conductivity of accelerating tube is high (electric resistance is low), heat generation is reduced and only small amount of cooling water is required.

For the accelerating tube, we joint 9 pieces of a 3m diameter and 3-ton tube and 20 pieces of a 1.5m diameter and 1.5-ton tube in series to construct one tunnel. However, this company had not so far performed copper electroforming for such a subject as heavy as 3 tons.
"First of all, we did not have a water tank for submerging such a gigantic item. Therefore we started from constructing a new dedicated factory." The biggest problem for this project was that the subject product was so large and heavy.

Only one test dummy was available. However, we completed the work for which no error is allowed within four years.

We had to prepare new large-scale equipment to construct a gigantic tank for water quantity of 15 tons and prepare the dedicated jigs to install a crane for lifting the accelerating tube. In the case of a usual small product, we can use tens of test dummy to find the best method. However, only one test dummy was prepared for the accelerating tube this time. 
"The technology had to be almost completed before actually testing the test dummy. We had to obtain good results in only one try and so had great pressure." 
In addition, electroforming is not the only work necessary for the accelerating tube. The inner surface of accelerating tube must be polished smoothly like a mirror surface because the smoother the surface is, generation of magnetic filed can be regulated the better. However, ordinary polishing with abrasive powder is not good enough and so electrolytic polishing is conducted. In this polishing, current is flowed in the direction opposite to that in the electroforming to melt and smooth the electroformed layer surface. The process from the electroforming to the electrolytic polishing is performed in a series of operations. 
Although a partial defect was found in our test using the test dummy, fortunately it was a minor defect that could be corrected in our final work. We started our work for the actual accelerating tubes in April 2000. It took us about four weeks to finish one accelerating tube, and we completed all the works four years later in Oct. 2004. 
"We did not make any major mistake and really felt relief when we had completed all the works. Test operation of the accelerator is already started, and the senior officials of J-PARC said, 'Your accelerator performs far better than those produced overseas', and we felt really happy."

Japan has been leading other countries in the nuclear physics since the late Hideki Yukawa won a Nobel Prize with his particle physics theory, and the technology of Japanese companies supports the prominence of our country in this field behind the scenes.

Asahi Metal Industry Co., Ltd.

Jun. 1948
99.5 million yen
225 (as of Dec. 2009)
Brief information:
Expanded its business to perform surface treatment (plating and electroforming) of parts for aircraft and space industry in 1976. Currently the company is performing R&D in the field of new energy.

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A water tank for water quantity of 15 tons was constructed to perform copper electroforming for the accelerating tubes. This tank is now used for other products.


Protons run through the center hole of cylinder and are accelerated by strong magnetic field generated by the coil around it. The line in the upper part is the pathway for the cooling water. The line is made by attaching wax during electroforming.


A 0.6mm thick pure copper layer is electroformed on the inner surface of accelerating tube. The inner surface is mirror-like finished in electrolytic polishing. In this method the surface can be polished far better than the method using polishing power.