ICHIRO Cavity and three young scientists (left to right): Daizo Iwai, Juho Hong, and Fumio Furuta.

On 13 June, an ICHIRO single cell cavity achieved a world record accelerating gradient of 53.5MV/m (megavolts per meter) at KEK.

The traditional design of cavities pays attention to maintaining a low electric field on the niobium surface, while achieving a high accelerating field gradient on the cavity axis. Some scientists believe, however, that the limit could actually be given by the high surface current on the surface of the niobium, which is determined by the surface magnetic field. Kenji Saito of KEK is one of the most outspoken advocates of this conjecture. Based on this belief, KEK co-developed a new shape of cavity with Jacek Sektuwicz of DESY known as the ICHIRO cavity, which is an outgrowth of the Low-Loss (LL) cavity concept that was initially conceived at Jefferson Laboratory.

Saito checked the maximum surface magnetic field in the TESLA type cavities when they achieved their record of accelerating gradient. By optimising the curved shape inside the cavity, he and the collaborators came up with a cavity design that would produce a substantially higher accelerating gradient for the same the surface magnetic field. Testing out the theory, KEK built and measured several ICHIRO single cavities and achieved a world record accelerating gradient. (Based on a similar analysis but with different optimisation, a group at Cornell University, led by Hasan Padamsee, is also working on also reentrant shape cavities.

Cavity preparation technology requires complex processes, such as mechanical polishing by stones and water, chemical brightening, electric field polishing with a combination of chemical reactions and electrical reactions, and high tension cleaning with ultra pure water – all of which has been dubbed the KEK recipe. If you do not follow a recipe for cooking, your meal might not result in high quality cuisine. Similarly, if you do not follow the recipe for processing cavities, you cannot obtain a high accelerating gradient.

Three young scientists contributed to this world record. KEK's Fumio Furuta, a part-time teacher, said with excitement, "We did it again." Furuta, who has been engaged in ICHIRO cavity work since the early design stages, was also a member of the team who achieved the last world record at KEK (see NewsLine 15 September 2005). Furuta decided to join KEK's team in November 2004 after listening to an impressive lecture that Saito gave at Nagoya University in July 2004. "Cavities are a very important part of the accelerator, and it is good to get involved," he said. "I want to be present when the next record appears."

A student from Korea who came to KEK in May, Juho Hong of POSTECH witnessed the world record first-hand when he started measuring ICHIRO cavities within the last month. He said, "I did not realise at first that it was a world record." Hong was sent by Pohang Accelerator Institute (PAL) to study superconductivity RF cavities in Japan. He mainly does cavity simulations at PAL. At KEK, he will study the whole process for preparing superconducting RF cavities, including assembly, simulation, measurement, and making new single cell cavities.

Daizo Iwai, of Shimizu Mfg. Co., Ltd., the third young scientist in the group, is a joint researcher from industry. "I was very glad to be present at the achievement of this brilliant record," he said. Iwai also joined KEK in May. His aim is to build an accelerating cavity which has the highest quality and lowest cost. Working with some foreign colleagues at KEK for the first time, Iwai has had a very good experience so far. "It is not so easy to communicate with each other, but such an environment is stimulating and very enlightening," he said.

KEK's Takayuki Saeki, who has been studying superconducting RF cavities
with Saito since autumn 2004, thinks it is essential for the young generation to participate in the ILC. "ILC needs a lot of participation from the young generation. If not, it cannot come true," he said. There will be a bright future for these young people who work hard and stay involved in the ILC.

-- Nobuko Kobayashi