Kei3 source

HIMAC

NIRSDevelopment of a compact ECR ion source

for various ion production

Abstract There is a desire that a carbon-ion radiotherapy facility will produce various ion species for fundamental research. Although the present Kei2-type ion sources are dedicated for the carbon-ion production, a future ion source is expected: 1) carbon-ion production for medical use, 2) various ions with a charge-to-mass ratio of 1/3 for the existed linac injector, and 3) low cost for modification. A prototype compact electron cyclotron resonance (ECR) ion source, named Kei3, based on Kei series has been developed to correspond to produce these various ions at National Institute of Radiological Sciences (NIRS). The Kei3 has an outer diameter of 280 mm and a length of 1120 mm. The magnetic field is formed by the same permanent magnet as Kei2. The movable extraction electrode has been installed in order to optimize the beam extraction with various current densities. The gas-injection side of vacuum chamber has enough space for an oven system or two-frequency microwave feeding.

Design concept of Kei3

Requirement to new source (Kei3)

CSD of Ne With gas mixing

Distance between plasma electrode and puller

Microwave frequency dependence Dependence of extraction voltage Optimal distance of electrode

M. Muramatsu1, A. Kitagawa1, S. Hojo1, Y. Iwata1, S. Sato1, K. Katagiri1, Y. Sakamoto1, N. Takahashi2, N. Sasaki3, K. Fukushima3, K. Takahashi3, K. Oshima4, T. Uchida4, Y. Yoshida4, Y. Kato5, S. Biri6, and A. G. Drentje1

1National Institute of Radiological Sciences (NIRS), 4-9-1 Anagawa, Inage, Chiba 263-8555, Japan 2Sumitomo Heavy Industries, Ltd., 19 Natsushima, Yokosuka, Kanagawa 237-8555, Japan

3Accelerator Engineering Corporation, 3-8-5 Konakadai, Inage, Chiba 263-0043, Japan 4Toyo University, 2100 Kujirai, Kawagoe, Saitama 350-0815, Japan 5Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan

6Institute of Nuclear Research (ATOMKI), H-4026 Debrecen, Ben ter 18/c, Hungary

Various ion production • H3

+ to Fe13+, H to Ne ion beam for biological experiment like an irradiation of mouse, Ar and Fe beam for irradiation of cell and physical experiment.

Improvement of beam intensity

• Charge to mass ratio of ion is up to 1/3, because, we don’t want to change the injector linac.

• Ion production from solid material. • Kei series were designed for production of C4+ ions. Therefore, it is difficult to

produce enough intensity of heavier ions and molecule ions.

Low cost • A change of expensive parts (magnets and microwave system) is not made so that it can

upgrade from the existing compact source easily.

Requirement values of various ion

Ion Required intensity [emA]

Kei2 intensity [emA]

material

H3+ 500 270 H2 gas

3He+ 300 He gas, 50% 3He 7Li3+ 100 ? 11B4+ 100 120 C2H12B10

12C4+ 200 680 CH4 gas 14N5+ 200 N2 gas 16O6+ 200 60 O2 gas 19F7+ 100 SF6 gas 20Ne7+ 100 Ne gas

• Low cost -> Same microwave system as the KeiGM

(9.75 – 10.25 GHz, 750 W) -> Same magnet as the KeiGM

• Improvement from existing Kei series for various ion productions

-> improvement of insulation (increase the extraction voltage) -> improvement of vacuum in extraction region (high voltage

extraction) -> movable extraction system (various extraction current

densities) -> 2 bottle of gas for gas mixing -> 2 waveguide for double frequency heating

• Ion production from solid material -> MIVOC method -> evaporator (resistance heating oven, induction heating oven)

Specifications •Ion source

Diameter 280 mm

Length 1120 mm

•Mirror magnets

Material NdFeB

Max. field strength (extraction side) 0.579 T

Max. field strength (gas injection side) 0.876 T

Minimum B strength 0.260 T

•Hexapole magnet

Material NdFeB

Maximum field strength

on the chamber surface 0.757 T

Length 105 mm

Inner diameter 58 mm

•Microwave

Amplifier TWTamp.

Frequency 10 - 18 GHz

Maximum power 250 W

Operation mode pulse/CW

High voltage

Kei3 with High voltage platform

Puller and Einzel lens

Puller and downstream vacuum chamber

waveguide and upstream vacuum chamber Kei3 source

Beam tests The ion source is being operated at a test stand. It consists of an analyzing magnet, four monitor boxes for Faraday cups, horizontal slits, an emittance monitor, and two vacuum pumps (500 l/s turbo molecular pomp). In order to study the basis performance of the source, a beam test is being conducted using CH4 and Ne gas. In order to know the basis performance of Kei3, dependence of the operation parameters were checked. The tuning parameters of the source are the gas flow, microwave power, microwave frequency, biased disk voltage, and its position. In this time, following operation parameters were checked, microwave frequency, extraction voltage, distance between the plasma electrode and puller, gas mixing effect.

Test stand for Kei3

Conclusion and next step We developed new compact ECR ion source, named Kei3, for various ion production. Preliminary beam test was already finished at test stand. The maximum beam intensity of C4+ and Ne7+ were 206 emA and 7.8 emA under an extraction voltage of 15 kV. We will test some improvement technique for increase the beam intensity. 1) increase the extraction voltage up to 30 kV, 2) optimization of extraction system, 3) increase the microwave power, 4) gas mixing method, and 5) two-frequency microwave feeding.

Cover for plasma chamber

Microwave: 10 GHz, 10 W, CW Microwave: 9.99 GHz, 10 W, CW

First plasma (2013.03.27) Gas: air (with leak) Vac.: 1.2e-2 Pa (upstream) 1.7e-2 Pa (downstream)