S. Arai

Construction and beam tests of a 25.5 MHz split coaxial RFQ for radioactive nuclei

Abstract A 25.5 MHz split coaxial RFQ with modulated vanes has been constructed at INS. The RFQ will accelerate radioactive nuclei with a charge-to-mass ratio greater than 1 30 from 2 to 172 keV/u. The cavity, 0.9 m in inner diameter and 8.6 m in length, comprises four unit cavities, each of which comprises three module cavities further. The modulated vanes have been made by using both of a three-dimensional cutting technique and a two-dimensional one, the former for the first unit cavity, and the latter for the other ones. The transverse radius of curvature of the vane-tip is variable along the beam axis in a low-energy part, and constant in a high-energy part (the boundary at 1.1 m down from the RFQ entrance). The vanes have been aligned with an error less than ± 40 μm before installation in the unit cavities. After completion of the four unit cavities, they have been aligned with an error less than ± 50 μm on the floor of an accelerator room. Low-power tests after cavity-tuning show that the longitudinal voltage flatness and the azimuthal field balance are better than ± 1%, the resonant frequency is 25.46 MHz, and the unloaded Q-value is 5800, corresponding to a resonant resistance of 22 kΩ. We have achieved so far the goal intervane voltage of 109 kV at a duty factor of 15%. Through acceleration tests with N+ ions, we have obtained the following results: the output-beam emittances are well in the design ellipses of 0.06π cm mrad normalized; the data of transmission efficiency versus intervane voltage agree well with PARMTEQ results and the transmission at the nominal voltage is measured to be 90%.

New ISOL-based radioactive nuclear beam facility at INS

Abstract An ISOL-based radioactive nuclear beam facility is just about to come into operation at INS. The present status of the INS radioactive nuclear beam project is reported. The capability of the facility and possible experiments are also discussed, including research programs of nuclear physics and nuclear astrophysics.

Development of an SCRFQ heavy-ion linac for RI beams

Abstract A split coaxial RFQ (SCRFQ) is being developed to accelerate RI beams from 1 to 170 keV/u as part of the Japanese Hadron Project (JHP). Our SCRFQ is equipped with modulated vanes. On the basis of the studies on a cold model and a proton accelerating one, a 25.5 MHz prototype for the JHP SCRFQ has been constructed. The prototype, consisting of three module cavities, is 2.1 m in length and 0.9 m in inner diameter, and accelerates ions with a charge-to-mass ratio (q/A) greater than 1 30 from 1 to 45.4 keV/u. The unloaded Q-value of the cavity is 6400, corresponding to about 84% of the calculated value, and the field imbalance between vanes is within ±0.6%. The designed intervane voltage of 109 kV for ions with q/A = 1 30 is achieved with a 70 kW peak power. By using ions of three species, N2+, N+ and Ne+, acceleration tests are conducted. The transmission efficiency attained with a N+ beam is better than 80% at normalized intervane voltages higher than 1.2.

Beam test results of the INS RFQ/IH linac

A linac complex for radioactive beams has been constructed at INS, which comprises a 25.5-MHz split coaxial RFQ (SCRFQ) with modulated vanes and a 51-MHz interdigital-H (IH) linac . The SCRFQ accelerates ions with a charge-to-mass ratio (q/A) greater than 1/30 from 2 to 172 keV/u. The beam from the SCRFQ is charge-stripped by a carbon-foil, and is transported to the IH linac through two magnetic-quadrupole doublets and a 25.5-MHz rebuncher cavity. The IH linac accelerates ions with a q/A greater than 1/10, and the output energy is variable in the range of 0.17 through 1.05 MeV/u. Beam tests of the linac complex performed with N ions show that the output beam energy and transmission efficiency agree well with predictions.

Development of a split coaxial RFQ at INS

Abstract A split coaxial RFQ with modulated vanes is being developed at INS for acceleration of the unstable and stable nuclei with a charge-to-mass ratio large

Status of the RNB facility at INS

A Radioactive beam facility using a thick target, an ISOL and heavy ion linacs will soon come into operation at INS, University of Tokyo. The status of the project together with experimental programs are reported.

First beam tests of the INS split coaxial RFQ for radioactive nuclei

A 25.5-MHz split coaxial RFQ has come into operation at INS. This linac was designed so as to accelerate ions with a charge-to-mass ratio greater than 1/30 from 2 to 172 keV/u. The maximum intervane voltage so far achieved is 91 kV. We have conducted acceleration tests by using Ne/sup +/ and N/sup +/ ions. Through N/sup +/ acceleration we obtained the following preliminary results. The output-beam emittances are well in the design ellipses of 0.06 /spl pi/ cm/spl middot/mrad (normalized). The data of transmission efficiency vs intervane voltage agree well with PARMTEQ results. The transmission at the nominal voltage is measured to be 90%.

Beam matching section in the INS heavy ion linac complex

The beam transport system between a 25.5-MHz split-coaxial RFQ and a 51-MHz interdigital-H linac has been designed. This transport system is composed of a charge stripper, a 25.5-MHz rebunching cavity and two quadrupole doublets. A 170-keV/u beam passes through the stripper and its charge state is increased up to a charge-to-mass ratio greater than 1/10. The rebuncher causes an aberration of the longitudinal beam profile due to its non-linear accelerating field. In order to contain the distorted beam profile by the aberration in the acceptance of the IH, the rebunching cavity must be operated at 25.5 MHz. We have carried out a beam trace by taking account of the aberration and the effects of the increase of the charge state, the energy-loss, the straggling and the scattering in the stripper, and compared its results with the design assuming a linear system.<<ETX>>

Interdigital-H linac for unstable nuclei at INS

In the prototype facility of the Exotic-arena at INS, unstable nuclei with a charge-to-mass ratio greater than 1/10 are accelerated from 170 to 1046 keV/u by an interdigital-H linac. The designed IH linac consists of four acceleration tanks and three sets of quadrupole triplets placed between tanks. Output energy is continuously variable by changing the rf power and phase of the last operating tank. A high shunt impedance is expected from an equivalent circuit analysis. The rf measurement on the low power models is now in progress. Preliminary results of the tank-4 model shows that a resonant frequency and a shunt impedance roughly agree with the design values.<<ETX>>

A heavy ion linac complex for unstable nuclei

A heavy ion linac complex for unstable nuclei is under construction at INS. The linac complex consists of a 25.5-MHz split coaxial RFQ (SCRFQ), a charge-stripper section and a 51-MHz interdigital-H (IH) linac. The SCRFQ with modulated vanes, 0.9 m in diameter and 8.6 m in length, accelerates ions with a charge-to-mass ratio (q/A) greater than 1/30 from 2 to 170 keV/u. The stripper is a carbon foil. The IH linac, 1.34 m in diameter and 5.54 m in total length, comprises four cavities and three magnetic quadrupole triplets placed between cavities, accelerates ions with q/A/spl ges/1/10 and varies the output energy continuously in the range 0.17/spl sim/1.05 MeV/u. The duty factor of the linac complex is 30% for q/A=1/30 ions.<<ETX>>