Yasushige Yano

A Compton camera for multi-tracer imaging

A high-energy resolution Compton camera consisting of two segmented Ge detectors is proposed for multitracer research. The basic parameters affecting its spatial resolution are described. Monte Carlo simulations were performed to optimize the detector system. Its suitability for multitracer technology was demonstrated by a test experiment.

Gamma-Ray Compton Imaging of Multitracer in Biological Samples Using Strip Germanium Telescope

The feasibility of using a Compton camera for multitracer imaging has been demonstrated with the results of two biological sample imaging experiments. The distribution of the multitracer administered to a soybean sample and a tumor-bearing mouse has been visualized for each nuclide simultaneously. Three-dimensional images of the multitracer have been obtained even though the samples were measured from a fixed direction.

First results from the new RIKEN superconducting electron cyclotron resonance ion source (invited)a)

The next generation heavy ion accelerator facility, such as the RIKEN radio isotope (RI) beam factory, requires an intense beam of high charged heavy ions. In the past decade, performance of the electron cyclotron resonance (ECR) ion sources has been dramatically improved with increasing the magnetic field and rf frequency to enhance the density and confinement time of plasma. Furthermore, the effects of the key parameters (magnetic field configuration, gas pressure, etc.) on the ECR plasma have been revealed. Such basic studies give us how to optimize the ion source structure. Based on these studies and modern superconducting (SC) technology, we successfully constructed the new 28 GHz SC-ECRIS, which has a flexible magnetic field configuration to enlarge the ECR zone and to optimize the field gradient at ECR point. Using it, we investigated the effect of ECR zone size, magnetic field configuration, and biased disk on the beam intensity of the highly charged heavy ions with 18 GHz microwaves. In this article, we present the structure of the ion source and first experimental results with 18 GHz microwave in detail.

Intense beam production from RIKEN 18 GHz ECRIS and liquid He free SC-ECRISs

Intense beams of heavy ions with medium charge states (1.3 mA of Ar8+, 200 μA of Xe20+) have been produced from a RIKEN 18 GHz electron cyclotron resonance ion source (ECRIS) using various kinds of techniques, e.g., utilization of an aluminum cylinder and a biased disk, and optimization of the plasma electrode position. Furthermore, we have recently constructed two superconducting ECRISs (operational frequencies of 14 and 18 Hz) which have unique characteristics, i.e., they do not need liquid He to obtain the superconductivity of solenoid coils and utilize the G–M refrigerator instead. These sources are suitable to generate intense beams of heavy ions with very high charge states. We obtained 10 μA of Xe30+, 5 μA of Xe33+, and 1.5 μA of Xe36+ at a radio frequency power of 700 W (14 GHz microwave) without using the gas mixing method. Through various experiments, we confirmed that not only the magnetic field strength and microwave power but also the characteristics of the plasma chamber surface play the ess...

Production of highly charged ions in the RIKEN 18 GHz ECR ion source using an electrode in two modes

Abstract We placed an axially movable electrode into the plasma chamber of the 18 GHz RIKEN ECR ion source in order to produce higher intensity of multiply charged ions and to study how the electrode effects the highly charged ion (HCI) production. We found that the effect of the electrode strongly depends on the local plasma parameters, mainly on the electrode initial floating potential. At lower floating potential, we need to increase the plasma density by means of biasing the electrode and injecting electrons into the plasma. The electrode operates as an electron source (Electron Donor or ED mode). At higher floating potential, the electrode works by changing the plasma potential. The best result is obtained when the electrode remains at floating potential (Plasma Tuner or PT mode). These two modes were checked and successfully found both in the continuous and in the pulsed mode operation. In both (ED and PT) modes, we generated higher HCI currents than without the electrode. In the PT mode, we successfully obtained 300 eμA of Ar11+ at 15 kV extraction voltage.

Effect of minimum strength of mirror magnetic field (Bmin) on production of highly charged heavy ions from RIKEN liquid-He-free super conducting electron–cyclotron resonance ion source (RAMSES)

Abstract We measured the beam intensity of highly charged heavy ions (O, Ar and Kr ions) as a function of the minimum strength of mirror magnetic field (Bmin) of the RIKEN liquid-He-free super conducting electron–cyclotron resonance ion source. In this experiment, we found that the optimum value of Bmin exists to maximize the beam intensity of highly charged heavy ions and the value was almost the same ( ∼0.49 T ) for various charge state heavy ions.

Construction of a variable-frequency radio-frequency quadrupole linac for the RIKEN heavy-ion linac

A new type of variable-frequency radio-frequency quadrupole (RFQ) linac has been constructed as a new preinjector for the RIKEN heavy-ion linac (RILAC). The RFQ resonator, based on a folded-coaxial structure with a movable shorting plate, is compact even in a low frequency region below 20 MHz. It accelerates ions with mass-to-charge ratios of 5.3 to 26.4 in the energy range up to 450 keV per charge, by varying its resonant frequency from 17.4 to 39.0 MHz. Moreover, the power loss is small in the low frequency region; the rf power consumption in cw mode is 7 kW at 17.4 MHz, and it increases to 30 kW at 39.0 MHz at the maximum intervane voltage of 36.8 kV. We initiated this project in 1991, and installed the new preinjector consisting of an electron cyclotron resonance ion source of 18 GHz and this RFQ in 1996. Since the installation, the beam intensity has become larger by more than 1 order of magnitude than that formerly obtained with the Cockcroft–Walton preinjector. Recently, the maximum power of the be...

Plasma buildup by short-pulse high-power microwaves

The buildup of a plasma produced by short-pulse (0.05–1.2 μs), high-power (60–100 kW) microwaves is studied in a pressure range of 10 mTorr–10 Torr, by measurements of the temporal variation of the current and the optical intensity. The plasma is produced in a cylindrical tube and confined by a minimum-B field. The buildup of the electron current and the optical intensity are found to continue beyond the end of the pulse, for a few to tens of μs depending upon the pressure, and a minimum in their peak values and buildup times occur around 1 Torr. Increase in microwave pulse duration increases the buildup rate and peak current, whereas the pulse repetition frequency (10–500 Hz) has only a weak influence. The results are discussed from the growth of electron temperature during the pulse, and the following plasma evolution after the end of pulse. Collisional wave absorption, electron cyclotron heating, and diffusion are found to play important roles in plasma production and maintenance over the pressure range.

Electron cyclotron resonance ion source developments in RIKEN (invited)

We have constructed four high performance electron cyclotron resonance (ECR) ion sources in RIKEN and produced a variety of intense beams of heavy ions (e.g., 2 emA of Ar8+, 0.6 emA of Kr13+, 0.3 emA of Xe20+). During the improvement of their performance, we found that several key parameters play essential role on increasing the beam intensity. The parameters are plasma electrode position, magnetic field configuration, property of the chamber wall material and position of a biased disk. To investigate how the parameters influence on the beam intensity, we made a systematic study using the laser ablation method. In these experiments, we observed that Bmin influences the electron density and confinement time of ECR plasma.

Improvement of RIKEN 18 GHz Electron Cyclotron Resonance Ion Source using Aluminum Tube

We measured the beam intensity of highly charged argon and krypton ions covering the inner wall of a plasma chamber with an aluminum tube. The beam intensity was enhanced strongly and gas mixing was found to be unnecessary.