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This study aimed to develop a new method to quantitatively analyze body shape changes in patients during radiotherapy without additional radiation exposure using an optical surface tracking system. This method's accuracy was evaluated using a cubic phantom with a known shift. Surface images of three-dimensionally printed phantoms, which simulated the head and neck shapes of real patients before and after treatment, were used to create a deformation surface area histogram. The near-maximum deformation value covering an area of 2 cm

We aimed to predict the minimum distance between a tumor and the gastrointestinal (GI) tract that can satisfy the dose constraint by creating simulation plans with carbon-ion (C-ion) radiotherapy (RT) and photon RT for each case assuming insertion of virtual spacers of various thicknesses. We enrolled 55 patients with a pelvic tumor adjacent to the GI tract. Virtual spacers were defined as the overlap volume between the GI tract and the volume expanded 7–17 mm from the gross tumor volume (GTV). Simulation plans (70 Gy in 35 fractions for at least 95% of the planning target volume [PTV]) were created with the lowest possible dose to the GI tract under conditions that meet the dose constraints of the PTV. We defined the minimum thickness of virtual spacers meeting D2 cc of the GI tract

The accurate measurement of the 3D dose distribution of carbon-ion beams is essential for safe carbon-ion therapy. Although ionization chambers scanned in a water tank or air are conventionally used for this purpose, these measurement methods are time-consuming. We thus developed a rapid 3D dose-measurement tool that employs a silver-activated zinc sulfide (ZnS) scintillator with lower linear energy transfer (LET) dependence than gadolinium-based (Gd) scintillators; this tool enables the measurement of carbon-ion beams with small corrections. A ZnS scintillator sheet was placed vertical to the beam axis and installed in a shaded box. Scintillation images produced by incident carbon-ions were reflected with a mirror and captured with a charge-coupled device (CCD) camera. A 290 MeV/nucleon mono-energetic beam and spread-out Bragg peak (SOBP) carbon-ion passive beams were delivered at the Gunma University Heavy Ion Medical Center. A water tank was installed above the scintillator with the water level remotely adjusted to the measurement depth. Images were recorded at various water depths and stacked in the depth direction to create 3D scintillation images. Depth and lateral profiles were analyzed from the images. The ZnS-scintillator-measured depth profile agreed with the depth dose measured using an ionization chamber, outperforming the conventional Gd-based scintillator. Measurements were realized with smaller corrections for a carbon-ion beam with a higher LET than a proton. Lateral profiles at the entrance and the Bragg peak depths could be measured with this tool. The proposed method would make it possible to rapidly perform 3D dose-distribution measurements of carbon-ion beams with smaller quenching corrections.

Purpose To estimate relative biological effectiveness (RBE) ascribed to secondary fragments in a lateral distribution of carbon ion irradiation. The RBE was estimated with the microdosimetric kinetic (MK) model and measured linear energy transfer (LET) obtained with CR‐39 plastic detectors. Methods A water phantom was irradiated by a 12C pencil beam with energy of 380 MeV/u at the Gunma University Heavy Ion Medical Center (GHMC), and CR‐39 detectors were exposed to secondary fragments. Because CR‐39 was insensitive to low LET, we conducted Monte Carlo simulations with Geant4 to calculate low LET particles. The spectra of low LET particles were combined with experimental spectra to calculate RBE. To estimate accuracy of RBE, we calculated RBE by changing yield of low LET particles by ±10% and ±40%. Results At a small angle, maximum RBE by secondary fragments was 1.3 for 10% survival fractions. RBE values of fragments gradually decreased as the angle became larger. The shape of the LET spectra in the simulation reproduced the experimental spectra, but there was a discrepancy between the simulation and experiment for the relative yield of fragments. When the yield of low LET particles was changed by ±40%, the change of RBE was smaller than 10%. Conclusions RBE of 1.3 was expected for secondary fragments emitted at a small angle. Though, we observed a discrepancy in the relative yield of secondary fragments between simulation and experiment, precision of RBE was not so sensitive to the yield of low LET particles.

Radiochromic films are useful as dosimeters in high-precision radiotherapy owing to their high spatial resolution. However, when a particle beam is measured using a radiochromic film, the dose cannot be estimated accurately because the film darkness varies with variations in linear energy transfer (LET). This paper proposes a novel method for estimating the LET and the dose based on the film darkness. In this method, after a high-LET particle beam, such as a carbon-ion beam, was incident on the film, the film was digitized and its net optical density was determined. Further, the non-linearity of the film response curve between the dose and the darkness, depending on LET, was used. Then, calibration curves were created using 290 MeV u−1 mono energetic carbon-ion beams. We used LETs of 20, 50, 100, and 150 keV µm−1 and a physical dose of 2–14 Gy. The calibration curves were approximated for each LET using a quadratic function. The correlations between the coefficients of the quadratic function and the LET were also obtained. To verify the proposed method, the films were irradiated under 12 different conditions corresponding to various depths and doses. Four depths of −2, −5, −10, and −20 mm with respect to the Bragg peak, and three different preset values were used for the film measurements. The films were analyzed in four groups, where each group comprised films irradiated at the same depth. The LETs obtained from the film analysis, ordered from the upstream of the beam, were 20, 41, 56, and 97 keV µm−1, and the doses for the lowest preset value were 3.95, 4.07, 4.03, and 3.99 Gy for the four groups. The LETs obtained from the film analysis increased toward the Bragg peak, and the doses measured in the ionization chamber were almost equal to 4 Gy.

PURPOSE To estimate relative biological effectiveness (RBE) ascribed to secondary fragments in a lateral distribution of carbon ion irradiation. The RBE was estimated with the microdosimetric kinetic (MK) model and measured linear energy transfer (LET) obtained with CR-39 plastic detectors. METHODS A water phantom was irradiated by a 12 C pencil beam with energy of 380 MeV/u at the Gunma University Heavy Ion Medical Center (GHMC), and CR-39 detectors were exposed to secondary fragments. Because CR-39 was insensitive to low LET, we conducted Monte Carlo simulations with Geant4 to calculate low LET particles. The spectra of low LET particles were combined with experimental spectra to calculate RBE. To estimate accuracy of RBE, we calculated RBE by changing yield of low LET particles by ± 10% and ± 40%. RESULTS At a small angle, maximum RBE by secondary fragments was 1.3 for 10% survival fractions. RBE values of fragments gradually decreased as the angle became larger. The shape of the LET spectra in the simulation reproduced the experimental spectra, but there was a discrepancy between the simulation and experiment for the relative yield of fragments. When the yield of low LET particles was changed by ± 40%, the change in RBE was smaller than 10%. CONCLUSIONS An RBE of 1.3 was expected for secondary fragments emitted at a small angle. Although, we observed a discrepancy in the relative yield of secondary fragments between simulation and experiment, precision of RBE was not so sensitive to the yield of low LET particles.

Outer space is an environment characterized by microgravity and space radiation, including high-energy charged particles. Astronauts are constantly exposed to both microgravity and radiation during long-term stays in space. However, many aspects of the biological effects of combined microgravity and space radiation remain unclear. We developed a new three-dimensional (3D) clinostat synchronized heavy-ion irradiation system for use in ground-based studies of the combined exposures. Our new system uses a particle accelerator and a respiratory gating system from heavy-ion radiotherapy to irradiate samples being rotated in the 3D clinostat with carbon-ion beams only when the samples are in the horizontal position. A Peltier module and special sample holder were loaded on a static stage (standing condition) and the 3D clinostat (rotation condition) to maintain a suitable temperature under atmospheric conditions. The performance of the new device was investigated with normal human fibroblasts 1BR-hTERT in a disposable closed cell culture chamber. Live imaging revealed that cellular adhesion and growth were almost the same for the standing control sample and rotation sample over 48h. Dose flatness and symmetry were judged according to the relative density of Gafchromic films along the X-axis and Y-axis of the positions of the irradiated sample to confirm irradiation accuracy. Doses calculated using the carbon-ion calibration curve were almost the same for standing and rotation conditions, with the difference being less than 5% at 1Gy carbon-ion irradiation. Our new device can accurately synchronize carbon-ion irradiation and simulated microgravity while maintaining the temperature under atmospheric conditions at ground level.

In a conventional carbon-ion radiotherapy facility, a carbon-ion beam is typically accelerated up to an optimum energy, slowly extracted from a synchrotron ring by a resonant slow extraction method, and ultimately delivered to a patient through a beam-delivery system. At Japan’s Gunma University, a method employing slow-beam extraction along with beam-acceleration has been adopted. This method slightly alters the extracted-beam’s energy owing to the acceleration component of the process, which subsequently results in a residual-range variation of approximately 2 mm in water-equivalent length. However, this range variation does not disturb a distal dose distribution with broad-beam methods such as the single beam-wobbling method. With the pencil-beam 3D scanning method, however, such a range variation disturbs a distal dose distribution because the variation is comparable to slice thickness. Therefore, for pencil-beam 3D scanning, an energy compensation method for a slow extracted beam is proposed in this paper. This method can compensate for the aforementioned energy variances by controlling net energy losses through a rotatable energy absorber set fixed between the synchrotron exit channel and the isocenter. Experimental results demonstrate that beam energies can be maintained constant, as originally hypothesized. Moreover, energy-absorber positions were found to be significantly enhanced by optimizing beam optics for reducing beam-size growth by implementation of the multiple-scattering effect option.

For the practical application of carbon-knife with fine carbon-ion beams, the quantification of the dose distribution is essential and requires a high spatial resolution. We propose a novel method to quantify dose distributions with a spatial resolution smaller than the dosimeter size. The proposed method innovates the iterative reconstruction technique. Using a diode dosimeter with a sensitive area of 1 mm2, two-dimensional dose-area-product (DAP) distributions were measured at a 0.1 mm step at the surface and near the Bragg peak depths for fine carbon-ion beams of ∼1 mm size at the full width at half maximum (FWHM). Then, the dose distributions were reconstructed with a spatial resolution of 0.1 × 0.1 mm2 from the measured DAP distributions. However, an unnaturally high noise was observed in the reconstructed dose distributions, which were considered to originate from the measurement reproducibility errors of the DAP distributions estimated to be 2.5%-3%. Therefore, a low-pass filtering process was implemented to reduce the errors on the reconstructed dose distributions. The optimum cut-off frequencies of the low-pass filter were estimated depending on the amplitude of the induced noise. Using the filtering process with the obtained optimum cut-off frequency, the dose distribution was quantified with an average error of approximately 3% or less with respect to the peak value, when the actual measurement had an error of 3%. In the reconstructed dose rate distributions, a steep penumbra P80-20 ∼ 0.2 mm was observed at the surface, and a dose rate at the center axis of ∼90 Gy s-1 and a beam size of ∼1.1 mm at FWHM near the Bragg peak were obtained. The proposed method is expected to be useful for the measurement-based determination of microbeam models for commissioning and dose distribution calculations toward carbon-knife applications.

Facilities for heavy ion therapies are steadily increasing in number worldwide. One of the advantages of heavy ions is their high relative biological effect (RBE). In a model used at NIRS (National Institute of Radiological Sciences), linear energy transfer (LET) spectra are required to estimate biological dose (physical dose × RBE). The CR-39 plastic charged-particle detector (CR-39) is suitable for measurement of LET. For the present study, done at the Gunma University Heavy Ion Medical Center (GHMC), we measured LET spectra at 11 depths in spread-out Bragg peak (SOBP) irradiation by a

The aim of this research is to develop a stereotactic-radiosurgery (SRS) technique using carbon beams to treat small intracranial lesions; we call this device the carbon knife. A 2D-scanning method is adapted to broaden a pencil beam to an appropriate size for an irradiation field. A Mitsubishi slow extraction using third order resonance through a rf acceleration system stabilized by a feed-forward scanning beam using steering magnets with a 290 MeV/u initial beam energy was used for this purpose. Ridge filters for spread-out Bragg peaks (SOBPs) with widths of 5 mm, 7.5 mm, and 10 mm were designed to include fluence-attenuation effects. The collimator, which defines field shape, was used to reduce the lateral penumbra. The lateral-penumbra width at the SOBP region was less than 2 mm for the carbon knife. The penumbras behaved almost the same when changing the air gap, but on the other hand, increasing the range-shifter thickness mostly broadened the lateral penumbra. The physical-dose rates were approximate 6 Gy s−1 and 4.5 Gy s−1 for the 10 × 10 mm2 and 5 × 5 mm2 collimators, respectively.

Precise measurement of the dose distribution of a carbon-ion pencil beam is essential for the safe delivery of treatment in scanned carbon-ion therapy. We developed an easy-to-use and quick dose-measurement tool that employs a silver-activated zinc-sulfide (ZnS) scintillator, which shows a smaller linear energy transfer (LET) dependency than conventional Gd-based scintillator, to measure the dose distribution of a carbon-ion pencil beam with high spatial resolution and small corrections. A ZnS scintillator sheet was set up perpendicular to the beam axis, and scintillation images were recorded using a charge-coupled device camera. We used 290-MeV/nucleon monoenergetic carbon-ion pencil beams at the Gunma University Heavy Ion Medical Center. The thickness of the water tank placed above the scintillator was remotely controlled to adjust the measurement depth. Images were acquired at different water depths, and the depth and lateral profiles were determined from the images. The results were compared with those of conventional Gd-based scintillator. The depth–light intensity profile of the ZnS scintillator matched the depth dose measured using an ionization chamber, which was better than that of a Gd-based scintillator. This result is advantageous for measurements using a carbon-ion pencil beam, which consists of primary carbon ions with a much higher LET than a proton, with smaller corrections. The ZnS scintillator showed good output characteristics, dose linearity (R2 > 0.99), and output reproducibility (deviations below 2%) and good agreement with the lateral-dose profiles measured using a diode down to ~1% of the central dose. The proposed tool can measure lateral profiles at the depth of the Bragg peak and tail in addition to the entrance. Our tool was used to quickly measure the dose distribution of carbon-ion pencil beam with high-spatial resolution and small corrections.

Facilities for heavy ion therapies are steadily increasing in number worldwide. One of the advantages of heavy ions is their high relative biological effect (RBE). In a model used at NIRS (National Institute of Radiological Sciences), linear energy transfer (LET) spectra are required to estimate biological dose (physical dose × RBE). The CR-39 plastic charged-particle detector (CR-39) is suitable for measurement of LET. For the present study, done at the Gunma University Heavy Ion Medical Center (GHMC), we measured LET spectra at 11 depths in spread-out Bragg peak (SOBP) irradiation by a 12C beam of 380 MeV/u. The lower threshold of the CR-39 to measure LET was about 5 keV µm-1 due to poor sensitivity for low LET. Then we calculated biological dose and survival fraction distributions and compared them with treatment planning results at GHMC. We used Monte Carlo simulation (Geant4) to calculate LET spectra. The simulation results were in good agreement with the experimental spectra. Moreover, the biological dose and survival fraction distributions estimated from the CR-39 reproduced the treatment planning. The CR-39 is suitable for estimating biological dose in carbon ion therapy.

We have succeeded to compress the energy spread of a laser-produced proton beam to 1.6% at FWHM by an RF electric field synchronous to the pulse laser. Protons generated by this laser originally had a continuous energy spectrum with no peaks. Radial focusing and defocusing effects caused by the transverse component of the RF field were also observed. Concerning these effects, we simulated the energy spectra from the calculated value of the electric field by POISSON; the simulation could almost reproduce the experimental results. By applying this beam as an injection beam of a synchrotron, a compact acceleration system for particle cancer therapy is expected to be realized.

A closed orbit is corrected for single-turn injection to perform laser cooling experiments of 40 keV 24 Mg + beam at the small laser-equipped storage ring (S-LSR). Closed orbit distortion (COD) corrections have been carried out using a downhill simplex method, and CODs of less than ± 0.5 mm have been achieved throughout the whole circumference. The injection orbit and the CODs are optimized to pass through the two aperture holes in the alignment targets located in the laser cooling section with an algorithm to maximize beam lifetime. The CODs at the aperture holes are reduced to be less than ± 0.2 mm , assuring an overlap between the laser and the 24 Mg + ion beam.

PURPOSE We developed an evaluation method for easily calculating displacement directly between the carbon beam axis and positioning X-ray axis. METHODS A verification image was acquired by irradiating an imaging plate with a carbon beam and X-ray. The X-ray passed through a lead plate inserted in the range compensator holder. The displacement was calculated on the verification image from the center of a wire irradiated with carbon using a multi leaf collimator (MLC) and a wire irradiated with X-ray also using MLC. The accuracy of the method was evaluated by moving the carbon beam axis, the X-ray axis, and the setup angle. The weekly changes of vertical and lateral beams in all rooms were also evaluated. RESULTS The displacements of the carbon beam axis and the setup angle did not influence the calculation results, whereas the displacement of the X-ray axis did (R=0.999). The displacements including weekly changes were all less than 1.00 mm. CONCLUSION An evaluation method for calculating the displacement directly and simply between the carbon beam axis and positioning X-ray axis was developed and verified. The weekly changes of displacement between axes were evaluated to be acceptable at our facility.

A short-pulse (~210 fs) high-power (~1 TW) laser was focused on a tape target 3 and 5 µm in thickness to a size of 11×15 µm2 with an intensity of 3×1017 W/cm2. Protons produced by this laser with an energy spread of 100% were found to be improved to create peaks in the energy distribution with a spread of ~7% by the application of the RF electric field with an amplitude of ±40 kV synchronous to the pulsed laser. This scheme combines the conventional RF acceleration technique with laser-produced protons for the first time. It is possible to be operated up to 10 Hz, and is found to have good reproducibility for every laser shot with the capability of adjusting the peak positions by control of the relative phase between the pulsed laser and the RF electric field.

In order to widely spread out particle beams utilized in cancer therapy, laser-produced ions are developed as the injection beam for an ion synchrotron dedicated for cancer therapy. Such a laser ion source is expected to contribute largely to the realization of compactness of the size and low cost of the cancer therapy accelerator. The energy spectrum of the laser-produced ions, however, has no peak, but their intensities decrease exponentially according to the increase of the energy. For the purpose of modifying such a situation, we have proposed a scheme to rotate the beam in the longitudinal phase space with the use of the RF electric field, which is phase-adjusted with the pulse laser. We aim for a reduction of the energy spread of ± 5% selected by an energy analyzer and slits to ±1% by such phase rotation. For this purpose, a quarter wavelength resonator with two gaps with the same resonant frequency as the source laser has already been fabricated, together with its RF power source. The above phase rotation system and its recent experimental realization are presented.

We report the first observation of indirect resonantly enhanced transverse laser cooling of a bunched, stored ion beam of 40 keV $^{24}\mathrm{Mg}^{+}$. The longitudinal velocity distribution and the horizontal beam size of the laser-cooled $^{24}\mathrm{Mg}^{+}$ ion beam with 280 nm laser light were simultaneously observed by the use of standard fluorescence-based techniques. Keeping the operation point at (2.068, 1.105), the synchrotron tune (${\ensuremath{\nu}}_{s}$) was changed from 0.0376 to 0.1299. A strong decrease in the cooled horizontal beam size and a corresponding increase in the equilibrium cooled momentum spread were observed at the expected synchrobetatron resonance coupling condition of ${\ensuremath{\nu}}_{s}=0.068$, which is the first observation of a resonantly induced coupling for enhanced indirect transverse laser cooling of an ion beam, and is an important step towards creating a crystalline ground state of the beam.

The dynamics of a MeV laser-produced proton beam affected by a radio frequency (rf) electric field has been studied. The proton beam was emitted normal to the rear surface of a thin polyimide target irradiated with an ultrashort pulsed laser with a power density of $4\ifmmode\times\else\texttimes\fi{}{10}^{18}\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$. The energy spread was compressed to less than 11% at the full width at half maximum (FWHM) by an rf field. Focusing and defocusing effects of the transverse direction were also observed. These effects were analyzed and reproduced by Monte Carlo simulations. The simulation results show that the transversely focused protons had a broad continuous spectrum, while the peaks in the proton spectrum were defocused. Based on this new information, we propose that elimination of the continuous energy component of laser-produced protons is possible by utilizing a focal length difference between the continuous spectral protons and the protons included in the spectral peak.

A phase rotation scheme of laser‐produced ions from a solid target by the application of a synchronized RF electric voltage with a pulsed laser has been experimentally investigated with the use of a 100 TW laser, J‐KAREN at JAEA, KPSI. Up to now, energy peaks of up to around 2.0 MeV have been created with a FWHM of 2.6% with good reproducibility using a two‐gap resonator of a quarter wave length with the same frequency as the source laser (∼80 MHz). It is also found that the position of the peak can be well controlled by adjusting the relative phase between the RF electric field and the laser, which is very promising for real applications of such laser‐produced protons. In order to also apply such a phase rotation system for higher energy protons (

At S-LSR, abrupt reduction of momentum spread of 7 MeV proton beam to ~2 times 10-6 at proton number of -2000 has been observed, which indicates phase transition to 1 dimensional ordered state. Attained proton temperatures after transition are 26 mueV and 1 meV for longitudinal and transverse directions, respectively, which compared with the corresponding values of 20 mueV and 34 meV for electron beam, indicates the magnetization of electron. Laser cooling of 24Mg+ has also been started and momentum spread of ~108 ions is reduced to 2 times 10-4, saturated with the momentum transfer from transverse degree of freedom by intra-beam scattering.

The ordering of protons has been observed at a new storage ring, S-LSR, at Kyoto University. Abrupt jumps in the momentum spread and the Schottky noise power were observed for protons for the first time at a particle number of $\ensuremath{\sim}2000$, upon applying electron cooling with electron currents of 25, 50, and 100 mA. The transition temperature was 0.17 and 1 meV in the longitudinal and transverse directions, respectively. The transverse temperature of the proton beam was much below that of electrons at the transition, which played an essential role in the ordering of protons.

At ICR, Kyoto University, an ion storage and cooler ring, S‐LSR has been constructed. Its mean radius and maximum magnetic rigidity are 3.6 m and 1.0 Tm, respectively. 24Mg+ ions with the kinetic energy of 35 keV are to be laser‐cooled by the frequency doubled ring dye laser with the wavelength of 280 nm. In order to avoid the shear heating, dispersion compensation is planned by the overlap of the electric field with the dipole magnetic field in all 6 deflection elements. Intermediate electrodes, which can be potential adjusted, are to be utilized so as to realize a uniform electric field radial direction within a rather limited vertical gap, 70 mm of the dipole magnet. Synchro‐betatron coupling needed for 3‐dimensional laser cooling is to be realized by placing the RF cavity at the siraight section with finite dispersion for the normal mode lattice, which is expected to realize 1 dimensional string. For the case of dispersion compensated lattice to suppress the shear heating, possibility of realizing “ta...

A compact ion cooler ring, S‐LSR is under construction in Kyoto University. One of the subjects of S‐LSR is a realization of the crystalline beams using the electron beam and the laser cooling. The ring is designed to be satisfied several required conditions for the beam ordering, such as a small betatron phase advance, a small magnetic error and a precise magnet alignment. The design phase advance per a period is less than 127 degree. The calculated closed orbit distortion and the stopband is less than 1 mm and 0.001 without correction, respectively.

An experiment to control dispersion of beams in one bending section has been carried out. This experiment is based on a theory that the dispersion of accumulated beams can be controlled, if they are bent by a cross field composed of magnetic and an electric fields. Suppression of the dispersion can ease a shear which affects the 3‐dimensionally ordered structure of the ultimate‐low‐temperature beams. In order to realize this scheme experimentally, we have manufactured a set of electrodes to create precise electric fields whose strength is 6.6 × 104 V/m for 24Mg+, 35keV beam. The electrodes have been inserted to the gap of dipole magnet. 3‐dimensional field calculation shows that the error of the electric fields is less than 0.1% within ± 5mm from the reference orbit. We also tested the effect of the electric field using a single set of bending elements. The result showed that the linear dispersion can be controlled or canceled by changing the ratio of magnetic and electric fields.

A single particle dynamics in beam bending elements including electrostatic fields is formulated. A general form of scalar potentials of electrostatic deflectors is obtained from solutions of the Maxwell equation having axial symmetry. Equations of motion of a charged particle in various types of the electrostatic deflectors are derived based on Hamiltonian formalism. The equation of motion in dispersion suppressors, which are a combination of the electrostatic deflectors and dipole magnets, are also formulated and generalized. Application of one of the dispersion suppressors to an existing heavy ion storage ring S-LSR provides the better condition for generation of a multidimensional crystalline beam. It is shown that this condition is achievable by real fabricated devices composed of a dipole magnet and an electrostatic deflector equipped with intermediate electrodes. The effectiveness of this dispersion suppressor for the real operation is shown by a particle tracking including the nonlinear field component.

An ECR ion source of Gunma University Heavy Ion Medical Center, so-called KeiGM [M. Muramatsu, A. Kitagawa, Y. Sakamoto, S. Sato, Y. Sato, H. Ogawa, S. Yamada, H. Ogawa, Y. Yoshida, and A. G. Drentje, Rev. Sci. Instrum. 76, 113304 (2005)], has been operated for cancer therapy and physical/biological experiment since 2010. KeiGM produces typically 230 μA of 10 keV/u C(4+) ions from CH4 gases. The vacuum pressure is kept between 1.2 × 10(-4) and 1.7 × 10(-4) Pa so as to suppress the pulse-to-pulse current fluctuation within ±10%. The extraction electrode is cleaned every 6-8 months in order to remove deposited carbon, which increases the leak current and discharge. In order to investigate the possibility of long-term operation without such maintenances, oxygen aging for the cleaning of the extraction electrode has been tested in the test bench. The same-designed ion sources at National Institute of Radiological Sciences and SAGA Heavy Ion Medical Accelerator in Tosu (SAGA-HIMAT) are also operated with stable C(4+) current, which are suitable for the continuous operation for cancer therapy.

The efficiency of indirect transverse laser cooling with synchro-betatron resonance coupling has been improved with the reduction in beam intensity by scraping the tail part of the beam. In order to measure the beam size at a low beam intensity, a new scheme to measure the beam profile by observation of the survival ratio with changing the scraper position has been established. With 104 particles, the transverse cooling time was reduced to 1.2 s, and the cooled horizontal and vertical beam sizes were 0.19 and 0.61 mm, corresponding to temperatures of 20 and 29 K, respectively, which is largely improved compared with that in our previous experiment [Nakao et al.: Phys. Rev. ST Accel. Beam 15 (2012) 110102].

Many applications of laser-accelerated ions will require beamlines with diagnostic capability for validating simulations and machine performance at the single bunch level as well as for the development of controls to optimize machine performance. We demonstrated prompt, in-line, single bunch transverse profile and energy spectrum detection using a thin luminescent diagnostic and scintillator-based time-of-flight spectrometer simultaneously. The Monte Carlo code, particle and heavy ion transport code systems (PHITS) simulation is shown to be reasonably predictive at low proton energy for the observed transverse profiles measured by the thin luminescent monitor and also for single bunch energy spectra measured by time-of-flight spectrometry.

A laser-cooling experiment of a 40 keV 24Mg+ beam was carried out in the small laser-equipped storage ring (S-LSR). A laser co-propagating with the beam and an induction accelerator were utilized in the experiment. The lowest longitudinal temperature achieved in the present experiment was 3.6 K for 3?104 ions stored in the ring. It was found that the number of stored ions is related to the temperature at the final equilibrium state of the laser cooling. This relation shows that the longitudinal temperature of the laser-cooled beam linearly couples with the transverse one through intra-beam scattering.

Laser ion production has been studied for downsizing of the accelerator dedicated for cancer therapy. For optimization of various parameters such as pre-pulse condition, target position, laser spot size on the target, laser pulse width and so on, time of flight (TOF) measurement utilizing the detected signal by a plastic scintillation counter played an essential role for real time measurement. Protons up to ~900 keV and ~600 keV are produced from the thin foil targets of Ti 3 μm and 5 μm in thickness, respectively. Modification of the energy distribution of the laser-produced ions with Maxwell distribution by utilizing an RF electric field synchronized to the pulse laser, which is the rotation of the ion beam in the longitudinal phase space (Phase Rotation), has been demonstrated for the first time. By using the Ti Sapphire laser of the wave length and pulse duration of 800 nm and a few hundreds fs, respectively, intensity increase of factor 3 in a certain energy bins is attained creating energy peaks with the energy spread about 7 %, which is found to be reproduced with good probability.