RF-knockout Method Research Articles

Slow beam extraction method from synchrotron for uniform spill and fast beam switching using an RF knockout method of multi-band colored noise signal—POP Experiment and simulation

A proof of principle experiment (POP) was performed at the WERC synchrotron on the innovative slow beam extraction method with use of RF-knockout. The goal of experiment was to demonstrate the usefulness of the concept of colored noise signals including many frequency bands around the betatron resonances to obtain the uniform beam spill and the fast beam switching off time. The beam experiment shows that a small standard deviation of spill fluctuation can be attained without the longitudinal beam bunching of circulating particles. It is also shown that a beam switching-off time of around 100 μs could be obtained with a uniform spill. The experimental results are compared with the simulation results.

Source of spill ripple in the RF-KO slow-extraction method with FM and AM

The RF-knockout (RF-KO) slow-extraction method with frequency modulation (FM) and amplitude modulation (AM) has brought high-accuracy irradiation to the treatment of a cancer tumor moving with respiration, because of a quick response to beam start/stop. However, a beam spill extracted from a synchrotron ring through RF-KO slow-extraction has a huge ripple with a frequency of around 1 kHz related to the FM. The spill ripple will disturb the lateral dose distribution in the beam scanning methods. Thus, the source of the spill ripple has been investigated through experiments and simulations. There are two tune regions for the extraction process through the RF-KO method: the extraction region and the diffusion region. The particles in the extraction region can be extracted due to amplitude growth through the transverse RF field, only when its frequency matches with the tune in the extraction region. For a large chromaticity, however, the particles in the extraction region can be extracted through the synchrotron oscillation, even when the frequency does not match with the tune in the extraction region. Thus, the spill structure during one period of the FM strongly depends on the horizontal chromaticity. They are repeated with the repetition frequency of the FM, which is the very source of the spill ripple in the RF-KO method.

A Pulse Stretcher by Slow Extraction Utilizing the Third-Order Resonance with the RF Knockout Method

A pulse stretcher operation of KSR using slow electron beam extraction by the third-order resonance in combination with an RF knockout method has been accomplished. The extracted beam energy, number of extracted electrons in a single pulse, maximum duration and duty factor are 60 MeV, 1.4×108, 40 s and 90%, respectively. The beam spill can be controlled from 0.2 s to 40 s by adjusting of the power for RF knockout.

Respiratory gated irradiation system for heavy-ion radiotherapy

Purpose: In order to reduce the treatment margin of the moving target due to breathing, we developed a gated irradiation system for heavy-ion radiotherapy. Methods and Materials: The motion of a patient due to respiration is detected by the motion of the body surface around the chest wall. A respiratory sensor was developed using an infrared light spot and a position-sensitive detector. A timing signal to request a beam is generated in response to the respiration waveform, and a carbon beam is extracted from the synchrotron using a RF-knockout method. CT images for treatment planning are taken in synchronization with the respiratory motion. For patient positioning, digitized fluoroscopic images superimposed with the respiration waveform were used. The relation between the respiratory sensor signal and the organ motion was examined using digitized video images from fluoroscopy. The performance of our gated system was demonstrated by using the moving phantom, and dose profiles were measured in the direction of phantom motion. Results: The timing of gate-on is set at the end of the expiratory phase, because the motion of the diaphragm is slower and more reproducible than during the inspiratory phase. The signal of the respiratory sensor shows a phase difference of 120 milliseconds between lower and upper locations on the chest wall. The motion of diaphragm is delayed by 200 milliseconds from the respiration waveform at the lower location. The beam extraction system worked according to the beam on/off logic for gating, and the gated CT scanner performed well. The lateral penumbra size of the dose profile along the moving axis was distinguishably decreased by the gated irradiation. The ratio of the nongated to gated lateral fall-off was 4.3, 3.5, and 2.0 under the stroke of 40.0, 29.0, and 13.0 mm respectively. Conclusion: We developed a total treatment system of gated irradiation for heavy-ion radiotherapy. We found that with this system the target margin along the body axis could be decreased to 5–10 mm although the target moved twice or three times. Over 150 patients with lung or liver cancer had already been treated by this gated irradiation system by the end of July 1999.

Ion-Trapping Effect in UVSOR Storage Ring

UVSOR is an electron-stage ring dedicated to vacuum ultraviolet synchrotron radiation research. The first beam was stored in the ring in November 1983, and from that time on, efforts have been devoted to improving the performance of the ring. Some inconvenient phenomena have been found during the accelerator studies. One of the most serious problems is the growth of the vertical size of the electron beam. This phenomenon is explained by the ion-trapping effect, in which the ions trapped in the electron beam change the operating point of the storage ring and enhance the coupling between horizontal and vertical oscillations, resulting in a considerable increase in the vertical beam size. This ion trapping was successfully cured by the RF knockout method, which excited the betatron oscillation.

Characteristics of Magnetic Focusing and Chromaticity Correction System for TARN

TARN is designed by a separated function F-D- lattice. Its main magnet system consists of eight dipole and sixteen quadrupole magnets. The relatively lower injection energy of TARN (ß ≃ 0.134) leads to large transverse coupling impedance and the relatively smaller intensity limit from transverse coherent instability (6 × 108 ions/pulse). In order to surmount the instability by Landau damping, a chromaticity control system with twelve sextupole magnets are designed and fabricated. The field properties of all the magnets are measured precisely before alignment and the result is taken into account by the calculation with the computer code SYNCH. The closed orbit is obtained by iteration and the nonlinear elements such as sextupole magnets are linearized in the neighbourhood of the closed orbit. The work line is also experimentally studied by an RF knock-out method. The chromaticities of TARN without correction sextupole magnets were measured at -1.59 and -0.47 in horizontal and vertical directions, respectively.