Search Results (7 total)

The 3-GeV rapid cycling synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC) was commissioned in October 2007, and successfully accomplished 3 GeV acceleration on October 31. Six run cycles through February 2008 were dedicated to commissioning the RCS, for which the initial machine parameter tuning and various underlying beam studies were completed. Then since May 2008 the RCS beam has been delivered to the downstream facilities for their beam commissioning. In this paper we describe beam tuning and study results following our beam commissioning scenario and a beam performance and operational experience obtained in the first commissioning phase through June 2008.

In the rapid cycling synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC), the longitudinal painting is important to alleviate the space-charge effects. It is known that the momentum offset injection and applying the second harmonic rf voltage improves the bunching factor, which is defined as the ratio of average and peak current. Our simulation studies show that the large-amplitude second harmonic, 80% to the fundamental, is optimum, and the second harmonic phase sweep improves the bunching factor at the beginning of the injection period. We performed the beam tests of longitudinal painting in the J-PARC RCS. We proved that the longitudinal painting with the 80% second harmonic, the momentum offset of -0.2%, and the second harmonic phase sweep improved bunching factors significantly.

The dual-harmonic operation, in which the accelerating cavities are driven by the superposition of the fundamental and the second harmonic rf voltage, is useful for acceleration of the ultrahigh intensity proton beam in the rapid cycling synchrotron (RCS) of Japan Proton Accelerator Research Complex (J-PARC). However, the precise and fast voltage control of the harmonics is necessary to realize the dual-harmonic acceleration. We developed the dual-harmonic auto voltage control system for the J-PARC RCS. We describe details of the design and the implementation. Various tests of the system are performed with the RCS rf system. Also, a preliminary beam test has been done. We report the test results.

The Rapid Cycling Synchrotron (RCS) of the J-PARC complex in Tokai, Japan, is designed to accelerate a high intensity proton beam from 181 MeV, and later 400 MeV to 3 GeV in 20 ms within the 40 ms machine cycle. The beam power up to 1 MW demands a stable beam control to avoid excessive losses and activation of the accelerator chain. The fully digital control system is based on quadrature modulation and demodulation. In the amplitude control loops standard FIR filters separate the harmonics (h=2) and (h=4) after down conversion. For the phase loops at (h=2) and (h=4), intended to damp synchrotron oscillations, the delay in a FIR filter would limit the loop stability. Cascaded integrator comb filters, also called CIC filters, provide a shorter delay because they filter the longitudinal beam signal only where it is necessary. The notches are located at multiples of the revolution frequency of the proton beam. For fixed frequency accelerator applications, digital comb filters with fixed clock frequency are widely used to improve loop stability. For variable frequency accelerator applications, as in a proton synchrotron, where the frequency swing is larger than the notch width, usually the clock frequency of the comb filter is variable and chosen to be an integer multiple of the particle revolution frequency. At J-PARC RCS, the clock frequency has to be fixed. Tracking the frequency would require a variable noninteger number of filter taps. Here we present a filter, based on the weighted output of 2 CIC filters with variable length, and one tap difference. The filter function looks like a CIC with smoothly varying coefficients, where the notches follow the revolution frequency of the proton beam. The delay of this filter is approximately half of the corresponding FIR filter, so that the phase loops have a higher stability margin.

A barrier bucket experiment with two dedicated barrier cavities was performed at the Brookhaven AGS. One of the barrier cavities was a magnetic alloy (MA)–loaded cavity and the other was a ferrite-loaded cavity. They generated a single sine wave with a peak voltage of 40 kV at a repetition rate of 351 kHz. A barrier rf system was established with these cavities and five bunches from the AGS booster were accumulated. A total of 3×10¹³ protons were stored without beam loss, and were successfully rebunched and accelerated. The longitudinal emittance growth was observed during accumulation by the barrier bucket, the blowup factor of which was about 3. The longitudinal mismatch between the rf bucket and the beam bunch was the main reason for the emittance growth. The potential distortions by beam loading of the ferrite cavity and the overshooting voltage of the MA cavity disturbed the smooth debunching.

Longitudinal bunch shapes in the KEK proton synchrotron were measured by a fast bunch-monitor system, which showed the rapid growth of the instability at the frequency of ∼1 GHz and significant beam loss just after transition energy. Temporal evolution of the microwave instability is explained for the first time with a proton-klystron model.

The decay of ₂₉⁵⁷Cu₂₈ produced with the ⁵⁸Ni(p,2n) reaction was identified by a 1112-keV γ ray occurring in its daughter nucleus ⁵⁷Ni and the half-life and β⁺ end-point energy were measured to be 223±16 ms and 7720±130 keV, respectively, applying a technique of fast transportation of irradiated targets. The logft value and Gamow-Teller matrix element of the ground-to-ground mirror transition of ₂₉⁵⁷Cu₂₈(T_z=-1 / 2)→₂₈⁵⁷Ni₂₉(T_z=1 / 2) was deduced to be logft=3.71±0.05 and 〈στ〉=0.37±0.11. The present results indicate a large reduction of 〈στ〉 from the single particle value (1.291) although ⁵⁷Cu is a nucleus obtained by adding one proton to the ₂₈⁵⁶Ni₂₈ core.