TH2I1
CIAE, Beijing, People’s Republic of China
The MW class proton accelerators are expected to play important role in many fields, attracting institutions to continue research and tackle key problems. The CW isochronous accelerator obtains high power beam with higher energy efficiency, which is very attractive to many applications. Scholars generally believe that the energy limitation of the isochronous cyclotron is ~1GeV. In order to get higher beam power by the isochronous machine, enhancing the beam focusing become the most important issue. Adjusting the radial gradient of average magnetic field make the field distribution match the isochronism. When we adjust the radial gradient of peak field Bhill, the first order gradient is equivalent to the quadrupole field, the second order, to the hexapole field, and so on. Just like the synchrotron, there are quadrupole, hexapole magnet and so on, along the orbits so as to get higher energy, as all we know. If we adjust the radial gradient for peak field of an FFAG’s FDF lattice, and cooperate with the angular width (azimuth flutter) and spiral angle (edge focusing) of the traditional cyclotron pole, we can control the working path in tune diagram very flexibly. During enhancing the axial focusing, the beam intensity and energy of CW isochronous accelerator are significantly increased. And a 2GeV CW FFAG with 3mA of average beam intensity are designed. It is essentially an isochronous cyclotron although we use 10 folder of FDF lattices. The key difficulty is that the magnetic field and each order of gradient should be accurately adjusted in a large radius range. As a high power proton accelerator with high energy efficiency, we adopt high temperature superconducting (HTS) technology for the magnets. 15 RF cavities with Q value of 90000 provide energy gain per turn of ~15MeV to ensure the CW beam intensity reaches 3mA. A 1:4 scale, 15 ton HTS magnet and a 1:4 scale, 177MHz cavity have been completed. The results of such R & D will also be presented in this paper.
GSI, Darmstadt, Germany
IMP/CAS, Lanzhou, People’s Republic of China
We develop a formula including the low-beta effect and the influence of long cable issues for estimating the original signal of cold BPMs. A good agreement between the numerical and the measured signal with regard to two kinds of beam commissioning, helium and proton beams, in a low-beta helium and proton superconducting linac, proves that the developed numerical model could accurately estimate the output signal of cold button BPMs. Analysing the original signal between the first and the last cold BPM in the cryomodule, it is found that the signal voltage in the time domain is increased with the accelerated beam energy. However, the amplitude spectra in the frequency domain has more high frequency Fourier components and the amplitude at the first harmonic frequency reduces a lot. It results in a decline of the summed value from the BPM electronics. The decline is not proportional to a variety of the beam intensity. This is the reason why BPMs give only relative intensity and not absolute value for low-beta beams with a Gaussian distribution.