Using a pulsed deflector for extraction of pulsed beams from the TRIUMF cyclotron
In the normal mode of operation, the TRIUMF cyclotron accelerates H/sup -/ ions to produce 500 MeV proton beams of 160 /spl mu/A with 4 nsec pulses separated by 43 nsec. A proposed experiment (/spl mu//spl rarr/e conversion) requires a 500 MeV beam with 100-200 nsec pulses separated by 1-2 /spl mu/ sec with an average intensity of 200 /spl mu/A. Two methods have been investigated to achieve this time structure. Both incorporate a pulsed electric deflector and take advantage of extraction by stripping. In the first case, a deflector with a thin septum deflects radially up to six accumulated turns onto a stripping foil in one turn. In the second, a pair of vertically deflecting plates are pulsed at a frequency to excite a coherent vertical growth, and the particles are eventually intercepted by a stripping foil. Under certain conditions extraction occurs in almost perfect synchronism with the driving pulse. Both methods will be described in detail and results of computer simulations will be presented.
Reducing phase-dependent emittance growth with local flattopping
The efficiency of the proposed H/sup -/ extraction in the TRIUMF cyclotron is improved by inducing a precessional component to the radius gain per turn by exciting a coherent radial betatron oscillation at /spl nusub r/=3/2. Beam test and computer simulation results show that accompanying this improvement is a growth in the transverse emittance of the extracted beam. The growth is, in part, due to phase-dependent mixing of the perturbed beam. This phase-dependence can be greatly reduced by flattopping the local energy gain per turn with the addition of a higher harmonic accelerating field in phase opposition to the fundamental. A 92 MHz, 4/sup th/ harmonic, /spl lambda4 cavity installed in the TRIUMF cyclotron has been used for such a purpose. Results of both computer simulations and beam tests will be presented.<<ETX>>
A variable duty factor beam chopper for a 300 keV injection beamline
A new beam chopper has been developed for the 300 keV Hbeam injected into the 500 MeV TRIUMF cyclotron. The beam chopper controls the duty factor of the beam between 0.1 % and 99.9 %. The chopper consists of a high-voltage modulat,or incorporating two stacked Field-Effect ‘IYansistor switches, operating in a “pushpull” mode, and a set of deflector plates. The required pulse magnitude is 5 kV at 3 kHz (continuous) with rise and fall times of less than 44 ns. The deflector plates are 12.7 cm long with a separation of 3.2 cm and are installed in the 300 keV injection line to the cyclotron. The circuit performance and the results of beam test measurements are presented.