| Popis: |
The TRIUMF cyclotron routinely accelerates ∼220 μA of H− ions, extracting protons simultaneously to four external beam lines. The radioactive beam facility ISAC, now operating at 10–20 μA ∼500 MeV protons, will soon require up to 100 μA at 500 MeV. The CHAOS experiment on the π+, π− secondary beam line also requires a high intensity beam (∼140 μA, 500 MeV) but with a short (2 ns) bunch length. High current operation with 2 ns beam has been facilitated by the 4th harmonic auxiliary acceleration cavity [4]. The 2 ns beam structure is now achieved by phase compression as the energy gain per turn increases near extraction. The paper focuses on improvements in the reliability of this cavity and its rf coupler. The higher energy gain per turn also reduces H− stripping losses (by about 33%) in the high energy region, hence increases the allowed beam intensity for a given beam activation. The total current will soon be increased to about 300 μA to allow for ISAC requirements. |
