11 MeV/u 16O7+ ion acceleration 7 November 2008 11 MeV/u 16O7+ ion acceleration E.E. Perepelkin and S.B. Vorozhtsov JINR, Dubna

Parameters Mass = 15.991 a.m.u. Z = 7 UECR = 13.29 kV UInflector = ± 4.7 kV ( instead of ± 3.68 kV ) B – map + 1.5 *(Trim coil N1 contribution at 650A of the main coil current) fRF = 20.386 MHz ( instead of 20.4 MHz ) RF harmonic = 2 UDEE = 49 kV φRF = – 8° at the 1st acc gap

For geometry courtesy of A. Vorozhtsov Central trajectories UDEE1 = 49 kV At the 1st gap φRF = − 8° Uinf = 4.7 kV fRF = 20.386 MHz UDEE2 = 49 kV For geometry courtesy of A. Vorozhtsov

Cyclotron B-map correction Trim coil N1 contribution for the main coil current 650 A Wk = 11 MeV/u BzTC1(r) Without TC1 RF phase = 28° Adjust fRF = 20.386 MHz Bxtotal(r,φ) = BzASV (r,φ) +1.5· BzTC1(r)

Standard trim coil N1 setting Wk = 11.021 MeV/u No TC1 +28°RF TC1 +2.5°RF RF phase shift ΔφRF = φRF – π/2 fRF = 20.4 MHz

For geometry courtesy of A. Vorozhtsov Centering Wk = 11.021 MeV/u Potential electrode Septum Wk = 11.021 MeV/u 2.8 mm Central trajectory 10.982 MeV/u For geometry courtesy of A. Vorozhtsov

Conclusions (1) Inflector voltage was increase up to 4.7 kV as compared with the initial estimation to minimize the particle axial momentum at the exit of the inflector, preventing this way large axial coherent oscillations, which lead to the heavy ion losses in the central region of the machine ( major cause of the particle losses there) The regime considered allows equal dee voltages to get through the channel inside the 1st dee, providing rather good centering of the orbits: No precession of the beam No crowded orbits at the mouth of the ESD.

Conclusions (2) Apparent shift of the reference trajectory from the central line of the channel inside the 1st dee leads to a necessity of modification of the central electrode structure in such a way as to match this channel to the reference track. => corresponding shift of the channel outward in radius is required. To compensate the side effect of the selected regime when crossing the 1st acceleration gap at −8°RF, the magnetic field modification by the 1st trim coil contribution was applied. As a result the beam RF phase moves from +28°RF to the top of the acceleration wave (~0°RF) in the main acceleration region.

Conclusions (3) Unlike the 14N5+ regime, simulated recently, there is no increase of the beam axial envelope near the final radius. Two possible reasons for the effect can be mentioned: Either symmetrical dee voltages prevent beam precession that permits to avoid particle crossing the region outside the final radius with the poor shaping magnetic field Or the radial range of the good magnetic field is larger than in the 14N5+ regime Or both