Investigations, Experiments, and Implications for Using Existing Pulse Magnets for "Topoff" Operation at the Advanced Light Source

Stray Field Reduction of ALS Eddy Current Septum Magnets

“…Currently the storage ring is filled at 1.525 GeV, once every several hours, so the stray field is tolerable. The ALS is now converting to "top-off" mode [1][2] [3] where beam is injected into the storage ring at the full 1.9 GeV energy every 20 sec. Under top-off mode, the stray field effect on the circulating beam would be larger and far more frequent, which is unacceptable.…”

“…The main drive current pulse is 5.3kV, producing +1.33 T maximum gap B field over a 125 µsec (half sine) period, and is the basis for simulations here. These results are compared to both field measurements using a (dB/dt) coil probe [3] made on a spare magnet, and to actual storage ring beam deflection measurements. For a half sine forward drive current pulse, I for = I 0 sin (ωt); ωt = 0 → π, the septum face (x = 0) eddy current density is proportional to dB/dt (a cosine from ωt = 0 → π).…”

“…Figure 6 shows the stray field inte- gral along the S.R. beam path, both calculated (damped, where B rev = 0.92B for ) and back-calculated from measured 30 µm horizontal deflection of the beam from a comparative test [3] for both half and full sine pulses (0.67 Gcm/micron). Deflection data is low-pass filtered (60 Hz cutoff).…”