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    User name Sirish

    Log entry time 22:06:28 on November25,2008

    Entry number 250744

    keyword=Compton Studies

    Did a thorogh study of beam steering through the Compton chicane to determine if there is vertical offset required to thread the beam through the chicane. The answer is NO! Using established standard procedure, the beam threads through the chicane fine!

    However, photon background rates remined stubbonly high at about 2kHz/uA. Beam steering and focussing had little effect.

    Experimenting with Hall B off and on we find the following:

    Hall A 2uA(Slits wide open), Hall B On; photon rate = 4000 Hz
    Hall A Off(slits wide open), Hall B On; photon rate = 3000 Hz
    Hall A 2uA(Slits closed down), Hall B on; photon rate = 100 Hz

    Leakage from Hall B is still the main source of background.

    Conclusion:
    1. No obstructions to threading the beam through the chicane was found. The old SOP for compton tune will remain unchanged.

    2. Background halo is coming from injector Hall B leakage. Until solved, Hall will run with injector slits closed down.