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One of Jefferson Laboratory’s research areas is in Superconducting Radio Frequency (SRF) science and technology. SRF cavities are tested in the Vertical Testing Area (VTA) at Jefferson Laboratory, within a series of large cylindrical dewars. The measured quality factor (Q factor) of the SRF cavity is directly influenced by any existing magnetic field. Because the VTA previously housed a cyclotron, all the rebars within the building have residual magnetic fields emanating from them. This magnetic field effect of the building renders the measurements of Q factor on the devices inaccurate and the testing data unreliable. A magnetic field scanning system must be employed to accurately map the magnetic field within the testing dewar so that an existing set of current-carrying coils installed around the dewar can be used properly for cancellation of the residual magnetic fields. This process will ensure the initial testing conditions are free of any unwanted magnetic fields that could cause unreliable testing data.
The proposed system will scan the residual magnetic field inside vertical dewars of varying sizes (16”- 34” diameter by 72”- 132” depth) in three dimensions and log data for later use, as well as display a visual mapping of the data to the operator through LabView. A sensor with a sensitivity of at least 0.1 milligauss will be attached to the bottom of a long pole that will be lowered into the dewar. Translation in the z direction, on the dewar’s central axis, will be achieved by using a pair of stepper motors controlling a rack and pinion set up on the center pole. To achieve incremental mapping in the x-y plane, an arm will be attached to the bottom of the pole that will house additional sensors. The platform holding the stepper motors will turn on a dial with degree measurements, allowing for rotational movement of the entire center pole and arm. By calculating the x-y values for each sensor on the arm at that set degree amount, mapping of set increments in the x-y plane can be achieved.
electrical and computer engineering, magnetic fields
Electrical and Computer Engineering | Engineering
Afroditi V. Filippas
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