The powering of the S800 magnets needs to follow three steps:
The power supply for each of the spectrograph dipoles has a dump switch that must be armed (closed) to send current through the dipoles. The dump switch is in place to protect the conductors inside the cryostat from melting in the event that the magnet becomes non-superconducting while energized with high current. When triggered, the dump switch provides a high-current short circuit path to dump the energy from the magnet. The kinds of error conditions that will trigger the dump switches are the same conditions that trip off power supplies to other superconducting magnets on the beamlines. Examples include: a lead drop fault error, a quench detection (read and set values not agreeing over a period of time), a cryogenic error condition (e.g., a low helium level or blown rupture disk), and a loss in flow of cooling water for the power supplies.
While designed to protect the magnet from a more expensive repair, if the magnet quenches when energized, it is possible that the dump switch can get damaged if triggered because of the large amount of energy involved. Therefore, the magnet should be ramped down before any planned trigger conditions occur.
The dump switches of the first and second dipoles are located on the bottom and middle level of S3. The dipole magnet is ready to be turned on when the front panel of the dump switch box shows the red label “closed”. The two pictures below show the dump-switch control “open” (not ready to be turned on) for the second spectrograph dipole. A label in the control box explains how to arm the switches.
The values of currents for the different magnets can be modified individually by clicking the button “details” in the Barney page (see upper-right corner in figure above). A list of magnets with their corresponding currents will be displayed as shown in the figure below. To change the current of a given magnet (e.g. I265DS), go to column Read Amps and click in the “cell” corresponding to the magnet (see red circle in figure below). A new window will pop-out; enter the new value of the current (e.g. 10 A) and click “Apply”.
Note: The following procedure describes how to set the trim-coil currents manually. In principle, it is no longer necessary because Barney sets the currents automatically once the rigidity of segment 8 has been entered.