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Turning S800 magnets On/Off

The powering of the S800 magnets needs to follow three steps:

Arming of Dump Switch


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.

In case the dump switches need to be open, make sure that the power supplies are turned off. Then, rotate the small trip handle to the “open” position.

Dump Switch Dump Switch

Turn on S800 magnets power supply

  • Troubleshooting: if a power supply cannot be turned on from PanelMate, check that the power supply module is ON. The modules for all S800 magnets are located in the S3 vault on the middle level under the stairs to the top level (see figure below). If all the modules seem to be running properly, but the problem persists, contact the operators in Control Room, ext. 305.

Power supply modules

  • Go to pages 5 and 6 and turn on the magnets by clicking in the box with the corresponding name of the EPICS channel (e.g. I228DS), followed by a click in the ON box.
  • Go to page 7 and select the steering magnets: I170DH, I197DH, I231DH. Note that some of the power supplies are connected to more than one steering magnet. If necessary, disable the steering magnet of the other line and enable the correct one.

PanelMate. File Thallps.ui, page 7

  • The magnet currents corresponding to a given setting are typically set using Barney. However, it is also possible to set them individually for an specific magnet, as explained here.

Set S800 magnets settings

  • Open Barney
  • Select page “A1900”
  • For each of the three segments (segments 6, 7 and 8), enter value of magnetic rigidity corresponding to the magnetic-rigidity setting and click on the button Set setting (see figure below).

Barney display for the S800.

  • Ensure that the analysis line and S800 are set to the right rigidity by selecting page “S3”. The figure below shows the rigidity value 2.9318 Tm for segments 6 and 7 (analysis line), and 2.5960 Tm for segment 8 (S800 spectrograph).

Barney display for the S800.

  • Ensure that the current in the dipoles are properly matched to the desired values (see section on NMR control)
  • Note: The currents in the Trim coils will be set automatically in Barney, once the rigidity in Segment 8 was entered.

Set magnet currents individually

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”.

Barney S800 "details" page.

Turn on the trim coils of the Spectrograph dipoles

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.

  • Check the currents in the Spectrograph dipoles by looking at the EPICS channels I265DS and I269DS. This can be done e.g. by clicking the button Details in segment 8 of the S800 Barney page (see figure below)
  • The values of the current in each of the two trim coils correspond to about 43.5% of the currents in the corresponding Spectrograph dipoles
  • Open the NCS application QTChan
  • Type the name of the EPICS channels for the trim coils (I255TC and I259TC) and wait until the currents are displayed
  • Type the new current values and type enter.
turning_magnets_on_off.txt · Last modified: 2019/05/15 11:58 by pereira