General Responsibilities of the Target Operator

• Maintain the integrity of the target cells and chamber - The $^{3}$He glass cells used in this experiment are quite fragile and everything that can be done needs to be done for their protection. The oven and target chamber can also be damaged by improper use of the lasers. The target operator should make sure the following is done to protect the target system:
  • Make sure MCC ramps the beam up slowly. They have a standard procedure for this, but if the operator sees this is not happening, the operator should call MCC and remind them to follow this procedure. The beam should ramp 1 microAmp every 3 seconds.
  • Make sure the raster is on when the polarized $^{3}$He cell or reference cell is in position. Again MCC should be aware of this, but the target operator should monitor this with raster++ available on adaqs2. The target cell can explode within minutes of taking beam with the raster off, so please check this regularly. If the beam has been off for a while, coordinate with your shift leader to put the target in the BeO position so the raster and beam position can be checked out.
  • If the oven cools down, make sure the lasers are turned off. Alarms are set up in case this happens, but the target operator should check the oven is near the set temperature.
  • The transverse lasers can only be on when the cell is in the Polarized $^{3}$He Cell position. Most likely this won't harm the cell, but it can damage the oven. Again, software interlocks are in place, but a target operator should make sure this is not done.
  • Turn the lasers on slowly, one at a time. Wait at least 1 minute between turning each laser on. This will reduce the thermal shock on the pumping chamber.
  • Watch the flow of the cooling jets. There are small jets of helium spraying on the end of the target cell. If the helium flow stops it becomes dangerous to have the beam on the target. This flow can be monitored on the RTD screen.
• Maintain polarization of the target - There are several things a target operator can do to maintain a high target polarization:
  • Minimize the number of NMR measurements - Every NMR measurement causes a small loss of polarization. Each shift there will be a set of instructions on how many NMRs to take and when to take them. If the operator follows these instruction they will be fine.
  • Never have the lasers on when the field is in the wrong direction - A target operator will have to be continually aware of what configuration the lasers are in, if the laser half-wave plates are in or out and the direction of the holding field. The following are valid configurations:
    • Holding Field = 0 degrees, Half-wave plates are out, lasers are in longitudinal configuration
    • Holding Field = 90 degrees, Half-wave plates are in, lasers are in transverse configuration
    • Holding Field = 180 degrees, Half-wave plates are in, lasers are in longitudinal configuration
    • Holding Field = 270 degrees, Half-wave plates are out, lasers are in transverse configuration
    All other configurations will reduce the polarization.
  • Minimize the time with the lasers off - The lasers must be turned off at certain times (when taking an NMR in the transverse direction, during any field rotation, when moving the target). The target operator should try to perform these actions promptly and try to do them correctly the first time. Of course, racing through and making mistakes is worse than doing it slowly!
  • Minimize the number of field rotations - There is a small polarization loss when rotating the field, so any extra rotations will reduce the polarization.
• Moving the target cell - The target can be moved to the following positions :
  • Pick-Up Coil position - In the target are a set of coils that detect the resonance signal during an NMR measurement. This is the position where that measurement is made.
  • $^{3}$He Target position - The position where the polarized $^{3}$He data will be taken
  • Carbon/BeO Target position - This position has the carbon foil targets for acceptance studies and the BeO target for beam positioning.
  • Empty position - No target, for background checks.
  • Reference Cell position - A reference cell filled with Nitrogen, $^{3}$He and $^{4}$He can be used for unpolarized data. This is the position where the reference cell is in the beamline.
• Rotating the Holding field - The main 25 Gauss holding field of the target can be rotated using the Holding field control panel. The target will be run in 0, 90, 180 and 270 degree configurations. NMR measurements can only be made in 0 and 180 degree configurations, so if the target is taking data in a 90 or 270 degree configuration, the field will have to rotated to 0 degrees for the NMR measurement and then back again for data taking.
• Performing and documenting NMR measurements - NMR is one of the two methods we use for measuring our target polarization. The target operator will be responsible for performing and documenting this measurement.
• Alerting the EPR expert when you need to take an EPR measurement - EPR measurements will be scheduled from time to time and it will be the responsibility of the Target Operator to page or call the EPR expert on call (this person will be listed on the white board).
• Keeping an eye on things - The target operator should watch the various indicators and make sure nothing is outside the proper range of operation.