~sober/manuals/tag_pwr_sup.txt    
					     rev. 27 July 1997

  	          Operating the Tagger Magnet Power Supply
    			
   1.  Cold start before run

      a)  Check that LCW is flowing.
      b)  Check that the 440 V breaker on the north wall is on.
      c)  Check that no undesired tools or materials are in the vicinity of 
           the magnet.
      d)  Plug in flashing red light, and post "Hazard - High Magnetic Field"
           signs at alcove and at both ends of the catwalk.
      e)  Turn on the power supply circuit breaker on the left front corner
           of the cabinet.
      f)  Check that the two air vent covers on the cabinet top are 
           unobstructed.  (The covers are taped down at one edge, and will
           swing upward when the fans are on.)
      g)  Press RESET on the control panel to reset the Air Flow (AFLOW)
           interlock, which is always off at power up.
      h)  Check that all lights on the Fault Module (FM) are on.
	  * If AFLOW light is off, check that the two air vents on the 
             cabinet top are uncovered.
	  * If WFLOW light is off, increase the water flow rate to the 
             power supply.
	  * If the SPR1 light is off, check the external interlocks
             (magnet water and magnet temperature).           
          * If the MG and SF lights are off, this indicates a blown fuse
             in the external interlock system.  Replace fuse F24EX in the
             TBEX terminal block behind the second door from the right
             in the rear of the cabinet.  (Spare fuses are stored inside
             the door.)
          Press RESET after correcting the condition.
      i)  Test the magnet temperature interlock by unplugging MGINT connector
           on top of cabinet, and press RESET after restoring the interlock.  
         | (We should install a normally-closed pushbutton switch somewhere 
         | to make this test automatic -- also for magnet water when the
         | flow switch is operational.)
      j)  Check that the Ready (RDY) light on the the Control Module (CM)
           is on.
      k)  The power supply powers up in REMOTE mode (REM light on, LOC light
           off on the Control Module (CM).  (For local operation, see
           instructions posted on the cabinet.)  
      l)  For remote control, the serial cable must be plugged into the 
           front of the Serial Interface Module (SIM), and the toggle
           switch on the SIM must be in the down (SERVICE) position.

  
   2.  Setting the magnet current 

      The tagger power supply is controlled by the operators in MCC, using
      an EPICS screen developed by Scott Higgins.  The nominal set current is 
      calculated automatically from the Hall B channel settings (using 
      a spline interpolation between raytrace values provided by D. Sober),
      and is displayed in the lower left of the screen.

      Request that the operators bring up the Tagger Magnet Control screen,
      and that they connect a video monitor to the Tagger Dump camera.

      After checking that the beam is off, the operator must
      a) click on PS CMD ON.
      b) enter the nominal set current value (displayed at the bottom of
          the screen) into the Set Current box and hit the <Enter> key.
      c)  within a brief timeout period, click on CONFIRM in respose to
           the request "Confirm Beam Off".
      The supply is then automatically taken through the prescribed 
      hysteresis procedure:
		Wait 3 minutes at 0 Amperes.
                Raise to I = 2400 Amperes and hold for 3 minutes.
 		Lower to the setpoint.
      In approximately 15 minutes, the magnetic field should be stable
      to the 0.01% level, or about 1 mm beam deflection at the tagger dump.  
      It should be possible to begin beam steering earlier than this, 
      starting approximately 5 minutes after the current setpoint is reached.

      The operator can adjust the magnet current by small amounts (<1%)
      using a slider bar on the screen.  The sensitivity of the slider 
      is variable, and should be set to steps of 10**-1 Ampere (about
      0.1 mm per step at 2.4 GeV).

      The surveyed nominal beam position is 5.3 mm above center on the
      tagger beam dump viewscreen.  ("Above" in real space is to the left
      on the video screen.  The ticks on the viewscreen axes are 5 mm
      apart.)


   3. Advice for beam tuning

      In all runs to date (December 1996 through June 1997, at 0.8, 1.4,
      1.6, 2.4 and 4.0 GeV) the nominal set currents were found to produce 
      a beam spot very close to the center of the viewscreen on the tagger 
      beam dump.  Hitting the surveyed nominal beam position (5.3 mm above 
      center) required a current setting about 0.5% below the nominal set 
      value.  This setting also produced the lowest background rates.

      The operator should be told to leave the tagger magnet current at its
      nominal setting until tuning is completed.  We have not yet seen any
      case in which adjusting the tagger magnet has had any useful effect
      on the tuning process.  After tuning is complete, the field may be
      adjusted to set the beam at its nominal position (5 mm above center.)


   4.  Changing the magnetic field

      Changes of less than 1% may be made without going through the
      hysteresis procedure, either by using the slider or by entering the
      new current setpoint directly.

      A change of more than 1% in the field must be made by going through
      the automatic hysteresis procedure described above.  The beam must
      be off when changes of more than 1% are made.


   5.  Controlled access to the Hall

      The tagger magnet should be left on during brief controlled accesses 
      to the hall, unless work is to be done in the immediate vicinity of 
      the magnet (e.g. collimator box, tagger hodoscope, radiator ladder.)


   6.  Degaussing the magnet

      After the entire photon run period is completed, ask the operator
      to turn the beam off and to click on the Degauss Magnet Enabled
      button.  The following program is run automatically:
	Set I=2400 A, hold for 3 minutes.
	Set I=0, hold for 3 minutes
	Turn off the power supply.
        Reverse the polarity to POSITIVE("NORMAL"), using the internal 
         reversing switch.
	Turn on the power supply.
        Set I to a preprogrammed set current (1000 A), wait until the
	 set current is reached, then hold for 15 seconds.
	Set I=0, hold for 3 minutes.
	Turn off power supply.
	Reverse the polarity back to NEGATIVE("REVERSE").
      If the degauss procedure is not run from MCC at the end of the
      photon beam run, the magnet may be degaussed later under LOCAL
      control.  Instructions for local operation are posted on the
      power supply cabinet, and are also found in the file 
      ~sober/manuals/tag_pwr_sup_local.txt .