Fisons VG-54

Operational Guide for baking out

 

Prepared by Merry Yue Cai, Paolo Montagna, Leopoldo Pena

 

May 14th  2009

 

 

Part I. Preparation (before taking anything apart!!!)

 

First, consult the main PIs of the TIMS lab (Steven Goldstein x8787, and Sidney Hemming x8471), set up a time with the electrician (Tom Protus at the moment of writing), Marty Fleisher, one or two senior members of the group (Gary Hemming is very knowledgeable about the TIMS as well).  Email VGTIMS@ldeo.columbia.edu about the need to bake out, it would be nice for all the new members of the group to observe and help out. The whole process takes ~7 working days (1 day prepare, take out the source, etc; 1 day take things apart, 3-4 days bake out, 1 day putting things back).

 

Have aluminum foil and plastic wrap handy to wrap the screws and connectors.

 

1. Clean the mass-spec room

 

Sweep, vacuum and wipe (if necessary) the floor!

We will have connectors resting on the floor so a dust-free environment is crucial for the success of the bake-out. Plus, this is probably the only occasion (other than maybe the Open House) to clean up the lab!

 

Wipe off all surfaces on the machine (top first) with Kimwipe and methanol.

 

2. Check for leakages

 

Before we bake-out it’s also a good time to check all the fittings to see if there are any leaks that need to be mended.

Squirt some methanol at the fittings while keeping an eye on the analyzer pressure, if the pressure changes when we do that, it means there are leaks!

 

3. Take out the source (the collimator) (See Plate 1)

 

This step requires venting the source housing, so it should be done the day before the actual bake out. Afterwards, the source housing should be pumped down before opening the LOS valve the second day.  Gloves must be worn at all times while handling the collimator or touching anywhere inside the source housing. A piece of clean paper, letter size or larger, should be lain below the source, above the turbo pump opening to prevent small screws from falling into the opening (picture 1a). 

 

Before opening the source housing, routinely check that the HT, ion gauge, oxygen valve etc. are off. First remove the exit slit (need to remove two little screws, Picture 1a). Be very careful not to damage the slit. (The exit slit should be cleaned every time a turret is changed).

 

Loosen the three screws that secure the source/collimator in place, but don’t take them out just yet.

Then we need to use a special tool called the collimator extraction tool (Picture 1c) that helps extracting the collimator outwards.  Insert the collimator extraction tool into one of the holes (Picture 1b) and extract the collimator (Picture 1d).  Wrap the entire collimator in plastic wrap and set it in a box carefully. Watch out for the spacers, ceramic rods and gold pins at the end. (We have a back up source that is missing some of these spacers and golden pins. Find it in the desiccator in the loading room or with Tom).

 

Someone with experience should take apart and clean the source (collimator) itself, a great observing experience for new members of the group. To return the collimator back to position, we need to use the tool again to insert the collimator first, make sure the holes for the three screws are aligned before the unit is in position and unscrew the collimator tool first before putting in the 3 screws because the collimator tool would prevent the collimator from completely being in place.

 

After taking out the source, we should wipe off the surfaces inside the source housing with methanol and Kimwipe (o-ring with water and dry Kimwipe), close the source housing and pump the source housing down overnight. This step ensures that after opening the LOS, the flight tube pressure remains the same, which makes baking shorter/less painful.

 

Please refer to page 3-9 of the User’s manual of Sector 54 for detailed instructions of taking off and cleaning the source/collimator components. Cleaning the source/collimator is crucial as it affects the ion beam focus.

 

4. Software ready

 

HT- set to 0, then switch to standby position, then turn OFF!

Filament current – set to 0

Magnet – set to mass 85 (reset mass)

Cups -- Set the cups to Nd setting maybe?? (Use the automatic collector setup program).

Write down the exact reading of the motor and the number reported on the computer in so that when we put the motors back they will agree. Picture 2

 

5. Turn off the computer

 

Otherwise the computer will freeze after we disconnect the electronics.

 

6. Turn off all electronics (well, most of them) (See Plate 2)

 

Leave the ion gauge on source filament for now (to preserve the analyzer filament in case of accidents) and monitor the pressure throughout the bake out.

There should be 2 filaments each for the source and for the analyzer, which are both located behind the source housing. To switch between the 2 filaments, use the switch below the magnet (picture 2a). To switch between the source and the analyzer filaments, use the switch on the control unit, first to off position, then change (picture 2b). The analyzer filament itself is in picture 2c and 2d. ** To change the actual analyzer filaments requires venting of the flight tube. To change the source filaments requires venting of the source housing. **

 

Leave the LOS control on.

Leave the ion pump on only if the analyzer pressure is lower than 5x10^-5 mbar

 

Control panel

Except the control unit for the Ion gauge/pirani gauge, turn off all other electronics on the control panel in the following sequence: the right panel first, left panel second, from top to bottom. On the right panel (picture 2e, right side), you will turn off: magnet supply, filament supply, HT (to standby position, and then off), power supply for the motor and more?? On the left panel (picture 2f, left side), you will turn off the 3 switches for the collectors/acquisition control unit.

 

7. Turn off the high voltage unit below the machine (See Plate 3)

 

Turn off the high voltage unit below the machine.

Turn off the HT unit (picture 3a) that connects the collectors and the Daly.

Leave the Ion pump on if the machine wasn’t vented, or if the analyzer pressure (on the ion gauge) is lower than 5x10^-5 (mbar).

Turn off the ESP supply unit (picture 3b)

 

8. Keep the LOS open (See Plate 4)

 

LOS needs to be kept open during the bake-out. To do that, we first need to take off the motor unit on top of the LOS (See picture 4a, it has a spring inside). Then, insert a metal Allen key in the left hole (one that is further away from the machine) to stop the LOS from closing when the air is off. Double check if the LOS is open by looking through the glass window of the source door (the source collimator should be out by now and you would see a dark path into the flight tube if the LOS is kept open.

 

The LOS has to be opened before turning off the air supply. The LOS WON’T open if there is a big pressure gradient, or under air pressure without the pumps on.

 

Turn off the air (See picture 4b, the control is on the shelf next to the machine, trace the white gas tubing to find out. Perpendicular position is close)

 

 

Part II. Take off all electronic connectors that would be under high temperature

 

1. Take apart the LOS control unit (See Plate 5)

 

All of the parts for the pneumatic controls have to come off, and the plate that holds the indicator telling you if the LOS is open or closed must come off too.

 

Make sure the air is turned off (picture 4b)

Loosen the screw that connects the air tubing. 

Take off the tubing. WRAP well.

Loosen the screw to the power box, unplug the power cable (picture 5a, 5b).

Loosen a few more screws that stabilize the pneumatic control unit and take off the unit completely. WRAP well, set aside. 

 

2. Take off the exterior connections to the high voltage feed through on the source (See Plate 6)

 

Make sure the HT is really off before unplugging anything here.

See picture 6a. First take off the 3 outer and 3 inner screws that fix the plastic cover on top of the wires.

Fit the plastic tube through the opening of the plastic cover so that one can reach the connectors.

Remove the connectors (Picture 6b). Remember to double-check the corresponding numbers on the cables (if number is missing, make one) and the numbers of the connectors on the machine. Our experience this time is that not all of them are clearly marked with the corresponding numbers to the ceramic sensors. (A small screw driver is needed to loosen some of them. No need to take any small screws off, leave them on.)

Now the whole high voltage wires as well as the plastic cover should be detached from the machine. WRAP well, set it on the floor.

 

If the warm-up unit on the opposite side of the source is covered with a plastic cover too, then remove the cover and set it aside as well.

 

3. Take off the turret motor drive and sensor for the turret (See Plate 7)

 

Unplug the power cord. Take off the sensor for the turret reset position.

Take off the blue motor control unit.

Then use an Allen key to loosen the two bolts in the brown cylinder (picture 7a) and take it off (picture 7b).

 

4. Remove the amplifier housing (See Plate 8)

 

Turn the Peltier temperature control unit to off position, then power off (picture 8a).

Shut off the valve connecting the backing pump with the amplifier housing at the back of the machine. Loosen the screw that fixes the tubing on the amplifier housing. Vent the amplifier housing slowly.

Unplug the tubing. Wrap well. There should be an extra bolt and rubber fitting inside.

Disconnect all cables connecting to the amplifier housing (picture 8b).

Disconnect the grounding wire so that we can remove the housing (picture 8c).

Be very careful, very straight and steady when removing the amplifier housing (picture 8d). NO GIGGLING AROUND!!! There are 10 pairs of gold pins inside the housing which enable the connection between the collectors and the electronic receivers, miss-match of any pair would disable the corresponding collector. This is a difficult step in putting things back together as well).

Cover the surfaces with aluminum foil.

 

5. Retract the magnet (See Plate 9)

 

Record the reading on the dial gauge attached to the magnet. (Picture 9a) (There is a smaller dial within, read that one as well. Everyone in the group should read it). Observe the marks on the rail that signify the rough position of the magnet, which we have to return it to (picture 9b).

There are two nuts that are stuck in between the magnet to prevent it from sagging. Remove them for now. The specific positions are not important. (Picture 9c)

Retract the screws on the side of the rail so that the magnet can slide on the rail.

Retract the magnet with the wrench (picture 9d). Use the wrench to move the magnet till the long screw comes out and the magnet can slide all the way to the rear of the bench.

 

6. Unplug the cable to the collector motor (See Plate 10)

 

Read the position of the axial cup before this step (picture 10a).

Remove the power cords connecting to the motor drives. (MAKE SURE TO RELABLE THE CORRESPONDING CONNECTORS BEFORE TAKING THEM OFF)

Remove all collector motors after ensuring the collectors are adequately spaced (Picture 10b).

You’ll need a long Allen key to reach the bolts (Picture 10c) and a small one to loosen the screws (picture 10d).  Make sure to have a partner so as to avoid loosing any parts. Set the motors on the table wrapped in plastic wrap.

 

Unplug all the suppressor cables connected to the collectors. (They should have all been marked already.)

 

7. Remove the photomultiplier tube (find its purple silk cover first) (See Plate 11)

 

The photomultiplier (picture 11a) is very sensitive to light, so all light should be turned off in the room first. It should be wrapped in the purple silk cover immediately after removal (picture 11b).

Remove all electrical cords connected to it first. The tube itself should be a twist off.

 

Kevin et. al. installed a small computer fan onto the scintillator (with air blowing outwards) to keep it from overheating (Picture11d). The scintillator window in picture 11c seems a bit burned already, that was before we started baking out this time.

 

8. Remove the high voltage connector and the aluminum cover from the Daly electrode Three bolts need to be loosened here.

 

9. Remove the electronics unit at the very rear end of the TIMS, see picture 90

 

Finally, check everywhere, the Oxygen valve is closed, that all cables, electronic parts, temperature sensitive parts have been disconnected from the machine before proceeding to the next part, heating.

 

 

Part III. Set up the heating components

 

Double check!!! All electronics, cables and plastic that could be covered under the blanket should have been removed before proceeding.

 

1. Locate all necessary parts for heating

 

4 ovens, 4 extension cords (in the drawer by the front entrance, one from Tom), heating blankets (in the cabinet next to the Triton), racks (kept under the AC unit in the lab), 3 functioning thermostats and the digital reader (the one in the tool box needs 9 volt battery).

 

2. Set up the racks and the ovens roughly following the schematic drawing below

 

Schematic drawing of the oven and thermo sensor positions. (Needs to be copied from the lab handbook.

 

 

 

 

 

 

 

 

 

3. Attach the thermo sensors

 

A sensor should be attached directly to: (1) the flight tube, (2) behind the source housing, and (3) most importantly at the rear end of the machine where the temperature sensitive scintillator is.

 

Target temperature:

Flight tube (130 degrees C)

Source housing (120 degree C)

Scintillator (below 80 degree C) If instead of the scintillator, we have a heat resistant unit installed, then we should make sure that the rear end has a higher temperature than the flight tube in order to create a temperature gradient that drives air towards the source housing.

 

4. Start heating

 

First, meet with all group member involved in the bake out and set up a monitoring schedule. The first day or two, the Analyzer pressure, the temperature and oven settings should be monitored every 15 minutes, until we are certain that an equilibrium temperature has been reached. Afterwards, decrease the monitoring frequency to once per 30 to 60 min.

 

Everyone has to record the Analyzer pressure, sensor temperature and oven setting on the log book. Also, mark the positions on the ovens, setting 1, setting 2, etc. The readings of the ovens do not really correspond to the actual temperature. In 2007, we set them to 250-300 degrees C to achieve the target temperatures.

 

Monitor the analyzer pressure of the ion gauge on the control unit (and of the ion gauge if it is turned on). If the analyzer pressure is higher than 5x10^-5, turn off the ion pump. If the analyzer pressure is higher than 5x10^-4, turn off the analyzer filament. Switch to the source filament. The source filament currently reads about one order of magnitude higher than the analyzer filament, bear that in mind. Also the analyzer filament also incidentally reads one order of magnitude higher than the dial of the ion pump.

 

It would also be a good idea to turn on and degas any newly installed source or analyzer filaments at this point.

 

The heater settings and equilibrium temperature (see schematic drawers):

2006, Heater 2, Heater 4, Heater 5, Heater 6.

May 2009, Heater 2, Heater 4, Heater 5, Heater 6.

 

 

 

 

 

 

 

 

 

After 1-2 days of heating, the pressure at the ion gauge should come down to 10^-7 and 3 hours after terminating the bake out (turning off the ovens) the pressure should be below 10^-8 torr.

 

 

Part IV. Putting things back together

 

After a good vacuum is retained and the machine has been cooled off for one night, we can take off the covers remove the rods and ovens from around the machine. At this point, another cleaning is necessary since lots of dust would have accumulated from the heating blanket onto the surface of the machine. So, another round of wiping with kimwipe or use the little hand held vacuum cleaner first (watch out for possible small screws left on the bench) before wiping off the surface. 

 

 

1. Reinstall the LOS unit

The first important task is to install the LOS pneumatic control unit and turn on the air so that we can close the LOS valve. Tom helped us with this step. If Tom is not around, make sure to install the electric unit first, use the automatic system to open the LOS, remove the wrench, then use the control unit to close the LOS. Afterwards, we can install the rest of the LOS.

 

2. Reinstall the turret motor control unit

 

This part is a little tricky, please check with Tom before putting it back together as there is a piece of thin metal piece inside the unit that keeps the rod from slipping that Tom made specifically for the new motor unit. Also the laser device that signals the reset position needs to be attached correctly so that it only signals at one position.

 

After installing the motor unit, we can then calibrate the turret position. Please refer to page 6-12 of the software manual for detailed instructions in how to calibrate the turret position.

 

3. Reinstall the source cables

 

It’s very important to attach the cables to the right connector for the HT, focusing, filament current to work properly. Hopefully we’ve marked them before we took them apart so that we can return the connecters back to their original positions. It’s better to first organize the cables and start from left to right and bottom up so that we won’t need to tangle the cables. The cables could break during the process, Tom knows how to fix them, but one should take care to avoid this extra step.

 

Reinstall the covers.

 

4. Reinstall the collector motors

 

After making sure that the collector motors are in the correct positions, reinstall them carefully. Do it with a partner. High cups are at the back and low cups are at the front of the machine.

Plug in the motor cables underneath.

Double-check the axial cup position. If it has been moved, return it to the reading recorded before. Remember that to move the high cups outwards is by turning the rod clockwise (I don’t recall which way it is for the low cups). Also remember to move the outer cups before the inner ones. Bumping cups together is BAD!

 

5. Wind in the magnet

 

After cleaning the bench, push the magnet towards the flight tube until the long screw can be installed in the magnet again. Then use the wrench to draw the magnet further back in smaller steps. Someone should stay at the back of the magnet to monitor the dial. Remember that the inner dial is reading a bigger unit than the outer dial. The final position of the magnet should be right where the markings are, which should also agree with the reading of the dials from before.

 

6. Reinstall the amplifier housing

 

Do it with a partner who will stand on the backside of the machine and help you align the contact probes under the amplifier housing with the cups. First make sure the metal pin fits into position in the amplifier housing, and then align the probes. DONNOT GIGGLE AROUND as it will probably damage the contact probes.

 

After the amplifier housing is reinstalled, plug in the two cables and the plastic tubing that connects to the backing pump. Make sure to put the o-ring on the metal part of the tubing first so that a good seal can be achieved through the screw and the o-ring. If there is a leak here, when we open the valve that connects to the backing pump, we would be pumping air into the source housing, which is very bad.

 

7. Reinstall the photomultiplier tube, and all other cables

 

8. Turn on the electronics

 

Start with the collector control, from bottom up, then the motor control unit, bottom up.

Turn on the ESF unit, the high voltage connected to the Daly, and then the Peltier temperature control (return to set position). At this point, check if the collectors show correct readings. If the readings are static, there might be a chance that the contact probes of the amplifier housing are not making contacts.

Turn on the computer.

 

9. Recalibrate the collector positions

 

Load a few standards (Sr, Nd, Pb) and a blank Re filament on a turret and close the source housing to pump down overnight.

The second morning, if the pressure of the source is good, and the Peltier temperature control shows green light, which means normal temperature, then we can turn on the HT, set the magnet to Re (187) and turn up the blank Re filament to check if we observe Re signal on all ten cups and whether a stable peak can be achieved. Temperature for observing Re is about 1890 degrees (open LOS at 1830 degree) for an aiming intensity of 8 milivolts.

After finding a Re signal, we can then turn up a Sr, or Nd standard and align the cups.

Save the new cup setting in the computer (use “read”, then “save”)

After the cups are aligned, do a CC gain calibration (we did 20 sequence, averaging 3 per sequence and 5 sec interval).

 

After the gain calibration, turn up a Sr standard and run it.

 

If the values are good…viola!