• Eight new ion pump elements.

They can be bought from DUNIWAY, www.duniway.com

• Vacuum pump
• A high voltage supply capable of 4000 V / 200 mA

This we have to buy one. CFA has always brought one for the repair.

• Vacuum valve key, ¼ inch "T" handle. See the "maser bag" I have put together.
• ½ inch deep socket. See the "maser bag" I have put together.
• Torque wrench.
• Vacuum valve flange type1.33-mini flange with a rubber gasket.

• One big copper O-ring for the Source assembly.

We have two spares in the "maser bag".

• One small copper O-ring for the Cajon Joint, type CU-2-VCR-2 from Swagelok.

We have six spares in the "maser bag"..

The maser can be moved to a convenient location to have easier access around it.

Shut off switches PUMP, VALVE and SOURCE.

Leave MAIN and THERMAL switch on at all times.

Remove the top, the sidepanels and the rear perforated panel.

Remove the Palladium valve heater (when it’s cool!!!) by removing the spring and sliding it off.

Unplug and remove the fan, 2 screws on the frame and 1 on the aluminium source cover.

Remove the two top halves (shield covers) covering the maser top.

Remove the 5 screws that hold the dissociator oscillator to the source flange.

Unplug the wires to the dissociator oscillator.

Remove the oscillator and set it aside.

Remove the dust cover on the vacuum pump valve.

Use a bag, which you purge with Nitrogen gas and put it over the opening flange for the vacuum valve. Use the hose (Nitrogen gas) to keep a positive pressure inside the bag while you slowly open the vacuum valve, using a ¼ inch "T" handle wrench about 1 turn to vent the vacuum chamber SLOWLY. Once up at atmospheric pressure remove the bag and close the valve, not tight.

Loosen the 20 nuts on the source flange using a ½ inch deep socket. Remove the 20 threaded studs (bolts) with a screw driver (leave the nuts on the bolts). Remove the 2 screws that hold the steel angle bracket to the Isolator box.

Disconnect the Cajon Joint where the Hydrogen line enters the source flange and remove the small copper gasket. (will be replaced by a new one later).

Swing away the steel bracket that supports the Nupro valve.

Lift the source up and out of the pump body and set aside. Cover the HEX Mag + support tube (4 inch diameter) with clean aluminium foil (to prevent anyone touching it since grease is bad to have in the vacuum chamber).

DO NOT GET ANYTHING INTO THE OPENING IN THE BOTTOM. THEN YOU ARE IN REAL TROUBLE. USE GLOVES WHEN YOU WORK INSIDE, NOT TO GET GREASE INSIDE.

If a lot of flakes are seen in the pump base, remove them with a vacuum cleaner.

First you cover the opening at the bottom with a piece of aluminium. Fix the aluminium on three sides with some tape. BE CAREFUL NOT TO BEND THE 2 SEMIRIGID COAX LINES THAT GO DOWN INTO THE CAVITY.

Make a note of how the ion elements are mounted.

Remove the steel straps that connect the anodes (on ion pump element) together and goes to the high voltage feed through connector and set aside on clean towels or aluminium foil.

Remove the pair of nuts (16 in total), that holds the elements to the sidewall. Place them on aluminium foil. Carefully bend the strap from the High Voltage Feed Through up and away from the element. Be careful not to put stress onto the HV Feed Through.

Remove the 8 elements.

Remove the screw and nut from the old elements that makes the connection to the anodes of all elements. On the new elements (remember there are 4 left and 4 right), which mount into the bays, bend the tab to a 90 deg angle to the anode.

Reinstall the screw and nut from the old elements.

Vacuumclean the bays of where the elements previously were and inspect using a torch. If very small particles can be seen on the sidewalls that the vacuumcleaner did not remove, use a dust free paper towel that has been dampened with a good grade of alcohol and wipe the surfaces clean.

Install the new left and right elements with the nuts previously removed. Do not tighten at this time. Take the high voltage straps and if there is a lot of blue flashing around the areas where the screw passes into the holes or slots, they can be cleaned using a piece of Scotch Bright to polish the overlapping areas of the straps. Clean the straps with alcohol to assure that no dust particles remain. Reinstall the straps and secure with the nuts. Leave loose. The most difficult one will be the one which comes from the high voltage feed through. Carefully bend the strap into position over the screw and install the nut. Tighten all 16 nuts that hold the elements to the sidewall.

Tighten the high voltage straps to the anodes with 7/16 inch wrench.

Remove the aluminium foil on the bottom and recheck the inside surfaces. If needed clean the surface where the tape was that was holding the foil down. Look at the 2 coax lines and make sure that they are not touching each other or the side walls of the pump body.

Remove the High Voltage connector and measure from the High Voltage connector to the cylinder (ground). You should read an infinite value.

Measure between the High Voltage connector and each anode of the ion pump elements. You should read a short circuit. Replace the High Voltage connector.

Take the source assembly and remove the old copper gasket. To remove it use a very small blade screwdriver and gently tap it so the tip goes under the gasket from the inner diameter of the seal. Don’t go too far in since you will scratch the source assembly. Twist the screwdriver and the gasket will pop out of its position. Clean the sealing surface of both flanges with alcohol. Place a new 8 inch gasket on the flange of the pump body, after a light wiping with alcohol.

Replace the source assembly onto the flange remembering to line-up the "witness marks" on the flanges. Mount the L-bracket for the Isolator unit. Put in the 20 threaded studs.

Install a new copper gasket on the Hydrogen feed line. Tighten to finger tight. Using a 3/8 inch and a 7/17 wrench. Tighten thereafter the fitting ¼ turn only. If you tighten too much you will break the copper gasket.

Tighten all the nuts hand tight, making certain that the Isolator box bracket is fully engaged to the studs. Start to tighten the nuts in a circular manor each one about 1/8 of a turn. Repeat this cycle about 5 times or until you are certain that all nuts are tight.

Install the vacuum pump out fitting to the pump out valve using the rubber gasket and 3 screws in every other hole. Make certain that the gasket is seated in the groves of the mating flanges. Tighten with a Ball Driver. Attach the Turbo Pump to the fittings. Tighten the pump out valve with the ¼ inch "T" handle a bit snug.

Turn on the Turbo Pump and watch the pressure readings on the control unit. When it reaches less than 2.5x10^-4 mbar slowly open the maser vacuum valve to no more than 2 turns.

When the pressure reaches 1x10^-3mbar, open the valve about 6 turns.

Keep pumping out the maser for about 4 hours and log the pressure reading every ½ hour or so.

When the pressure is about 2x10^-5 mbar, the external high voltage supply can be turned on. To do this, disconnect the High Voltage BNC from the internal supply on the rear (grey box) and connect it to the external HV supply. A safety ground strap should also be attached to a good location on the maser (from the ext. supply to the maser). Turn on the HV supply.

The pressure will rise up to the 10^-4 range. The voltage on the supply will be about 400 V and the current at about 150 mA or so.

IMPORTANT

Do not keep the HV on at these power levels for more than 10 – 15 minutes at a time (the ion pump elements gets quite hot). Turn off the HV at this time. Turn back on after about 15 minutes. Repeat until current is less than 20 mA. Thereafter you can leave it running.

When the pump current is between 5 or 6 mA the maser pump out valve can be closed and tightened.

It is important to tighten just slightly more than last time it was tightened. Last time (2002-03-29) it was at 89 IN/Lbs. You have to keep a log of this torque for the next maintenance.

IT IS IMPORTANT TO HOLD THE BODY OF THE VACUUM VALVE WITH ONE HAND WHILE TIGHTENING WITH THE OTHER.

Otherwise you can break a gasket sitting under the valve. Close the valve to the Turbo Pump and loosen the 3 screws on the maser pump out valve flange to vent the line.

Disconnect the vacuum pump lines and place the dust cover on the pump out valve.

Reconnect the Isolator box with the 2 screws. Install the Source Oscillator with its screws.

Keep the external power supply to the maser running at least 12 hours.

The pump current after this time should be in the range of 500 uA.

The external supply can be turned off and the cable connected to the internal supply.

Turn on the PUMP Switch and record the voltage and current on the meters. Remount the top covers and install the fan. Turn on the VALVE switch after installing the Palladium Valve Heater and securing it with the spring clip. When the Palladium VALVE voltage is stable at about 10 – 12 V, turn on the SOURCE switch. The discharge will light and be red in color. If the humidity is very high the color could be a bit blue. This will clear up soon. Replace all panels and Good Luck.