800 MHz US 2 NMR system

Transcription

1 800 MHz US 2 NMR system To achieve ultra-high-fields (>700 MHz), the magnet must be cooled to below (ambient pressure) liquid He temperature. The He cryostat is divided into two sections. The upper section remains at 4.2K. The magnet sits in the lower section, which is cooled to ~2K. With this design, the He temp in the magnet bath doesn t depend on atmospheric pressure, room temp, etc (as in conventional cryostats). However, the stability of the system does depend on the He cooling system. If the cooling system goes down, the magnet will quench in 8-12 hours. Because of the cryostat design and the method of subcooling, the He temp in the magnet bath is extraordinarily stable, with variations only in the 0.1 mk range. This type of magnet is known as ultrastabilized.

2 The upper and lower sections of the cryostat are connected by narrow channels so the pressure is always the same in both (slightly higher than ambient). Cooling is done by a Joule-Thomson cooling unit. Liquid He is allowed to expand through a needle-valve into a heat exchanger. All that is necessary to keep the whole thing running is a small pump that keeps the pressure in the heat exchanger <30 mbar. If the pump completely stops the magnet will quench in 8-12 hours. However: There are two backup pumps. The pumps are on emergency power and powered by a UPS that will keep them running for ~9 hours. We have a small gas-powered generator that can power the pumps in case the power goes out entirely.

3 Active Shielding Extra coil sections wound in the opposite direction to the main magnet cancel most of the magnetic field outside the magnet. Part of the field in the bore also gets cancelled, so the field strength of the main magnet (minus the shielding section) has to be larger than the nominal field strength of the magnet. This is why the cryostat of our shielded 800 is the same size as the cryostat of the 900. The radial 5 gauss line of an unshielded 800 is 20 feet from the center of the magnet. With a shielded 800, it s only 7 2. The stray field is smaller than that of an unshielded 500. Because our NMR magnet is both ultrastabilized and ultrashielded, it is called 800 US 2.

4 Top view of platform and equipment Note: the north side of the platform has the same cross-bracing as does the east side (seen in the diagram below). BMPC pumps south wall BCU 05 west wall North desk console North B M P C Side view of stairway This view is actually from under the platform facing east.

5 Room Diagram - showing relevant pieces of equipment Wall socket CU 2/4 50 ft adaptor cable Extra vacuum line Power cord for P3 N generator pumps BMPC Flammable cabinet (gas cans inside)

6 BMPC and pumps One pump must always run otherwise the 800 will quench in 8-12 hours. Ordinarily, pump 1 (P1) always runs. If P1 has a problem, the system automatically switches to P2. P1 and P2 are the smaller, identical pumps at the right and left sides of the pump box. The BMPC controls and monitors the system. If anything goes wrong it sets off an alarm and starts calling the people on the emergency call list. B M P C P1 P3 P2 toolbox extra pump The pump box is underneath the stairway of the platform. If P1 and P2 both fail, P3 can be turned on manually by plugging it into the 220 volt wall socket (CU-2/4) or into the gas powered generator.

7 Pump box

8 BMPC

9 Guide to BMPC Errors These are all of the alarms that the BMPC gives: Alarm# Type 1 T1 or T2 too high 2 P1 too high 3 P1 too low 4 F (flow) too low 5 Automatic failure 6 UPS; low battery There are only a few causes for all these errors. A short description of the causes and what steps to take follows. The Bruker manual titled SC Magnetsystem contains comprehensive descriptions of all possible errors and troubleshooting. The SC magnetsystem manual is located on top of the pump box underneath the stairway.

10 Alarm 1: T1 or T2 too high. These are temperatures measured at the bottom and top of the magnet coil, respectively. Usually accompanied by alarm 2 or 3, and alarm 4. Possible reasons: pump failure, closed valves at the pumping unit, leak in the pumping line, closed or blocked needle valve. Alarm 2: P1 too high. The pressure in the pumping line is too high. Should usually sound before alarm 1. Possible reasons: pump failure, closed valves at the pumping unit, leak in the pumping line. Alarm 3: P1 too low. Should usually sound before alarm 1. Possible reasons: butterfly valve on top of the cryostat is closed, closed or blocked needle valve. Alarm 4: F too low. The He gas flow through the pumping line is too low. Should usually sound before alarm 1. Possible reasons: pump failure, closed valves at the pumping unit, closed butterfly valve on top of the cryostat, closed or blocked needle valve. Alarm 5: Automatic failure. Failure of the automatic mode. BMPC switched to manual mode. Alarm 6: UPS; low battery. Main power supply failed and the UPS has almost used up its battery capacity. Possible reasons: power outage.

11 Alarms 1-4 mostly have the same possible reasons. These are: A. Pump failure B. Closed valves at the pumping unit C. Leak in the pumping line D. Butterfly valve on top of the cryostat is closed E. Closed or blocked needle valve Here is a chart to help you determine the cause of an alarm: P1 too high closed valves at the pumping unit or Pump failure leak in the pumping line normal too low butterfly valve on top of the cryostat is closed or closed or blocked needle valve Pressure reading or Flow reading is wrong too low normal too high Flow

12 A. Pump failure If no pump is running, the first thing to do is to switch on pump 3, which is the larger pump in the middle of the pump box. To switch on pump 3, just plug the power cord (see room diagram) into the 220 volt outlet on the wall, and turn on the manual butterfly valve above pump 3 (shown below just turn it 90 degrees). Once P3 is on, the magnet will be safe. Then you can determine which pump failed and replace it. See the SC Magnetsystem manual for further details. This is the pump box located under the stairway. MV P1 P3 P2 Location of the manual valve for pump 3 (shown in the off position).

13 B. Closed valves at the pumping unit Turn on pump 3 as described on the previous page. Then the magnet will be safe and you can try to determine what the problem is. Switch the BMPC to manual mode by pushing the auto off button (located on the front panel of the BMPC). Once the BMPC is in manual mode, you can turn on and off the various pumps and valves manually just by pushing the buttons; P1, V1, P2, V2, on and off. Try to figure out which valve is closed. If you can t fix the problem, it s OK to leave the system with pump 3 running. See the SC Magnetsystem and BMPC manuals for more details.

14 C. Leak in the pump line If this is the problem, immediately close valve C (90 deg turn) as seen in the diagram below. This disconnects the cryostat from the pumping line, and will prevent ice blockage of the needle valve. Then you will have to install the temporary pumping line using the spare pump and the vacuum hose (next page). vacuum hose attaches here Valve operation (general) b side view Open Closed a c vacuum hose attachment point He transfer line Top of magnet (as seen from the stairway)

15 Connecting vacuum lines using vacuum clamps All the vacuum line connections described above are made by connecting the two lines with an O-ring between, and clamping them together with a vacuum clamp. Example: vacuum line attached to The vacuum seals and O-rings Vacuum hose attachment point. should fit together snugly. Vacuum line O-ring Vacuum hose attachment point (on magnet) Vacuum clamp is tightened around the seal. All necessary O-rings, vacuum clamps and adaptors can be found in the toolbox under the stairway.

16 The pump is shown here. The port on the left is the exhaust line. This can be left open, or the plastic cap can be loosely placed on it. The port in the middle is the vacuum line. All the vacuum line connectors needed are in a ziplock bag in the box with the spare pump. The pump just has to be plugged in and turned on.

17 D. Closed butterfly valve on top of cryostat If this is the case, one of the butterfly valves (C or A in the diagram below) was manually closed. Reopen the closed valve (s). vacuum hose attaches here Valve operation (general) b side view Open Closed a c vacuum hose attachment point He transfer line Top of magnet (as seen from the stairway)

18 E. Closed or blocked needle valve The needle valve controls the He flow through the Joule-Thompson cooling unit. Our system was set so that the He flow is around 193 ml/hour (there is a He flow gauge on the front of the BMPC). If the needle valve is closed, then the He will warm up and the magnet will quench, even if the pumps are running. First turn on pump 3 as described previously (plug it in and turn on the manual valve directly above the pump). Switch the BMPC to manual mode (described previously). Switch on P2, then V2 (buttons on the front of the BMPC). Open the needle valve completely (clockwise from the top is open), and see if the He flow increases (watch the flow gauge for five minutes or so). If the flow doesn t increase, close the needle valve all the way, then open it all the way again and watch the flow. Keep doing this until the flow increases. Once a high flow is reached (i.e., higher than 193), wait until the coil temperatures T1 and T2 reach values lower than standard operating conditions* (continued next page). *T1 and T2 are displayed as VT1 and VT2 on the small LCD display at the upper left of the BMPC. They are not displayed as temperatures, but as resistances: the higher the resistance, the lower the temperature. Under normal operating conditions, the values are: VT1 ~20113 VT2 ~15108 So you should wait until VT1 and VT2 are higher than these values.

19 Turn off pump 3 and the manual valve above pump 3. Watch the He flow for some time. If the flow remains above the standard operating value, turn off V2, then P2. Watch the He flow for some time. If the flow remains high, begin to slowly close the needle valve. Try to reach a point at which the flow is ~20% higher than the normal value, and leave it at this higher value. See the SC Magnetsystem manual for more details. **Whenever you turn the needle valve, watch the He flow gauge on the BMPC for about five minutes to assess the effect. It takes some time for the flow to respond to the change. Needle valve Top of magnet (as seen from the stairway)

20 If the alarm was alarm 5, it just means that the BMPC switched to manual mode. This is normally not dangerous, but you must make sure everything is working properly. Check that pump one is running and that V1 is on. Check that the He flow is normal (around 193). Make sure that VT1 and VT2 are at their usual values (around and 15108). If the alarm was alarm 6, then the power is probably out. Plug pump 3 into the wall outlet and see if it goes on. If it does, then maybe something is wrong with the outlet that the UPS is plugged into. If this is the case, leave pump 3 on and the manual valve above pump 3 open. Then the magnet will be safe while you determine why the power isn t on. ***If the power is completely out, then you must use the gas powered generator to power either pump 3 or the spare pump (next page).

21 All instructions for the generator are in the manual (sitting on top of the generator). Filling the gas tank: Gas cans are in the flammable cabinet. Do not remove the lid/pour spout. To pour gas, click plastic piece into place, invert can and push down hard on the plastic hook on the lid (described on the can). Instructions on filling the generator s gas tank can be found on page 27 of the generator manual. Starting the engine: Instructions for starting and stopping the engine can be found on page 29 of the generator manual. It s just like starting a lawn mower. Operating the generator: Honda gas powered generator EB3500X In order to power the pumps, the voltage selector must be set to 120V/240V. The pumps must be plugged into the L14-20 style receptacle labeled 120V/240V on the generator. Instructions for AC operation of the generator can be found on pages of the manual. The generator should be run outside the building if possible. There is a 50 ft long adaptor cable (L6-20 receptacle to L14-20 plug) on the floor next to the generator. If it s raining, then the generator must be kept inside. If you have to run it inside, keep the doors open and stay outside as much as possible.

22 The power cord for P3 terminates in an L6-20 plug: This plug matches the wall socket (CU-2/4), so it can be plugged directly into the wall. However, the 240 volt socket on the generator is an L14-20 type receptacle: There is an L6-20 receptacle to L14-20 plug adaptor sitting on top of the generator. By using this adaptor, P3 can be plugged Into the generator.

23 In addition, there is an extra pump, which is identical to P1 and P2, in a box under the stairway. As a last resort, this pump can be used to manually pump the magnet. There is a power cord in the box with the extra pump. Its receptacle plugs into the back of the pump, and looks like this: On the other end of this power cord is an L6-20 plug, which can be plugged into the wall socket or into the generator (with the adaptor), the same as the P3 power cord. There is also a 20 ft extension cord with a female L6-20 on one end and a male L6-20 on the other end. The extra pump can be attached to the magnet pumping line by means of a vacuum line. The vacuum line is stored on the floor to the west of the closet (see room diagram).

24 If any of these errors occurs, you should first stabilize the magnet then call someone at Bruker for further instructions. The BMPC is supposed to fax Bruker Germany if any alarm goes off. So someone there should be trying to call the lab (unless it s the middle of the night). Here are the contact numbers in the order that you should call them: Bill Bartsch: (978) extension 5317 (978) (cell) Pavel Kostikin: (978) extension 5360 (978) (cell) Bruker Germany Doug Lyons (978) (cell) Bruker USA (Billerica) (978) #1 for NMR. Then #2 for service. Bruker West Coast (510) UCLA Facilities Management, 24 hour emergency number: If the BMPC calls you Enter the code to acknowledge that you received the call: *. You must enter the numbers slowly you should hear a beep after each character you enter.