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Section 4 Cryogenics

Contents

1. HELIUM LEVEL INDICATOR (HLI) WITH THE RMMU:.......................................................................3

2. CHECKING IF LIQUID HELIUM IS INSIDE THE MAGNET..................................................................3

3. DETERMINING THE TEMPERATURE INSIDE AN F2000 MAGNET...................................................4

4. LIQUID HELIUM FILLING ....................................................................................................................6

4.1. Only qualified engineers for helium filling ..............................................................................................6
4.2. Bottom fill procedure .............................................................................................................................6
4.3. Safety precautions when working with liquid helium..............................................................................7
4.4. Tools needed for filling helium...............................................................................................................8
4.5. Liquid helium transfer lines....................................................................................................................8
4.6. Special conditions and actions for mobile magnets .............................................................................11
4.7. Liquid helium fill procedure..................................................................................................................12
4.8. Transfer problems ...............................................................................................................................16
4.9. Helium leak test...................................................................................................................................16

5. APPENDIX A: MONITOR CHART HELIUM FILLING F2000 MAGNETS...........................................17

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1. HELIUM LEVEL INDICATOR (HLI) WITH THE RMMU:

To measure the helium level inside an F2000 type magnet, the RMMU has to be installed. Notice that the
RMMU can be used stand-alone, which means that the fibers to the host computer are not connected.

NOTE

The Helium Level Indicator (HLI mounted inside the Remote Magnet Monitoring Unit, RMMU) allows the
operator to monitor the level of liquid helium inside the helium vessel. The HLI is an indicator only and is
intended to give an approximate measurement of the liquid helium level. The inaccuracy is ±5% of the full
scale, which equals 80 litres!
________________

Procedure to measure the helium level with a Digital Volt Meter (DVM):

1. If not yet done, connect the RMMU to the mains and to the magnet via the instrumentation cables:
- MRJ4 at the RMMU to MBJ1 at the MIB.
- MBJ3 at the MIB to MB1 at the magnet.
2. Connect the DVM (set to 100 mV) to the voltage jacks on the RMMU.
3. Press the HLI button.
4. Read the DVM after 30 seconds; reading in mV equals '%'.

With a fully installed MR system, the helium level can be measured as follows:

1. Login: Intera
2. Select: Scan Control
3. Select: Scan Utilities
4. Select: Read helium level
Helium level is ...%.

2. CHECKING IF LIQUID HELIUM IS INSIDE THE MAGNET

If, for whatever reason, you think that the magnet could be completely empty, it is necessary to measure the
temperature inside the helium vessel.
Three situations are possible:

1. The helium vessel contains more than 0 litres of liquid helium.

Filling can be done with the refrigerator installed and running.
If the refrigerator is not installed yet, install it as soon as possible.
In this case the 'normal' helium filling procedure must be followed.
2. The helium vessel is empty and the temperature is lower than 150 K (*).
Start filling helium as soon as possible. Use the bottom fill procedure. See paragraph 4.2
3. The helium vessel is empty and the temperature is higher than 150 K (*).
In this case the magnet needs to be precooled with liquid nitrogen.
For this action you have to ask assistance at the MR Helpdesk.

(*) See the following paragraph for determining the temperature inside the helium vessel.

MR/Intera-SMI-101 03.0 BCD 4 - 3

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3. DETERMINING THE TEMPERATURE INSIDE AN F2000 MAGNET

Tools and documents:
• Flexible current leads (+) and (-).
• 20 V power supply (laboratory type, capable of supplying > 1 mA).
• Digital Volt Meter (input impedance > 1 MOhm for DC volts range).
• The 'Electrical Interconnection Drawing 3001' delivered with each magnet.
This document is helpful in understanding the measurement, but is not strictly necessary.

Conditions

The measurement can be done on the bare magnet, without cabling and without magnet power supply
cabinet. Installation of the magnet inside the RF shielded room is not necessary.

CAUTION

Do not perform a temperature measurement on an F2000 magnet, which is on field! If the magnet is on field,
its temperature is always 4.2 K.

________________

Procedure:

1. Make sure that the magnet is ramped down.

2. Insert both current leads into the magnet.
3. Measure the resistance between the positive and negative current lead. Do not measure at the
jacks on the current leads, but measure on the big connectors at the end of the current leads.
If the resistance is smaller than 0.5 Ohm, the magnet winding and/or the magnet main heater are
still super conductive, meaning that the temperature inside the magnet is lower than 10 K. If the
resistance is higher than 0.5 Ohm proceed with step 4. In the latter case the measured resistance is
unreliable due to the presence of the magnet main heater.
4. Disconnect the instrumentation cable FM1 from the magnet.
5. Connect the output of the power supply between the big connector of the (-) current lead and pin J
of the 41-pin connector MJ1 on the magnet see Figure - Magnet temperature measuring set up and
Figure - Instrumentation connector. A current of about 0.5 mA should flow.
6. Measure the voltage Ucm between pins C and M of the 41 pin connector MJ1 on the magnet
7. Calculate the magnet resistance Rm as
follows: Ucm (mVolt)
Rm = [Ohm]
0.5 (mA)
8. Use Table 1. to determine the approximate temperature of the coils.
9. Remove the power supply and reinstall the instrumentation cable FM1.

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Figure 1 - Magnet temperature measuring set up

0.5 mA

CURRENT LEADS CURRENT LEADS

10 V

20 k A 20 k Z
20 k C 20 k k 20 V

V V

20 k M 20 k c
MAIN MAIN
HEATER 20 k J HEATER 20 k e

INSTRUMENTATION INSTRUMENTATION
CONNECTOR CONNECTOR

FLINT MAGNET FLINT-F AND F2000 MAGNETS

PV81.DRW

Figure 2 - Instrumentation connector

E F G
D H
C c J
b d
B K
a n p e
A L
Z m t q f

Y M
k s r g
X N
j h
W i P
V R L
U T S

INSTRUMENTATION CONNECTOR
PV88.DRW

MR/Intera-SMI-101 03.0 BCD 4 - 5

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Table 1 - Conversion table from resistance to temperature for F2000 magnets.

0.5 Tesla 1.0 Tesla 1,5 Tesla 3Tesla Temperature
53 Ohm 125 Ohm 200 Ohm 774 Ohm 300 K
37 Ohm 81 Ohm 142 Ohm 720 Ohm 200 K
24 Ohm 55 Ohm 90 Ohm 667 Ohm 150 K
10 Ohm 24 Ohm 38 Ohm 615 Ohm 100 K
20 Ohm 5 Ohm 9 Ohm Tbd Ohm 50 K
0.4 Ohm 1,0 Ohm 1,7 Ohm Tbd Ohm 10 K

NOTE

When the refrigerator system is working and the magnet is running out of liquid helium, leave the refrigerator
system on!
________________

4. LIQUID HELIUM FILLING

4.1. ONLY QUALIFIED ENGINEERS FOR HELIUM FILLING

Filling helium on field is only allowed for qualified engineers. The service engineer can be considered
'qualified' when he/she has participated in a training that included the helium filling process and safety
aspects and he/she has experienced one filling action. With 'experienced' we mean actually inserting the
transfer line into the dewar / magnet and being familiar with the 'whistling' sound produced by a transfer line
when the dewar is almost empty. Just being present with a filling action is not enough.

NOTE

If 'warm' helium gas has entered a ramped down magnet during helium filling, it is not allowed to ramp-up the
magnet within the first 12 hours. If the magnet is ramped up before this time has passed, a magnet quench
may be the result! It can take up to 12 hours before 'warm' gas has cooled down enough inside the magnet
to allow for ramping up again.

________________

4.2. BOTTOM FILL PROCEDURE

The liquid helium filling procedure described in paragraph: 4.7 should be used when there is still some liquid
helium inside the magnet.
If no liquid helium is inside the magnet and the temperature inside the magnet is lower than 150 K, the
'bottom fill procedure' should be used.

The bottom fill procedure is almost identical to the ‘normal’ helium filling procedure as described in
paragraph: 4.7. The only difference is: Insert the transfer line all the way down into the bottom fill funnel. By
wiggling the transfer line one can determine if it is seated properly in the bottom fill funnel. Notice that the
minimum transfer line length you need to reach the bottom fill funnel is 64 cm. Check if your transfer line has
this minimum length.

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4.3. SAFETY PRECAUTIONS WHEN WORKING WITH LIQUID HELIUM

Liquid helium must be maintained inside the helium vessel to keep the windings super conductive. Liquid
helium level probes are installed inside the helium vessel to monitor the level of liquid helium. The probes are
connected to the Helium Level Indicator (HLI).

In general, the helium level is monitored once every 24 hours to make sure that the level of liquid helium is
sufficient. For a magnet that is on field this level should be higher than 30% for 0,5T – 1,0T – 1,5T magnets.
For 3T magnet the minimum helium level is 72%. Under normal circumstances the liquid helium
consumption will be approximately 1 % / week.

The following safety precautions must be adhered to when working with liquid helium:

• Always store and transport liquid helium under positive pressure and in closed systems to prevent
contamination of the liquid helium with air.
• Do not permit condensed air on transfer lines to run down into the magnet or dewar opening as it may
freeze up and block the release of helium gas.
• Keep pressure relief devices free and clear.

WARNING

• Only use non magnetic helium dewars.

• Keep the gas supply bottles outside the 0,5 mT line
• During helium filling, it is important to have room ventilation for escaping helium gas. The door of the RF
cage should always be open during helium filling. For mobile systems the hatch must be opened to
ensure good ventilation.
• Helium gas supply bottles must be kept outside the 5 gauss line.
• Liquid helium is extremely cold. The liquid, or cold vapor from the liquid, can cause cold contact burns
and damage to the eyes and skin. Do not touch vapor plumes or frosted pipes or valves. Protective
equipment and clothing approved for use with cryogenics must be worn to protect the eyes and skin
whenever handling or working with the liquid helium or cold vapor from the liquid. For details about
helium see the Material Safety Data Sheet MSDS MR-005.
________________

CAUTION
1. Check for leaks several hours after helium fill has finished. After this time the helium should have
built up sufficient pressure to make it possible to detect leaks.
2. Cold/frozen O-rings should NEVER be mechanically loaded. The O-rings have to be at room
temperature before the compression fittings of the ports are tightened.
3. Be sure that the helium fill opening contains the following parts and that a spare set is available:
12.7 mm ½ inch 15.88mm 5/8 inch
- O-ring 4522 130 73601 4522 150 24111
- Small metal ring 4522 130 73611 4522 150 24531
- lock cap 4522 130 73621 4522 150 24541
- Metal plug 4522 150 10801 N/A.
If one of these items is not present, the seal is not leak tight. See Figure - Compression fitting.
4. Do not leave the magnet open for a long time. If the magnet does not have over-pressure, air can
enter the helium vessel where it will freeze solidly and cause icing problems
________________

MR/Intera-SMI-101 03.0 BCD 4 - 7

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Figure 3 - Compression fitting

SMALL METAL
RING LOCK CAP METAL PLUG
O-RING

PV44.DRW

4.4. TOOLS NEEDED FOR FILLING HELIUM

Tools needed:
• Liquid helium transfer line (not standard delivered with the system). See paragraph: 4.5.
• High pressure cylinder of helium gas or self pressurising dewar.
• Non-magnetic liquid helium dewars.
• Pressure regulator for helium gas with fittings and hose. Pressure regulator not needed if self-
pressurised dewars are used. Fittings depend on the dewar configuration. With the pressure regulator it
should be possible to adjust the pressure between 0 and 10 psi / 700 mBar.
• Protective gloves and face shield.
• Aluminium step ladder, height about 180-200 cm.
• Snoop, for checking on leaks. Delivered with the system.
• Heat gun of minimum 1500 Watt.
• Spare compression fittings.

4.5. LIQUID HELIUM TRANSFER LINES

The position of the helium filling port on a F2000 magnet is higher than on previous magnet types.
Therefor the length of the transfer line that goes into the magnet is important. Table 2 shows transfer lines
that can be used, provided that the ceiling height is sufficient.

Table 2 - Helium transfer lines

Philips 12 nc Vendor p/n Vendor Min ceiling Min ceiling Figure:

height NT height F2000
4522 300 02892 621.0635 OMT 2716 3080 Figure 4
4522 150 00143 30114-01 IGC-T5/NT 2620 3186 Figure 5
4522 150 23101 N/A Air products 2555 2885 Figure 6
4522 150 23101+23481 N/A Air products -- 2650 Figure 6
Not available On request Linde L-form 2565 3085
Not available On request Linde -dip tube Inserting outside
Not available 3 221 3451 Linde U-form 2735 2915
4522 150 23611 K0007 IGC-F2000 2620 2620 Figure 7

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Figure 4 - OMT helium transfer line

80mm 2265mm 80mm

VACUUM PUMP
OUT FITTING

(3) FLEXIBLE TUBE

NW 25 FLANGE

12.70mm

640mm
1440mm
592mm

(5)
EXT. PIECE
(4)
EXT. PIECE (1) = (2) + (3)
370mm
320mm

(2)
120mm MAGNET END

DEWAR END
PV41.DRW

Figure 5 - IGC helium transfer line

VALVE

514

976

MAGNET END

790

DEWAR END PV50.DRW

MR/Intera-SMI-101 03.0 BCD 4 - 9

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Figure 6 - Air Products helium transfer line

FLEX LINE 2438mm

(C)

VALVE

VACUUM
VACUUM PUMPOUT
PUMPOUT

(D) 400mm
MAGNET STINGER
DIAM= 12.7mm

55mm
VACUUM 155mm
PUMPOUT
(B) 100mm
DEWAR STINGER 1550mm (E)
DIAM= 15.87mm MAGNET STINGER
DIAM= 15.88mm F2000 STINGER

A=B+C+D
HELIUM TRANSFER LINE
PV43.DRW

Figure 7 - IGC F2000 helium transfer line

65 65

VALVE

100
DIAM. 5/8" (15.88mm)

903

BOTTOM FILL
EXTENSION PIECES
1702

MAGNET END 799

DEWAR END
PV08.DRW

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4.6. SPECIAL CONDITIONS AND ACTIONS FOR MOBILE MAGNETS

There are some small differences between filling a stationary magnet and a mobile magnet.
These differences are:
1. The helium transfer line for filling a mobile is longer. See Figure - Mobile IGC helium transfer line.
2. The helium fill procedure for filling a mobile is slightly different.

Figure 8 - Mobile IGC helium transfer line.

6000mm
250mm

FLEXIBLE TUBE

12.70mm 12.70mm

914mm
476mm

DEWAR SIDE MAGNET SIDE

PV57.DRW

Please take notice of the following remarks:

1. The mobile liquid helium transfer line differs from the stationary transfer line.
The mobile system is standard delivered with a special mobile version. The length of the
transfer line is significantly longer, because of the longer distance between dewar and
magnet.
2. Because of the greater length of this transfer line the efficiency will be lower than of a
stationary transfer line. As a reference use 70 % (compared to 80% for a stationary transfer
line).
3. Because the space above the magnet is limited, the hatch must be opened during the fill
procedure. Also because of escaping helium gas, which can result in dangerous situations
(oxygen replaced by helium gas), the hatch must be opened.
4. The transfer line is stored somewhere inside the trailer.

Differences in the helium filling procedure in case of mobile systems.

1. Place the dewar outside the trailer, close to the opened rear door. Insert the transfer line
slowly, procedure identical with the stationary fill procedure. See for dewar preparation the
stationary fill procedure.
2. Pre-cooling of the transfer line will take more time than pre-cooling of a stationary transfer
line. Wait until a white plume is visible at the end of the transfer line. The service engineer
must be on top of the magnet during pre-cooling of the transfer line, to make it possible to
insert the transfer line as soon as the line is cold.

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3. Insert the transfer line into the magnet and continue as described in paragraph: 4.6 for the
stationary situation.
4. If a second dewar is used to fill a mobile magnet, follow the next procedure:

• Define, e.g. by checking the HLI meter, the expected time that the dewar will be empty. If this moment is
actual, position the second dewar close to the one in use. Be sure that the dewar side of the transfer line
can be inserted into the second dewar easily.
• The over-pressure inside the second dewar shall be positive, but low (~ 0.5 PSI / 30 mBar).
• Close the supply of helium gas or switch off the heater, of the dewar in use.
• Wait until the pressure in the dewar is almost zero. Be sure that the second dewar is ready to receive the
transfer line (all couplings checked and loosened).
• If the flow of liquid helium through the transfer line has become almost zero, remove the transfer line as
quickly as possible from the first dewar. Insert the transfer line as quickly as possible into the second
dewar. Lowering the dewar part of the transfer line shall be done not too fast, to avoid sudden pressure
variations.
• As soon the transfer line has reached the bottom of the dewar, raise it a few centimetres. Tighten the
coupling on top of the dewar. The pressure inside the second dewar must be increased to approximately
8 PSI / 550 mBar.
• Continue with the filling procedure.

4.7. LIQUID HELIUM FILL PROCEDURE

Definition of the valves on a liquid helium dewar.

Safety valve : This is a valve that opens when the pressure inside the dewar gets higher than
a certain pressure (e.g. 1 PSI). This valve MUST be open during transport and
storage but closed during helium filling.
Vent/supply valve : This valve can be used to vent down the helium pressure inside the dewar. It is
also used to supply external pressure from a helium gas supply station to the
dewar in case of a non self-pressurizing dewar.
Vent valve : This valve can be used to vent down the helium pressure inside the dewar. This
valve is not always available and not used in this procedure.
Top valve : This valve is on top of the dewar and is used to insert the transfer line.

NOTE

If the configuration of your dewar differs from this one, refer to the instructions on the dewar and/or call the
supplier of the liquid helium for more information. If necessary, adapt the filling procedure.
In case self-pressurising dewars are used for this helium fill, then the vent/supply valve is only used for
venting, which simplifies the procedure.

________________

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Figure 9 - Helium dewar valves configuration

TOP VALVE

SAFETY VALVE VENT VALVE

(FOR TRANSPORT AND STORAGE) (NOT ALWAYS AVAILABLE)

VENT / SUPPLY VALVE

TO GAS
SUPPLY STATION
DEWAR

PV45.DRW

When the safety precautions have been followed and all the necessary items are available, fill the magnet
using the following procedure:

1. Log the progress of the helium fill in the monitor chart ( see paragraph: 5).
2. When the IGC F2000 transfer line is NOT used; mark the magnet end of the helium transfer line
such that it cannot be inserted deeper than 40 cm (16 inches) into the magnet.
This to prevent a bottom fill.
3. Check if the magnet has sufficient over-pressure by checking the helium pressure gauge reading.
Pressure should be > 5 mBar.
Open the yellow ball valve.
Notice that the yellow ball valve is ONLY open during helium filling and during ramping (up or down)
of the magnet. It is closed at all other times. See Figure - Top of the magnet.
4. Make sure that the (spare) compression fittings are in place at both ends of the transfer line.
Check what transfer line length is needed for the dewar and, if necessary, attach an extender tube
to the dewar end of the transfer line.
5. Move the helium dewar to a position where the transfer line can be inserted.
6. Open the vent valve of the dewar and vent down the pressure to almost atmospheric pressure (i.e.
venting flow nearly stops).
7. Before inserting the transfer line into the dewar, provisionally close the exit of the magnet end of the
transfer line with a rubber stop or place a rubber hose over the transfer line and close it by bending
the hose.
8. Open the valve on top of the dewar and insert the transfer line slowly into the dewar till it hits the
bottom. If not yet done position the dewar in its final location. Raise the transfer line inside the
dewar 2 cm so that eventual solid parts cannot block the entrance of the transfer line and tighten
the compression fittings where the supply line enters the liquid helium dewar.
- Leave the vent valve of the dewar open.

NOTE

With this procedure, frozen material may still block the line and slow down the transfer or even block the
transfer entirely. If this happens, the line must be removed from the magnet and from the dewar and warmed
up to room temperature before starting again.

________________

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9. Loosen the compression fitting of the helium fill port on top of the magnet.
10. Close the safety vent valve on the dewar and, if present, remove the temporary stop on the magnet
end of the transfer line.
11. Externally pressurized dewar: Connect the helium gas supply station to the dewar via the
vent/supply valve (do not forget to flush the air from the hose). Open the vent/supply valve on the
dewar. Increase the pressure on the supply dewar, but keep the pressure below 140 mBar (2 psi).
12. Self pressurizing dewars: Close the vent/supply valve of the dewar. Switch on the power of the
pressure device of the dewar. Keep the pressure below 140 mBar (2 psi).
13. Before inserting the transfer line into the magnet, it is essential that there is a 'slow and steady'
stream of liquid helium passing through the transfer line. The associated heavy plume with flowing
liquid helium has a distinctive appearance.
14. Remove the compression fitting of the helium fill port and slowly insert the short end of the transfer
line into the magnet. This insertion should take approximately 30 seconds.
15. Once the magnet end of the transfer line is inserted 40 cm (16 inches)(or 10 cm for a F2000 type
transfer line), tighten the associated compression fitting.
16. Using the regulator and associated fittings and hoses, increase the pressure to about 350 mBar
(about 5 psi) during transfer.

Figure 10 - Top of the magnet

COLD HEAD

INSTRUMENTATION
CONNECTOR

HELIUM
FILL PORT
YELLOW BALL VALVE
1 PSI (68mBAR)
1/7 PSI (10mBAR)

BURST DISK
10 PSI (680mBAR)

TACONIS DAMPENING KIT

DPS
PV05.DRW

17. Calculate the estimated helium fill level, while assuming an efficiency of 80%. Use the table in
paragraph: 5 during the filling.
18. Monitor the progress of the helium transfer by taking a helium level reading every 5 minutes and
estimate the time the transfer will be completed.

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Helium level reading with the F2000 magnet:

Using application software:

1. Login: Intera
2. Select: Scan Control
3. Select: Scan Utilities
4. Select: Read helium level
Helium level is ...%

Using a DVM:
1. Connect a DVM, set to 100 mV, to the voltage jacks on the RMMU.
2. Press the HLI button.
3. Read the DVM after 30 seconds; reading in mV equals '%'.
Write down the value, date and time in the MRL.

CAUTION

When the supply dewar becomes empty, there is a chance to flush warm helium gas from the high-pressure
cylinder, through the supply dewar and into the magnet. This warm gas inside the magnet may quench the
magnet or prevent a successful ramping up of the magnet. The magnet will quench during ramping up or
shortly after being ramped up. To avoid this, keep a close eye on the transfer, and listen for the 'whistling'
sound associated with an empty supply dewar.
________________

The transfer speed can vary between 250 and 500 litres/hour depending on the transfer line used. The time
required depends on several factors, such as the supply pressure, length and size of the transfer line, the
amount of liquid helium inside the supply dewar, and the back pressure of the valves. The maximum transfer
pressure is 350 mBar (5 psi).

19. When the dewar becomes empty, one can hear a kind of 'whistling' sound coming from the transfer
line. At this time the pressure inside the dewar will drop. Open the safety valve on the dewar.

The pressure on the dewar must be vented down to prevent possible transfer of warm helium gas
into the magnet:

When externally pressurized dewars are used: Close the vent/supply valve. Close the pressure
regulator of the helium supply station. Disconnect the gas supply station. Open the vent/supply valve
and vent down the pressure in the dewar completely.

When self-pressurizing dewars are used: Switch off the self-pressurizing system on the dewar. Open
the vent valve and vent down the pressure in the dewar completely.

NOTE

Remove the compression fittings together with the transfer line.

Removing the transfer line through the fitting may cause damage to the O-ring in the fitting.
________________

20. When the pressure inside the dewar is (almost) vented down, remove the transfer line from the
magnet and close the helium fill port of the magnet with its compression fitting.
21. Close the yellow ball valve on top of the magnet when no more dewars have to be transferred.
22. Move the dewar, with the transfer line still inserted, to a position where it is possible to remove the
transfer line from the dewar.
23. Remove the transfer line from the dewar and close the valve on top of the dewar.

MR/Intera-SMI-101 03.0 BCD 4 - 15

Copyright © 2003 Philips Medical Systems Nederland B.V.
ALL RIGHTS RESERVED
Section 4 Intera 0.5 T Intera 1.0 T Intera 1.5 T Intera 3.0 T Intera
Omni/ Power/ Omni/ Power/ Master/ Explorer/ Master/
Standard
Stellar Pulsar Stellar Pulsar Nova Nova Dual Quasar

24. Open the safety valve and close the vent/supply valve of the dewar.
25. In case you want to transfer another (full) dewar into the magnet, heat up the transfer line to room
temperature to prevent air from freezing solidly inside the line. Record the amount of helium inside
the magnet and the time of the reading. Return to step 4 of this procedure to continue with the helium
transfer.
26. If not already done: Close the yellow ball valve on top of the magnet.
27. Record the HLI reading 1.5 hour after the transfer has been completed. It takes some time to
establish a thermal equilibrium inside the helium vessel. Only then a reasonably accurate reading
can be obtained.
28. Write the HLI reading and the amount of liquid helium used in the MRL.

4.8. TRANSFER PROBLEMS

In case the helium transfer has stopped (the helium level is not increasing in time) check the following items:

1. The pressure inside the helium vessel is equal to the pressure inside the dewar. Probably caused by
a blocked venting system. Check if the yellow ball valve on top of the magnet is open.
2. The entrance to the transfer line inside the dewar is blocked by ice or because the transfer line hits
the bottom of the dewar. In case the transfer line hits the bottom, raise it two centimetres and the
transfer will continue.
3. The helium gas fill pressure has dropped because the helium gas cylinder is empty.
4. Check if the helium exhaust pipe of the system is not blocked, e.g. by a bird-nest.

4.9. HELIUM LEAK TEST

If there is no over-pressure, or even under-pressure in the magnet, it is possible there is a leak somewhere.
There are four possibilities for having a low helium pressure without having a helium leak:
1. After a helium transfer.
2. After ramping the magnet.
3. After blowing hot helium gas inside the magnet.
4. After a very rapid increase of air pressure.
With each of these possibilities, the pressure will rise again within 36 hours for an F2000 magnet. For a T5,
Flint and Flint-F magnet, this is 12 hours. This is a normal situation.

If the pressure inside the magnet does not build up any more, there is a leak. This is a serious situation,
which has to be solved within two days. In the meantime switch off the refrigerator system. The boil-off
without the cold head running is much higher. In this situation the risk of getting ice inside the magnet is
much smaller. There are three possible ways to find the helium leak:

1. Using snoop (delivered with the system).

2. Using snoop and the 100 mBar pressure gauge.
3. Using the portable helium leak tester (4522 980 39441).
Notice that when there is a big leak the helium back ground level inside the examination room is so high that
using snoop is easier than using the helium leak tester!

Parts which have to be checked:

• All O-rings on top of the magnet.

• Burst disk.
• Helium fill and current lead ports.
• All one way valves.

To check the helium pressure real time a helium pressure-measuring tool has been added to the tool list.
12nc 8122 102 52721. The helium pressure gauge can be mounted at the helium-input port of the magnet.
The helium pressure gauge is a little bit magnetic but can be used in a magnet field. On Fint-F and F2000
magnets the helium pressure is installed permanently.

BCD 4 - 16 03.0 MR/Intera-SMI-101

Copyright © 2003 Philips Medical Systems Nederland B.V.
ALL RIGHTS RESERVED
Intera Intera 0.5 T Intera 1.0 T Intera 1.5 T Intera 3.0 T Section 4
Omni/ Power/ Omni/ Power/ Master/ Explorer/ Master/
Standard
Stellar Pulsar Stellar Pulsar Nova Nova Dual Quasar

5. APPENDIX A: MONITOR CHART HELIUM FILLING F2000 MAGNETS

Moment of fill Date: ..... - ..... - ____ time: .... : .... h

Magnet type 0.5T / 1.0T / 1.5T / 3.0T

Equipment used
Transfer line used OMT / IGC-T5 / IGC-NT / Linde / Air products / IGC-F2000
Other ___________________________
dewar contents .......[liters]

Last ramp
Date .... - .... -____
at field no / yes

Starting point
Cold head running more than 5 days Yes / if no, for how many hours? .....h.
Connected to the gas-recovery no / yes
Liquid helium level before fill .......... liter
Estimate fill level (eff. 80%) .......... liter
Liquid helium level 1h. after fill .......... liter

Efficiency ........ %

Time Helium level actual pressure Fill remarks

[liters] [mBar] pressure
[psi]
00:00 < 140mB/2psi insert Transfer line in dewar (≈30 seconds)
Before inserting the transfer line into the magnet, it is essential that there is a 'slow and steady' stream of
liquid helium passing through the transfer line. The associated heavy plume with flowing liquid helium has a
distinctive appearance.
00:01 < 140mB/2psi insert Transfer Line in magnet (≈30 seconds)
00:05 ≈ 350mB/5psi continue transferring at ≈350 mBar
00:15
00:30
00:45
01:00
00:15
00:30
00:45
listen for the 'whistling' sound: stop transfer immediately and remove the pressure on the dewar
02:00
00:15
03:00 Record helium level

MR/Intera-SMI-101 03.0 BCD 4 - 17

Copyright © 2003 Philips Medical Systems Nederland B.V.
ALL RIGHTS RESERVED