9T Horizontal Field Magnet Operation Manual 

Table of Contents: 

I. Prepping 

II. Sample Loading Procedure 

III. Sample Unloading Procedure 

IV. Power Supply Operation 

V. If a Leak Develops in the Sample Well 

VI. Temperature Control With LS340 

VII. Problem Solving 

VIII. System Specifications 

IX. Contacts 

X. System Drawings/ Additional Info. 
I. Prepping 

1. Pump on the outer vacuum space until the pressure is less than 1x10-4 torr, but 

preferably just let it pump overnight. 

2. Pump out the sample well using a rough pump, then backfill with helium gas. 

Repeat this three times, the last time leaving the well filled with gas and seal off. 

NEVER exceed a pressure of 5psi in the sample well space, a slight overpressure 

(1-2psi) is all that is necessary. 

3. Using the rough pump, pump out the annulus with the needle valve closed and 

purge with He gas to prevent condensation from forming during the cooling 

process. Repeat the process twice more, the last time sealing the He gas in the 

annulus. Then do the same thing to the liquid helium reservoir, the last time 

sealing the He gas in it. 

4. Leave the needle valve and annulus exhaust valve closed and open the He exhaust 

valve. Begin filling the He reservoir with LN2 through the helium fill port and let 

the system cool to 77K. The magnet temperature sensors will have a resistance of 

~7.6 Ω at this point (~30Ω equals room temp.). After one hour begin filling the 

liquid nitrogen reservoir as well. When the liquid nitrogen reservoir is full stop 

filling both reservoirs and check the level in the liquid helium reservoir using a 

bakelite stick. If there is greater than five inches of liquid nitrogen close the two 

open valves and let the system sit overnight. If there is less than five inches 

continue filling another 15 minutes then check again, repeating until there is 

greater than five inches of liquid nitrogen present. 

5. When the magnet has cooled to nitrogen temperature (normally after sitting 

overnight), the remaining nitrogen in the helium reservoir needs to be blown out. 

The best way to do this is to blow warm He gas, at about 5 psi, in through the He 

exhaust port. There is a piece of stainless steel tubing with a Teflon tip that is 

attached to the magnet cart, attach a rubber hose to the end and place in the He fill 

port. The nitrogen will spray out here, so you may want to catch it in a small 

dewar. Remove the large brass relief valve from the He exhaust and replace with 

a blank-off flange to build up enough pressure. 

6. Continue to blow the warm helium through until the magnet temperature has risen 

to ~90K (9-10 Ω) to be sure all the nitrogen has been removed. You may use the 

magnet heater to boil off the last bit of liquid nitrogen. The current through the 50 

Ω heater should not exceed 1 Amp. 

7. Replace the large brass relief valve and then, as in step 3, pump purge the He 

reservoir with He gas three times, the last time sealing the He gas in it. 

8. Now you can fill the helium reservoir with liquid helium. There should be a brass 

fitting in the small parts box that needs to be put on the end of the transfer line 

that goes into the cryostat. (This is because our transfer tubes are smaller than the 

fill port and we don’t want He spraying out of that port.) Make sure the He 

exhaust valve is open. Shortly after starting the fill open the needle valve, begin 

pumping on the annulus with a rough pump and slowly open the annulus valve. 

This will pull a steady flow of He gas through the needle valve to prevent it from 

blocking. Be careful not to overwhelm the pump, obvious by the smell of oil and 

or loud noises, and avoided by closing down the needle valve almost all the way. 

The liquid nitrogen should also be topped off during this time. 

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9. Once the magnet has reached helium temperature (~2.6Ω) you can monitor the 

progress with the He level sensor. The meter measures in millimeters and the 

reservoir is full when the sensor reads 240mm or above (anything greater than 

that is an erroneous reading that is equal to 240mm). 

10. Refill LHe when the level gets below 40mm and top-off the liquid nitrogen every 

time you fill helium. 

II. Sample Loading: 

1. Note the sample mounting dimensions below and make an appropriate sample 

holder. These dimensions come from physical limitations in the sample well. 

The only dimension with little restrictions is the space above the beam 

because the stick can be moved up to accommodate the sample holder. 

Distance to beam from top of airlock 

= 1363 mm 

Distance from beam to bottom of 

 sample well = 17 mm 

Max diameter = 28.5 mm 

Mounting Surface: 8x M3 tapped 

holes, 0.15” depth on 24mm diameter 

and 5/16”-18 tapped hole in center, 

0.25” depth. 

28.5 mm 

Sample 

Neutron beam

17 mm

2. Mount the sample onto the sample stick and mark the clamp location. (Note: 

the 1363mm distance is correct only when the sample stick is cold, when 

warm it will be too long by ~4mm.) If the sample is a single crystal, also mark 

appropriate orientation information. Lightly grease the entire length of the 

stick to prevent leaks from forming around the o-rings inside the green fitting. 

3. Make sure the gate valve is closed. 

4. Mount the sample stick in the airlock and tighten the clamp. Make sure the 

height adjustment clamp is properly tightened so that the stick is secure. 

5. Connect a turbo pump to the airlock evacuation valve and pump it out to 1 x 

10-4 mbar and then close the evacuation valve. 

6. Open the gate valve and slowly lower the stick after loosening the height 

adjustment clamp. When it is in the correct position tighten the clamp and fine 

tune the height and alignment using a neutron camera. 

III. Procedure for Unloading the Sample 

1. Loosen the height adjustment clamp. 

2. Slowly pull the stick all the way up. If the sample well has been cold, you may 

have to stop and let it warm up several times along the way. The cold stick freezes 

the o-rings, but they can be warmed using a heat gun. Do not force the stick 

through the O-rings, or they may crack and cause leaks and do not overheat them 

because they will melt. 

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3. Secure the height adjustment clamp to hold the stick up and close the gate valve. 

4. At this point the sample can be removed by venting the airlock. However, if the 

sample is sensitive to condensation connect helium gas to the airlock evacuation 

valve and fill the airlock with a foot or two of gas by pinching off the latex tube. 

Do not over pressure the airlock as there is no relief valve. 

5. Allow the sample to warm. There should be no condensation on the airlock when 

the sample is ready to be removed. 

6. Loosen the upper airlock clamp and remove the stick. 

7. Cap the airlock with a blank flange then pump it out to 1 x 10-4 mbar and finally 

close the evacuation valve. 

IV. Procedure for Adding Exchange Gas 

It may be necessary to add some helium exchange gas to the sample well. This is done 

once when the magnet is first cooled down. After that, it may be necessary to add helium 

due to the loss of exchange gas after multiple sample changes. If the sample temperature 

and the control temperature are not in reasonable agreement, then adding helium 

exchange gas is a possible solution. 

The sapphire windows at the bottom of the sample well are fragile, and easily dislodged 

by over-pressurizing the sample well! Exchange gas is always introduced in small, 

controlled amounts. 

1. Adjust the regulator on the helium supply to ~2 psi outlet pressure. 

2. With helium flowing to purge the line, attach the helium hose to the closed airlock 

evacuation valve. 

3. Pinch off the helium hose tightly approximately 6 inches from the airlock 

evacuation valve. This trapped volume is the amount that will be introduced to the 

sample well. 

4. Open the airlock evacuation valve to suck in the trapped volume of helium and 

then close it again. There may be a momentary rush of cold helium exhaust from 

the helium reservoir when this action is performed. 

5. If the sample well is warm and evacuated, add enough exchange gas to bring the 

pressure up to 10in Hg, which is less than 1 atm, or 0 psi on the pressure gauge. 

6. If the sample and control temperatures do not come into reasonable agreement 

within 5-10 minutes contact a member of the sample environment team. DO 

NOT continue to add more helium gas! 

7. As the sample well cools, the pressure will drop, due to the ideal gas laws, and the 

gauge will read 30in Hg (which is the bottom of the gauge), but there is still gas in 

there. When you add gas, you may not see the pressure rise on this gauge. 

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8. If you add exchange gas while the sample well is cold notify a member of the 

sample environment team. What is a reasonable pressure at low temperature can 

quickly get unreasonable at warmer temperatures, so it is necessary to keep an eye 

on the pressure as the system warms up. 

V. Lakeshore 622 Magnet Power Supply Operation 

This supply is setup to be controlled remotely from the SANS instrument control 

program. However, it may be necessary or preferable on occasion to run the magnet 

manually. Below are the basics to let you get by even if you have never used this supply 

before. 

1. Connect the leads from the supply to the connections on the top of the cryostat. 

The polarity does not matter unless you care about the direction of the field 

through the bore. 

2. Turn on the supply and if you are running it remotely connect the RS-232 

connection and move to the instrument control computer. The screen should look 

something like this: 

Settings: Outputs: 

0.0000T 0.0000T 

Current: 0.000A 0.000A 

Compliance: 3.501V 0.165V 

Ramp Rate: 0.0050T/s LVL: 104.2% 

Ramp Enable: <ON> FLD: 0.000T 

Persistence: <ON> 

3. To run the magnet manually from zero field first turn on the persistence switch 

heater by using the cursor down arrow until the cursor points to “Persistence”. 

Then press the up or down key on the number pad to turn persistence off. A small 

red light below the power button will light to indicate that the heater is on. 

4. Once the heater has been on for longer than one minute you can ramp the supply 

to the desired current to set the desired field in the magnet. To do this move the 

cursor up to the large number labeled Tesla and set the number by using the right 

arrow, hitting a number key and finally pressing enter when the correct value is 

set. 

5. When the supply has settled in at the desired current either leave the system as is, 

non-persistent, or turn off the switch heater, wait a minute and ramp the leads to 

zero to make the magnet persistent. 

6. To then change the field when in persistent mode ramp up the leads by entering 

the previous set point, turn on the switch heater and set the field to the desired 

value. 

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VI. Temperature Control: 

Temperature control is done using a Lakeshore 340 controller that has two sensor 

inputs and two heater outputs. There are two sensors that are used during operation of 

the system both of which are Cernox type sensors. The first is located on the VTI heat 

exchanger and is used for control. The second is located near the bottom of the sample 

stick and is used for a more accurate reading of the sample temperature. Similarly there 

are two heaters on the system as well. One is located on the VTI heat exchanger and has 

a resistance of 50 ohm and maximum current of 1 amp. The other is located near the 

bottom of the sample stick and has a resistance of 100 ohm and a maximum current of 

100mA. The VTI heater is used for normal control of the temperature over the entire 

temperature range of the system. The sample stick heater, when necessary, is used for 

fine control at lower temperatures 

9. Turn on the controller using the button on the right side of the back of the unit. 

Verify which sensor, VTI or Sample, is connected to which input, A or B, by 

reading the labels on the cables and the back of the controller. 

10. Plug in the VTI Heater cable single banana plugs into the High and Low plugs on 

the back of the controller 

11. Set the control channel to the VTI sensor by pressing the Control Channel button, 

selecting the appropriate channel and then pressing Enter. 

12. Set the desired temperature by pressing the Setpoint button, then entering the 

temperature using the number pad and finally pressing Enter. 

13. Set the correct heater range by pressing the Heater Range button, selecting a range 

using the Up or Down Arrow buttons and then pressing Enter. The temperature 

range you are working in should determine the heater range. The maximum 

heater range is needed to reach room temperature, but lower temperatures may 

only require, and may have better control, using a lower range. 

14. You know the heater is on by seeing a non-zero percentage of the heater power on 

the display under the heater range. Keep in mind that if the temperature of the 

sensor is above the set point the heater will not turn on until necessary. 

15. If the temperature is not dropping to your set point it may be necessary to open 

the cold valve on the top of the cryostat to increase the cooling power. The valve 

can be opened wide for a quick cool down over a large range, but should always 

be closed as much as possible once the set point is reached to conserve helium. 

16. There will almost always be some difference between the sensors even after 

staying at one temperature for a long time. The best thing to do is to use the VTI 

for control and the sample as the actual temperature. This is because the VTI 

sensor is placed near the heater and controls the temperature of the bottom of the 

sample well that shields the sample. If a specific sample temperature is needed 

simply offset the set point on the VTI to compensate. 

17. The sample stick heater can also be used if none of the above solutions works. 

Please contact Evan Fitzgerald (see contacts on last page) before attempting this. 

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VII. Problem Solving: 

If a leak develops in the sample well: 

1. Remove the sample stick and cover sample well with blank flange. 

2. Remove three bolts on the top of the green fitting and pull apart. 

3. Inside are two o-rings, separated by a spacer. Clean with alcohol, then grease the 

o-rings and reassemble. 

4. Make sure the length of the sample stick is cleaned and re-greased before 

inserting it into the sample well. 

5. Follow sample loading procedure as usual. 

 pull apart 

o-rings 

Note: Possible symptoms of a sample well leak include: stuck sample stick, 

inefficient cooling in sample well, and increased pressure in sample well. 

If the Cold Valve Gets Blocked: 

 

A blockage may occur on the initial cooldown, after refilling cryogens, after an 

extended period of having the valve closed or after the helium has run dry. The cold 

valve is blocked if the VTI temperature is not dropping with the needle valve and the 

annulus valve open. You should also normally be able to feel some flow of helium gas 

out the annulus valve if things are working correctly. Depending on the severity of the 

block you may be able to fix the problem with the following steps: 

1. Close the cold valve and annulus valve completely. 

2. Connect a rough pump to the annulus valve and after opening it pump/purge 

the annulus with helium gas multiple times. 

3. With the annulus pumped out and the pump on open the cold valve and 

monitor the VTI temperature. 

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4. If the temperature drops steadily you have removed the block. If it does not 

drop you should repeat the above steps again. If this fails again continue to 

the next step. 

5. The next option is to raise the temperature of the sample well to 300K and 

hope that is warms the cold valve assembly enough to melt away the 

blockage. Once the VTI has reached 300K repeat steps 1 – 4 again. 

6. If this does not work the system will need to be warmed by blowing off the 

cryogens. Contact a member of the sample environment team for assistance 

before attempting this. 

If the Magnet Quenches: 

The magnet has quenched when for some reason it goes normal (nonsuperconducting) while carrying current. Normally the sudden resistance produces 

enough heat, depending on the amount of current in the coils, to boil off all the helium 

and warm the magnet to 30 or 40K. The boil off will occur within a matter of a few 

minutes and is pretty unmistakable. The power supply should also indicate a quench 

especially if it occurs during ramping. No matter how it happens a member of the sample 

environment team should be contacted immediately to assist in the recovery as well as 

determine what went wrong. 

 

VIII. System Specifications: 

Sample Probe 

Mounting Surface: Gold plated copper (green part is anodized aluminum). 

 8x M3 tapped holes on 24.0 mm diameter with 0.15” depth. 

 1x 5/16”-18 tapped hole centered with a 0.25” depth. 

Maximum Sample Size: 28.5 mm diameter. 

Distance to field center: Top plate surface: 923 mm 

 Top of airlock assembly: 1363 mm 

Field center to bottom of sample well: 17 mm 

Sensor Type: Calibrated Cernox 

Heater Resistance: 100 Ohm, 100mA (max) 

Wiring: User twisted pair: Enameled manganin 1.2mm 

Sensor: PTFE sheathed constantan 1.25 mm 

Heater: PTFE sheathed Stranded copper 28 AWG 

Cryostat 

Liquid nitrogen reservoir: Depth: 227 mm 

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 Volume factor: 1.15 L/cm 

 Capacity: 26 L 

Liquid helium reservoir: Depth: 225mm 

 Volume factor: 1.0 L/cm 

 Capacity: 23.5 L 

Heater Resistance / Max Current: Reservoir: 26 Ohm, 1 Amp 

 Magnet: 50 Ohm, 1 Amp 

 Heat Exchanger: 50 Ohm, 1Amp 

Static He boil-off: 0.22 L/hr 

Magnet 

Central Field constant 0.07565 T/A 

Current for 9 Tesla 118.9 Amps 

Max field achieved in test at 4.2 K 9.08 Tesla (120 Amps) 

Homogeneity over 10mm DSV 2.3 x 10-3 

Homogeneity over 20mm DSV 8.9 x 10-3

Nominal Coil inductance 32.0 H 

Remnant Magnetization 55 Gauss (5.5 x 10-3 T) 

Maximum ramp rate 0.18 Amps/sec 

Persistent mode switch normal state current 17.9 mA 

Switch heater resistance (Pins 1-2) 132 Ω 

Switch heater resistance (Pins 5-6) 134 Ω

Switch opening voltage 1.7 V 

Recommended switch voltage 2.2 V 

Horizontal magnet bore 94 mm 

Vertical/horizontal split bore 43 mm 

Diameter of stainless outer vessel 254 mm 

Overall length 244 mm 

IX. Contacts: 

Main Magnet Contact: Evan Fitzgerald (x6657, Rm. A123, cell: 240-498-3941) 

Secondary Magnet Contact: Dan Dender (x6225, Rm. A118, cell: 443-676-5073) 

SANS Contacts: 

 NG3: Bryan Greenwald (x5797, Rm. A113) 

 NG7: Jeff Krzywon (x6650, Rm.A113) 

X. System Drawings/Additional Info. 

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