The Helium Cryotarget manual

PiP/TOF experiments 2002

Computer: macroidle
File: /home/a2online/helium/manual2002/helium_manual.html

Setup of the cryotarget system: 100 l dewar (left), cryotarget within the dE detector (right)

Filling Helium

Refill liquid nitrogen, see next section. This can be done in parallel to the transfer of liquid helium.
Turn on the liquid Helium level meter. Plug in the local 50 Ohm resistor into the short BNC cable end. (righthand side of PiP)
Open the valves at the Helium pressure bottle right to the tagger door:
- Open the main (high p) valve first,
- adjust the reduction valve to a low p < 1 bar,
- open the low p valve
Place the ladder behind the 100 l Helium can stand
Climb the ladder and open the black valve on the top of the transfer pipe in the 100 l can
Close the relief valve ("exhaust") at the 100 l Helium can. Keep the inner handle open so the pressure sensor measures the can pressure
Pressurize the Helium can. Carefully open the "pressure" valve and watch the pressure meter (red digits, pressure in the Helium can shown in mbar)

Warning: Do not exceed a transfer pressure of 120 mbar! Open the "exhaust" valve if the pressure goes beyond 110 mbar.

Keep the flux always below 5 l/s , i.e. not more than half a turn per second on the flow meter.
If the pressure is below 50 mbar, the transfer is interrupted, you blow in gas again and you probably have to restart the filling procedure, which causes the flow to increase. This is a time and Helium consuming process and can happen even if the can is almost full. You should increase the pressure to more than 50 mbar in such a case.
Always watch the vacuum gauge. If the cell has a cryo leak, it might happen, that the vacuum in the cryostat moves up to pressures like 0.1 mbar. In such a case you should turn off the turbopump ("STOP"), until the vacuum is better than 10-2 mbar, then turn it on again ("START").
Phase 1 (5 min):
- The transfer line will cool down.
- The Helium flux through the flowmeter is rather low (high flux resistance for gas)
Phase 2 (5-10 min):
- liquid Helium reaches the cryostat
- The Helium flux through the flowmeter increases dramatically (all Helium boils out immediately in the target)
- the pressure in the 100 l dewar increases even without pressurising the dewar
- If the transfer pressure exceeds 120 mbar: Open the exhaust valve!
Phase 3 (3-10 min)
- the rate of the flowmeter drops
- the transfer pressure drops, when the "pressure build-up" valve is closed
- the Helium level (as seen on the level meter) will rise slowly
- maintain a rather constant transfer pressure of 80..100 mbar
- the cryotarget is full at 88 % on the level meter. The pointer then will jump to > 100%.
- Close the top valve of the transfer line quickly.
- Open the the back line at the Helium can "exhaust".
Remove the local 50 Ohm resistor from the Helium level meter.
Check the monitors in the Messraum. Sometimes the lamp and/or the cameras are displaced, so that the displays are not readable. Correct, if necessary.
Check, whether the 100 l dewar needs a refill: Check the scheduled refill volume at the flowmeter left to the entrance to the compressor room. If the actual volume is larger than the scheduled volume, you should refill it immediately (see acc. section)
Otherwise: Close the hall, proceed with the measurement

Valve system at the helium pressurised bottle

Valve system of the 100 l dewar

Filling liquid nitrogen

Move the carriage with the LN₂ can parked beside the tagger wall to the ⁴He--can platform.
Take the isolated hose and connect it to the outlet of the nitrogen dewar of the target (instead of one of the Bunsen valves).
Slowly open the valve at the can and watch the LN₂ flow. It usually takes less than 5 min to refill.
If the nitrogen tank is filled (fountain out of the hoses), quickly close the valve.
Allow the isolated hose to warm a bit to avoid breaking.
Put the carriage and the LN₂ hose back to their original places.
Check that there is no object between the target and the ToF wall.
If the can is empty:
Move the carriage out of the hall, but continue with the measurement!
- unscrew all connections marked "O" on the photograph
- remove the metal ring
- pull out the transfer system, put it to a safe place
- refill the LN₂ dewar at the big tank of the MPI (across the backyard of the institute, if you don't have the key: the inner handle of the door can be opened with a cardboard tube)
- put the carriage back
- remount the transfer system
- put the carriage back during the next Helium refill and fill LN₂

Valve system of the nitrogen dewar

Helium protocol

Most of the Helium target parameters can be supervised from the Messraum. The following displays can be watched on three monitors in the noisy Messraum: Camera positions

Positions of the cameras

Monitor 1: Evaporated Helium gas volume [m³]
Monitor 2: Pointer of the Helium flowmeter (10 l/revolution)
Monitor 3:
- Status of the turbopump (the "ok" lamp should be on, the "over" lamp should be off)
- high vacuum pressure (Balzers gauge), should be below 10^-5 mbar
- Helium level (pointer on the analog scale)

The Helium level probe should be read via a millivolt meter (PM 2518X in front of the monitors). Due to the fact, that the level probe heats up the Helium there is no steady display of the level. You have to put a 50 Ohm resistor into the according cable in front of the meter (marked "Helium level") for ~3 seconds to read the level [mV].

Note the values in the paper file as well as in the helium protocol program. This program is (I hope so) self explaining and resides on the offline analysis machine "macrobusy" in the directory /home/a2online/helium and can be called by typing in "heprot".

The estimated refill times may differ slightly depending on the method used. You should definitely refill the target when the level meter shows 18.7 mV. Due to the fact, that the level meter has a "dead end" of ~1 cm and 18.7 mV corresponds to the upper end of this zone, the level meter display won't go beyond that value. A buffer time of ~30 minutes is still left when the estimated refill time has been reached.

Taking a helium reading:

Measure the evaporation time for one litre
note the vacuum pressure
note the meter reading (in m³) and
check the turbo pump display.
measure helium level putting in the 50 Ohm and note the clock time.

Refilling the 100 l helium can

Dismount the transfer line:

Use gloves!
Put the long ladder between the target and the 100 l dewar stand
Open the brass nut in the transfer line, pull out the end of the hose
Dismount the (flexible) L-piece:

unscrew the nut at the target cryostat (1 turn)
pull out the end of the L-piece completely, be careful!
put the L-piece to a safe place near the 1000 l dewar
close the hole for the transfer line in the target with the according plug (it is sitting in the brass ring which holds the target)

Dismount the T-piece (in the 100 l dewar)
a tall person is needed, a second person should assist
- open the inbus screw holding the T-piece in the tripod
- open the brass screw at valve V3 (one turn)
- pull out the T-piece, be careful!
- close valve V3 (vertical line) quickly
- put in the metal plug (hanging on a little chain)
- remove the support tripod on the 100 l can
- close valve V1
- close the "storage dewar" valve at the other end of the exhaust hose mounted on the tagger wall (righthand to the beam line) In no case close the other valve labeled "target". It will make the target cell blow!!!
- dismount the hoses attached to "exhaust" and "pressure build-up" at the 100 l dewar and disconnect the cable mounted to the gauge.

Lift the can with the crane using the short orange ropes
Put the can on the scales in front of the Helium liquefier
Note the starting weight of the can, an empty can has a weight of 130 kg, 100 l of LHe correspond to 12.6 kg.

Refill the can
- Connect the exhaust metal hose to the "exhaust" valve (should be lying around near the scales) both to the "exhaust" valve of the can and the exhaust connector of the liquefier (see photograph)
- Open valve V1 and the "exhaust" valve
- Remove the plug from valve V3, open the brass nut (one turn)
- Insert the flexible(horizontal) part of the L-piece into the connector on top of the 1000 l dewar, fasten the big brass nut
- Slowly insert the vertical pipe of the L-piece into the 100 l dewar: Open V3, when the pipe reaches the valves
- insert the pipe completely
- Fasten the brass nut at V3
- Open the top valve of the transfer system on top of the 1000 l dewar
- connect the cable leading to the pressure meter "Druck 450 l Dewar" with the pressure gauge of the 100 l dewar
- if the meter is turned off: Turn on the mains switch on the rear side (a bit difficult to reach), perhaps you have to turn on the power supply of the crate as well.
- stand in front of the Helium computer monitor and watch the pressures
  - The pressure in the 1000 l dewar should be in the range of 220..280 mbar
  - If it is too low: Turn on the heating (inside the 1000 l dewar) to increase the pressure. Do not exceed 300 mbar!
  - The pressure in the 100 l dewar will first rise and will reach the pressure in the 1000 l dewar.
  - The weight of the 100 l dewar will decrease by at least 1 kg, before it starts to fill
  - The pressure in the 100 l dewar will be ~ 50 mbar below the pressure in the 1000 l dewar.
  - The pressure in the 100 l dewar will rise dramatically, when the can is full
  - There are two other signs, that the can is filled:
    - The total weight reaches 144.7 kg (with additional valves and gauge attached) or 142.6 kg resp. (without the gauge/valves)
    - The exhaust hose will be covered with a lot of ice and start to shake strongly
- close the transfer valve on the top of the 1000 l dewar
- pull the L-piece out of the 100 l dewar, use gloves!
- Quickly close valve V3, put the plug in, close the nut
- Open the brass nut at the other end of the L-piece, pull the connector out
- put the L-piece to a safe place
- check, that the heating is turned off.
- close the hall and continue with the measurement

Scale for the 100 l dewar, Tara subtracts the mass of the empty can

Control rack of the Helium filling system

Opening the transfer valve

When you enter the hall for the next target refill, you have to reinstall the 100 l dewar first:

close the exhaust valve
disconnect the cable of the pressure gauge
disconnect the can from the exhaust hose
cover the exhaust hose at the liquifier side with the brass blank
note the volume of Helium as displayed on the flowmeter left to the entrance of the compressor room. Make a note like
- "refilled at ... with ... m³"
- "scheduled refill at ... m³" (add 65 m³ to the start volume)
put the 100 l dewar back to the stand
mount the exhaust hose and the pressurising hose back to the 100 l can
open the exhaust valve and the valve V1 at the can and the "storage dewar" valve at the tagger wall.
mount the little tripod onto the can
carefully insert the T-piece into the can, open valve V3 (vertical), when it is reached
place the long ladder between the target and the can stand
remove the steel plug from the target filling hole, put it in the brass ring, which holds the target (there is one hole with an inset, the plug fits just in).
insert the L-piece carefully into the target until the thicker part just fits into the holding ring, do not push it in completely!
firmly fix the L-piece using the screw in the holding ring
close the steel nut, where the L-piece goes into the target
connect the other end of the L-piece with the T-piece of the transfer line
close the brass nut
proceed with the Helium target refill as usual

Optional remote refill

You can fill the 100 l dewar can while you continue the measurement:

Start the refill process as described in the previous section
Adjust the voltage of the heating ("Heizung") to 15 V, leave it turned on permanently
Close the hall and continue with the measurement
watch the filling process via the WWW:
- open the address http://mwpc:5800
- enter the target password
- watch the pressure in the 100 l dewar (blue curve)
- when the pressure after at least 1 hour increases dramatically, you should enter the hall
close the transfer valve on top of the 1000 l dewar
turn off the heating
check the weight of the can: 144.7 kg means "full"
close the hall and continue with the measurement

Connection of the exhaust hose after
filling

Dismount the Helium target

Turn off the turbopump ("STOP" on the orange control box on top of PiP)
Close the black vacuum valve at the cryostat
dismount Helium the transfer line
dismount the tripod
disconnect the power supplies of the turbo pump and the vacuum gauge (on top of PiP)
turn off the Helium level meter, disconnect the power supply and the cable to the actual sensor (in the target)
remove the cables from the turbopump (fan and power supply)
remove the cables from the vacuum gauges (Pirani and Penning)
Only after the turbopump came to rest: Unplug the power supply of the vane pump (marked VP)
Quickly open the connection between the vane pump and the metal hose leading to the turbopump
Dismount the hose between the turbopump and vane pump
open the conection between the turbopump and the vessel (see photograph!)

Connection of the turbopump and the vessel

close the exhaust valve at the tagger wall labeled "target"
disconnect the exhaust hose at the target without delay: open the middle connection
dismount the turbopump carefully (2 Persons!), put it to a clean and safe place
attach the short cables with green hooks to the crane and the 4 rings on the target holder
remove the 4 inbus screws which fix the target holder on the green I-bars
lift the target (at least 2 persons needed):
- use the crawling gear only (righthand side of the crane control panel)
- Check, that the target does not hit the the holding ring of the inner dE detector
Lifting the target
Fiddeling the target vessel through the holding ring
Lifting the target over the gallow
- lift the target in crawling gear to the uppermost position
- check, that the target can be lifted over the red I-beams
- put the target into the gray rack:
- Fix the table on the rack
- move the target out of the hall
- Dismount the meters on top of PiP
- Reconnect the pumps and turn them on (unless you have to open the target to replace the cell)
Torsten Hehl, 15/3/2002