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--- cso:instruments:sharcii:cryo [2014-07-12 00:46]
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+++ cso:instruments:sharcii:cryo [2014-07-17 02:15] (current)
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+====== Cryogenics ======
+===== Fridge =====
+SHARC II incorporates a <sup>3</sup>He sorption fridge to cool the detectors to about 350 mK.
+This fridge must be cycled every day prior to the start of observing. The cycle takes a bit more than 90 min.
+Before cycling the fridge, please consult with the staff and any other observers about the weather forecast and the observing plan.
+==== Cycle ====
+The <sup>3</sup>He fridge is controlled electronically. Normally the staff will set up the controller and its software. To cycle the fridge:
+  - [[cso:observing:remoteobs#connect_to_the_vnc_desktop_s|Connect]] to view the fridge monitor. \\ ''comp% **csovnc.pl -l sharc sharc.fridge**''
+    * Consult staff for passwords.
+    * There should be three windows: the fridge program (top), an xterm (lower left), and a clock (lower right).
+    * The fridge server and client processes should already be running. If they are not, see [[#setup]] below.
+  - For an immediate cycle:
+    - Verify the **Start Immediately** box is checked.
+    - Verify the **<sup>3</sup>He cycle only** and **<sup>3</sup>He cycle only** boxes are //unchecked//.
+    - Press **START**.
+  - For a delayed cycle:
+    - Uncheck the **Start Immediately** box.
+    - Verify the **<sup>3</sup>He cycle only** and **<sup>3</sup>He cycle only** boxes are //unchecked//.
+    - Enter the delay in the **Delay til start (hrs)** box.
+    - Press **START**.
+  - //**Warning:**// Do //not// logout (exit) from the xterm. This will abort the server and client processes, stopping the cycle.
+  - Close the vnc viewer window if desired.
+Examples of the fridge monitor at the start, middle, and completion of the cycle. \\
+{{http://www.submm.caltech.edu/%7Esharc/operating/cycle_start.gif?250}}
+{{http://www.submm.caltech.edu/%7Esharc/operating/cycle_middle.gif?250}}{{http://www.submm.caltech.edu/%7Esharc/operating/cycle_complete.gif?250}}
+==== Setup ===
+The Neocera LTC-21 controller must be powered up, connected to the sharcii computer with a serial cable, and connected to the cryostat. Two processes must be running on sharcii for properly fridge cycling: a background server that controls the Neocera and logs temperatures and a graphical client. Only one server should be running but multiple clients can run at the same time. For simplicity, these are run in a detached (vnc) desktop.
+Normally the staff staff will set up the controller and its software. To start or restart the fridge processes:
+  - [[cso:observing:remoteobs#connect_to_the_vnc_desktop_s|Connect]] to view the fridge monitor. \\ ''comp% **csovnc.pl -l sharc sharc.fridge**''
+    * Consult staff for passwords.
+  - There should be three windows: the fridge program (top), an xterm (lower left), and a clock (lower right).
+      * If the xterm or the clock is missing, (left) click on a blank area in the and select from the pop up menu.
+  - Login to sharcii if necessary. In the (lower left) xterm, \\ ''kilauea% **ssh sharc@sharcii ** ''
+  - If necessary, stop the existing processes.
+    - Check what processes are running. \\ ''sharcii% **ps -ef | grep java** ''
+    - The server and client each show up as java 1.4 processes. For example, <code>
+sharc   598     1  0 14:18:00 pts/0    0:03 /home/sharcii/sharc/j2sdk1.4.2_30/bin/java -Djava2d.font.usePlatformFont=true F
+sharc   600     1  0 14:18:14 pts/0    0:04 /home/sharcii/sharc/j2sdk1.4.2_30/bin/java -Djava2d.font.usePlatformFont=true G
+sharc   621   606  0 14:22:05 pts/1    0:00 grep java
+</code>
+  - Determine the server and client PIDs (second column) and kill them. \\ ''sharcii% ** kill -9 //PID// ** ''
+      * Other than the sequence of the PIDs, it is not possible to distinguish the server and client processes in the ''ps'' listing.
+      * If in doubt about what processes are running, kill all of the java 1.4 processes.
+  - Start the server program. \\ ''sharcii% ** cd ~/recycle ** '' \\ ''sharcii% ** cycle ** ''
+      * After a few seconds, a message should appear similar to \\ ''10  Minutes;Both; 500;One Shot;0;''
+  - Start the graphical client. \\ ''sharcii% ** gclient **''
+      * There will be several warning messages, none crucial.
+  - //**Warning:**// Do //not// logout (exit) from the xterm. This will abort the server and client processes, stopping the cycle.
+  - Close the vnc viewer window if desired.
+==== Troubleshooting ====
+Cycle logs are on sharcii in ~sharc/recycle/logs/. Temperatures can be read directly from the Neocera front panel near the instrument. The left temperature is a "charcoal pump" temperature (<sup>3</sup>He or <sup>4</sup>He), which is normally 6.7 K except during a cycle. (For the pump temperature, there is a scale factor difference between the front panel and the cycle logs.) The right temperature is the detector temperature, which is normally 0.36 K in operation.
+If a cycle hangs in a state where continuous heat is applied to the refrigerator, the heating can be stopped by pressing the Monitor button on the Neocera front panel.
+==== Warm Detector ====
+Normally the initial cooldown is done many days in advanced to allow the detectors to passively cool to 4 K. During the cooldown, the detector temperature will be between 10 K and 100 K. If necessary, the cooldown may be accelerated by  actively cooling the detectors. Active cooling uses more LHe than passive cooling. Run a "<sup>3</sup>He only" cycle then wait for the detector temperature to drop below 8 K. If one "<sup>3</sup>He only" cycle was not sufficient to cool the detectors below 8 K, try another one. Once the detectors are below 8 K, follow with a standard cycle.
+In 2003 August and 2004 January, the first standard cycles ran succesfully, but the detector took several hours to cool below 0.4 K and the liquid <sup>3</sup>He ran out prematurely. This problem disappeared by the next day. The best explanation is a poorly heat sunk component that causes a transient heat load on the <sup>3</sup>He system. Performing the first <sup>3</sup>He cycle as much as a day in advance is a suitable way to address this problem.
+===== Cryogens =====
+During the work week, the CSO staff handle cryogen service.
+Please consult the staff about the schedule and the plan for weekend and holiday service.
+Please service cryogens yourself only if you are trained by the staff and wear the proper safety equipment.
+==== Liquid Nitrogen ====
+The LN<sub>2</sub> reservoir must be filled at least every 48 h, i. e., at least every other day.
+The LN<sub>2</sub> fill port is in the middle of the cryostat.
+To allow access for the funnel, position the telescope at a zenith angle of 45° (''__uip__> **za 45**'').
+The reservoir capacity is 7 liters and the usage is about one white pail per day.
+==== Liquid Helium ====
+SHARC II needs LHe every other day during active observing, i. e., when the <sup>3</sup>He fridge is cycled. Otherwise, the LHe reservoir must be refilled every six days.
+The LHe fill port is the one closest to the edge of the cryostat.
+To allow access for the fill tube, position the telescope at a zenith angle of 45° (''__uip__> **za 45**'').
+The reservoir capacity is 11 liters.
+The distance from the bottom of the reservoir to the exit hole is 20.5 in and the reservoir is 7 in deep.
+Before the <sup>3</sup>He fridge is cycled, the LHe depth should be at least 3 in.
+Please replace the downward-pointed black rubber hose assembly after filling the LHe.
+This helps prevent ice plugs.
+In case of a suspected ice plug in the SHARC II LHe reservoir, //**CALL STAFF IMMEDIATELY FOR ASSISTANCE**//.
+Ice plugs can eventually result in a cryostat explosion.