X23A2 Howto: Setting Gases for the Ion Chambers

Figure 1 The mixing station for the various gases.

Figure 2 The gas patch panel inside the hutch.

Figure 3 Gas connections to the ion chambers.

Mixing station

• We have a standard compliment of gases at X23A2, including He, N₂, Ar, and Kr. The gas cylinders are plumbed into a mixing station that is outside the hutch and mounted on the upstream wall of the hutch. This mixing station is shown in Figure 1.
  
  

  Each of the four individual gases go into one of the four needle gauges on the left side of the mixing station. These are the yellow-ish gauges. The He line should always be flowing at about 40 during your experiment. This feeds He into the box containing the harmonic rejection mirror, which is needed to reduce attenuation through the flight path and to protect the surface of the mirror from ozone. Even at high energies where the mirror is dropped out of the beam path, He should be flowing.
  
  

  The other three gauges are then used to feed gas to the ion chamber or to other things inside the hutch.
  
  

  The four needle gauges on the right -- the white-ish ones -- feed two mixed-gas lines. The two on the left are used to mix He and N₂ into a single line. The two on the right are used to mix N₂ and Ar into a single line. You can use these lines as additional single gas lines (by turning off one of the two feeds) or to customize the gas flow for a particular experiment.

Patch panel

• Inside the hutch, under the table, mounted on the upstream wall, you will find a patch panel which is connected to the mixing station, shown in Figure 2. From left to right, the patch panel feeds He, N₂, Ar, Kr (labeled "Aux"), He/N₂, and N₂/Ar. Each feed in the patch panel is equipped with the female end of a quick-connect. There are a variety of labeled tubes with male terminations ready to be clicked into the patch panel.
  
  

  To release a gas line, pull forward on the housing around the female connector and detach the gas line. To connect a gas line, simply press the terminator into the housing in the patch panel until you hear a click. The housings in the patch panel are normally closed, thus will halt the flow of gas when nothing is connected.
  
  

  All gas connection from the mixing station to anything in the hutch must go through the patch panel. Do not plumb any gas lines into the hutch which bypass this system without consulting Bruce or Joe.

Ion chambers

• The gas lines are labeled at both ends, so it should be easy to pair a feed from the gas panel with any of the ion chambers. The ion chambers are all equipped with female quick-connects that are normally open. Figure 3 shows the top of the I₀ chamber. The input N₂ feed line is attached to the upstream end. The downstream end is attached to a line going to the I_t chamber. In this way, the I₀ and I_t chambers are daisy-chained and will share gases. The I_t chamber can be given its own gas supply by removing the daisy chain and attaching a feed line to its input quick connect.
  
  

  These quick connect housings are a bit harder to manipulate that the kind in the patch panel, but they work similarly. To attach or detach the male end, pull forward on the housing around the female end.
  
  

  Note that the connection to the box housing the harmonic rejection mirror is not a quick connect. You should never remove the He line from that box without consulting Bruce or Joe. If you need He, use the He/N₂ mix line with the N₂ turned off.

Setting the gas flow

• One the plumbing is all correct, open the appropriate needle gauges to begin the gas flow. When purging the chambers, it is ok to turn the gas up to the top of the range on the gauge. Once the contents of the ion chambers has stabilized, turn the flow rate down to about 30 or 40 so as not to waste too much of the gas cylinder.
  
  

  Use Hephaestus (which is installed on the PC near the mixing station) to determine appropriate contents for your chambers. Remember that below the Kr K edge energy of 14326 eV, the advantage of using Kr rather than Ar is rather slim. The first element on the periodic table for which Kr is an advantage in a K edge measurement in the fluorescence detector is Y. Am (really!) is the first element for which Kr is an advantage in an L3 edge measurement. Please do not waste the beamline's supply of Kr unless you are working on an element whose main fluorescence line is above the Kr K edge energy.