T962 Preamp Box Description ------------------------------- Original Rev. 24-JAN-2008 Current Rev. 25-JAN-2008 This file is a description of the preamplifier box for the T962 experiment. Answers to Questions: --------------------- > Is the weight of the inner box and its contents large enough that > spacers are needed on the bottom, between the inner and outer boxes ? Yes - there are adjustable feet on the bottom of the inner box that will support the bulk of its weight. There is no intent to cantilever the inner box off of the readout pipe. These feet also provide electrical insulation between the inner and outer boxes. > If so, do they need to be adjustable to minimize the stress on the > feedthrough flange ? Did the Bo boxes have a problem in this area ? The Bo preamp box had adjustable feet only at its far end. The Bo box is smaller and lighter and one end of it hangs off of the readout pipe and the far end has jack screws. > From which direction do the inlet pipes for the cooling air enter > the outer box ? The T962 setup is very similar to the Bo setup so people can look inside the Bo outer preamp box to see how this works. The cooling air enters through the vertical side of the outer preamp box that faces away from the cryostat. There are short pipe stubs in the wall of the outer box. Once inside the outer box this stub ends and the cooling air goes through an insulating section of pipe and then connects to aluminum pipes that runs across the top and bottom of the inner box. These pipes on the inner box are perpendicular to the beam direction. These pipes run almost the whole way across the top and bottom of the inner box to the side of the inner box where the readout pipe flange is. Then these pipes make a 90 degree bend and enter the inner box through its top and bottom. The intent of this setup of to accomplish two things: - The cooling air first reaches the preamp FET's and we need these parts to be as cold as possible. The noise performance of the preamps will depend on how cool we can keep these FET's. The rest of the preamp-filter circuit boards just need to be cooled like normal electronics to keep them from cooking themselves. There is a total of about 250 Watts inside the inner box. - The cooling air inlet holes in the inner box put a big hole in this shield box right near the input components that you need to keep electrically as quiet as possible. The long aluminum tube running across the top or bottom of the inner box with its 90 degree bend forms a waveguide. For all frequencies of interest to the LArTPC signals this waveguide is well beyond cutoff, i.e. it has very high attenuation. The 90 degree bend blocks any direct window via which an external electro static noise field could reach the input of the preamps. > Do the pipes go directly from those penetrations to the inner box > or are they routed internally ? They are routed internally so that the cooling air first reaches the preamp input FET's. > Is an outer box exhaust port needed, or can we rely on the space > between the outer box and the signal pipe from the cryostat ? The vertical surface of the inner box that is furthest away form the cryostat and the vertical surface of the outer box that is furthest away from the cryostat are both perforated to allow the cooling air to exhaust from the preamp box. The perforations in both boxes are backed up with a sheet of metal that has matching but offset perforations. Notes that these perforations are on the surface of the preamp box that should be the least sensitive to noise pickup, i.e. this surface is the output side of the preamps, it is where the output pleated foil cables run and where the power supply cables run. Thus the cooling air both enters and exits through the same surface of the preamp box. > Does the bottom of the outer box have any penetrations or air vents, > i.e., can the outer box be supported from a shelf instead of an > angle-iron frame as shown in your drawings? Nothing enters or exits through the bottom of the outer box. The outside bottom of the outer box is flat and can thus sit on a shelf. There are bolts that will go through the bottom of the outer box and the shelf to hold the preamp box on the shelf. > How exactly does the electronics box get attached to the elbow > flange ? Only the inner box is attached to the flange on the readout pipe. This is a critical connection. This is the single path via which the preamps sense the "ground" with respect to which they will measure the input signal. The outer preamp box has a hole that is a "loose" fit over the horizontal part of the readout pipe. > Specifically, do the inner/outer boxes "slide" over the signal ISO > flange somehow, or are the boxes constructed in place around the ISO > flange ? Both boxes are constructed in place. The backs of both boxes (i.e. the vertical surface closest to the cryostat) are split on a vertical line. The back of each box has a vertical strip of metal that connects together the two halves of the back once they are slipped past the readout pipe flange. The back of the inner box has a hole pattern so that it can mount onto the back of the readout pipe flange. The back of the outer box has a single hole that is about 0.2" bigger in diameter than the horizontal section of the readout pipe. My plan is to not cut these holes until the preamp boxes can be test mounted onto the cryostat and we can accurately see where the readout pipe actually ended up wrt the preamp box support platform. See: top_view_inner_and_outer.pdf to get a general idea of how all of this works. > If the boxes do "slide" into place over the ISO flange, how far onto > the arm of the elbow will they have to slide during install ? As you can see the inner box mounts onto the "back" of the flange on the readout pipe. Note that it requires extra long bolts to assembly this flange (which are needed anyway to accommodate the thickness of the feedthrough card). Once the flange plate and feedthrough card are bolted up to the readout pipe flange then the back of the inner box can be put in place and nuts used to pull it up against the back of the readout pipe flange. There are ground straps that fit between the back of the inner box and the back of the readout pipe flange that were not shown in the drawing for clarity. The external readout cables must be plugged into the feedthrough card before the back of the inner box is put in place and pulled up against the back of the readout pipe flange with nuts. Recall that both the warm and cold connectors on the feedthrough card must face in the same direction. The back of the inner box is 80 mils thick. There is 1 inch between the back of the inner and outer boxes. The back of the outer box is 59 mils thick. So from the back side of the readout pipe flange the preamp box structure occupies about 1.140" along the horizontal section of the readout pipe. > We're trying to determine how long to extend the horizontal arm of > the elbow in order to allow clearance between the electronics box > and the top-flange of the cryostat. If we add 3 inches to the > horizontal arm, we calculate that there will be a 2 inch gap between > the outside of the electronics box and the top-flange when > everything is installed. We want to know if this 2 inch gap is > enough to actually allow the box to be installed on the elbow, or if > there will be clearance issues while installing. We can certainly > add additional length to the elbow, but we just want to understand > the procedure for installing the box onto the elbow flange. A 2" clearance between the back of the outer preamp box and the top flange of the cryostat when everything is assembled should be just fine. The only thing that I need to get at back there are the 5/8" long button head allen cap screws that hold the preamp boxes together. A 2" gap should be just fine.