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For SpinQuest it will be difficult to get the positioning of the target perfectly aligned with the beam. This is because all fiducials that we can get while the system is warm and open will change once we are running with liquid helium. We have X, Y positioning measured from averaged vertex reconstruction but this takes at least 1 month of data to produce, and this will only give the mean with a very large variance. This means we need to get the information we need from the survey and the final set of surveys will need to contain some cold target information. The precision in the target cell to beamline positioning needs to be good to mitigate large absolute errors while running. This is estimated to be on the sub-millimeter level (based on simulations being confirmed). There are several factors that can lead to false asymmetries relating to this precision. There can be a bias produced in the detector if there the beam is off center. There can be less polarized scattering if the beam is not aligned and missing part of the target (beam profile dependent, also being checked). There can be greater scattering off the aluminum ladder on one side as compared to the other. Most of these manifest from X being off but if Y is off over 1 mm then the same issues start to manifest with the ladder as well but this may not result in false asymmetry and only result in additional heat load to the coils. During our discussions with the survey crew it was suggested to install transparent windows so we could do an optical survey on the magnet and target cells while cold. This would be great to do but I do not think this is possible at FNAL. I don't believe we would ever pass a safety review to do that. The next best option is to do surveys using liquid nitrogen. We could calculate the level of contraction for both LN2 and LHe. We can then measure the contraction during an open system survey with LN2 in the magnet and in a nose with a window on it. The set of survey would go like this:
1.) Survey on The dock survey should be with a fully open system (no nose, no nitrogen shield, no beam windows). Survey We will survey the magnet aperture , opening planes and the target ladder. The insert ladder should only be studied in X for this setup (put top cup in the near beam-line position using piston configuration). We should move the magnet to some level place on the dock and set it up on to a tooling table. We should try to do as much of the preliminary setup ourselves (and with techs as needed) so the survey crew can come in and setup quickly. To survey the aperture opening planes we should get the location of each of aperture corners and three points between each of the corners. This is a total of 16 points per plane (32 points all together). The distance from these points to the a set of references on the top flange will need to be measured. The locations of these reference points on the top flange will need to be chosen by us. We will also setup the top target cell with front and back cross-hairs and measure the x, y, z of the cross-hairs and the inner cell wall with respect to the top flange. Several positions at 3mm increments should be chosen on the target cell. We should get the location of each of the magnet opening corners and at least two point in between in each of those points along the aperture openings. The aperture outline and ladder-X should be projected as outside fiducials and referenced to the top flange.
Work needed to optimize the survey:
1.) Make sure piston and target insert are ready
2.) Setup cross-hairs on target cell (may need to discuss with survey folks)
3.) Chose locations on target cell and top flange for measurements and reference
4.) Finish target insert and refrigerator work
Its also possible to make the bottom can so we return to the same measured locations when can is removed and put back into the cave (using high percission dowel pins). I’m not sure this is necessary because we will not use the bottom part of the can to reference against anything. Slight rotations from starting should be addressed by Mitchell's alignment setup.
insert along X only, and the outside fiducials (can and top flange). The primary goal of this survey is to generate fiducials on the can and top flange to help align when going into position in the cave. This part of the survey should be able to be measured with error at less than 0.5 mm. The fiducial on the can is meant to use to align the top and bottom to our best precision. The tolerance of the drawings is 0.5 mm. Use the leveling pads to level the magnet on the dock before survey. This survey can be use to check the variation when leveled and re-leveled or if the magnet is plumb not the top flange is slightly off level. Working on the dock for this survey will have the advantage of space unlike in the cave. We can also flip the insert and check target cell up stream and down stream differences.
2.) Survey in cave using LN2 in nose and magnet. This would be a partly open survey with a special nose put on with transparent windows on either side for optical survey. The nitrogen shield and beam widows on the vacuum are left off for this. This survey in the cave will be of the magnet aperture, the target insert along X, Y, Z, and the outside fiducials (can and top flange and reference locations in the cave). Crosshairs will be use in the front and back of the target cell to help determine degree of twisting in the cell. Cross hairs in the can windows can also be use to set the rotational alignment of the can. The target insert carbon fiber is not expected to contract very much but the aluminum ladder can. The primary goal of this survey is to compare to calculations of contraction and measure positioning of target cell with respects to magnet aperture and also with respect to the beamline. There should be a hard stop setup on the actuator that positions the top target exactly in the beam line (to test repeatability of the string potentiometer and gears). We also need to take the stick out and few times and test the scale of deviation in reproducibility in target cell shifts and bends. This will take two surveys to do since we will need to machine the piece for this hard stop after this first cold survey measurement. In order to do this the actuator and motor should be installed so we can move up and down with reasonable repeatability. This repeatability can also be tested during this survey. The drawings indicate a change of 4.5 mm up when cold.
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