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20100918 Referencing The Alignment Laser With Wire Scanners

Wire Scanner Measurements

Flange and Window Dimension - Aperture

The 'OTR Alignment Laser' that runs parallel to the electron beam through the beam pipe is inserted into the beam pipe between ZH4X (closest to extraction) and ZV7X. It travels approximately 34m to the detector.

The laser is around 1cm in diameter to the eye at the detector. It reaches the detector uninterrupted - ie there is a clear path of at least 5mm (the size around the LWIP) all the way along in a straight line.

This was shown by removing the vacuum flange and beam pipe between B5FF (the bending magnet) and QD6FF. The beam pipe consists of the following:

to FF - QD6FF BPM - Bellow - LW Window Flange - Box in B5FF - Bellow - QF7FF BPM - to DR

Fig 1 shows the beam pipe between B5FF and QD6FF. This part of the beam pipe was removed with the bellow still attached to allow the laser to exit the beam pipe. It was also found at this point that the box part of the beam pipe in B5FF was free to move around and its position was only set by the resting place of the bellows. Both QD6FF and QF7FF quadrupoles on either side are on movers and so if they move, so would or window potentially clipping our signal. This box section will have to be fixed.

LW signal window vacuum pipe piece

Figure 1 : Photograph of the piece of vacuum pipe that contains the window for the laser-wire signal.

Additionally, referencing the laser beam with the wire scanners around the LWIP will allow us to know that that vector will give a clear path to the detector. The box will also have to aligned and fixed.

Wire Scanner Measurements

The pieces of beam pipe immediately after MW1X and MW2X were removed to allow a WinCam to be placed directly after the wire scanner. The position of the wire scanner that corresponded to the diffraction patter being centred on the laser beam was noted. Additionally, the image of the beam with no wire and the wire displaced by 5mm were recorded for reference. The table below details the location of the wire that was found to be central on the laser beam for both wire scanners and dimensions. The 'default' scan range (the previously used one) that the wire scanners had is also noted as if this is where the electron beam is, this is where we would expect to find the laser - assuming the electron beam is roughly straight along the accelerator.

For MW2X, the laser was found very close to these 'default' scan ranges, however, for MW1X, these were quite different. These are only the last used scan coordinates and could be atypical. If not, this would explain a lack of detected laser-wire signal as the e-beam would be at a decent angle at our IP.

These wire-scanners are between the two quadrupoles around the LWIP. The X wires are 50 um and the Y wires 10 um (need to check if this is radius or diameter). The beam line is as follows:

to FF - QD20X - MW2X - LWIP - ZV11X - SLAC OTR - MW1X - QF19X - to DR

Wire Scanner Dimension E-beam Scan Range Laser Intersection (mm)
MW1X X 38-40 23.3995
Y 68-70 52.4980
MW2X X 36-38 37.1490
Y 66-68 61.2980

Below are all the recorded images of the diffraction patterns.

The images from MW2X (after our IP) are note-worthy because of something clipping the beam in the bottom left corner. Alex also observed this whilst aligning the OTR Alignment laser at our IP with the OTR setup, however it was observed at the top left. This is possible due to the SLAC OTR which are currently displaced and have a narrow aperture.


Figure 2 : MW1X no wire.


Figure 3 : MW1X X aligned to laser beam at 23.2995mm.


Figure 4 : MW1X X displaced by 5mm for scale at 23.9005mm.


Figure 5 : MW1X Y aligned to laser beam at 52.4980mm.


Figure 6 : MW1X Y displaced by 5mm for scale at 52.9990mm.


Figure 7 : MW2X no wire.


Figure 8 : MW2X X wire aligned to laser beam at 37.1490mm.


Figure 9 : MW2X X wire displaced by 5mm at 37.6515mm.


Figure 10 : MW2X Y wire aligned to laser beam at 61.2980mm.


Figure 11 : MW2X Y wire displaced by 5mm at 61.8010mm.

Flange and Window Dimension - Aperture

There is also some discrepancy between the schematics of the flange containing the signal window given to the group. Fig 12 shows the specified dimensions from the schematics - giving us a 3.5mm wide window for signal with the current detector position. The actual measured sizes are shown in Fig 13 which give us more room to work with. Additionally, plans to move the detector in front of the flange attached to the bellows (around 15cm in front of the signal window) will mean we can use the full window for signal.


Figure 12 : Schematic of the signal window flange as depicted in provided schematics.


Figure 13 : Schematic of the signal window flange as measured.

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Topic revision: r6 - 21 Nov 2010 - LauraCorner

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