1. Update on electron spectrometer measurements Introduction Setup, measurements carried out Some raw images Results and conclusions L. Deacon, M. Wing (UCL) S. Mazzoni, B. Biskup, A. Goldblatt (CERN) AWAKE collaboration meeting, Thurs 10 March 2016, ITS Lisbon

2. Introduction To protect CCD camera from radiation damage, the electron spectrometer to be imaged from TSG4 ~17m away, via 3 mirrors. Image from Ans Pardons’ integration talk yesterday TSG4 TCC4

3. Introduction To obtain good signal from this distance with good resolution, a Nikon 400mm f/2.8 lens was chosen We tested the resolution of the system using back-lit targets with line pairs of varying widths

4. Camera installation Rail mounted on tripod 17m from target

5. Layout 1 Target image via mirror

6. Layout 2 Direct view of target X position adjustable across full field of view buy sliding the target assembly along the lower rail

7. Measurements carried out 6 targets with different #line pairs per millimetre, and a blank target. image taken of each target using layout 1 (target image reflected 90 degrees via mirror). Layout 2: image taken using each screen at 6 horizontal positions between image centre and 50cm offset. Layout 3: using a better quality mirror.

8. Measurements carried out Different distances (direct view of screen, no mirror): 21.5m, 15m, 2.5m Screen ‘out of focus’ – z offset by 10cm, 20cm … 50cm

9. Some raw images – direct line (no mirror) Top to bottom bar widths (lppmm): blank, 0.5mm (1), 1mm (0.5), 2mm (0.25)

10. MTF vs x 2 mm bar width visible, 1mm bar width barely visible MTF does not change significantly with x position of target

11. MTF vs lppmm The mirrors do not significantly affect the resolution Resolution significantly worse at 21.5m (compared to 17m)

12. MTF vs lppmm Scale (px/mm): –15m: 2.01 –17m: 1.77 –21.5m: 1.45 So overall resolution is close to CCD resolution in all cases

13. MTF vs z Resolution rapidly worsens with z, but 1lppm still visible (MTF ~ 0.05) Should try to image screen at 90 deg., however 45 deg. might still be acceptable (edges of screen will be 40cm from focal plane)

14. Conclusions The results confirm the choice of camera lens in achieving the desired resolution. The resolution did not depend on use of a low quality or high quality mirror or no mirror. Screen should be imaged at 90 degrees to maintain optical resolution across entire image.