Summary of OTR measurements taken at the exit of the acceleration tube Recycler Weekly Departmental Meeting October 3 rd, 2007 L. Prost, A. Shemyakin A. Warner, M. Sutherland, K. Carlson, A. Burov

2 GOALS  Getting ready for YAG measurements  Fix/improve data acquisition software (T. Bolshakov)  Verify mechanics of the correction procedure  Understand timing (gate w.r.t. beam pulse)  Try to understand (better) what we see on the images  Shape of the beam Optics  Drop of intensity when pepper-pot is inserted Beam temperature  Eventually, we have mostly worked on trying to focus the camera properly and calibrate the image for dimensions (i.e. pixels/mm)

3 Prelude  The camera used for the data presented is different from the one used during commissioning  CID (now) vs CDD  Gated (now) vs non-gated  Slightly different controls  All the images, extracted profiles,… shown in this presentation are for fixed camera biases  Screen = 6 kV  MCP = -700 to -770 V  Gate/Photo cathode = -170 V  THE TIMING SETUP WAS NOT PROPER FOR PART OF THE MEASUREMENTS REPORTED HERE  Beam conditions: 5 kV (C.E. = -5 kV), 2  s pulse, nominal focusing settings

4 Gated camera  The camera we are using now makes it possible to acquire gated images  Requires more attention to synchronization with beam pulse,… Acquisition window Gate pulse Control electrode pulse ‘Real’ gate position w.r.t. beam pulse depends on cable length… Beam image believed to be at flat-top of the beam pulse

Timing

6 ‘2  s – 1  s’ image vs gated image  ‘Old’ analysis taking the difference of two images with different pulse length is likely inadequate  Caveat: It is possible that the MCP was saturated 2  s – 1  s pulse 1  s Gated Good timing data Note: this profile is quite different from previously published analyses (i.e. DIPAC’07) Note: this profile is in somewhat better agreement with previously published analyses (i.e. DIPAC’07)

7 Gate scan  Changed delay of the gate (300 ns width) to scan the whole beam pulse and find ‘real’ flat-top  The actual delay between the real gate pulse and the one reported on the scope appears to be ~800 ns First visible image First visible image ns First visible image ns First visible image ns First visible image  s First visible image  s There is no real flat-top !! Good timing data

8 Dependence on the gate width  The total light collected is not proportional to the gate width  Even though the image is not saturated it is possible that the MCP was in a non-linear regime  Timing is also an issue, especially since the ‘flat-top’ is very small ~×2.5 Gate ratio: 5 ? 100 ns 20 ns Wrong timing data

9 Comments on timing  From the gate scan and the very obvious difference between subtracting two images of different beam pulse lengths and the gated image of the equivalent width, we conclude:  A gated camera is a requirement for any analysis of the beam optics in a pulse mode  Because of the very short effective flat top, time jitter plays an important role in the quality of the data The importance of time jitter should decrease as we go to shorter gate width

Calibration (dimensions)

11 Calibration of the dimension  We have relied on known displacements of moving parts in the set up (OTR screen, 2-mm hole) and their corresponding images in order to try to calibrate distances  No fiducial available at this time  Different issues for X (horizontal) and Y (vertical) dimensions No moving parts horizontally Vertical expansion because of the angle between the camera and the OTR screen not quite 45   Off-line scaling (rough): pixels/mm  Distortion also appears to be close to nominal at ~1.2  By recording the displacement of the 2-mm hole while moving the OTR screen (vertical direction) we find a calibration of 12 pixels/mm  This resolution is quite poor and significantly less than with the previous camera (20 or even 40 pixels/mm, depending on the lens)

12 Estimation of distortion  If one assumes no overall convergence/divergence angle in the beam, one can use the pepper-pot image to estimate dimensions at the OTR screen  The pitch is 0.8 mm mm 11 pixels/mm in X-direction 13.5 pixels/mm in Y-direction Ratio: 1.2 Note the poor resolution of the pepper-pot image

13 Estimation of distortion (cont’)  Based on the theoretical geometry  Angle between OTR screen and camera 38.9  Distortion ( i.e. expansion/compression ratio) is 1.2 Consistent with result from pepper-pot estimation but… … looking at the angle (over 4 hole images in this case) that the pepper-pot holes make as a function of the upstream lens current, we find a non-constant ratio !?

Focusing limitations

15 Focusing depth limitation  Properly focusing the camera is essential to resolve temperature but also to resolve sharp edges (i.e. beam boundaries)  If we consider that what limits the resolution is when the ‘blur’ is larger than the pixel size (  ~ 0.07 mm), we should not be out of focus by more than  ~ 0.7 mm D L   With D = 35 mm, L = 350 mm    0.1  ‘blur’  Object Image

16 Focusing depth limitation (cont’)  With current settings, we cannot focus the whole beam properly  Issue for determining the edge of the beam  Issue for pepper-pot images  = 5 mm   = 0.5 mm 45  10 mm Focus  At the edge of the beam the blur is larger than the diameter of the pepper-pot hole images (~0.35 mm)

17 Illustration of focusing flaws with pepper-pot images  Moving the beam with upstream corrector results in much sharper pepper-pot images (than for default values)  i.e. better focusing Nominal corrector settings Some ‘better’ settings Between the two images, the beam moved by several mm onto the OTR screen Out of focus area Good timing data

18 Attempts to focus the camera have been quite unsuccessful  Tried to move the OTR screen while keeping the image at the same position with the whole beam  Quite inconclusive as for which profile is sharper Wrong timing data

19 Attempts to focus the camera have been quite unsuccessful (II)  Using pepper-pot images is not very conclusive either OTR = 67 mm OTR = 63 mm OTR = 61 mm Best focusing ? Wrong timing data

20 Comments on focusing  We also tried  To use the edge of the pepper-pot screen as a reference of a sharp object The boundary looks very odd and not sharp at all in all cases  To use an external light source and used the camera in the un- gated mode We failed to record an image  Focus on wires which are in front of the OTR screen We could only see phantoms

Other effects/anomalies

22 Collected intensity depends on the location of the beam on the OTR screen (vertically)  Because the light generated at the OTR is directional, the total light captured by the camera varies as a function of the vertical position of the beam G. Kazakevich  Should not be a problem for YAG measurements 2005 data with old camera system (un-gated)

23 September 2007 data – Same observations Pulse to pulse integrated light varies by ~ < 1% (20 pulses sample) When the beam is moved with upstream correctors the integrated light varies by several percent (decrease by 6% here) Good timing data

24 Time and/or position jitter  Consecutive images show signs of beam motion and/or time jitter ‘Differential’ images The crescents indicate beam motion (or jitter) between one image and the reference Profiles across the crescents (positive and negative sides) Zero Motion: ~12-18 pixels with ~12 pixels/mm (i.e mm) 12 pixels Good timing data

25 Intensity drops when inserting pepper-pot and 2-mm hole (sometimes)  Difference image between the whole beam and the 2-mm hole scraped beam Nominal corrector settings ‘Better’ settings Focusing (or lack thereof) does not seem enough to explain the pepper-pot image Good timing data

26 Other anomaly  Aliasing  Probably due to wrong timing setup Only affects Sep 27 & 28 data Wrong timing data

27 Look out  Some of the measurements (Sep 27 & 28) were made with the wrong timing configuration  Increased time jitter Makes focusing that much harder  May explain problems with un-gated acquisition Un-gated acquisition plus external light source could be a better way to focus the camera  Probable cause for aliasing

28 Prospective for YAG measurements  Goal of YAG measurements:  Resolve and eliminate ellipticity of the electron beam at the exit of the cooling section We want to resolve e = 1 – (minor radius/major radius) < 0.1  OTR measurements provide  Tests of the various procedures to acquire data  Resolution information Any blur will decrease the achievable resolution for e –Timing, focusing, calibration pix/mm for X/Y

29 Conclusion  So far OTR measurements are unsatisfactory but are serving their purpose  Did not firm up the method(s) by which to ensure that focusing and camera alignment are adequate for quality images Our struggles have been beneficial for the general understanding of the way measurements should be taken and issues to be aware of  With proper timing settings and the gained experience, we should be able to improve upon some of our issues Lack of focusing depth is not one of them and would require a smaller camera aperture –Enough light ?  Java data acquisition program is working (Timofei)  Just need some tweaks for the image analysis part

30 Conclusion (II)  Even with the timing issue being resolved…  We do not see a good explanation of why the pepper-pot image intensity is so low It looks like this is not the case for the 2-mm hole, with proper focusing  It is not clear that we can distinguish between camera misalignment, bad focusing and actual beam temperature In addition, with the current setup, the camera resolution is too poor anyway  We will revisit once more all the issues presented and hopefully come to a point where we are confident that YAG measurements will be successful