Summary of OTR Summary of OTR measurements taken at the measurements taken at the

exit of the acceleration exit of the acceleration tubetube

Recycler Weekly Departmental MeetingOctober 3rd, 2007

L. Prost, A. ShemyakinA. Warner, M. Sutherland, K. Carlson, A. Burov

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GOALSGOALS

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)

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PreludePrelude

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

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Gated cameraGated 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

TimingTiming

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‘‘2 2 s – 1 s – 1 s’ image vs gated images’ 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 – 1s pulse

1s 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)

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Gate scanGate 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 + 300 ns

First visible image + 600 ns

First visible image + 900 ns

First visible image + 1.2 s

First visible image + 1.5 s

There is no real flat-top !!

Good timingdata

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Dependence on the gate widthDependence 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

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0 20 40 60 80 100 120 140 160

P ix e ls

Inte

nsi

ty

G ate = 100 ns G ate = 20 ns

~×2.5

Gate ratio: 5

?100 ns

20 ns

Wrong timing data

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Comments on timingComments 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 (Calibration (dimensionsdimensions))

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Calibration of the dimensionCalibration 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): 14-15 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)

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Estimation of distortionEstimation 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

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2 3

1

2

3

0.8 mm

11 pixels/mm in X-direction

13.5 pixels/mm in Y-direction

Ratio: 1.2Ratio: 1.2

Note the poor resolution of the pepper-pot image

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Estimation of distortion (cont’)Estimation of distortion (cont’)

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1.02

1.04

1.06

1.08

1.1

1.12

1.14

1.16

1.18

1.2

6 7 8 9 10 11

SPA06, A

K

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X, pixels

Y, p

ixels

6 7 8.5 9 9.5 10.5

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 limitationsFocusing limitations

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Focusing depth limitationFocusing 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

L

D With D = 35 mm, L = 350 mm 0.1 ‘blur’

Object Image

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Focusing depth limitation (cont’)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

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10 mm

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)

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Illustration of focusing flaws with pepper-pot Illustration of focusing flaws with pepper-pot imagesimages

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

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Attempts to focus the camera have been quite Attempts to focus the camera have been quite unsuccessfulunsuccessful

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

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X , pix e ls

Inte

nsi

ty

OTR pos ition 71 mm OTR pos ition 67 mm

Wrong timing data

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Attempts to focus the camera have been quite Attempts to focus the camera have been quite unsuccessful (II)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

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Comments on focusingComments 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/anomaliesOther effects/anomalies

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Collected intensity depends on the location of the beam on Collected intensity depends on the location of the beam on the OTR screen (vertically)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

-200 -100 0 100 2000

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75

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125

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0-Y

+Y

Electron beam was aligned with Bx/y/cA05 & Bx/y/cA07; TRA07 beam spot has no motion withchanging of SPA07 current

Upulse=4.5 kV; Set.2SPA06=17 A;2 s; Gain:600Scale: 15.93 pix/mm

Inte

gra

l, arb

. units

Y, pix

B: Jul.27/05 D: Aug.08/05 G. Kazakevich

Should not be a problem for YAG measurements

2005 data with old camera system (un-gated)

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September 2007 data – Same observationsSeptember 2007 data – Same observations

0.0E+00

2.0E+05

4.0E+05

6.0E+05

8.0E+05

1.0E+06

1.2E+06

1.4E+06

09_0

6_07

_142

5241

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09_0

6_07

_142

5351

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09_0

6_07

_142

5431

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09_0

6_07

_143

0003

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09_0

6_07

_143

0233

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09_0

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_143

0463

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Inte

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ted

lig

ht

[arb

. un

it]

0.0E+00

5.0E+05

1.0E+06

1.5E+06

2.0E+06

2.5E+06

3.0E+06

Corrected Nominal

Inte

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lig

ht

[arb

. un

it]

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

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Time and/or position jitterTime 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

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Pixel #

Inte

nsi

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Profiles across the crescents (positive and negative sides)

Zero

Motion: ~12-18 pixels with ~12 pixels/mm (i.e. 1-1.2 mm)

12 pixels

Good timing data

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Intensity drops when inserting pepper-pot and 2-mm hole Intensity drops when inserting pepper-pot and 2-mm hole (sometimes)(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

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Other Other anomalyanomaly

Aliasing Probably due to wrong timing setup

• Only affects Sep 27 & 28 data

Wrong timing data

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Look outLook 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

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Prospective for YAG measurementsProspective 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

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ConclusionConclusion

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

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Conclusion (II)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