• Overlap Integral Fits done using 20130205_1627/fit_parameters_input.dat on shift - the previous week's M2.
• Overlap Integral Fits done using 20130210_1637/fit_parameters_input.dat for post shift analysis of quad scan

20130207 Shift

Plans

Accelerator

• SAVE OPTICS!!!!
• Increase charge to ideally between 0.7 and 1.0
• Spend a little time to optimise linac / transport for higher charge and stability

Optics

• Load Lw optics
• Upstream steering to minimise background (before FF)
• Vertical Dispersion measurement / correction at LWIP - using Glen's FS tool. Measure after correction as well to verify - sometimes takes more than once
• Coupling correction - using upstream OTRs?
• Steer to centre of QM16FF
• BBA QM16,15,14,13 and 12FF - manual or using Glen's FS tool
• Most importantly 14, then 15, but ideally both.
• Reduce ipangle to < 100urad in both dimensions
• Check background

OTR

• Verify vertical beam size
• Quick quad scan to optimise QM14FF strength
• Update horizontal size in EDM

CBPM Resolution Logs

• Move chamber until MFB2FF not saturated - ie at minimum ADC counts - use CBPM panel
• Log 5 sets of CBPM data using CBPM EDM - 500 pulses per set - for resolution measurements
• Vertical Dispersion measurement / correction at LWIP - using Glen's FS tool. Measure after correction as well to verify - sometimes takes more than once

Laser-wire Startup

• Spatial Alignment
• Temporal Alignment
• Optimise, Vertical, Phase, Horizontal; repeat.

• Charge ramp - Log 1000 pulses on collisions
• Laser ramp - Log 1000 pulses on collisions
• Charge ramp - Log 1000 pulses off collisions (ie laser off but same position)

PLIC Detector

• Turn up vertical scale on PLIC and compare laser on laser off on collisions - anything at all?

Data Synchronicity

• While on collisions, block laser beam upstairs for a couple of pulses; repeat about 10 times in 500 pulse log
• Use single shot mode of accelerator to fire one electron bunch during say 500 pulse log; repeat about 10 times
• Check syncrhonicity of refc1amp, cherenkov, laserenergy, photodiode

Laser-wire Angular Dependence

• Back on collisions
• Move QM14FF on movers slightly to affect angle at LWIP - need to make large steps in angle +- 200urad in angle
• Compare laser on, laser off signal to background ratio at each point with two separate logs

Scans

• check optimisation of laser-wire via
• Phase scan
• Long range horizontal -2200 -> +2200 chahor, 80 steps, 15 samples at each
• Vertical scan - usual - 70 points, 20 samples
• Vertical scans at +- 25um, 50um, 75um, 100um horizontally - may need to use linear scan for larger ones at sides as nonlinear too narrow

MFB2FF Alignment

• Save positions for optimal laser-wire position - 100 pulse log (for bpm information)
• Move chamber for best MFB2FF position
• Save positions here - 100 Pulse Log

The Almighty LW Quad Scan

• NOTE quad scan should go in order - NOT middle first, then out, to avoid hysteresis or drift of accelerator effects in results
• Save accelerator set file at beginning!!! for e beam modelling purposes!
• 11 point quad scan
• Centre +- 1,2,3,5,7A on QM14FF
• At each point:
• Horizontal scan -2000 -> + 2000, 50 points, 10 samples -> move to centre at end
• Small linear vertical scan to centre properly
• Nonlinear vertical scan - 70 points, 15 samples

The Almighty OTR Quad Scan

• Repeat above quad scan, but with OTR images
• 3 samples at each magnet current

RELOAD OPTICS

• Save our optics!
• Quads
• Steering
• Optics save again

On Shift

The Best Laid Plans...

Laser build up time had increased yesterday, but not significantly. I have avoided using the laser due to damage on the etalon and this only gets worse with use. Today, the build up time was much longer again. The maximum output from the regen is 4mJ, which is very low. Slight tweaks really didn't improve it at all. Tried various pockel's cells timing, but no improvement. Removed etalon and unseeded regen output is 17mJ, which is down from last week's 24mJ. So, likely cavity is also degrading, but still expect around 12/24mJ (with etalon / without etalon - last week) out, which would be around 8.5mJ with etalon.

Further damage is evident on the etalon in the new position and there isn't much space to move the laser beam anywhere else.

So, current regen output around 4.2mJ. Maximum output from laser around 70mJ upstairs.

Took access and checked alignment downstairs - corrected slightly. Tweaked green upstairs on energy meter.

Optics

Loading set file ***.dat. Changing magnets QM15,14,13,12FF.

• Laser-wire signal attenuation was 9dB last week to take best advantage of ADC range. Typical background level was 8800 ADC counts.
• Changed attenuation to 14dB - aim for 5000 ADC counts background with this attenuation or lower.

OTR

• Horizontal (otr switch) scan with focus scan at each location
• Focus Scan

initial position ip:otrlens:z 14.25000, scan range: 12.4 - 14.4, step: 0.1 mm, best position - 13.4000

• OTR Focus Scan:
  

• Quad Scan

scan range QM14FF: -80 - -100 A, step 2.5 A, best position: -89.37171

• quad.jpg:
  

QM14FF Current
-80.0

01:30 LW

• Positions saved after OTR and before LW alignment - 20130208_0126_pos.dat

02:00 Alignment

• Set manipulator to 8820 (where laser was before)
• Vertical & Horizontal scans with chamber -> look at wire-scanner detector
• Set V:185, H:250
• Timing ok - Set voltage to 5.0V

Horizontal Alignment	Vertical Alignment

• Initial scan - collisions!
• Within 20um of aligned position.
• Signal:Background ~ 1:8 so not great, but visible
• Laser energy downstairs is estimated to be 33mJ post-ip although this is a slight underestimate
• Comparing to previous shift, signal to background is approximately the same accounting for lower laser energy

Phase scan suggested a voltage of 4.47V and we set to that. Then repeated vertical scan, but signal vastly reduced. Setting back to original 5.0V and rescanning vertical.

• Charge dropping off - Mod #2 very sensitive. Alex retuning linac
• Signal was dropping off despite returning to same position - not clear what's happening
• Laser energy the same both before and after LWIP (photodiode & laseren)

• Phase, Horizontal, Vertical again...

• Phase set to 4.74V, Horizontal set to 62. Vertical scan nonlinear about chaver:151, 60 points, 20 samples
• Vertical scan quite good!!! Shows 1.7 +- 0.23um. Larger size before must have been due to horizontal offset.
• Amplitude 0.72 vs background 4.2

Re-aligned Proper Vertical Scan	Apparently small...

More Sensible...	Pretty Good

Horizontal Slicing

• Centre is chahor:62
• Using cherenkovcnbgslen

ChaHor	Filename	Size
62 (centre)	20130208_0418_lws	1.71 +- 0.26um
72	20130208_0437_lws	0.73 +- 0.23um
82	20130208_0453_lws	1.73 +- 0.25um
92	20130208_0504_lws	1.23 +- 0.18um

* Not showing clear dependence -> step size too small. Also better to take a few scans at each location.

* 62, +-50, +-100 -> 3 scans as each location

ChaHor	Filename	Size
62	20130208_0418_lws	1.71 +- 0.26um
62	20130208_0517_lws	2.35 +- 0.16um
62	20130208_0527_lws	2.63 +- 0.18um
72	20130208_0536_lws	1.50 +- 0.2um

*set file: set13feb080608.dat

LW Quad Scan

• Vertical Linear - 20 steps - 10 samples - +-20um
• Horizontal Linear - 30 steps - 20 samples - +-700um
• Vertical Nonlinear - 50 steps - 20 samples - default range

• Repeat above pattern for each quad setting.
• After each scan, set that axis to its centre
• Do quads in order to avoid hysteresis or beam wander effects

QM14FF	FilenameV	FileNameH	FileNameNL
80	20130208_0614_lws	20130208_0618_lws	20130208_0631_lws
84	20130208_0639_lws	20130208_0643_lws	20130208_0653_lws
86	20130208_0701_lws	20130208_0712_lws	20130208_0723_lws
88	20130208_0730_lws	20130208_0732_lws	20130208_0742_lws
89	20130208_0750_lws	20130208_0752_lws	20130208_0802_lws
90	20130208_0810_lws	20130208_0812_lws	20130208_0822_lws
91	20130208_0829_lws	20130208_0832_lws	20130208_0842_lws
92	20130208_0849_lws	20130208_0852_lws	20130208_0902_lws
94	20130208_0910_lws	20130208_0913_lws	20130208_0923_lws
96	20130208_0930_lws	20130208_0939_lws	20130208_1010_lws
100	20130208_1019_lws	20130208_1021_lws	20130208_1031_lws

Reanalysis post shift in table below

QM14FF	Vertical Fit	Horizontal Fit	NonLinear Using s_ex = 235.0	Nonlinear using s_ex = horizontal
80	5.21 +- 0.84	202.2 +- 9.1	6.1 +- 0.3	6.27 +- 0.33
84	2.29 +- 0.6	138.1 +- 9,3	5.0 +_ 0.3	6.25 +- 0.32
86	5.39 +- 0.44	162.0 +- 6.3	4.26 +- 0.3	5.21 +- 0.34
88	1.23 +- 0.27	192.5 +- 6.2	3.0 +- 0.4	3.39 +- 0.38
89	1.38 +- 2.02	161.7 +- 12.6	1.3 +- 0.6	2.18 +- 0.47
90	1.5 +- 1.05	174.4 +- 13.1	3.1 +- 0.5	3.67 +- 0.44
91	1.14 +- 1.44	304.4 +- 43.1	3.2 +- 0.5	2.59 +- 0.58
92	1.86 +- 0.83	150.3 +- 9.0	0.74 +- 0.5	1.91 +- 0.31
94	2.35 +- 1.05	184.2 +- 9.5	2.11 +- 0.4	2.64 +- 0.40
96	1.38 +- 2.02	200.8 +- 13.1	5.12 +- 1.24	5.54 +- 1.37
100	4.96 +- 1.53	201.6 +- 45.5	3.74 +- 1.30	2.52 +- 1.40

• 20130208_0701_lws - problem with this file

The uncertainty on the sigma from the initial vertical scans is obviously very high (and even unphysical), however, the purpose of this scan is purely to determine the centre vertically for the best horizontal scan and although there is insufficient data for an accurate vertical vertical measurement, the reduced data provides a quick scan and sufficient data to ascertain the vertical centre to within a few microns - adequate for both the horizontal scan and the subsequent non-linear vertical scan.

QM14FF	Vertical Fit	Horizontal Fit	Nonlinear using s_ex = horizontal
80
84
86
88
89
90
91
92
94
96
100

• quad_LW.png:
  

• Log on collisions with charge varied
• Log on collisions with laser energy varied
• Log with no laser for background

OTR Quad Scan

Corresponding OTR quad scan to LW scan. Three samples at each point. Repeat in same order as laser-wire.

• quad_OTR.png:
  

• Laser-wire optics saved - set13feb08_1102.dat
• Restored previous ATF2 optics set13feb07_19

Quad Scan / Shift Analysis

Firstly, having a look at the vertical sigma from both the quick linear vertical scans for centring and the full resolution nonlinear vertical scans. There isn't the clear parabola that one would ideally expect from a quad scan. However, there is an approximate minimum. From the scans above it is clear that the signal to noise ratio is too low near the end of the quad scan - due to degraded laser energy at the end of the shift as well as the accelerator conditions changing as the machine heats up in the day.

Vertical Sigma	Vertical Sigma (NL Scans)

Next, the horizontal sigma. This shows no clear pattern and changes quite dramatically through the quad scan.

Horizontal Sigma

Having a look at the centre of the horizontal and vertical scans, the vertical has a clear and linear sweep in centre throughout the quad scan, however, the horizontal centre shows no clear trend.

Horizontal Centre	Vertical Centre (NL Scans)

From this quad scan it is clear that the time for scans must be minimised. The quick vertical scans for alignment produce reasonable results due to the short time they are recorded over and therefore the consistency of experimental conditions. The high resolution nonlinear scans obviously have a lower uncertainty, but this could be even lower if the beam / conditions were more consistent throughout the scan. Swings in charge normalised background can be seen in the raw data for the quad scans (above ones are background subtracted - linear model between first and last 5% of data). This is linked directly with tuning of the linac. The linac energy is unstable on the timescale of about 5 - 15 minutes, which is the approximate timescale for a detailed laser-wire scan. The horizontal laser-wire scans are the longest purely due to the distance required for the chamber to travel. It is unlikely that we can change the behaviour of the linac so therefore we must shorten scan times.

All of this is because there is some dispersion at our location. Changes in the energy affect the size and the position of the beam. Therefore, even without touching the linac during a scan, it will still drift and we'll be sensitive to it. Dispersion must be at least measured and ideally corrected. Furthermore, the beam based alignment wasn't performed so there was a clear drift in position with change in magnet strength.

It is also possible that the beam is coupled coming into the LWIP area. In this case, the quad scan would rotate the beam as well. If the rotation angle is on the order of about 20mrad, the projected beam size by the laser-wire will be almost double its original value - dependent on proportions of electron beam of course and the unknown angle between the laser-wire axis and the nominal electron beam axis.

Analysis files were put in 20130213_1436_qwd in ana directory manually.

Improvements to be made

• Software to automatically analyse the quad scan from a list of files for each scan type
• ControlPlot2 showing cherenkov, cherenkovcn, cherenkovcnbgs, cherenkovcnbgslen
• Increase horizontal chamber speed to 50um/s - currently 20um/s to at least halve horizontal scan time
• Don't tune linac during any scan - if transmission drops off - stop scan, fix, repeat scan
• Perform Dispersion measurement and correction
• Perform BBA on magnets around us
• Perform coupling measurement and correction