1. Profile measurements at CTF
BDI DAY 2004
14 January 2004
C.Bal, E.Bravin, S.Burger, C.Dutriat, T.Lefevre, R.Maccaferri

2. CTF3 beam & diagnostic requirements
Injector
[100mA, 5.4A], [300ns, 1.5ms]
[30nC , 8mC]
Beam Size : 1-10mm
140keV
Screen + camera
Linac &
Spectrometer lines
[65mA, 3.5A], [300ns, 1.5ms] [20nC, 6mC]
20MeV
40MeV
Beam Size : 3-20mm
Screen + camera
SEM grid
Spectrometer
Beam Size : mm
Linac

3. New radiation hard camera : First prototype built for CTF3
Beam profile monitors
Screen and Camera
Screen
Spatial resolution
Temporal resolution
Emission spectrum
N0 ph/el
Optical system
Transmission
Magnification
Field depth
Aberration
Camera
Sensitivity
Photocathode size:
12 x 9 mm
Spectral sensitivity:
[400, 600nm]
Video signal :
360 x 280 (h x v)
Frame grabber
1024 x 1024 (h x v)
New radiation hard camera : First prototype built for CTF3
Camera sensitivity in july : >109 photons (102 less efficient than a CCD)
Camera sensitivity now : x 10 (increasing the voltage on the vidicon tube)

4. Thermal analysis : Material study
Electron beam :
: beam size
N(t) : beam current
Target :
e : Emissivity
d : Thickness
cp : Specific heat
r : Density
k : Thermal conductivity
Heating term
Use of thin foils to avoid the reabsorption of the X-rays
in order to minimize the energy deposition dE/dx
The ‘collision’ stopping power changes by less than a factor 2
among Be, C, Al, Si,Ti,Mo, W
Cooling terms
Heat exchange is negligible within the pulse duration
Heat exchange due to black body radiation is small (mW)
Material cp
J/gK k
W/mK
Tmax ºC Be
1.825
190
1287 C
0.7
140
3527 Al
0.9
235
660 Si
150
1414 Ti
0.523 22
1668 Mo
0.25
139
2623 W
0.13
170
3422
Need thin foil of a material with a
High fusion temperature
High specific heat cp
High thermal conductivity
(for graphite DT=12% after 1ms)
Good candidates : Be (poison), Graphite

5. Thermal analysis : Material study
Calculations for the injector
profile monitor
Calculations for the linac
profile monitors
I = 5.4A , E = 140keV , s = 1mm
tp (ms)
T 10Hz
C Al
T 50Hz
0.2
103 83
164
132
0.8
272
194
558
421
1.56
440
434
1003 x
I = 3.5A , E = 150MeV , tp =1.56ms
s (mm)
T 10Hz
C Al
T 50Hz
0.25
1730 x
2250
0.5 -
0.6
510
650
Carbon screens will stand the full beam intensity
for the maximum repetition rate at every energy
Other material like aluminum can only be used for a reduced bunch charge and a lower repetition rate

6. Electron-photon conversion process
Optical Transition radiation
140keV
20MeV
150MeV
The number of OTR photons emitted by an electron in the wavelength range [la,lb]
Electrons energy (MeV)
0.14 20 40
150
[400,600]nm OTR photons per electron
[400,600]nm OTR photons on the camera
4 108
6 1010
7 1010
9 1010

7. Injector profile monitor
Radiation hard
camera
Gated (>5ns) and
intensified camera
(proxitronic)
Layout of the system
Two screens
manipulator
P47 Phosphor (Y2SiO5:Ce) deposit on a 10mm thick aluminum foil
5mm thick with 1mm grain size
Spectral response : [370, 480nm], Max at 450nm
Decay time : 100ns (90-10%) , 2.9ms (10-1%)
400 ph/el in 2p and 0.1 ph/el on the camera
Lot of light : ph for 30nC
High risk of damage
Thin carbon foil (OTR)
5mm thick
Spectral response : visible region [ nm]
Temporal response : few fs
ph/el (total), ph/el (camera), (proxitronic)
Few photons : ph for 8mC
Need light intensification
but fast time response

8. Injector profile monitor
Calibration :
200mm/pixel – 5.5cm total
4cm
P47 is sensitive enough to observe
dark current from the grid (10-100mA)
sx = 1.6mm
sy = 1mm x y
Emitted light intensity is reduced by 77% after a total charge
lower than 1C/cm2 (20days, 15minutes per day, 5Hz and 100nC)
(Expected value 5C/cm2 for a 50% light intensity reduction)

9. Injector profile monitor
Backward OTR
Forward OTR
Observation of forward OTR from a graphite foil e-
Backward OTR depends on the material reflectivity
Provided the screen is very thin, the beam quality and beam size are not perturbed and the OTR light emitted in the forward direction is 5 times higher than the backward emission
[0-100]ns
[ ]ns
[ ]ns
1 A beam current : 100nC photons over 100ns
Images taken using a factor 500 light amplification (compared to a CCD camera)
Temporal evolution of the beam profile
within the pulse duration
Possible improvements using
a better light collection system

10. Spectrometer line profile monitor
Calibration :
200mm/pixel
5.5mm total
‘ ph’
OTR screen :
100mm thick aluminum foil
Size : 10cm x 4cm
ph/el (on camera)
Observation for a beam with a minimum charge of 90nC (~ photons)
Radiation
hard camera
CCD camera
Minimum energy dispersion ~ 0.9% (s = 3.6mm)
SEMgrid profiles
~ 1 A – 320 ns – 25.5 MeV
Problems for higher
beam charge that
need to be understood

11. Linac profile monitor OTR Light View port e- OTR foil Beam profile
Calibration :
150mm/pixel – 40mm total
Beam profile
sx = 7.6mm
sy = 2.1 mm
sx = 4.7 mm
sy = 3.3 mm
OTR screen :
100mm thick carbon foil (26% reflectivity)
Size : Ø3cm
ph/el (on camera) for 20MeV electrons
‘ photons ’
Possible improvements using
an aluminum screen for the
observation of lower beam charge

12. OTR measurements for CTF3 and CLIC
OTR light : Emission characteristics
The OTR light is a radiation emitted at the interface between two media with different permittivities (vacuum-material) and results from the constructive interferences between the radiation emitted by the particles in these consecutives media.
(f)
OTR Backward emission
(q)
Specular
reflection
For beam diagnostic, we look at the backward OTR from a
screen rotated at a =45 degree with respect to the beam trajectory

13. OTR measurements for CTF3 and CLIC
Measuring beam divergence
Changing the beam divergence using a sets of quadrupoles
Imax
5 Amps
8 Amps
Imin
10 Amps
Fitting the beam divergence from the Imax and Imin values
In the experimental conditions:
Measured divergences from 2 to 6 mrad
The precision of the fit procedure was estimated to 0.25mrad

14. Laser wire scanner : Principle
High power laser
Scintillator + PM
or X-rays CCD
Thomson
Scattered
photons
Bending
magnet
Scanning
system
Beam
dump
e- bunch
Thomson scattering process
hn0
hnsc=2 g02 hn0
‘By counting the number of the scattered particles
(or photons) as a function of the laser position
the bunch profile is reconstructed ‘
Y=/2
q  1/g0
(b0 ,g0) e-
(bsc, gsc)

15. Remotely controlled delay line
LWS test on CTF2
X-ray detector
600 photons
with 17keV
averaged energy
Detection angle
26mrad
(Can tolerate 5mrad
misalignment)
3 GHz
Photo-injector
3 GHz
Accelerating cavity
Focusing
triplet
Current and Position
Monitor
Electron beam
size of 160 m rms
50MeV, 1nC
Laser shutter
Laser focusing
& scanning systems
(1mm resolution)
IR filter
Remotely controlled delay line
100m thick
Al Window
Laser
Photodiode (2.5mJ)
virtual focus
(30mm over 1cm)
Spectrometer
262nm, 10J, 4ps
IR to UV
doubling crystals
Nd:YLF laser
1047nm, 3mJ, 4ps
Beam dump

16. LWS test on CTF2 in photos
3 GHz
Photo-injector
3 GHz
Accelerating cavity
Focusing
triplet
Current and Position
Monitor
X-ray detector
IR filter
Spectrometer
Laser
virtual focus
Beam dump
Nd:YLF
laser
Laser
Photodiode
Laser shutter
Remotely controlled
delay line

17. LWS test on CTF2 : Background subtraction
Laser off values are used to evaluate the background signal
: RMS error of the
background subtraction
technique
Give an estimate
of background level

18. LWS test on CTF2 : Thomson photons
Total of 9 scans with a S/N ratio better than 1/10
and a RMS error smaller than 1mV
No scan : Acquiring data at fixed position
Overlap position
Offset position 1mm
Averaged value
1.04mV
Averaged value
-0.06mV

19. LWS test on CTF2 : bunch length
Expected signal (/2)
Longitudinal profile : Scan ±18ps
1.5ps offset compared to the overlap values (2ps offset maximum)

20. LWS test on CTF2 : Beam size
Expected signal (/2)
Vertical profile : Scan ± 250m
25 m offset compared to the overlap values (150 m offset maximum)