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

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 : 0.25-4mm Linac

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)

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

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 (ºC) @ 10Hz C Al T (ºC) @ 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 (ºC) @ 10Hz C Al T (ºC) @ 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

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 7.2 10-4 7.3 10-3 8.6 10-3 1.1 10-2 [400,600]nm OTR photons on the camera 4 108 6 1010 7 1010 9 1010

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 : 6.1010 ph for 30nC High risk of damage Thin carbon foil (OTR) 5mm thick Spectral response : visible region [400-600nm] Temporal response : few fs 7 10-4 ph/el (total), 3 10-6 ph/el (camera), 7 10-7(proxitronic) Few photons : 1.5 108 ph for 8mC Need light intensification but fast time response

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)

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 [100-200]ns [200-300]ns 1 A beam current : 100nC - 4 105 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

Spectrometer line profile monitor Calibration : 200mm/pixel 5.5mm total ‘4.1 108- 7.2 1010 ph’ OTR screen : 100mm thick aluminum foil Size : 10cm x 4cm 2.8 10-3 ph/el (on camera) Observation for a beam with a minimum charge of 90nC (~ 1.2 109 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

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 0.9 10-3 ph/el (on camera) for 20MeV electrons ‘ 1.1 108-3 1010 photons ’ Possible improvements using an aluminum screen for the observation of lower beam charge

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

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

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)

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

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

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

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

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

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)