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Update on Laser Beam Lines Christoph Hessler, Mikhail Martyanov, Valentin Fedosseev (CERN laser team) Thanks to M. Battistin, N. Chritin, F. Galleazzi, J. Hansen AWAKE Collaboration meeting Greifswald, 25.09.2014
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Overview Different laser beam lines for AWAKE: Laser beam line to plasma cell Diagnostic beam line (“virtual plasma”) Laser beam line to electron gun 25/09/2014C. Hessler2
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Beam Line to Plasma Cell Civil engineering works: Start of laser core drilling scheduled for 15 th September. Trenches: Planning of the excavation work on-going and should start after the laser core drilling Vacuum components: Preliminary design made Now on hold, awaiting vacuum compatibility test results from TE/VSC for motorized opto-mechanical components: – Mirror mount tested, report from TE/VSC should be available soon. – Translation stage is expected to be delivered in October and will be tested right after arrival. 25/09/2014C. Hessler3
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Vacuum Laser Line 25/09/2014C. Hessler4 General overview:
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Laser Room Side 25/09/2014 C. Hessler Vacuum tank frame in the laser room: 5 1800mm 1000mm 700mm
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Proton Tunnel Side 25/09/2014C. Hessler6 Vacuum tank frame in TT41: N. Chritin (EN/MME)6 Protection needed! 1315mm 750mm
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Laser Safety Shutter 25/09/2014C. Hessler7 N. Chritin (EN/MME)7
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Laser Trench in TT41 C. Hessler Dimensions of pits are defined 8
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UHV - Picomotor TM Optical Mounts 25/09/2014C. Hessler9 UHV - Picomotor TM ClearEdge Optical Mounts Features: Customized Picomotor 1.0, 2.0”, and 3.0” in (25.7, 50.8, 76.2 mm) mirror mounts – Clear Edge ΘX, ΘY Adjustments with angular resolution of <0.7urad UHV Compatible 10^-9 Torr Kapton wires ideal for X-ray, UV or EUV applications All vented holes Integrated polished carbide pads
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Diagnostic Beam Line Purpose: To measure the laser beam properties at different locations in the plasma cell. Direct measurement in plasma cell not possible. Therefore, the leakage of a mirror will be used to monitor the beam profile in the same distance as the plasma cell: 25/09/2014C. Hessler10 Merging chamber Diagnostic beam line Virtual plasma observation point
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Diagnostic Beam Line 25/09/2014C. Hessler11 300mm 320 mm 7800mm 520mm 1095mm 7800+400mmm New support for optical station 19930mm 2235 mm 2615mm +5000mm +5000mm 8000+400mmm 8000mm
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Diagnostic Beam Line Decided to use a folded geometry of the beam line. Advantages: – Shorter than a straight geometry. – Returning mirror fits between two magnets – Possible to observe the beam profile at the entrance, centre and exit of the plasma cell simultaneously. 25/09/2014C. Hessler12 Plasma cell entrance cam Plasma cell exit cam Plasma cell centre cam
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Beam Line to Electron Gun The electron beam current is not limited by the laser energy (we could take 10% of the ionizing beam), but by the ablation threshold (if copper cathodes are used) and therefore by the quantum efficiency of the cathode. Ways to increase the achievable electron beam current: – Increase beam size (will increase the emittance as well) – Improve the QE of copper cathode using dedicated cleaning techniques (e.g. heat treatment, ion cleaning) – Use cathode material with higher QE, like e.g. Cs 2 Te – Be lucky and have a cathode with a good QE For point 2 and 3 it is essential to have cathode transfer system under UHV available (e.g. as it presently exists at PHIN). 25/09/2014C. Hessler13
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Beam Line to Electron Gun QE of copper cathodes: reports QE values between 4e-5 and 1.1e-4 reports QE values in the mid e-5 range, and problems with ablation during laser cleaning (5 mJ/mm 2 ) Measurement at PHIN: QE of 3e-4, “too good to be true”, maybe some Cs contamination? 25/09/2014C. Hessler14
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Beam Line to Electron Gun 25/09/2014C. Hessler15 IR transfer
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Beam Line to Electron Gun 25/09/2014C. Hessler16 UV transfer
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Beam Line to Electron Gun Laser energy of the second output from the laser (2.5 mJ) is not sufficient to drive the electron gun. Solutions: – New amplifier, – Take 10% of the main beam for the gun. Disadvantage: Gun cannot be operated at a higher rep rate than the main beam. For efficient UV beam generation from a Ti:Sapphire laser beam, fs pulses are needed. Therefore, – the IR beam first needs to be compressed (with compressor used in Munich?), – then converted to UV, – and afterwards stretched to the desired pulse length (10 ps). The installation place of these components can be in the laser room or the electron gun room, but the laser room seems more favourable: – More space and clean + temperature controlled environment – Accessible during electron gun operation – Clearly defined interface to the laser Delay line is needed (optical path calculated) Aim is to buy a complete system from Amplitude. 25/09/2014C. Hessler17
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Laser Room: Ventilation System Design of ventilation system is on-going. Ventilation unit has been moved outside laser room Open question: Which humidity level can be accepted? 25/09/2014C. Hessler18
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Laser Room: Support Structures 25/09/2014C. Hessler19 ~ 2.3 m ~ 2 m Structure to support duct, shelves, tube to e-gun, cables Structure to support mirror chambers Decoupled from other structure
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Laser Room Integration Integration is on-going, but some important facts are still missing: – Arrangement of laser components on optical table: Waiting for proposal from Amplitude – Detailed Layout of compressor (Waiting for Amplitude’s quotation) – From which point of the laser will the beam for the electron gun taken? Is additional Amplifier needed? Waiting for Amplitude’s quotation for laser extension for electron gun. 25/09/2014C. Hessler20
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