Status and plans of drive beam components and tests Status and plans of drive beam components and tests CLIC review, March 1 st, 2016Steffen Döbert, BE-RF  Drive beam injector introduction  Technology challenges  Development program past and future  Status and prospects

CLIC Layout at 3 TeV Drive Beam Generation Complex Main Beam Generation Complex Post CDR optimization 600 Klystrons, 20 MW Post CDR optimization 600 Klystrons, 20 MW

Phase coding 180  phase switch Acceleration 0 Deflection 0 / 2 Sub-harmonic bunching 0 / 2 CTF3 example Phase coding by sub-harmonic bunching

Satellites bunch population estimated to ~8 %. Satellites High bandwidth buncher and rf source needed Phase switch: Phase switch within eight 1.5 GHz periods (<6 ns).

Technology challenges and requirements  Long pulse source, high average current, phase switching, wide band power sources, satellites, ultra high efficiency rf system, cost-driver, high beam power, stability stability stability !  The DB is the CLIC power source and its stability is critical for the main beam quality  Luminosity (timing, current and phase, beam quality, repeatability) o final bunch length: 1 mm, 1% tolerance o 0.2 degrees bunch phase error at 1 GHz o Beam current error 0.1% o rf power error 0.2% o rf phase error 0.05 degrees o voltage stability for the modulator ( 6 kHz – 4 MHz)

Drive Beam cost and power consumption  ~ quarter of the cost, 80 % is rf system  ~ half of the power consumption comes from the drive beam

Development program  Critical items list: Beam parameters and stability requirements, feedback and feedforward, satellites, electron source, rf power system, acc. Structure, develop industrial base, cost and power  Corresponding development program o Full beam dynamics design of injector o Beam studies in CTF3 as far as possible, feedback and feedforward o Front end component prototyping with CLIC specs, no integrated beam facility (Bare minimum to touch the above requirements, limited by resources) o Possibility to do integrated beam testing in the future DB front end facility > 2018

CLIC DB front end, CLIC DB front end, Post CDR Project For time being only major component development: GUN, SHB, high bandwidth 500 MHz source, 1 GHZ MBK, modulator and accelerating structure in an high power test stand Gun SHB PBBuncherAcc. Structures Solid state, 500 MHz Modulator-klystrons, 1 GHz, 20 MW ~ 140 keV ~ 12 MeV Diagnostics ~ 3 MeV

CLIC DB injector specifications ParameterNominal valueUnit Beam Energy50MeV Pulse Length140 / 244  s / ns Beam current4.2A Bunch charge8.4nC Number of bunches70128 Total charge per pulse590 CC Bunch spacing1.992ns Emittance at 50 MeV100mm mrad Repetition rate100Hz Energy spread at 50 MeV1% FWHM Bunch length at 50 MeV3mm rms Charge variation shot to shot0.1% Charge flatness on flat top0.1% Allowed satellite charge< 7% Allowed switching time5ns

Beam Dynamics design  Longitudinal and transverse dynamics basically finished, some additional investigations with possible improvements ongoing All specified beam parameters reached, very low losses and satellite content (2%). Big improvements to CDR. Collaboration with IPM (Iran)  Design of sub-harmonic bunchers, pre-buncher and travelling wave buncher done Collaboration with IPM  First investigation on rf-gun beam dynamics and design (IPM)  Iterations with drive beam linac design needed, compromises in beam parameter choice possible. (Collaboration with Turkey)

Photo injector option Advantages No satellites or tails, phase coding on the laser side No or less bunching needed, possibly better emittance Flexible time structure Better phase space Concerns Cathode lifetime Challenging laser, peak and average power Intensity stability Maintenance and operation Some work within the PHIN program but mainly not followed because of lack of resources

Development of a very high efficiency L-band multi-beam klystron with industry for the CLIC Drive Beam 1 GHz, 20 MW, 150  s, 50 Hz, > 70% efficiency Thales Electron Devices: 10 beam multi beam klystrons 77 % efficiency calculated Toshiba: 6 beam multi beam klystrons 75 % efficiency calculated Delivery and test in 2016, see as well CLIC workshop session on high efficiency rf

CLIC Klystron modulators main specs Pulsed voltageV kn 180kV Peak nominal power P out 29MW Rise/fall timest rise 3μs Flat-top lengtht flat 140μs Rep. rateRep r 50Hz Pulse repeatabilityPPR10-50ppm 29 MW x 1300 klystrons = 38GW of pulsed power! 1300 modulators synchronously operated Hot R&D topics: Distribution grid layout optimization Active compensation of power fluctuation (new converters topologies) High efficiency, high bandwidth, high repeatable power electronics HV fast pulse transformers design Highly repeatable HV measurements Redundancy, modularity, availability 1300 klystron modulators 2 Km in length CLIC modulators R&D

 Test stand: 2 modulators – one in 2016 and one in 2017 ETH Zurich (CH) collaboration: develop & deliver full modulator in 2016 LAVAL Uni. (CA) collaboration: develop & deliver design files for construction in industry, delivery to CERN in 2017 Nottingham Uni. (UK) collab.: deliver studies on grid layout optimization and gives inputs to others collaborations, experimental validation CERN: Study common issues to all collaborations, i.e. repeatability & high precision measurements  Status Topologies selected (Nottingham & CERN inputs) Reduced scale prototypes tests at LAVAL/CERN Full power modules under test at ETHZ to be delivered in April

Sub-harmonic bunching system Status: RF design existing, mechanical design done, Prototype fabricated at CERN Power source: 500 MHz, kW, wide band (60 MHz) sources needed for fast phase switching. Solid state chosen Collaboration with RRCAT (India) delivered 20 kW prototype SHB 1SHB 2SHB 3 Beam velocity0.62 c Current5 A Voltage15 kV30 kV45 kV Bunch form factor Detuning1.6 MHz12.1 MHz12.7 MHz

Sub-harmonic buncher  Collaboration with Iran and India  Prototype in Aluminium fabricated at CERN  Wide band power source development with RRCAT in India (solid state, 4 kW and 20 kW)

Thermionic Gun design in collaboration with CEA/CESTA and SLAC

Gun Test Facility High Voltage test successfully done, beam tests to start

6 × 42kV 10A 150µs 20Hz = Status Tested up to 42 kV, 20 Hz Flattop < 1% EMC issue on low level 50 Hz  New active short circuit protection tested on 5 stages Future Increase of frequency and voltage Implementation of SC protection on the whole modulator Marx-Modulator for DB gun Prototype developed by CEA

What remains to be done  Many successful and efficient collaborations for the DB work: CEA/CESTA, Pakistan, India, Iran, SLAC, ETHZ, Laval, Thales, Toshiba  Short falls of the current program: Integrated testing, producing real beam and verify stability, we will not have a injector for the DB Only modest industrial efforts towards CLIC for major components No effort for photo injector option  GUN/Buncher: Full-scale Marx-Generator, Testing the gun and buncher at full specs, demonstrate requirements harvesting the results and documenting  MBK/Modulator: Complete test stand, extensive testing of klystrons and modulators, demonstrate stability requirements  Build and test with high power DB accelerating structure prototype

Interest beyond CLIC  Modulators (Davide Aguglia) Knowledge for high power interconnection to the grid for cycling loads with no power fluctuation (application FCC or linear accelerators) Demonstration of highly repeatable power converters (more and more requested for injection-ejection pulsed magnets – link with CLIC Modulator work) Pushing the boundaries for high precision and repeatable measurement acquisition system (applicable for current measurement!!)  Electron sources Corresponding knowledge at CERN, needed for any project involving electrons (LHeC, FCC-ee, ILC)  High efficiency, klystrons and solid state amplifiers Identified as R&D priority at CERN and EU, essential for future projects, FCC, ILC, LINAC4, SPS, Medical  AWAKE, SRF Awake profited a lot form these CLIC activities, this made AWAKE possible in this time scale. Front end components might be used for other test facilities.

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