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Overview of the DB accelerator complex

Overview of the DB accelerator complex. B. Jeanneret CERN/ABP WG6 at IWLC_2010. Beam as requested by Decelerators. AIM : produce a gradient of 100 MV/m at f 0 =12 GHz for the Main Beam. Beam energy E=2.37 GeV Beam current I = 100 A 2×24 such trains for 3 TeV 2×5 0.5 TeV.

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Overview of the DB accelerator complex

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  1. Overview of the DB acceleratorcomplex B. Jeanneret CERN/ABP WG6 at IWLC_2010

  2. Beam as requested by Decelerators AIM : produce a gradient of 100 MV/m at f0=12 GHz for the Main Beam • Beamenergy E=2.37 GeV • Beamcurrent I = 100 A • 2×24 such trains for 3 TeV • 2×5 0.5 TeV This part to ensure flat filling of the PETS (talk O. Kononenko) This part for constant beamloading in DBLinac Tolerances on Drive Beam for luminosity ΔL/L = 1% (D. Schulte) 2922 bunches 5.25×1010 e-each Δtbb = 0.083 ns (12GHz) 87 ns 156 ns MB train 87 ns

  3. The way to producethesebeams • Whymakeitsocomplicated ? 292 -----

  4. Frequency Multiplication • Producing short pulses (243 ns) with klystrons is not efficient • Lowerfequency klystrons are more efficient • No gun canproduce a current I = qb×f0 = 100A • The CLIC way : • Drive BeamLinac : 1 GHz klystrons, 0.5 GHz bunchspacing • Use FM (DL, CR1,CR2) to interleave 24 pulses  12 GHz • Produce 24 trains in continuous to feedeachdecelerator Pulse length in DB Linac : Dt = 24×24×237ns = 140 μs • Use full beamloading for maximum efficiency

  5. Drive Beam Combination Steps fbeam= 4 * 3 * 2* fbuncher Picture borrowedfrom O. Kononenko 12 GHz 3 GHz 1 GHz 0.5 GHz EvenOdd bunches

  6. Optimized Pulse Shape for the Full Bunch Response in PETS Picture borrowed from O. Kononenko (seehis talk) Energy Spread ≈ 0.08 %

  7. Beam production • Gun must producen = 2922×24×50 = 3.5×106bunches/s (current I = 4A) • Must alternate trains withodd/evenbunches • Odd/evenbunch structure must be programmable inside the rise-timeperiod (recipe by Olexsiy, see former slide). • Timing tolerance for the beamat the entrance of the DB Linac: • Δφ1 = 0.1°@1GHz ⇔ 85 μm ⇔ 0.3 ps • Timing at 12 GHZ (synchonisation DB/MB & MB e+/e-) : • Δφ2 = 0.2°@12GHz ⇔ 14 μm ⇔ 46 fs (46 × 10-15 s) • Need active phase feed-back aftereach-turnaround to match Δφ1 and Δφ2 • Need (mostlikely) a site-wide timing network offeringthisprecision Dedicated session in WG2+6+7+8 yesterday Can a thermo-ionic gun, followed by a bunching System, do this ? Will a reliable laser gun exist ? Seetalks by Simona and Marta

  8. DB Linac • Dedicated session after coffee with WG4  • RF system : studied by E. Jensen and R. Wegner • Modulators : pre-study by D. Nisbet and D. Siemaszko • Optics and beamdynamics : A. Aksoy • Overall dimensions and power needsat hand • Stillmuchworkahead

  9. 2m Top view of the Linac building 3.1m Top view (half) … 0.75m 3m 5m 3m RF Structures 2.0m Coupler 0.5m 0.6m Q+BPM+? Building : Width: 2 × 12.5m ≈ 25 m Length : 820×3.1m = 2540 m  Total for 2 Beams : 1640 Klystrons + modulators

  10. End-view of the linac building Loads ~25 m Installed power Total ~ 290 MW 0.115 MW/m Crane 3m Modulators, RF control Klystrons 2.5m 2m Outstanding issues : Power management Reliability Beamquality Safety Water, cables 3m 6m

  11. More on tolerances for the DB LInac • Timing toleranceat the entrance of the DB Linac : • Δφ = 0.1°@1GHz ⇔ 85 μm ⇔ 0.3 ps • This to ensureΔφDB/MB = 0.2°@12GHz in the Main Tunnel • The factor ∼10 is must begranted by the active feed-back ateachturn-around in the Main tunnel • As for the DB Linacitself , in the segment before compression: • Gradient : ΔG/G < 2×10-3coherent over 100 klystrons, < 2×10-2 per klystron • Phase : Δφ = 0.05° to avoidunduebunchlenghtening (A. Aksoy, D. Schulte) • This in turn for modulator : ΔP/P < 10-5 • The last two values are certainly a nice challenge. Theyrequiremuch attention in the near future

  12. The DB Linaccomplex in the landscape Loop for phase- feed-back, compression • The DB Linacis the power source of CLIC • It shallreceive more attention in the future • Structures (beamloading, ageing ,…) • Klystron studies & prototypes • Modulatorsstudies • Power management • Beam management, collective effects • Phase and gradient tolerances 2120 m Gun

  13. Frequency Multiplication & transport to tunnel - I • Changes 2010 : • Twice longer lines (DL1, CR1,TA) to allow for good isochronicity, achromaticity and flexibility • Addition of a second Delay Line for energy scan between 1 & 3TeV (longer trains atlowerenergies) • Endorsed by the Tech. Comm. and Civil Engineering

  14. Frequency Multiplication & transport to tunnel - II • Strategy and work for CDR • Fullywork-outoptics of CR1 (see talk by Piotr) • Withnowlargerradii in DL and TA’s , good opticscanbederivedfrom CR1 to other rings/lines • A magnet catalogue isat hand , muchdetailed for all the lines (talk by Alexey Vorozhtsovwed.) • It wasused for the power and costestimateexercise (CDR) • It willbemuchuseful for anyvariationalwork • Concentrate on still open issues • Vacuum, SR, CSR, collective effects • Options for power & costreduction

  15. Synchrotron Radiation impact on hardware • X-ray @ 6 keV : Labsorption = 50 µm (Aluminium) • Impact angle : α ≈ 0.2 rad • ∆T = 80 K @ 50 Hz (CR2 & TA’s) • Compare to ΔTuts = 180 K • Risk of rapidageing • As of today : not solved B ∆x = Labs× α ≈ 10 µm • Power / dipole ~ 1 KW • Vacuumwiththis flux of photons ? • Spec for ion instabilities : p = 10-10 Torr • As of today : not studied

  16. Options for Dipoles & Vacuum vs. SR • Super-conductingsuper-ferricmagnets • s.ccoils, but classicalC-yoke for fieldshaping • More expensive, but power ÷5 • Costsavingswith time • Cold pipe (∼20-30K)  Thermal expansion vanishes • Another vacuum regime to study • Classicalresistivemagnets • Berylium pipe atSR-impact • Transparent to 6 KeVX-rays • SR absorbed in water behind • Be disliked for safetyreasons ⇔negotiable ? Ageingsolved

  17. SR impact on beam • ΔEturndifferent E inside trains through CR1 and CR2 • Converts to Δzafter final compression chicane • Annoying for synchronisation withirregular time structure • Beyond a certainspread , reduces PETS efficiency • To bere-workedwith new optics • Considers.c. super-ferricmagnets in CR1, CR2 (minimise CSR, optimise SR) (old data) R56 = -0.33 m 24 bunches x 121 17

  18. Collective effects • Ion instabilities : hard constraints on vacuum • DB Linac : p < 5 × 10-11 Torr Not Studied • FM, transport : p < 10-10 Torr Not Studied • Multi-bunchresistivewallinstabilities • The deformation of the trajectory of the rearbunches of a train goeslike • Need large pipe radius • CSR • With large pipe radius, the energylossissimilar to SR loss • Small SR losseslow B, large L for constant BL • Small CSR losses short L • So, screening CSR would help , i.e. allow to optimise SR • But CSR & n-bunchinstabilities are in conflicts • Anotherreason to look atsuper-ferricmagnets • Betterconductivitywouldallow for smaller radius  screening , … Withcopper chamber

  19. Operability RF deflector Kicker RF kicker (phase synchro) • Total longestpath for a train : 29 km • Through : • 820 klystrons • 14 RF deflectors • 3 Kickers • 5 compression chicanes • 1 RF kicker • 2 loops • 2 rings, severalturns 24 times • The 24 trains • must Survive with: • Beamlosses < 10-3 • Bunchlenghtening < few % • δz ∼ 10 μm Klystrons : 80 740 DB linac ∼20 km

  20. Future (post-CDR) • Manyoustanding issues to beworked-out • Can CTF3 validate the requirements for the CLIC Drive Beam ? • If not, what do weneed to do so ? • Seetalks by Roberto and Frank thisafternoon Myworries : Mismatchbetweenwork to do & manpower • Activityscattered in toomany ‘sub-projects’ An item for the round-tablethisafternoon …

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