LC Technology Hans Weise / DESY

Transcription

1 LC Technology Hans Weise / DESY

2 All you need is... Luminosity! L σ 2 N e x σ y σ y σ x L n b f rep Re-writing reflects the LC choices... L P E b c. m. N e σ σ x y... beam power... bunch population... Ac-to-beam efficiency L N e σ x, y luminosity nbr. of e per bunch beam sizes n b f rep P b nbr. of bunches per pulse pulse repetition rate beam power

3 Linear Collider schedule readiness gradient tests luminosity efficiency technology

4 CLIC 3 GeV c.m. Layout km 10 km km e - Main Linac (30 GHz 150 MV/m) Final Focus From Main Beam Generation Complex e - e + Detectors Final Focus Main Beams 9 GeV/c 154 bunches of 4 x 10 9 e + e - 20 cm between bunches e + Main Linac Laser γ γ Laser Drive Beam Decelerator 624 m Injector Drive Beam Accelerator Delay 937 MHz GeV MV/m 78 m 182 Klystrons 50 MW 92 µs 78 m 39 m e - e - 39 m 312 m Combiner Rings Bunch Compression 4 x 312 m 39 m 92 µs 22 drive beams of 1952 bunches at 1.18 GeV charge 31 µc / beam - energy 37 kj / beam 92 µs 42,944 bunches up to 16 nc / bunch at 50 MeV total charge 690 µc 92 µs 352 trains of 122 bunches at 1.18 GeV total energy 812 kj

5 The CLIC Idea 50 mm 25 mm CLIC Drive Beam Structure (SICA type) 2 m C-PETS (12 damping slots) Transfer Structure Quad Transfer Structure Quad 230 MW, 30 GHz Acc. Struct. Acc. Struct. Acc. Struct. Acc. Struct. 2 mm Tapered-Damped Structure (30 GHz)

6 NLC TeV c.m. High Energy HEP Detector Final Focus Final Focus Compressor Low Energy HEP Detector e - Injector e + Target e + Pre-Damping and Damping Ring e - Damping Ring e - Injector

7 TESLA TeV c.m. 33 km X-ray laser e + linear accelerator linear accelerator e - damping ring positron preaccelerator HEP experiments positron source damping ring electron sources

8 CLIC Tapered Damped Structures (TDS) Design criteria: Short & long range wakefields Shunt impedance Operation frequency 30 GHz RF mode 2π / 3 Accelerating Gradient 150 MV/m Iris diameter 2 mm Iris thickness 0.55 mm Alignment tolerances 10 µm Four waveguides with SiC loads guarantee heavy local damping Field limitations due to electrical breakdown and related surface damage required changes in the TDS design. Just recently 150 MV/m peak unloaded gradient were reached in a low group velocity structure with tungsten irises. Testing was limited by rf power source pulse length: 15 ns instead of the required 130 ns. Damping and detuning (1st dipole passband) methods at 30 GHz under study.

9 NLC Next Linear Collider NLC / JLC Rounded Damped-Detuned Structure (RDDS) Operation frequency 11.4 GHz RF mode 2π / 3 Accelerating Gradient 70 MV/m Iris diameter mm RF Input Beam RDDS Cutaway View (8 of 206 cells) HOM Manifold Accerator Cell (Iris diam mm) Made with Class 1 OFE Copper. Cells are precision machined (few µm tolerances) and diffusion bonded to form structures. Fill time attenuation time 100 ns, i.e. length 1.8 m. Operated at 45ºC with water cooling. RF losses approx. 3 kw/m RF ramped during filling to compensate beam loading (21%). In steady state approx. 50% input power goes into the beam.

10 NLC Next Linear Collider Design criteria: Travelling wave structures Disc loaded design Iris surface roughly constant Gradient profile shaped by varying RF group velocity RF time structure influenced by RF attenuation Result: 206 cells, 1.8 m overall length 12% 3% group velocity 70 MV/m, i.e. cost minimum But breakdown related damage!!!

11 NLC Next Linear Collider Surface damage problems An unexpected problem... During conditioning of the first long NLC structures changes in the field profile were observed. A careful inspection has shown - surface damage due to field emission - crater with approx. 30 µm diameter are covering a few percent of the surface - after 1000 h high power operation a 20 deg. phase error was measured at the input coupler s structure end; no error at the other end of the structure - previously built short structures had no problems A possible explanation... Field emission / breakdown cause an RF power absorption being proportional to the group velocity squared. For long structures the group velocity is much higher at the input coupler. before 1000 h of high power operation Bead -pull measurement of the DS2 phase profile after 1000 h of high power operation C. Adolphson et al., RF Processing of X-Band Accelerator Structures at the NLCTA, LINAC 2000 Conference Remark: π-mode standing wave structures have v g 0.

12 High Gradient Structures Goal: 70 MV/m unloaded for 0.5 & 1 TeV Compare performance versus different initial structure group velocity and length cell machining and cleaning methods structure type: traveling wave vs. standing wave 12 structures (5000 h at 60 Hz) processed so far Systematic study of rf breakdown measure breakdown related RF light sound X-rays current gas measure surface roughness / cleanliness / damage with SEM, EDX, XPS and AES Improve structure handling and cleaning methods 53 cm Traveling-Wave Structure Group velocity 3.3% 1.6% c

13 Superconducting Accelerating Structures for TESLA Goal during past decade Increase cavity gradient from 5 to 25 MV/m Reduce costs by a comparable factor 1256 mm 1036 mm mm HOM coupler power coupler Common effort of almost all laboratories using s.c. accelerating cavities, e.g. (CERN), Cornell, DESY, INFN, (KEK), Saclay, TJNL 35 partners from 11 countries rf pick up HOM coupler Improved material quality check New cavity preparation procedures 1400 ºC annealing with a titanium getter ultra-pure, high pressure water rinsing high peak power processing One standard 9-cell TESLA accelerating structure operated as a π-mode standing-wave cavity. One 230 kw rf input coupler, an rf pick up antenna and two Higher Order Mode antennas are assembled to each cavity.

14 Preparation of TESLA Cavities

15 TESLA Cavities Made with solid, pure (RRR >300, high thermal cond.) Niobium Nb sheets are deep-drawn to make cups ( 100 µm tolerances), which are electron beam welded to form structures. Fill time 420 µs, i.e. Q ext =Q beam 3 x 10 6, f 400 Hz RF pulse length (400 µs filling µs flat top) = 1320 µs. Operated at 2 K in superfluid Helium bath. RF losses approx. 1 W/m. RF amplitude and phase adjusted during filling and flat top to compensate beam loading. In steady state essentially 100% rf input power goes into the beam. Q f o = 2π 1 frequency f Q o = = f quality factor f 1Hz LC G R s f 0 = 1,300,000,000 Hz L C f R s

16 High Gradient Performance Unloaded Quality Factor Q 0 Exciation Curves for Cavities from the 3 rd Production Series TESLA goal TESLA goal TESLA goal The First Three Production Series TESLA goal Accelerating Gradient ( MV/m ) Approx. 70 cavities were produced in three production series. Gradient and gradient spread improved a lot. Five accelerator modules with 8 cavities each were assembled. Three of them were used in the TTF Linac. Modules 4 and 5 are going to be tested in early spring The First Five Accelerator Modules

17 35 MV/m for 800 GeV c.m. Electro-polishing (EP) instead of the standard chemical polishing (BCP) eliminates grain boundary steps. First electro-polished single cell cavities Gradients of 40 MV/m at Q values above are now reliably achieved in single 0.5 mm cells at KEK, DESY/CERN and TJNAF. 0.5 mm BCP Surface (1µm roughness) The highest gradient achieved was 42 MV/m. EP Surface (0.1µm roughness) Unloaded Quality Factor Q 0 Excitation Curves for Cavities from the 3 rd Production Series TESLA goal TESLA goal Unloaded Quality Factor Q 0 First TESLA 9-cell cavity above 35 MV/m TESLA 800 goal TESLA 800 goal Accelerating Gradient ( MV/m ) Accelerating Gradient ( MV/m )

18 TESLA Cavity Operation The maximum operating gradient of s.c. cavities is set by cavity quench, field emission, or Q-degradation not by structure breakdown is not a hard limit. It results in high cryogenic load, radiation, and dark current does not trip off cavities in ns but in typ. 100 µs if cavities are operated at the threshold During operation at the TESLA Test Facility Linac it was demonstrated that the trip threshold can be determined easily. An exception handler as part of the LLRF can avoid quenches. Action can be taken prior to the next pulse. High Gradient long pulse run in spring 2002 stable beam operation at 21.5 MV/m (5% below limit) beam energy 195 MeV, beam current 5 ma, 800 µs Accelerator module 39 days at 19.5 MV/m, 800 µs, 5 Hz 4 days at 20.0 MV/m, 800 µs, 1 Hz 6 days at 21.5 MV/m, 800 µs, 1 Hz typ. module on-time 90% Cavities in module 3 (limit at 22.7 MV/m) were operated for approx. 10,000 hours w/o any degradation. 10,000 hours 50% of the time at 800 µs Mostly MV/m 1 Hz rep.rate, during FEL operation

19 NLC vs. TESLA Efficiencies & Power LLRF Klystron 55% RF Distribution 85% Modulator 80% NLC: 10% 13 MW Cryogenics 20 MW Other 8 MW AC-to-Beam Efficiency 139 MW Cooling 15 MW Other 3 MW TESLA 24% Modulator 85% 97 MW 23 MW RF Distribution 94% Klystron 65% LLRF

20 NLC Linac RF Unit Low Level RF System (not shown) One 490 kv 3-Turn Induction Modulator Eight 3 kw TWT Klystron Drivers (not shown) Eight 75 MW PPM Klystrons Delay Line Distribution System (2 Mode, 4 Lines) Eight Accelerator Structure Sextets

21 NLC Induction Modulator Prototype 10 core test 22 kv, 6 ka, 3µs Klystron (5045 for testing) Water Load MetGlas Cores Capacitors IGBTs 10 cm Driver Circuit

22 NLC XP-Klystron Program 50 MW Solenoid Focused Tubes were built for testing Solenoid Power = 25 kw Periodic Permanent Magnet focusing is used for XP type klystrons. The first tube finally reached 70 MW, 3.1 µs, limited by the modulator. The next generation tubes are still not performing well. Eight tubes in total are needed for the 8-pack test with DLDS and accel.structures (scheduled for mid 2004).

23 JLC PPM Klystron Program KEK with Toshiba have built a 75 MW, 1.5 µs tube (PPM-2) which basically meets the JLC design goals. PPM-2 Peak Power Efficiency Puls Width Repetition rate Design 75 MW 55% 1.5 µs 150 Hz Achieved 75.1 MW 56% 1.4 µs at 74 MW 1.5 µs at 70 W 25 Hz New tubes with 60% efficiency (PPM-3) and easier manufacturability (PPM-4) are foreseen.

24 NLC DLDS System Feeding of six structures RF Power Distribution incl. Pulse-Compression from 75 MW / 3.2 µs to 600 MW / 0.4 µs mid 2004

25 TESLA RF Unit 1 klystron for 3 accelerating modules, 12 nine-cell cavities each vector modulator MBK Klystron DAC DAC Low Level RF System circulator stub tuner (phase & Qext) coaxial coupler Mechanical tuner (frequency adj.) and piezo-electric tuner (Lorentz force compensation) cavity #1 cavity #12 vector sum pickup signal ADC ADC accelerator module 1 of 3 vector demodulator

26 TESLA Modulator Based on good experience with three FNAL Bouncer Type Modulators the next generation features A constant power High Voltage Power Supply Matching to TH2104C (5 MW) and TH1801 (10 MW MBK) Integrated Gate Commutated Thyristor (IGCT) Switches instead of IGBT or GTO Technology A Lower Leakage Inductance Pulse Transformer Partially manufactured in industry IGCT Stack HV Power Supply Capacitor Bank Bouncer Pulse Transformer

27 TESLA Multi Beam Klystrons MBKs reduce HV requirements and improve the efficiency because of lower space charge. Seven beams, 18.6 A, 110 kv, produce 10 MW with 70% eff. Three Thales TH1801 Multi Beam Klystrons were produced. Achieved efficiency 65% RF pulse width Repetition rate Operation experience 1.5 ms 5 Hz > 5000 h Approx. 10% of operation time at full spec s

28 CLIC Test Facility CTF3

29 JLC Japan Linear Collider Accelerator Test Facility

30 JLC Japan Linear Collider Cavity Production Damping Ring Wire-Scanner S-Band Linac Wiggler-Magnet

31 NLC Test Accelerator (NLCTA) Goals: RF system integration test of a NLC linac section test efficient, stable and uniform acceleration of a NLC-like bunch train Construction started in 1993 using first generation RF component design. In 1997, 15% beam loading compensation of a 120 ns bunch train to <0.3% was demonstrated. klystron SLED II pulse compression X 4 3db hybrid 40 m resonant delay lines beam accelerating structures

32 TESLA Test Facility Linac e - beam diagnostics undulator bunch compressor e - beam diagnostics laser driven electron gun photon beam diagnostics superconducting accelerator modules preaccelerator 250 MeV 120 MeV 16 MeV 4 MeV

33 TESLA Test Facility - Operation The TTF Linac is operated 7 days per week, 24 hours. Approx. 50% of the time is allocated to FEL operation including a large percentage of user time. The FEL requires very stable beam conditions. In its different set-ups, approx. 13,000 hours beamtime were achieved since Based of the TTF experience several FELs using superconducting accelerator technology are proposed. DOWN 8% OFF 6% DOWN 6% OFF 8% USERS 0% Beam uptime and operational uptime (users or acc.studies) TUNING 19% TUNING 25% 100% STUDIES 4% USERS 63% STUDIES 61% 80% 60% week 3 / 2002 week 7 / % 20% FEL User Operation Accelerator Studies week

34 TESLA Test Facility Linac Phase II FEL User Facility in the nm Wavelength Range Six accelerator modules to reach 1 GeV beam energy. Module #6 will contain 8 electro-polished cavities. Engineering with respect to TESLA needs. Klystrons and modulators build in industry. High gradient operation of accelerator modules. Space for module #7 (12 cavity TESLA module). Commissioning RF in spring 2003 FEL in fall 2003 experimental area bypass 1000 MeV 450 MeV 150 MeV BC 3 BC 2 4MeV undulators seeding collimator #7 #6 #5 #4 #3 #2 module #1 RF gun 250 m

35 TESLA R&D Schedule Structures long-term operation at full 500 GeV c.m.specs. module 1* at 25 MV/m 7 10 / 02 module 4 & 5 above 25 MV/m (rf test) 3 5 / 03 high gradient 35 MV/m tests for 800 GeV c.m. ongoing one complete module in Power Sources testing HV cables 2003 lifetime MBK (multi-beam klystron) on hold Power distribution circulators for upgrade to 800 GeV c.m. ongoing Injectors, Damping Rings etc. laser R&D for polarized source ongoing kicker magnets & pulser ongoing, instrumentation (identical to all LC projects) ongoing

36 NLC R&D Schedule Structures study break down damage ongoing build final NLC structure long-term testing of final NLC structure 2004 Power Sources build 3 x XP-3 klystron 2002 test 2-pack + SLED II 2003 build 6 x XP test 8-pack incl. MDLDS etc. plus 6 Acc.Structures 2004 Power distribution SLED II test 2003 MDLDS test mid 2004 Injectors, Damping Rings etc. conventional e+ source undulator e+ source instrumentation (identical to all LC projects) BDS crab crossing on hold proposed ongoing on hold

37 Summary CTF3 in 2006 ILC-TRC Report in 12/ pack test mid 2004 TESLA 500 now 35 MV/m to be tested in 2003 / 2004