Status and R&D program of the CLIC Power Extraction and Transfer Structure (PETS) Igor Syratchev for the CLIC team
A fundamental element of the CLIC concept is two-beam acceleration, where RF power is extracted from a high-current and low-energy beam in order to accelerate the low-current main beam to high b d l h l b h h energy. Drive beam PETS Main beam Accelerating structures RF power
PETS design development chart Extraction efficiency Drive beam current & energy Drive beam current & energy On/OF capability RF power constrains RF power constrains RF power production needs PETS design RF components RF components Beam transport and stability Module layout and fabrication technology fabrication technology High power High power tests
PETS design 1 / 2 = × − a B m ( L L ( a ) m ) R / Q For the fixed phase Av extr − 2 = a a C C advance and iris advance and iris G G = × − L L n L 1. For the chosen layout ( L UNIT ) and the V thickness: Av struc T gr number of PETS per unit, the aperture is C C uniquely defined. I G = B 2. In general the bigger aperture (longer R / Q 4 P n PETS) favors the beam dynamics. 2 2 2 struc = = ω ω P P I I L L F F 3 3. The longitudinal slots are mandatory to The longitudinal slots are mandatory to b b 0 0 provide transverse HOM damping V 4 g As a result of multiple compromises, the PETS aperture a/ λ = 0.46 (m = 2) × − ( L n L ) was chosen. struc T = − L L L L ( a ( a ) ) extr extr m Drive beam Quad PETS PETS n 100 A 2 2 ω = I F C = struc × P P 2.4 GeV � 0.24 GeV (0.87 km) b 0 I Deceleration: ~6MV/m m 135 MW 135 MW P – RF power 240 ns Main beam I – Drive beam current 1.2 A L – Active length of the PETS 9 GeV � 1500 GeV (21 km) Accelerating structure x4 Acceleration: 100 MV/m F b – single bunch form factor ( ≈ 1) PETS cross-section The PETS are large aperture, high-group velocity and overmoded g g p y periodic structures. In its final configuration, PETS comprises eight octants separated by 2.2 mm eight octants separated by 2.2 mm wide damping slots.
The PETS bars Special matching cell E E max (135 MW)=56 MV/m (135 MW) 56 MV/ Electric field RF power density H max (135 MW)=0.08 MA/m One of the eight PETS bar
PETS RF power extractor Baseline design Damped modification (in progress) 11.424 GHz couplers 0 Electric field 12 GHz couplers measured face-to-face (blue) reflection and as simulated with HFSS (red) eters, dB 20 0 S pareme 10 isolation 40 rameters, dB 20 60 30 30 S par Magnetic field 11.5 11.7 11.9 12.1 12.3 12.5 Ferquency, GHz 40 50 11.7 11.8 11.9 12 12.1 12.2 Frequency, GHz
HOM damping in PETS In the high group velocity structures, the frequency of the transverse mode is rather close to the operating one (13.0 GHz in our case). The only way to damp it is to use its symmetry properties – damping with the slots. Transverse modes spectra HFSS 1 . 10 4 GDFIDL GDFIDL No slot No slot E-field (color maps) and pointing vectors (arrows): V/A/m/mm (log) 1 . 10 3 With slot 100 Re (Zt) V 10 10 1 0.1 0 12 15 30 45 60 Frequency, GHz ω z ⎧ ⎫ ⎛ ⎞ − ω z β z ⎜ ⎟ 2 Q ( 1 − β ) c = × × ⎨ − ⎬ W ( z ) 2 q K sin e 1 ⊥ ⊥ ⎝ ⎠ ⎩ − β ⎭ c L ( 1 ) − β β 1 1 = > W ( z ) 0 , z L ⊥ β In the presence of the longitudinal slots, the transverse mode field pattern is dramatically distorted. The new, TEM-like nature of the mode significantly increases the group velocity, in our case from 0.47 c to almost 0.73 c . However there is practically no damping in this configuration. To do that we must to introduce the radial impedance gradient in the slot that we must to introduce the radial impedance gradient in the slot - to create the radial component of the pointing vector.
HOM damping in PETS PETS transverse impedances Moderate damping (tg δ =0.1) Strong damping (tg δ =0.32) With the proper choice of the load With the proper choice of the load configuration with respect to the material properties makes it possible to couple the slot mode to a number of heavily loaded modes in dielectric of heavily loaded modes in dielectric. This gives a tool to construct the broad wakefields impedance. eps eps The material for the load optimization was chosen in 2006! Fixed eps=24 Currently, we can not get from industry the ceramic with C tl t t f i d t th i ith reproducible properties, however certain suggestions towards absorbing ceramic for the PETS can be done: 1 1. Th The load geometry can be adopted in every particular case. l d t b d t d i ti l In general, lowering eps., the load volume will be increased. Making it higher does not really help! It can be tg δ recommended to target the eps range between 15 and 25, with preference towards higher values. ith f t ds hi h l s 2. The tg δ of at least 0.3 (and higher) would be the choice. 3. The wide frequency band 9-18 GHz must be addressed.
PETS testing chart RF power sources External RF power source Drive beam RF high power g p source RF power RF power RF power in out out Drive beam CTF3 (CERN + Collaborations) CTF3 (CERN + Collaborations) ASTA (SLAC) Objective: to understand the limiting factors for the PETS ultimate performance. Two beam test stand (CERN + Collaborations) Objective: to demonstrate the reliable production of the nominal • Access to the very high power levels (300 MW) CLIC RF power level throughout the deceleration of the drive beam. and nominal CLIC pulse length. • High repetition rate – 60 Hz. Test beam line (CERN + Collaborations) Test beam line (CERN + Collaborations) Objective: to demonstrate the stable, without losses, beam transportation in a presence of the strong (.50%) deceleration.
PETS high power tests at CERN (TBTS) • Different scenarios of the drive beam generation in the CTF3 • In order to demonstrate the nominal CLIC power level and pulse length, it was decided to implement a different CTF3 #1 PETS configuration – PETS with external re-circulation. DL CR DBA Round trip efficiency: 75% To the Load Round trip delay: 22 ns CTF2 CTF2 <30A <30A TBTS TBTS V Variable Splitter i bl S litt CLEX Variable (coupling: 0 → 1) phase shifter #2 PETS output PETS input PETS input Drive beam 14 A #3 #3 Expected PETS power production with re-circulation. The calculation followed the measured performance of all the components 4 A Tc Tp p 150 150 CLIC Pn nominal • To compensate for the lack of current, the ⋅ Pn 0.9 active TBTS PETS length was significantly 6.0 A MW increased: from the original 0.215 m to 1 m. 100 5.0 A Power, 4.0 A Operation mode #1 #2 #3 CLIC Current, A <30 14 4 101 3.5 A 50 Pulse length, ns 140 <240 <1200 240 240 ns Bunch Frequency, GHz 12 12 3 12 CLIC nominal PETS power (12 GHz), MW <280 61 5 135 0 0 200 400 600 800 Time, ns
PETS high power tests at CERN (TBTS) 0 0 0 0 F 10 0.5 20 B S11, dB B S12, dB 1 30 1.5 40 S11 S11 S12 S12 50 2 11.7 11.8 11.9 12 12.1 12.2 Frequency, GHz
PETS high power tests at CERN (TBTS) Number of the standard and new RF waveguide Number of the standard and new RF waveguide components were designed and fabricated to operate the TBTS at a high RF power. 3dB H-plane splitter Variable high power RF power splitter Variable high power RF power splitter Variable high power RF phase shifter Variable high power RF phase shifter Variable high power RF phase shifter 3dB hybrid Dry stainless steel high power RF load Directional coupler Parts of the dry stainless steel high power RF load
PETS high power tests at CERN (TBTS) PETS processing history in 2008 PETS processing history in 2008 Typical waveforms with recirculation Typical waveforms with recirculation model measurements current 15.11.08 14.12.08
PETS high power tests at CERN (TBTS) … and we can explain how it works!
PETS installed in the ASTA bunker 11. 424 GHz PETS measurements after final assembly 0 0 Assembly of the eight PETS bars. 11.422 − 0.18 10 0.5 S11, dB S12, dB 20 1 − 26.5 30 1.5 S11 S11 S12 S12 40 2 11.25 11.35 11.45 11.55 11.65 11.75 Frequency, GHz 11.424 GHz PETS ready PETS installed into the ASTA test area at SLAC
PETS processing at ASTA in 2008 … and in 2009 Typical pulse shape “…At the moment the PETS are running at Evidences of breakdown ~100 MW peak with 133 ns pulse width. The 132 ns progress is very slow. The reason for the p g y w. f extremely slow slope is that when a breakdown occurs it is very violent! In some cases it trips the ion pumps and we have to wait for a while to be able to start them f m Traces of breakdown Traces of breakdown again. This is not a reasonable way to run or make progress. Hence the idea is to take the PETS out and to examine it. If we see the reason for this behavior we learned something, if not, we do something, either clean, etch or back them 264 ns and try again.” Message from Sami Tantawi (11.02.09) g ( ) 100 Hours In 100 hours, the PETS was processed up to ~ 95 MW x 132 ns (cf. 135 MW and 240 ns in CLIC). For most of the time the processing was limited by heavy out gazing inside the system including PETS.
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