CLIC Power Extraction and Transfer Structure. (2004)

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1 CLIC Power Extraction and Transfer Structure. (24) CLIC linac subunit layout: CLIC accelerating Structure (HDS) Main beam 3 GHz, 2 MW per structure Drive beam (64 A) CLIC Power Extraction and Transfer Structure (PETS) with On/Off option. I. Syratchev, CLIC Meeting, 3 December 24.

2 Drive beam current, A Transverse wake, n/s 3 C L I C Mission: PETS should generate 8 MW, 42 ns, 3 GHz RF pulses (8 bunches spacing HDS design ). Following present CLIC main linac layout ( PETS x 4 HDS), the PETS active length should not exceed.7m P=8 MW L=.7 m Beam aperture, mm Beam aperture, mm Circularly symmetric structures Drive beam energy, GeV E surf., MeV/m v 3 2 Beam aperture, mm HDS level Beam aperture, mm INTRODUCTION PETS aperture: For the given length and RF power of the PETS, beam current scales as: I = and transverse wake amplitude: W Constraints: P 4 Vgroup 2 LPETS R / Q ω k k I β β R / Q #. Drive beam accelerator length/cost scales inverse proportionally with the drive beam current. #2. Combining rings. In general higher energies require larger rings. #3. PETS reliability. One should not accept a design, when electric surface fields in PETS exceed values of that in a main linac. #4. Transverse wake in a PETS should be within acceptable level. As a compromise, PETS apertures from 2 mm to 25 mm were chosen for detailed study. V group I. Syratchev, CLIC Meeting, 3 December 24.

3 Phase advance and aperture PETS longitudinal impedance (by GDFIDL) Drive beam current, A P=8 MW L=.7 m 25 mm 22.5 mm 2. mm Phase/cell degrees 2.2 GeV 2.7 GeV 3.66 GeV V/pC/m Frequency, GHz 66 GHz check PETS parameters: W, normalized mm 22.5 mm 25 mm PETS Phase/cell degrees The higher phase advance, the less HOM damping. F= GHz Aperture = 22.5 mm R/Q = 32.2 Ohm/m Beta =.798 C ϕ/cell = 4 I Drive beam = 64 A RF power = 8 MW Active length =.7 m Damping slots: 8 x 2 mm I. Syratchev, CLIC Meeting, 3 December 24.

Eight HOM damping slots are placed symmetrically around the circumference splitting the whole structure into 8 identical pieces.

4 PETS machining prototype CLIC PETS in general Finally adopted PETS is represented by 22.5 mm diameter circular waveguide with shallow (~.3 mm deep) sinus-type corrugations with 4 phase advance per period ( mm). Eight HOM damping slots are placed symmetrically around the circumference splitting the whole structure into 8 identical pieces. To simplify the fabrication, the active profile of each of 8 racks was chosen to be flat The damping slot width (2 mm) and slot s rounding radii (.8 mm) provided quasiconstant surface electric field distribution. This technology is very similar to that was chosen for HDS accelerating structure. PETS geometry provides certain margins towards active length and RF power to be produced without affecting beam stability along the decelerator. PETS architecture at 8 MW E max = 35 MV/m H max =.22MA/m PETS regular part Matching section PETS Power Extractor (PPE) I. Syratchev, CLIC Meeting, 3 December 24.

Transverse modes damping in PETS The transverse HOM mode in

practically identical to the decelerating one.

Damping mechanism in PETS can be explained as a coherent

period of corrugation into the infinite radial slot.

slot is replaced by the brad-band RF matched load: Wt,

5 Transverse modes damping in PETS The transverse HOM mode in PETS to taken care of has a frequency and group velocity practically identical to the decelerating one. The only way do damp it is to use its symmetry properties. Damping mechanism in PETS can be explained as a coherent radiation of many RF sources represented by the individual period of corrugation into the infinite radial slot. The angle of radiation here depends on the phase advance and distance between them. The higher the phase advance, the smaller the angle and less the damping. In any case radiation (damping) is strongest when phase advance and period are matched. Individual RF sources For the practical reason the infinite slot is replaced by the brad-band RF matched load: Wt, V/pC/m/mm Transverse wake amplitude (GDFIDL) Damped Un-damped V/A/mm/m 4 Transverse wake spectra (GDFIDL) 3 Un-damped Damped Distance, m Frequency, GHz I. Syratchev, CLIC Meeting, 3 December 24.

6 .3.2. Z C L I C Bunch q i Transverse modes damping in PETS. HFSS versus GDFIDL. Z =5.857σ Two modes time domain approximation 2 z i z = exp.5 An qi = σ i z z k z zk z z W ( z) = 2 k iqk sin ωi exp ωi 2 β k, i c vi Qi Ls β Power extraction F, GHz Q k, V/pC/mm/m M (52).27 M (56).2 β=.87 F, GHz Q k, V/pC/mm/m M x.2.4 x Damped σ=.88 mm.5 x.2.4 x Damped σ=.77 mm.5 x.2.4 x Un-damped σ=.77 mm I. Syratchev, CLIC Meeting, 3 December 24.

7 Beam jitter amplification PLACET simulations (Daniel) Transverse modes: M M2 Kt, V/pC/m/mm F, GHz Beta.876 C.646 C Q loaded (HFSS) 4 38 Practically no effect on the beam transport of the transverse HOM can be observed now! I. Syratchev, CLIC Meeting, 3 December 24.

8 RF power extraction. Adiabatic matching section Reflection regular cells Matching section S2 TM S TM 3 33 Power.5. S TM Transmition 4 S TM2 S2 TM2 5 matching cells Number of matching cells Number of regular cells PETS is a very over-moded RF system. Any geometrical perturbation can provoke coupling of the decelerating mode to the number of HOMs. In order to extract RF power into the smooth waveguide efficiently, a long adiabatic section is needed. A number of gradually reduced corrugations (periods) was optimised to bring the reflection and mode conversion to better than 4 Db. Total length of matching section is 58 mm (5 periods). I. Syratchev, CLIC Meeting, 3 December 24.

9 C L I C HFSS simulations PETS 3 GHz 8 cannel quasi-optical RF power extractor Low power prototype Losses, db 2 3 Backward Forward 2 mm Frequency, GHz Power extracted % level No Ohmic losses Frequency, GHz E max : 88 MV/m at 8 MW I. Syratchev, CLIC Meeting, 3 December 24.

PETS 3 GHz 8 cannel quasi-optical RF power extractor (continued) Prototype low power RF measurements Power budget per channel: Reflection E mode launcher Matching transformer S Expected P cannel

10 PETS 3 GHz 8 cannel quasi-optical RF power extractor (continued) Prototype low power RF measurements Power budget per channel: Reflection E mode launcher Matching transformer S Expected P cannel Measured Power channel.36.2 (.)..25 Efficiency: 97. %.3.2 S Power extracted.5..5 Average expected Average extracted a a. S Channel number I. Syratchev, CLIC Meeting, 3 December 24.

11 Full geometry HFSS simulation R3. Power Extractor R2.75 Output Matching section Regular PETS (6 cells) Input Matching section Extraction, db Isolation, db S() S(2) S2(2) S2() Frequency, GHz Extractor resonances Matching ring (S 3.mm) Frequency, GHz I. Syratchev, CLIC Meeting, 3 December 24.

12 Ranking (TRC report) CLIC PETS ON/OFF principle of operation Few examples:. Length.7 m, β (CLIC PETS) For constant impedance structure, the RF power distribution along the structure can be expressed as: 2 z R / Q I ω D ω ( ) D ω β ωd P z = cos exp 4 z z dz β C 2 2 C β Q β C o If we need to avoid power production at the end of the structure, than the detuning should be sufficient (without losses) if: β C F D = F ± ( β ) L Where F D is a new detuned synchronous frequency, L length of the structure and β - group velocity. For CLIC PETS F D = 3.69 GHz: 2 Output power.. First Zero Frequency (FZF) Detuned frequency, GHz 2. FZF versus group velocity and structure length Power Distance, m ON OFF FZF, GHz CLIC PETS L=.5 m L=.9 m V group /C L=.7 m I. Syratchev, CLIC Meeting, 3 December 24.

ON/OFF mechanism description PETS parameters evolution during wedges movement. 9.9 35 ON OFF V group /C.85.

2 mm) slit between the wedge and damping slot unfortunately forces the radiation of generated RF power.

The solution is to introduce another slot along the edge of the wedge.

13 Ideally, by insertion of 4 (.6 mm thick) wedges through the damping slots, sufficient PETS synchronous frequency detuning can be achieved: CLIC PETS ON/OFF mechanism description PETS parameters evolution during wedges movement ON OFF V group /C.85.8 R/Q, Ohm The need to have a technological (~.2 mm) slit between the wedge and damping slot unfortunately forces the radiation of generated RF power. This potentially can destroy the RF loads which are not designed for the high power use. The solution is to introduce another slot along the edge of the wedge. For that we pay by certain field enhancement in a technological slit when the wedge passes its intermediate position. Straight wedge Slotted wedge Q-factor Wedges position, mm Ohmic value Esurf., V/mxW Wedges position, mm Field enhancement inside the slit Wedges position, mm Wedges position, mm Radiation Q ext =5 Q ext =3x 6 I. Syratchev, CLIC Meeting, 3 December 24.

14 34 C L I C CLIC PETS ON/OFF mechanism description (continued) Damping animation 33 FZF Frequency, GHz Wedges inserted V group /C 7.5 Surface field Amplitude, norm. 3.5 PETS aperture Power Wedges position, mm The ON/OFF operation can be performed with the proposed method. The FZF point is established at a radial position of the wedge of 2. mm. If variable attenuation option is required, the danger of undesired field enhancement in a technological slit does appear. I. Syratchev, CLIC Meeting, 3 December 24.

Corrugated slotted wedge CLIC PETS variable attenuator

.5 Surface field Power 3 2 3 4 Wedges position, mm I.

15 Corrugated slotted wedge CLIC PETS variable attenuator option. Draft. Hans (CLIC meeting, 2.2.4) Not very much- OFF position OFF position 34.5 Esurf., V/mxW. 4 5 Frequency, GHz FZF Amplitude, norm..5 Surface field Power Wedges position, mm I. Syratchev, CLIC Meeting, 3 December V group /C Wedges position, mm

5 mm E-field Phase, degree 9 E Z E E Z Amplitude E x External Q-factor: 4.8x 4 Cooper Q-factor:.

16 To simplify the geometry for HFSS, the two adjusted racks were moved by.5 mm in radial direction(see picture). Structure symmetry radial distortion V. Pointing density.5 mm.5 mm E-field Phase, degree 9 E Z E E Z Amplitude E x External Q-factor: 4.8x 4 Cooper Q-factor:.2x 4 The imperfection in radial positioning of the single rack (within acceptable tolerances) does not create problems neither with power damping, nor with any transverse action on the beam. I. Syratchev, CLIC Meeting, 3 December 24.

17 Ongoing activity #. Structure The technical drawings of 4 cm PETS full scale prototype are under preparation. The brazed version of extractor is on a waiting list. #2. ON/OF mechanism RF design of the variable option to be finalized (incl. GDFIDL runs). Future studies #. Structure The use of damping slot for monitoring of the beam position inside PETS. #2. ON/OF mechanism Mechanical design for the fast switching should be developed. I. Syratchev, CLIC Meeting, 3 December 24.

International Technology Recommendation Panel. X-Band Linear Collider Path to the Future. RF System Overview. Chris Adolphsen

International Technology Recommendation Panel X-Band Linear Collider Path to the Future RF System Overview Chris Adolphsen Stanford Linear Accelerator Center April 26-27, 2004 Delivering the Beam Energy