AUP HL-LHC RFD Cavity RF Design Zenghai Li - SLAC HL-LHC RFD Design - - PowerPoint PPT Presentation

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AUP HL-LHC RFD Cavity RF Design Zenghai Li - SLAC HL-LHC RFD Design - - PowerPoint PPT Presentation

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AUP HL-LHC RFD Cavity RF Design Zenghai Li - SLAC HL-LHC RFD Design Freeze Review FNAL March 15, 2018 Outline Issues to be addressed for the HL-LHC crab cavity to meet HiLumi operation requirements High HOM beam power at 760 MHz

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SLIDE 1

AUP HL-LHC RFD Cavity RF Design

Zenghai Li - SLAC

HL-LHC RFD Design Freeze Review – FNAL – March 15, 2018

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SLIDE 2

Outline § Issues to be addressed for the HL-LHC crab cavity to meet HiLumi operation requirements

§ High HOM beam power at 760 MHz mode § High octupole current for compensating HOM effects

§ RFD design Improvements

§ Cavity shape - to minimize HOM beam power at 760MHz § HOM couplers - to minimize HOM impedance

§ Dimension sensitivity analysis § Summary

Zenghai Li - HL-LHC RFD Design Freeze Review - Mar. 15, 2018 2

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SLIDE 3

LARP Prototype RFD Crab Cavity

  • No lower order mode
  • Compact, clears the second beam pipe
  • Minimal multipole fields with shaped pole face

Zenghai Li - HL-LHC RFD Design Freeze Review - Mar. 15, 2018

FPC H-HOM (Hi-pass filter) V-HOM (selective coupling)

E B

LARP Prototype RFD Crab Cavity Frequency (MHz) 400.7 9 Operating Mode TE11 Lowest dipole HOM (MHz) 633 Lowest acc HOM 715 High R/Q acc HOM 760.9 Iris aperture (diameter) (mm) 84 Transverse dimension (mm) 281 Vertical dimension (mm) 281 Longitudinal dimension (w/o couplers) (mm) 556 RT (ohm/cavity) 433 VT (MV/cavity) 3.34 Bs (mT) 55.5 Es (MV/m) 32.6

3

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SLIDE 4

760 MHz Mode Issue of the LARP Prototype Cavity

§ Impedance meets beam dynamics requirements (2016) § (Elias Métral, Joint LARP CM26/Hi- Lumi Meeting, SLAC, 19/05/2016)

Zenghai Li - HL-LHC RFD Design Freeze Review - Mar. 15, 2018

  • Acc. HOM mode at 760.94 MHz too close

to beam resonance at 761.50 MHz

  • Resulting in beam HOM power >10kW
  • Design spec for beam power: < 1kW

1.0E+01& 1.0E+02& 1.0E+03& 1.0E+04& 1.0E+05& 1.0E+06& 1.0E+07& 0.4& 0.6& 0.8& 1.0& 1.2& 1.4& 1.6& 1.8& 2.0& R"[acc(ohm/cav),"dip(ohm/m/cav)]" F"(GHz)"

RFD"HOM"Impedance"

R_acc& R_dip_X& R_dip_Y& acc_req& dip_req&

1.0E-01 1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 0.50 0.75 1.00 1.25 1.50 1.75 2.00 P (W/A^2) F (GHz)

RFD cav17f Beam HOM Power

International Review of the Crab Cavity Performance for HiLumi April 3-5, 2017 CERN

4

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SLIDE 5

Require attention

Requirements from recent beam dynamics study

§ Most HOMs require negligible octupole current, even if they fall on the couple- bunch line

Zenghai Li - HL-LHC RFD Design Freeze Review - Mar. 15, 2018

§ In order not to affect the operational scenarios we need to keep the CC HOMs below 1 MΩ/m​

Ultimate scenario 2760 b, 2.3x1011 ppb, b* = 40 cm, en = 2.1 µm (no other sources of impedance)

  • S. Antipov, D. Amorim, N. Biancacci, X. Buffat, L. Carver, F. Giordano,​ G. Mazzacano, A. Mereghetti,
  • E. Metral, S. Redaelli, B. Salvant​, 7th HL-LHC Collaboration meeting, CIEMAT, Madrid – 15.11.17​

(Nov. 2017)

1.47 GHz 2.01 GHz

(Nov. 2017)

5

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SLIDE 6

Requirement Summary § 760 MHz beam HOM power <1kW § Transverse impedance < 1MΩ /m § HOM Filters Output Power ≤ 1.5 𝑋 at 400.79 𝑁𝐼𝑨 § Longitudinal HOM shunt impedance 𝑆01 < 200 kΩ § Field multipole of operating mode Most important, sextupole 𝑐7 < 1000 mT/m2 at total 10MV deflection voltage

Zenghai Li - HL-LHC RFD Design Freeze Review - Mar. 15, 2018 6

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SLIDE 7

Minimizing 760 MHz Mode beam power, by detuning HOM frequency farther off beam resonance

§ Various options explored to detune the 760 mode § Approach adopted: reducing gap volume around beam pipe region § 400 MHz dipole and 760 MHz monopole modes

  • pposite in dF sensitivity

§ lowers frequency of 760 mode (target: |dF| > 6MHz)

Zenghai Li - HL-LHC RFD Design Freeze Review - Mar. 15, 2018

§ Operating mode frequency § tuned to 400.79 MHz by adjusting rounding “R” by -1.76mm

Achieved -9 MHz detuning of the 760 MHz mode from beam resonance of 761.5MHz New frequency of this longitudinal HOM : 752.2 MHz

R=~102 dR=-1.76mm

Beam line spacing: 40.079 MHz, 19th harmonic at 761.5 MHz

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SLIDE 8

Beam HOM Power Reduced from ~10kW to ~ 500W

§ HOM power calculated for 1-AM beam § σz=76mm

Zenghai Li - HL-LHC RFD Design Freeze Review - Mar. 15, 2018

Beam HOM power below 1 kW. Meet design requirement.

1.0E+00 1.0E+01 1.0E+02 1.0E+03 0.400 0.900 1.400 1.900 Beam HOM Power (W/1AM^2) F (GHz)

Beam HOM Power (RFD12 cav4g, run9)

1 10 100 1000 0.5 1 1.5 2 Beam Power (W) (1AM beam) F (GHz)

Beam HOM Power Extraction via HOM Ports

VHOM port HHOM port

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SLIDE 9

New Design Parameter Comparison

  • Frequency of high beam power mode (760MHz) 9.3 MHz below beam resonance
  • Good RF parameters maintained

Zenghai Li - HL-LHC RFD Design Freeze Review - Mar. 15, 2018

RFD Crab Cavity LARP Prototype New Design Frequency (MHz) 400.79 400.79 Lowest dipole HOM (MHz) 633 636 Lowest acc HOM 715 699 High R/Q acc HOM 760.9 752.2 Transverse dimension (mm) 281 281 Vertical dimension (mm) 281 281 RT (ohm/cavity) 427 431 VT (MV/cavity) 3.34 3.34 Bs (mT) 55.5 55.1 Es (MV/m) 32.6 35.0

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SLIDE 10

Multipole B3, B5, B7

  • Multipole components barely changed as compared with LARP prototype design
  • b3 < 1000 mT/m2, meet design requirement

Zenghai Li - HL-LHC RFD Design Freeze Review - Mar. 15, 2018

Assume Def mode symmetry (only cos term) Eacc(r,ϕ) = Eacc

n rn n

∑

cos(nϕ) (e jωz.c included in Eacc

n )

Δ p⊥

(n)(r,ϕ) = 1

c F

⊥ dz = L

∫

je ω nrn−1 ˆ ur cos(nϕ)+ ˆ uϕ sin(nϕ)

( )

Eacc

n (z)dz L

∫

bn = B(n) dz =

L

∫

1 ec F

⊥ (n) dz = L

∫

nj ω Eacc

(n) dz L

∫

Δ p⊥

(n)(r,ϕ) = e

 VT (r,ϕ) = e bnrn−1

n

∑

ˆ ur cos(nϕ)+ ˆ uϕ sin(nϕ)

( )

Vdef = b

1

Component Value (total VT=10 MV) b3 429 mT/m2 b5

  • 1.8e6 mT/m4

b7

  • 4.9E+08 mT/m6

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SLIDE 11

HOM Impedance Improvements

§ Cavity shape modification altered the damping of HOM § Re-optimized both H-HOM and V-HOM couplers § Simplified port interface

Zenghai Li - HL-LHC RFD Design Freeze Review - Mar. 15, 2018 FPC H-HOM (Hi-pass filter) V-HOM (selective coupling) 11

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SLIDE 12

H-HOM Coupler Cutoff waveguide stub + high-pass filter

§ HHOM coupler and filter in low field region – minimizes RF heating § Waveguide stub add additional rejection of operating mode – loosening tolerance on filter dimensions

Zenghai Li - HL-LHC RFD Design Freeze Review - Mar. 15, 2018

!70.0% !60.0% !50.0% !40.0% !30.0% !20.0% !10.0% 0.0% 0.4% 0.6% 0.8% 1% 1.2% 1.4% 1.6% 1.8% 2% S12$(dB)$ F$(GHz)$

Hi.pass$Filter$Transmission$

rejection of

  • perating

mode

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SLIDE 13

HHOM Coupler Modifications to Enhance Damping

Zenghai Li - HL-LHC RFD Design Freeze Review - Mar. 15, 2018

H-HOM hook 35 degree angle Transition +10mm higher H-HOM width +5mm wider Larger waveguide stub size (170x40)

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SLIDE 14

V-HOM Coupler Cutoff waveguide stub + hook pickup

§ Waveguide stub selectively couples to acc and vertical HOMs – no filter needed § Hook provides both electric and magnetic coupling, improving damping of HOMs at higher frequencies § Waveguide stub dimension slightly larger, (same as HHOM) , to enhance coupling

Zenghai Li - HL-LHC RFD Design Freeze Review - Mar. 15, 2018 14

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SLIDE 15

FPC and Field Pickup Port

(minor location adjustment from the LARP prototype )

FPC: § Waveguide stub + hook § Qext: 5x105

Zenghai Li - HL-LHC RFD Design Freeze Review - Mar. 15, 2018

Pickup port: § On the V-HOM side of cavity § Need to pickup ~ 1.5W. Qext ~ 2x1010

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SLIDE 16

Port Interface Simplified to Same Dimension

§ Diameter for all ports, HHOM, VHOM, field pickup: 37.879 mm § One feed through design for all ports

Zenghai Li - HL-LHC RFD Design Freeze Review - Mar. 15, 2018

H-HOM V-HOM pickup

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SLIDE 17

HOM Impedance of the New Design

Zenghai Li - HL-LHC RFD Design Freeze Review - Mar. 15, 2018

HOM impedance below 1 MΩ/m up to 2 GHz Longitudinal shunt impedance < 200 k Ω Meet requirement

1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07 1.0E+08 0.400 0.600 0.800 1.000 1.200 1.400 1.600 1.800 2.000 R F (GHz)

RFD12 cav4g, run9c

Acc dip_X dip_Y

1 MΩ/m

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SLIDE 18

RF Heating of Coupler Elements

Zenghai Li - HL-LHC RFD Design Freeze Review - Mar. 15, 2018

Power [W/(3.4MV/cavity] LARP Prototype AUP HL-LHC New Design FPC hook 69 73 Copper NC H-HOM hook 0.0007 0.0014 Nb SC V-HOM (probe) HOOK 0.47 0.51 Copper NC Field pickup probe 0.09 Copper NC

Low RF heating on coupler elements No thermal issue

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SLIDE 19

Multipacting

Zenghai Li - HL-LHC RFD Design Freeze Review - Mar. 15, 2018

LARP prototype (RFD11-cav17f) New design (RFD12-cav4g) Multipacting mostly

  • n end-plate

Similar to LARP prototype cavity. Will not be a problem

Impact Energy Enhancement Counter

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SLIDE 20

Cavity Dimension Sensitivity to HOM Impedances

  • Assume depth of the pole kept unchanged
  • Pole gap change same amount as cavity transverse dimension
  • Resulted in very small frequency deviation

Zenghai Li - HL-LHC RFD Design Freeze Review - Mar. 15, 2018

End plate tilt

Trim

x/ytank (+delta)

Pole depth (unchanged)

gap (+delta)

Transverse dimension

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SLIDE 21

Cavity Transverse Size Error

  • Frequency offset within tuner range
  • HOM Impedance maintained with a simple

mitigation by rotating VHOM hook angle

Zenghai Li - HL-LHC RFD Design Freeze Review - Mar. 15, 2018

(VHOM coupler hook orientation rotated for a mode at above 2 GHz (2.05) for better damping)

§ +0.75mm

1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07 1.0E+08 0.400 0.600 0.800 1.000 1.200 1.400 1.600 1.800 2.000 R F (GHz)

RFD12 cav4g, run9c

acc dip_X dip_Y 1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07 1.0E+08 0.400 0.600 0.800 1.000 1.200 1.400 1.600 1.800 2.000 R F (GHz)

RFD12 cav4g, run9c

acc dip_X dip_Y

§ -0.75mm x/ytank (+delta)

Pole depth (unchanged)

gap (+delta) HOM impedance maintained in 1MΩ/m level with realistic cavity dimension error

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SLIDE 22

End Plate Tilt Error

Zenghai Li - HL-LHC RFD Design Freeze Review - Mar. 15, 2018

+2mm

1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07 1.0E+08 0.400 0.600 0.800 1.000 1.200 1.400 1.600 1.800 2.000 R F (GHz)

RFD12 cav4g, run9c

acc dip_X dip_Y

  • 2mm

1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07 1.0E+08 0.400 0.600 0.800 1.000 1.200 1.400 1.600 1.800 2.000 R F (GHz)

RFD12 cav4g, run9

acc dip_X dip_Y

End plate tilt HOM impedance maintained in 1 MΩ/m level with realistic cavity dimension error

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SLIDE 23

HOM Coupler Dimension Sensitivity to HOM Impedances and Operating Mode Rejection

Zenghai Li - HL-LHC RFD Design Freeze Review - Mar. 15, 2018

gap_bar gap_top gap_probe bar_radius tank_radius rot_about_z (+) rot_about_x (+) ytip

Pickup gap V-HOM H-HOM

23

  • HOM damping
  • Filter performance - rejection of 400.79 MHz operating mode
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SLIDE 24

HHOM coupler filter bar-gap

(design: bar_gap=2.8mm)

Zenghai Li - HL-LHC RFD Design Freeze Review - Mar. 15, 2018

  • 0.2mm

1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07 1.0E+08 0.400 0.600 0.800 1.000 1.200 1.400 1.600 1.800 2.000 R F (GHz)

RFD12 cav4g, run9c

acc dip_X dip_Y

+0.4mm

1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07 1.0E+08 0.400 0.600 0.800 1.000 1.200 1.400 1.600 1.800 2.000 R F (GHz)

RFD12 cav4g, run9c

acc dip_X dip_Y

Bar-Gap

Impedance insensitive to bar gap error Filter bar-gap dimension error barely affect impedance

24

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SLIDE 25

HHOM coupler filter tip-gap

(design: tip_gap=5mm)

Zenghai Li - HL-LHC RFD Design Freeze Review - Mar. 15, 2018

tip-Gap

1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07 1.0E+08 0.400 0.600 0.800 1.000 1.200 1.400 1.600 1.800 2.000 R F (GHz)

RFD12 cav4g, run9c

acc dip_X dip_Y 1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07 1.0E+08 0.400 0.600 0.800 1.000 1.200 1.400 1.600 1.800 2.000 R F (GHz)

RFD12 cav4g, run9c

acc dip_X dip_Y

delta_gap = +1mm delta_gap = -1mm Impedance insensitive to tip gap error Filter tip-gap dimension error barely affect impedance (Similarly with other filter dimension errors)

25

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SLIDE 26

0.00 0.50 1.00 1.50 2.00 2.50 3.00

  • 1
  • 0.5

0.5 1 Power (W) at VT=3.4e6 dimension error (mm)

Power Leakage (W) vs filter dimension error

bar gap .p gap tank radius bar radius top gap

Power Leakage Due to HHOM Filter Dimension Errors

§ Filter dimension errors may weaken rejection of operating mode, lead to RF power leakage

Zenghai Li - HL-LHC RFD Design Freeze Review - Mar. 15, 2018

top-gap tank radius bar radius tip-Gap Bar-Gap

With achievable filter dimension tolerances, RF power leakage will be contained within 1.5 W

1.5 W total

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SLIDE 27

Dimension Error Mitigation

§ Dimension tolerance shown to be achievable § There are readily available mitigation means could be utilized to further minimize dimension errors effects

Zenghai Li - HL-LHC RFD Design Freeze Review - Mar. 15, 2018

Example: adjusting HHOM tip-gap improves degraded rejection due to bar-gap error

probe/hook replaceable

  • Rotating, tweaking HOM coupling hook
  • Effective to cavity dimension errors
  • Adjusting HHOM pickup probe depth/dimension
  • Effective to HOM coupler dimension errors

Effect of dimension errors can be mitigated via re-tuning of demountable HOM couplers

coupler demountable 27

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SLIDE 28

Summary

q RFD cavity was re-optimized to resolve two important design issues 1) Reduced beam HOM power of the “760MHz” mode meet 1 kW requirement 2) Improved HOM damping meet 1 MΩ/m requirement q New design meet all requirements q Accelerating mode shunt impedance: < 200 k Ω q Field multipole: b3 < 1000 mT/m2 q HOM filter power leakage : can be controlled within 1.5 W limit q Sensitivity of HOM impedance on cavity and HOM coupler dimensions analyzed q Tolerance on dimension errors achievable q Sensitivity table generated for developing engineering tolerance specifications

Zenghai Li - HL-LHC RFD Design Freeze Review - Mar. 15, 2018 28