Main Injector Cavity Simulation and Optimization for Project X...Apr 07, 2011 · 1.2 53.396 56.68...

Main Injector Cavity Simulation

and Optimization for Project X

Liling Xiao

Advanced Computations Group

Beam Physics Department

Accelerator Research Division Status Meeting, April 7, 2011

Background

- Project X Conceptual Design

- Current FNAL MI RF Cavity

- New Project X MI RF Cavity I and II Designs

MI Cavity I & II Simulations

MI Cavity II Optimization

Summary

Outline

L. Xiao, ARD Status Meeting, April 7, 2011

2

Project X Conceptual Design

120GeV 2MW Neutrinos

2GeV 1mA CW

Experimental Hall

8GeV RCS

Recycler Storage Ring

Main Injector Accelerator

Project X will use FNAL existing RR/MI complex,

but require upgrading MI RF system.

8GeV 190kW

Single turn transfer @

8GeV


3

http://projectx.fnal.gov/gallery/conceptual-design.shtml

H-

Current FNAL MI RF Cavity• Using ferrite tuners to tune cavity frequency to the velocity of the circulating beam starting

from low to the speed of light.

• Changing μ of ferrite to tune the cavity frequency by applying a variable external B-field to

the ferrite.

Project X requires:

4 X the current number of particles

3 X the current beam intensity

6 X the current beam power


Current 30+ yrs MI RF cavity does not have enough power to accelerate 1.6e14 protons

to 240GeV/sec for a total power of 2.3MW for Project X even with additional PA.

4

New Project X MI RF Cavity Designs

Cavity I

Cavity II Advantage:

1. Requires only a single vacuum ceramic.

Tuner, driver, and HOM dampers will be

at atmospheric pressure for easy

installation and repair.

2. Conical shape gives support for the

inner conductor lever arm.

New MI RF Cavity I & II:

1. A quarter wave coaxial resonator with

a single accelerating gap using a

perpendicularly biased ferrite tuner

results in a compact cavity design.

2. A bias field perpendicular to the RF

field reduces losses in the ferrite.

Cavity II


5


Parameter Value Units

R/Q 50 Ω

Q 10000

Max. Voltage 240 kV

Harmonic number 588

Frequency 52.617-53.104 MHz

Number of Cavities 20

FNAL & SLAC signed a MOU to perform the new MI cavity I & II simulations and

optimization to meet the requirements for Project X.

New Project X MI Cavity RF Parameters

6

Outline

Background

MI Cavity I and II Simulations

- Operating Mode RF Parameters

- Tuning Range vs. Tuner Coupling

- Maximum Surface E/B-Fields

- Power Distributions

- HOM modes


Summary


7

Finite element parallel eigen-solver Omega3P code for the cavity I&II RF simulations.

Tetrahedral meshes with curved surfaces and 2nd order basis functions.

About 400k mesh elements for converged results.

30 ferrite cores with 5mm separation:

εr=13.5, tan()=0.0002,

μr=2.5 ~ 1.2, tan()=0.0002

(external B=300~2250Gauss)

Ceramic window:

εr=12, tan()=0.0001,

μr=1, tan()=0.0001

Copper coated wall:

σ=5.8e7s/m

MI Cavity I & II RF Simulations

Meshed Computational Models

Cavity I

Cavity II


8

The cavity II has a slightly higher R/Q and f than the design values that can be easily

adjusted by changing the cavity coaxial line radius and length.

Operating Mode RF Parameters

E BE


Tuner intrusion is 55mm. Required F=52.617 ~ 53.104MHz, R/Q=50Ω, Q0=10000

MI Cavity μr F(MHz) Q0 R/Q (Ω) ΔF (KHz)

I 2.5 52.812 9613 51.23 584

1.2 53.396 9457 56.68

II 2.5 53.557 9679 56.95 539

1.2 54.096 9529 61.30

BE

9

Tuning Range vs. Tuner Coupling

Intrusion d

0 mm: Tuner center conductor is positioned at the cavity outer surface for both cavity I & II.

85/95 mm: The maximum tuner intrusion for cavity I/II, respectively.

Adjusting the tuner intrusion can change cavity tuning range.

Required tuning range is 490KHz with 50 mm tuner intrusion (d).


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maxEs=7.4MV/m

@ μr=2.5 and μr=1.2

with 20mm gap rounding

maxEs=10.8MV/m

@ μr=2.5 and μr=1.2

with 20mm gap rounding

The cavity II has higher maximum peak Es than the cavity I. The magnetic

permeability of the ferrite won’t affect the maximum surface E-field.

Maximum Surface E-Field @ Vgap=240kV

Maximum Surface Field - Es

Cavity I Cavity II

For comparison: RHIC 28MHz Cavity: Es=7.8MV/m


11

Both the cavity I & II have strong maximum peak Bs at the edges of the tuner loop at

ur=2.5. When ur=1.2, the maximum surface B-fields locate at the rounding area

between the tuner tank and the cavity.

Max. Bs location

Maximum Surface B-Field @ Vgap=240kV

Maximum Surface Field - Bs

Cavity I Cavity II

maxBs=32T @ μr=2.5

maxBs=18T @ μr=1.2

with fully rounded the tuner loop

For comparison: RHIC 28MHz Cavity: Bs=8T (without ferrite tuner)


maxBs=39T @ μr=2.5

maxBs=19T @ μr=1.2

with fully rounded the tuner loop

12

Tuner intrusion is 55mm. Vgap=240KV. Ferrite and ceramic are lossy

MI Cavity μr F(MHz) R/Q

(Ω)

Q0

(wall)

QL1

(ferrite)

QL2

(ceramic)

P (kW)

(wall)

P (kW)

(ferrite)

P (kW)

(ceramic)

I 2.5 52.812 51.23 9613 29162 1700058 117 39 0.7

1.2 53.396 56.68 9457 134802 3809242 108 8 0.3

II 2.5 53.557 56.95 9679 35918 156190 104 28 6

1.2 54.096 61.30 9529 140978 143691 99 7 7

The cavity II has more power dissipation in the ceramic window and less in the ferrite

cores than the cavity I. Moving the ceramic window away from the accelerating gap

couldn’t reduce power dissipation in the window much.

Power Distributions

Power dissipation in the ferrite cores can cause a temperature rise which will increase

the μ-value of the ferrite.


13

E-field patterns @ μr=2.5

The cavity II monopole HOMs have lower shunt impedances than the cavity I, but they

still need to be damped by HOM couplers.

Monopole HOMs

Monopole modes will induce longitudinal coupled-bunch instability.


<300MHz

μr F (MHz) R/Q

(Ω/cavity)

Q0 Rs

(kΩ/cavity)

Cavity I

2.5 161.83 22.06 16580 366

269.72 15.45 19973 309

1.2 164.42 15.44 15310 236

269.17 17.75 20026 355

Cavity II

2.5 166.51 19.34 14476 280

279.17 11.84 18157 215

1.2 169.25 12.70 14113 179

279.07 12.13 18114 220

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MI-Cavity I (<300MHz) F(MHz) R/Q_T (Ω/cavity) Q0 Rsh_T (kΩ/mm/cavity)

Ur=2.5

H-dipole 205.39 16.79 20210 1.46

261.08 15.60 23769 2.03

261.63 4.03 29714 0.66

V-dipole 206.39 17.05 20005 1.47

260.52 5.71 28421 0.89

261.52 0.53 32045 0.09

Ur=1.2 H-dipole 205.31 16.65 20161 1.44

261.09 19.75 22103 2.39

V-dipole 206.04 17.13 20000 1.48

263.50 17.61 21500 2.09

E-field

patterns

@ μr=2.5

Dipole HOMs in Cavity I

There are additional dipole modes in the cavity I at μ=2.5 due to the coupling of the

cavity to the ferrite tuner. L. Xiao, ARD Status Meeting, April 7, 2011

15

MI-Cavity II (<300MHz) F (MHz) R/Q_t (Ω/cavity) Q0 Rs (kΩ/mm/cavity)

Ur=2.5 H-dipole 248.24 1.47 21566 0.17

V-dipole 249.76 1.61 20264 0.17

Ur=1.2 H-dipole 247.57 1.57 20555 0.17

V-dipole 249.36 1.57 20082 0.17

The cavity II has only one pair of dipole modes below 300MHz, and smaller

transverse shunt impedances than the cavity I.

E-field

patterns @

μr=2.5

Dipole HOMs in Cavity II

U

crV

U

V

Q

R zT

T

2

0

22)/*/(

)(

)/(**_)(_ cQtQ

RtR

Horizontal Dipole Vertical Dipole


16

Due to the ferrite vessel, the vertical dipole modes are all off-center from the ferrite vessel.

The vertical dipole modes can be excited and generate transverse instability even the beam

is on beam axis.

Vertical Dipole HOMs

Cavity I:

F=263.50MHz @ μr=1.2 off

center=57mm

The cavity II vertical dipole modes have smaller off-center shifts than the cavity I.

Cavity II:

F=249.76MHz @ μr=2.5

off center=29mm


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@μr=2.5, Vgap=240kV, tuner intrusion=55mm MI-Cavity-I MI-Cavity-II

Operating Mode

R/Q (Ω) 51.23 56.95

F (MHz) 52.812 53.557

Tuning range Δf (KHz) 584 539

Max. Es (mV/m) 7.4 12.2

Max. Bs (T) 39 32

Power Distributions P(kW) (wall/ferrite/ceramic) 117/39/0.7 104/28/7

Monopole HOMs Max. R/Q (Ω) 22 19

Horizontal Dipole HOMs Max. R/Q_T (Ω) 17 1.5

Vertical Dipole HOMs Max. R/Q_T (Ω) 17 1.6

Max. center shift (mm) 43 29

The cavity II has better RF performances than the cavity I, and is chosen for the

Project-X MI cavity design.



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Outline

Background



- Optimal 1MHz tuning range

- HOM damper

- High-Pass Filter

- Input coupler

Summary


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Optimal 1MHz Tuning Range

The tuning range of 487KHz is required for 6GeV to 120GeV operation.

Optimal design for the new MI cavity would be 1MHz tuning range.

1MHz tuning range with larger tuning intrusion may cause vacuum break down.

There are additional three ways to increase the cavity II tuning range.

1. Using shorter tuner tank

(495mm->460mm)

3. Moving tuner tank away

from the rear end of the

cavity (5mm->20mm)

2. Using narrower tuner loop

(120mm->60mm)


All the three ways are used for optimal 1MHz tuning range.

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Optimal 1MHz Tuning Range

New @70mm

Ori.@90mm

Cavity II

@ur=2.5

d (mm) @ 1MHz

tuning range

F

(MHz)

R/Q

(Ω/cavity)

P (kW)

(wall)

P (kW)

(ferrite)

P (kW)

(ceramic)

original 90 52.787 53.1 112 49 6

Optimal 70 52.697 52.6 114 53 6

The new design will increase the power dissipation in the ferrite cores without

affect other RF parameters significantly.

Max. d allowed

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* *

HOM Damper w/o Filter

There are two dangerous monopole HOMs to be damped by HOM dampers.

HOM dampers should be equipped with a fundamental mode rejection filter.

HOM dampers can handle a certain amount of power.

HOM damper is constructed within 1.0/2.3”

coaxial line for a larger power capacity.

HOM coaxial damper with a large loop located

at the rear end of the cavity can damp many

HOMs.

HOM damper with 45 degree orientation can

damp both monopole and dipole modes.

Rounded loop design can suppress MP

activities at HOM damper.

Bended HOM coaxial damper can take less

space for installing two more RF cavities (18-

>20).

Cavity II with two mirrored HOM

dampers w/o filter


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Mode Damping w/o Filter

E-fields @ ur=2.5

F=167MHz, R/Q=19.3Ω, Qext=112, Q0=14476 F=280MHz, R/Q=11.8Ω, Qext=92, Q0=18757

The two prominent monopole modes and dipole modes can be heavily damped with

two mirrored HOM dampers.

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F=250MHz, R/Q_t=1.6Ω, Qext=203, Q0=21566 F=249MHz, R/Q_t=1.5Ω, Qext=215, Q0=20264


Monopole Modes

Horizontal Dipole Vertical Dipole

High Pass Filter

A high-pass filter is a better option for the HOM damper filter design in a cavity with a swing.

Higher element filters can provide a sharper rejection response at the fundamental frequency.

Filter constructed within larger coaxial lines can handle more power extracted by HOM dampers.

RHIC 56 MHz SRF Cavity HOM Damper (Courtesy: Q. Wu)RHIC 28 MHz Cavity HOM Damper (Courtesy: J. Rose)

5-element high-pass filter 7-element high-pass filter

Cu cavity:

SRF cavity:

Rejection ~60dB

Rejection ~80dB


24

25mm

15.2mm

XX

High-Pass Filter Transmission Curve

L1 L2 L3 and L4 are formed by rods, whose lengths

can be adjusted by tuning stubs at their ends on the

outer can.

C1 C2 and C3 are coaxial low loss Sapphire rings

with copper spacer. Sapphire ring: εr=9.5

HOM

output

L4

L2

L1

L3

C2

C3

MI cavity HOM 7-element high-pass filter

The fundamental frequency at ~50MHz can be strongly

attenuated by the filter (~-80 dB).

The signal frequency can be transmitted with a less than

-7 dB of attenuation over 140MHz to 600MHz.

Fundamental mode

First strong HOM

C1


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Power Input Coupler Eimac 8973 power tetrode is chosen as the power source for the new MI cavity.

It can operate at both 53MHz and 106 MHz with more than 1MW output power.

E-coupling with larger disk at the end of the antenna is used to enhance the input coupling.

50Ω coaxial line

(D230/100mm)


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Eimac 8973 Power Tetrode

Using existing MI RF PA

d

Input Coupling


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(β=2.5, d=35mm)

The input coupling should be matching when the maximum beam current is accelerated.

Required input coupling β=Q0/Qload=10000/4000=2.5.

MI Cavity II Conceptual Design

Finalizing the MI cavity design is ongoing to meet the requirements for Project X.

Tuner

Window

Input Coupler

HOM dampers

w/ filter


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Cavity I and II Simulations

• Evaluated FNAL cavity I and II baseline designs

Cavity I

Cavity II Optimization

Achieved optimal 1MHz tuning range.

Realized a HOM damper design with high-pass filter.

Designed input power coupler.

Finalizing the design is ongoing.

Cavity II

Summary


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SLAC will continue to collaborate with FNAL on a second-harmonic cavity design.

Thank Uli Wienands for helping us prepare this MOU.

Thank Cho Ng, Ioanis Kourbanis, and Joseph Dey for their helpful

discussions and advices during our monthly phone meetings.

Acknowledgments


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Main Injector Cavity Simulation and Optimization for Project X...Apr 07, 2011 · 1.2 53.396 56.68...

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Transcript of Main Injector Cavity Simulation and Optimization for Project X...Apr 07, 2011 · 1.2 53.396 56.68...