RFQ Thermal Analysis

Scott Lawrie

Vacuum Pump Flange

Vacuum Flange Coolant Manifold

Cooling Pockets Milled Into Vanes

Potentially Bolted Together

Tuner & Coupler Ports

Vanes

Vane Cut-Back

Vane End

Cooling Pocket Shaped to Follow Vane Cut-Back

Tuner & Coupler Ports

O-Ring Joint to Mount to End Wall

RFQs normally use cooling channels

Indian SNS:Six per quadrant

American SNS:Four per quadrant

Chinese SNS:Five per quadrant

HINS (FNAL):Three per quadrant

Replace distributed channels with one cooling pocket

Set of cooling channels drilled along length of vane

Replace distributed channels with one cooling pocket

Pocket milled into vane from air side

Plate bolted on to cover the pocket and allow water in/out

Baffle attached to cover plate; shaped to leave 2-3mm gap

Water flow directed along gap between pocket and baffle

Replace distributed channels with one cooling pocket

Cooling PocketDisadvantages Advantages

• New, untested design

• Complicated water flow

• Unknown cooling efficiency

• Lots of material removed

• Novel

• Allows for 3D heat distribution

• Simple to manufacture

• No vacuum to water interfaces

• Flow can be directed where

needed

• Highly configurable

• Easily adjusted & maintained

• Gap can be replaced with

channels

• Could be the new standard!

ANSYS Coupled solver process

Model geometry(from Autodesk Inventor)

Simplified model with applied boundary conditions

Vacuum body inside cavity

Vacuum port pumping-slot cooling channels

Tuner & coupler ports with integrated cooling

Cooling pocket and baffle

Vane end cut-back

Eigenmode SolverSurface H-Field Results

Highest magnetic field intensity at vane end cut-back

Magnetic field strongest at corners e.g. at tuners

2m

Eigenmode SolverMagnetic Field Vector Results

H-Field flowing around vane cut-backs

H-Field flowing past tuner port and vacuum pump slots

Eigenmode SolverSurface E-Field Results

Eigenmode SolverElectric Field Vector Results

Quadrupole Mode333.56 MHz

(should be 324 MHz)Dipole Modes 330.02 MHz

Frequency varies with RFQ length

Mode Frequency / MHz

LC

10

Resonant Frequency:

Total Surface Power Loss

surface

iiisolver dAHP 2

2

2

2 isolver

reali HP

PF

00f

Heat Flux Per Element

Psolver = Calculated total surface power (W)ρ = Surface resistance (Ω)H = Tangential magnetic field at surface (T)dA = Area of surface mesh element (m2)f = Cavity resonant frequency (Hz)µ0 = permeability of free space (H m-1)σ = Conductivity of cavity walls (S m-1)F = Heat flux due to surface losses (W m-2)Preal = Expected total surface power (W)

where:

Surface heat flux

Large power losses at vane end cut-back

Relatively high heat loads at coupler, tuner and vacuum pump ports

Heat flux / Wm-2

800 kW total peak RF power in 4 m RFQ 2.5 kW average power in this 1/32 model

Thermal solver solution

Water-bath HTC = 3000 W m-2 K-1

Ports are well cooled

Cooling pockets are able to remove bulk body heat

Vane ends are not sufficiently cooled

Copper Temperature / °C

Structural solver solution

Walls move outward

Vanes move inward

Net 25 µm transverse expansion of vanes is within machining tolerances

Longitudinal expansion of vane ends is unacceptably large

Y-displacement Z-displacement

Vane ends grow toward end wall by 70 µm

Frequency shift vs. RF powerFrequency Decrease / kHzMaximum Temperature / °C

Cooling Pocket HTC = 1000 Wm-2K-1

Cooling Pocket HTC = 3000 Wm-2K-1

Vane end temperature

Cavity frequency shift

Max Temperature = 37 °C

60W input RF power

ANSYS Simulation

Cold Model Tests

Temperature Rise

15 °C 15.6 °C

Frequency Shift

-78 kHz -89 kHz

Max Structural Deformation = 0.3 mmRFQ cold model with 60 W DC input RF power and no cooling applied.

Conclusions

• FETS RFQ will have a novel cooling system• ANSYS used to assess performance• Full 4m RFQ will have a higher frequency• Cooling pockets successfully remove RF

power• Vane end not sufficiently cooled• Vane displacements should not affect beam• CFD simulations needed to predict HTCs• Overall, cooling strategy seems to work!