anatoly krasnykh, franz-josef decker et. al. slac national ... · blasting with al2o3 grit of...

RF Surface Resistance of Treated WR-284 Inner Surfaces(All-metall RF Load Concept)

11-20-2014

Anatoly Krasnykh, Franz-Josef Decker et. al.SLAC National Accelerator Lab

Thermal Spray Coating Technology OverviewBy an experience all-metal design using aresistive coating on the inside walls of WR-284waveguide looks a promising concept.

We are interesting to employ the thermal spraytechnology in a design of a high peak power RFload for the SLAC linac.

Diagram shows the simplified classification ofvarious thermal coating processes in terms ofparticle temperature and velocity.

There are several key technological steps whichdetermine the quality and attenuation rate of thecoated waveguide (WG). One of these steps is asurface preparation of the inner WG walls.Typically many thermal spray coatingtechnologies employ the blasting to improveadhesion qualities by increasing surface area.The RF surface resistivity (Rs) and attenuationrate depends on an roughness of inside wallsurfaces. Thermal spray of the absorption layerincrease the attenuation rate. However there isno information in the rise of the attenuation ratefor each step (the blast and the spray).

Q: What is a best technology for a formation of the resistive layer?

Q: What is the RF attenuation rate in waveguide if the same media of coat is used but for different technologies? Q: What is attenuation rate after the blasting?

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Basic of All-metal Waveguide Attenuation

RF Surface Resistance of Treated WR-284 Inner Surfaces

2

2 2

2 1 12120 120

1 12 2

s sR Raa b

a a

Attenuation of the TE10 mode in the WR284 waveguide

WR284: a= 2.84” and b=1.34”

where

10.88 ∗ 10 ∗10 1

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Halves for Tests


Al2O3 Grit

SiC Grit Al2O3 Grit & NiCr

SiC Grit +FeCrAl

StockL-shapes

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Reference: Aluminum Alloy WR284 Waveguide


Parameter Value

Measured s21 0.03

Length, m 0.94

α, dB/m 0.032

α, Np/m 0.00367

Rs, Ohm 0.0216

σ, S/m 2.4E7

There is an agreement with published data of Aluminum Waveguide Loss (low/high edge = 3.11/2.13 dB/100m)

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Q: Whether the surface resistivity depends on the blasting media or not?


• The Metal Fusion, Inc. (RWC, CA) facility was employed for technology of blasting and waveguide fabrication

• Aluminum Alloy 6065-T5 was used as a material for the WR284 waveguide• Al2O3 and SiC grits used in experiment

Al2O3 – dielectric blast media SiC- semiconductor blast mediaThe SiC resistivity is 2,000+ S/m

Whether SiC particles left on the waveguide walls or not.

Attenuation Rate of Al WR-284 after Grit Blast Process

Grit Size is Mesh #24Air Pressure is 80 psiDistance range is 6-8 inches

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Blasting with Al2O3 Grit of Aluminum Alloy WR284 Waveguide


Measured s21 0.41

Length, m 0.94

α, dB/m 0.436

α, Np/m 0.05

Rs, Ohm 0.295

σ, S/m 0.013E7

Sigma(S/m)

Rate(dB/m)

Rs(Ohms)

Al WG 2.4E7 0.032 0.0216

Al WG Al2O3 grit

0.013E7 0.436 0.295

Gain is 13+ times

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Blast with SiC Grit of Aluminum Alloy WR284 Waveguide


Measured s21 0.35

Length, m 0.94

α, dB/m 0.372

α, Np/m 0.043

Rs, Ohm 0.252

σ, S/m 0.018E7

Sigma(S/m)

Rate(dB/m)

Rs(Ohms)

Al WG 2.4E7 0.032 0.0216

Al WG SiC grit

0.018E7 0.372 0.252

Gain is 12 times

9

Blast with Al2O3 Grit and Arc Wire Spray for NiCr Coat


Measured s21 0.69

Length, m 0.94

α, dB/m 0.73

Rs, Ohm 0.5

σ, S/m 45,800

Sigma(S/m)

Rate(dB/m)

Rs(Ohms)

Al WG 2.4E7 0.032 0.0216

TreatedWG

45,800 0.73 0.5 Gain is 23+ times

Air Pressure (psi) 40Spray Distance (in) 6

Arc Current (DC A) 200-220

Arc Voltage (DC V) 35- 36

Robot Scan Speed (in/min) 550

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Blast with SiC Grit and Plasma Spray for FeCrAl Powder


Measured s21 1.38

Length, m 0.94

α, dB/m 1.47

Rs, Ohm 0.99

σ, S/m 11454

Sigma(S/m)

Rate(dB/m)

Rs(Ohms)

Al WG 2.4E7 0.032 0.0216

Treated WG

11,450 1.47 0.99 Gain is 46 times

Gas Pressure, primary (psi) 100 (A)

Gas Pressure, secondary (psi) 50 (H)

Gas Flow, primary (scfh) 80

Gas Flow, secondary (scfh) 15

Arc Current (DC A) 500Arc Voltage (DC V) 66

Powder Feed Rate (lbs/hr) 6


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Blast with Al2O3 Grit + NiCr+Plasma Spray for FeCrAl Powder


Measured s21 1.51

Length, m 0.94

α, dB/m 1.6

Rs, Ohm 1.08

σ, S/m 9700

Sigma(S/m)

Rate(dB/m)

Rs(Ohms)

Al WG 2.4E7 0.032 0.0216

Treated WG

9,700 1.6 1.08 Gain is 50 times

Spray Distance (in) 7

Gas Pressure, primary (psi) 100 (A)

Gas Pressure, secondary (psi) 50 (H)

Gas Flow, primary (scfh) 80

Gas Flow, secondary (scfh) 15

Arc Current (DC A) 500

Arc Voltage (DC V) 66

Powder Feed Rate (lbs/hr) 6


Spray distance is 17% larger

High Velocity Air Fuel Coating Technology (KERMETICO Inc.)

H2

Fuel

Powder

Air In

Jet Nozzle Combustion Chamber

Ceramic Catalytic Insert

Gas Mixing Chamber

Powder- Hydrogen Mixer

Due to relatively low temperature of air-fuel combustion, even in conventional thermal spray mode the spray particles are not overheated, minimizing oxidation and thermal deterioration of spray materials. This is the key factor of improved coating quality achieved in High-Velocity Air-Fuel (HVAF) spraying. There are no data concerning the RF properties based on this technology.

HVAF Spray Mode and RF Absorption Rate Air 82 psi, Propane 74.3 psi, Propane flow 130 SLPM, Combustion chamber pressure 59.5 psiCarrier gas (nitrogen) flow 20 SLPMPowder: Fe-15Cr-7Al-0.5Y, -45+15 micron (added Al2O3 grit)Powder spray rate: 8 RPM (4 kg/hour)Standoff distance 9 inchesGun travers velocity 900 mm/sGun Shift 2 mm per passTotal coating thickness: 0.008”

Sigma(S/m)

Rate(dB/m)

Rs(Ohms)

Al WG 2.4E7 0.032 0.0216

Al WG & HVAF

6.750E3 1.3 0.88

Result

Gain is 60+ times (however the result contains both: the blast and the spray steps)

RF Attenuation after Plasma Spray FeCrAl Matrix (by APS Material Inc., Dayton, OH)

• PCA1 and PCA2 were coated, WGs were fabricated, WG rejected after LLRF test due to low attenuation rate (APS mistakenly change the technology of coat).

• PCA3 and PCA4 halves were returned for recoat, recoated, WG fabricated and rejected after LLRF test due to low attenuation (APS recoated but thickness of second layer is not enough).

• Three potential WG channels have acceptable attenuations (#5, #9, and #10).• PCA #8 WG channel has the Reference Load attenuation but has areas where there are

lifted layers. PCA #8 WG channel was rejected • Attenuation of PCA #7 WG is a current record

0

2

4

6

8

10

12

14

PCA #1 PCA #2 PCA #3 PCA #4 PCA #5 PCA #6 PCA #7 PCA #8 PCA #9 PCA #10

One pass attenuation (72 in long and kerfs on H-plan walls), dB

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High Power Test of PCA #8 (FeCrAl matrix, APS coat)


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High Power Test of PCA #7 (FeCrAl matrix, APS coat)

Insert Presentation Title in Slide Master

It was not added compressed airjets to the gun to blow off dust andsmoke residue from the coatingsurface. Surfaces are blacker thanthe rest halves.

This is a start of conditioning

After two weeks conditioning RE is more stable but the PCA #7 needs more processing time.

Proposed Steps: Combining in Series of Two WG Channels

For high power test PCAs #2, #3, and #4 could be assembled with the PCAs #6, #9, and #10 WG channels.

Three 180 deg H-plane WG bends will be needed. A design of 180 deg bend done and two bends are in fabrication mode now.

0

2

4

6

8

10

12

14

PCA #1 PCA #2 PCA #3 PCA #4 PCA #5 PCA #6 PCA #7 PCA #8 PCA #9 PCA #10

One pass attenuation, dB

X X

What Was a Major Problem in a Pilot RF Load Design?

Unevenness of E- and H- WG wall sizes

Angle of the gun nozzle was notoptimal. In some cases the coat anglewas better optimized.

Proposed Design

A next extrusion: the H-plane wall isthe same as for the pilot RF load.There will be four welding corners.The gun nozzle can be optimizedbetter.

Extrusions are delivered

One Pass Attenuation vs. Gap *)

*) This is HFSS result. A surface conductivity is 11,700 S/m based on the Metal Fusion, Inc. plasma spray technology of the FeCrAl matrix. Length is 72 inch.

≅ 0.56 ∗ 21.4

Att >10 dB for Gap= 0.787” ( ~ 12% reduction against the present kerf sizes) A uniform coat of the deeper valleys (?) Thermal and electrical issues of the stressed ribs (?) S11 is increased Extrusion (~$)

Next Extrusion:~$27 per foot(i.e. >$160 per 6 ft. load)

ConclusionThere is not a sufficient difference between Al2O3 and SiC blast grit in theattenuation rate. Both technologies of the surface preparation showpractically the same rise in the surface resistivity. A range of the surfaceresistivity is 12- 13 times higher than no blast surface preparation.

Arc Ni-Cr Wire Spray technology forms the RF attenuation layer with thesurface resistance 0.5 Ohm. The attenuation rate for this case is 0.7 dB/m.Higher attenuation rates show the thermal spray technologies of KANTHALtype matrixes.

The rate in the Rs rise during a surface preparation is sufficiently higher (afactor of 4-5 times) than the rate of the thermal spray of FeCrAl matrix. Thisfact triggers another all-metal RF load concept: a surface etching with aspecial pattern according to the absorbing wavelength.

PCA#1&PCA#8 did not pass the High Power Acceptance Test and it was rejected.PCA#7 is currently on the high power test stand for a conditioning.Two 180-deg H-plane bends are in a shop.

An upgraded extrusion of the H-plane wall is suggested.

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anatoly krasnykh, franz-josef decker et. al. slac national ... · blasting with al2o3 grit of...

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