High power continuous wave test of
RF couplers for the RFQ of the Linear
IFMIF Prototype Accelerator.
DE FRANCO Andrea for the LIPAc team
第20回日本加速器学会年会 - 29th August – 1st September 2023
Injector
Beam
dump

HEBT

D-plateRFQMEBTMEBT Extension Line

Linear IFMIF Prototype Accelerator (LIPAc)

Rokkasho Fusion Institute (BA Site)

Author list
De Franco A. †, Hirosawa K., Ishimura K., Kaneko N., Kondo K., Kubo N., Masuda K., Nakayama T., Narita T.,
Sugimoto M., Yanagimachi T., National Institutes for Quantum Science and Technology (QST), Rokkasho,Japan
Caballero C., Gonzalez-Gallego S.C. L., Maindive L., Morales J.C., University of Granada, Granada, Spain
Garcia J. M., The Centre for Energy, Environmental and Technological Research (CIEMAT), Madrid, SpainGex D., Moya I., Scantamburlo F.1, Fusion for Energy (F4E)
1also at National Institute for Nuclear Physics (INFN), Legnaro, Italy

29/08/23 – 1/09/23

第20回日本加速器学会年会 – De Franco A.

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Linear IFMIF Prototype Accelerator
International Fusion Materials Irradiation Facility (IFMIF) will address the need of a neutron source for material tests toward
future Fusion Power Plant

IFMIF conceptual design

Linear IFMIF Prototype Accelerator (LIPAc)@QST in Rokkasho, Aomori, Japan
EU-Japan Broad Approach agreement
D+, 0.1MeV, CW

RF input –175MHz, 1.3MW

SRF LINAC
will be installed (5MeV→9MeV)
5MeV, 125mA

More on LIPAc/IFMIF:
Masuda: “Status of Linear IFMIF Prototype
Accelerator in 2023” – TWSP16
Hirosawa: “High-Power tests of repaired
circulator for LIPAc RFQ” – FRP33
8 RF couplers(200kW; CW)

Fisheye view of LIPAc

29/08/23 – 1/09/23

Beam dump
5MeV→0.6MW
9MeV→1.1 MW

第20回日本加速器学会年会 – De Franco A.

4 of the 8 coaxial lines supplying RF to RFQ

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RFQ RF couplers

2D cut view of RFQ and its O-ring couplers before cooling enhancement.

Ceramic seal

O-ringBrazedMaterialAll Cu

Mostly SUS + 50µm Cu

Vacuum gauge XOArc sensor

APD on window

Optical fibre + PD

Antenna depth 34.86 mm

45 mm

Cooling

Loop + jacket + cold
finger + forced air

Loop + around ceramic +inner conductor

Inner nearwindowRound near ceramic

Perpendicular nearceramic

29/08/23 – 1/09/23
16/12/22

O-ring couplers damaged
during RF conditioning at highduty cycle.
Improved heat extraction
design and re-installed in RFQ.
High-power test of Brazed
couplers started.

第20回日本加速器学会年会 – De Franco A.

Alumina window after O-ring melt.
Visible O-ring debris. Cu black
deposits at high filed region on
ceramic and anchor.

4RFQ RF couplers

2D cut view of RFQ and its O-ring couplers before cooling enhancement.

Ceramic seal

O-ringBrazedMaterialAll Cu

Mostly SUS + 50µm Cu

Vacuum gauge XOArc sensor

APD on window

Optical fibre + PD

Antenna depth 34.86 mm45 mmCooling

Loop + jacket + cold
finger + forced air

Loop + around ceramic +inner conductor

Inner nearwindow

Round near ceramic

Perpendicular nearceramic

29/08/23 – 1/09/23
16/12/22

O-ring couplers damaged
during RF conditioning at highduty cycle.
Improved heat extraction
design and re-installed in RFQ.
High-power test of Brazed
couplers started.

第20回日本加速器学会年会 – De Franco A.

Alumina window after O-ring melt.
Visible O-ring debris. Cu black
deposits at high filed region onceramic and anchor.

5High Power Test Bench
Before can be used in RFQ need:• Thermomechanical validation with forward power > 200kW in CW• RF conditioning

Dummy load

CPL2

CPL1

Bridge cavity

Schematic view of test bench

29/08/23 – 1/09/23

Photo during test bench assembly

第20回日本加速器学会年会 – De Franco A.

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High Power Test Bench - 2Cooling
Loss in cavity ~12%
12 L/min each coupler (3 circuits)
55 L/min cavity cooling (4 circuits)

Shielding2 x 1 mm thick Pb curtain

Max T =
63.5°C

Thermal simulations of cavity at CW with FWD 220kW.

Vacuum80 L/s TMP + scroll pump
72 hours baking at 100°C
29/08/23 – 1/09/23

Instrumentation
RGA+ Cold cathode vacuum gauge
Arc sensor in each coupler
9 PT100
2 IR camera
Dose counter (outside shield)
Remote movable tuner
Calorimetry on CPL1

第20回日本加速器学会年会 – De Franco A.

Pb shielding around test bench.

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RF conditioning
1. Increase FWD to 220 kW, 10 µs pulse width, 1 s rep. period
2. Decrease rep. period to 10ms
3. Elongate pulse width
REV pulse shape + vacuum H20 splits in O and H→Multipacting/Plasma?

Cavity frequency
detuned ~30kHz1 ms
Rev pulse shape for different resonant frequency adjusted with tuner.

29/08/23 – 1/09/23

2D scan of FWD and its frequency. No overlap with flat and small on average REV.

第20回日本加速器学会年会 – De Franco A.

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Multipacting

Pareto front of REV shape and average.

Multipacting is present in any combination of FWD/frequency the system iscapable to operate at. End of the test?
Example pulse shapes along the Pareto front of REV shape and average.

29/08/23 – 1/09/23

第20回日本加速器学会年会 – De Franco A.

9Thermomechanical design validation
TRA too low to conclude on CPL2
CPL1 in much stricter conditions than originally intended.
→ sufficient for design validation!
Pulse shape at 96% d.c. with at PW ~ 3.8 ms, RP = 4 ms.

MP in cavity, not in CPL1 because:• CPL1 T increase minimum• Cavity tuning changes pulse shape• No light observed at CPL1 view port
• High SEY of Al• Cavity visual inspection after test

PLPL2

S integrated inhrs at 2 d cwith F200entralstu

Pulse shape at duty cycle = 96%

29/08/23 – 1/09/23

PLPL2Integrated dose at d.c. 2% FWD 200kW over 48hrs. Low dose on central stub.
→ X-ray from gap in cavity (no MP in CPL1)

第20回日本加速器学会年会 – De Franco A.

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Surface Temperature at 96% duty cycle

PLa ity

27.6 °C

25.8 °C

28.5 °C

26.4 °C

27.7 °C

27.1 °C~75W~600W
etrodeA pCouplers are not hot at duty cycle = 96%

29/08/23 – 1/09/23

CPL2

PL2

PL

PL2

CPL1

第20回日本加速器学会年会 – De Franco A.

Couplers not hot at duty cycle = 96%. Heat measured withcalorimetry hardly compatible with MP in CPL1.

11Cavity visual inspection
Cu layer not well attached - melted

MP / Arcs , protruded and melted RF fingers

Cu layer on SUS input flange not well attached, RF enter gap and create loop,
which further melt and deform. Heat marks on the nearby coupler are visible.

RF loss on cuts for air pocket evacuation

Traces of MP on cavity surface near tuner. Also,visible deformed andmelted RF fingers.

RF loss induced heat in the cuts used for evacuation of air pocket near O-ring.

29/08/23 – 1/09/23

第20回日本加速器学会年会 – De Franco A.

12Cavity visual inspection
Cu layer not well attached - melted

MP / Arcs , protruded and melted RF fingers

Replace with Cu platingEdges/gaps of tuner in high E region notideal.
Remove tuner and replace with flat lid.
Cu plating of entire inner surface.
Cu layer on SUS input flange not well attached, RF enter gap and create loop,
which further melt and deform. Heat marks on the nearby coupler are visible.

RF loss on cuts for air pocket evacuation
Bridge gap with Cu mesh

Traces of MP on cavity surface near tuner. Also,visible deformed andmelted RF fingers.

RF loss induced heat in the cuts used for evacuation of air pocket near O-ring.

29/08/23 – 1/09/23

第20回日本加速器学会年会 – De Franco A.

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Conclusion
••
•
•
•

29/08/23 – 1/09/23

LIPAc RFQ RF conditioning and beam commissioning towards CW ongoing.
RF couplers identified as critical system.
O-ring based couplers used so far were improved and re-installed
Original coupler`s thermal design validated with a high-power high duty cycle test bench
Bridge cavity will be improved to complete test/conditioning of the series.

第20回日本加速器学会年会 – De Franco A.

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