RT Operations

RF Power SourcesLinac Systems

System Operation

Ivan Konoplev, JAI Oxford UniversityPeter McIntosh, STFC ASTeC

Introduction & Goals

• Accelerator technologies:– RF Sources– Linacs– Operational Experiences

• Quality• Reliability• Size/Modularity• Servicing/Maintenance• Costs

• Questions issued (non-exhaustive), collate feedback, try to converge on an optimum RT approach.

• What are technology development opportunities:– efficiency, robustness, simplicity, stability

Session Programme

13:45 – 14:00 Introduction & Goals

14:00 – 15:45 RF Sources & Linacs (I Konoplev, P McIntosh)

Affordable Linacs (U Amaldi)

• Quality

• Reliability

• Size/Modularity

15:45 – 16:15 Coffee

16:15 – 17:45 Operational Experience (J Van Dyk)

• Service/Maintenance

• Operability

• Costs

Klystron – based on inertial bunching mechanism of RF generation

• Efficiency - up to 85% (research) and 60% (commercial) –running cost savings

• Commercial availability in broad frequency range operating range from 0.1GHz up to 15GHz

• Versatile, reliable they are operating at 100s (A) beam current and 10s (kV)

• Can be high average power up to 1MW

• However they are more expensive Basic schematic of two cavity klystron

Technical drawings of a multi-cavity cavity klystron

Example of typical operation data

Example of absolute rating

What to expect from vendors

• The tube price is about £100k and can be negotiated with up to 15% reduction if one buys 10 of them.

• Spec. for life time is 5000 hours (sure can run > 10 000 but not specified as such in official offers).

• Tube can be repaired (new cathode) for 30% of initial price. • New tube as compared to existing tubes with similar peak power should save

>30% of modulator cost (low voltage, no oil tank) and it is very compact (1/3 of standard modulator in volume).

Magnetron – M-type tube generates RF if electrons are losing “potential” energy

• It is an Oscillator and cannot be used as an amplifier

• Not expensive (1/3rd of klystron price) but not as reliable, life time is an issue for HP devices

• Power up to 3MW (peak power) good for low energy LINCAS (up to 6MeV)

• Operating frequency range 0.1GHz to high 10s GHz

• Versatile but not stable and operating frequency

may walk around

The cathode in a magnetron is harder to cool than

in a klystron and gets additional heating from back

bombardment so the maximum output is far less

than a klystron

Magnetron

Schematic view of the magnetron and its operation

Cathode is heated to generate the electrons but it is also heated by the electrons coming back –erosion of the cathode

Magnetrons are cheap to manufacture but it cannot be controlled to the level of the klystron

Example of magnetron controls

Magnetron and Klystron

Cost

Solid state RF power supply

• Efficiency - comparable with klystron but less

• Water cooling is required

• Modular

• High power (1MW level) will be available at 750MHz soon

• At frequencies above 1 GHz the high power will be available in the next 3-5 years

• Expensive but relatively easy to run

Typical table from one of the vendors

Klystron SSA-1 SSA-NIOT

Example of SSA RF power supplies

One of the most complicated parts are power combiner and cooling

Vacuum Tubes vs SSA

Just to make it more complex the following subsystems are needed

Regardless of the power supply chosen to drive the accelerator

Klystron vs Magnetron vs SSA Klystron Magnetron SSA

Efficiency 50%-70% Up to 90% 50%-70%

Frequency (GHz) 0.1 – 15 0.1 – 15 up to 1

Peak Power (MW) Up to 10 Up to 3 <1

Stability high low high

Life expectancy high low high

Cooling yes yes yes

Maintenance complex complex simple

Size compact compact large

Mobility yes yes yes

Modularity partial partial yes

Capital Cost high intermediate high

Run Cost intermediate intermediate intermediate

SSA is a good solution for the future but klystron is the answer to have reasonable cost/quality ratio

Accelerator technology standing wave and traveling wave

LINACs

Standing wave LINAC

Traveling wave LINAC

VariabilitiesFrequency, gradient, phase velocity, geometry, shunt impedance, Q Factor

Standing wave LINAC

More compact c.f. TW structures (particularly when optimally coupled)Typically utilised for heavy ion, proton or short pulse electron linacs

Traveling wave LINAC

Electron bunch propagates with the wave in accelerating phase

Short fill time structures c.f SW structuresNormally utilised for short beam pulse machines, linear colliders or SR injectors

TW vs SWIncr. loss Incr. Trans-time

SW Side-Coupled optimised to reach >100M/m with small beam-pipe (6mm)Resonant coupling – maximise group velocity

Comparison of Standing-Wave and Travelling-Wave Structures, R Miller (SLAC), Linac86

SW

TW

Dominated by RF source costs

S-Band SW Structures (SAMEER)

Compton X-Ray Source

Parameter Value

Frequency (MHz) 2998

# Cells 24

Coupling Mode Side /2

Effective Shunt Impedance (M/m) 87

Q Factor 15000

Length (m) 1.12

RF Input Power (MW) 5.5

Energy (MeV) 15

S-Band TW Structures (TTX)

Parameters Units

Length 1.5m

Mode 3/4π

Cell length 39.3mm

Number of cells 38(with coupler)

f ~2856MHz

a 10.6mm-8.1mm

vg/c 0.83%~0.3%

Rs 64.6MΩ/m~71.8MΩ/m

Filling Time 960ns

Eacc(Pin=30MW) 30MV/m

C-Band SW Structures (Tsinghua U/Nuctech)

Parameter Value

Frequency (MHz) 5712

# Cells 12

Coupling Mode On-axis

Effective Shunt Impedance (M/m) 130

Q Factor 10500

Length (m) 0.29

Eacc (MV/m) 21

RF Input Power (MW) 2.16

Energy (MeV) 6

C-Band TW Structures (SwissFEL)• Structures are machined “on tune”, no

provisions for dimple tuning!

• Cup manufacturing with micron precision at VDL ETG Switzerland

• Coupler manufacturing at VDL ETG

• Stacked by robot at PSI

• Vacuum-brazed at PSI

• Production rate: 1-2 / week

• Production finished August 2016

• High power results for first structure: Conditioned to 52 MV/m Break-down rate at 52 MV/m

≈ 2 x 10-6

At nominal 28MV/m, break-down rate negligible (well below the specified threshold of 10-8)

R. Zennaro et al., “Measurement and High Power Test of the First C-Band Accelerating Structure for SwissFEL”, Proceedings of LINAC2014, Geneva, Switzerland

X-Band SW Structures (SLAC & BIEVT)

• Performance of two of them was limited to gradients lower than 55 MV/m by breakdowns in the couplers.

• Breakdowns may be related to the high RF magnetic and moderate RF electric fields on the sharp edges at the waveguide-to-coupler cell opening.

SLAC BIEVT

X-Band TW Structures (CLIC)

25 cmMicron–precision disk

• 11.994 GHz, X-band• 100 MV/m accelerating gradient• Input power ≈50 MW• Pulse length ≈200 ns• Repetition rate 50-400 Hz

Linac Comparison

S-Band C-Band X-Band

SW(SAMEER)

TW(TTX)

SW(TU/Nuctech)

TW(SwissFEL)

SW (SLAC)

SW(BIEVT)

TW (CLIC)

Frequency (MHz) 2998 2856 5712 5712 11400 9300 11994

Operating Mode Side /2 3/4 On-axis /2 2/3 On-Axis

On-Axis/2

2/3

Eff. Shunt Impedance (M/m) 87 71.8 130 80 81.9 133 112

# Cells 24 38 12 113 15 11 24

Q Factor 15000 16566 10500 10000 8600 7100 6265

Length (m) 1.12 1.5 0.29 2 0.2 0.15 0.23

RF Input Power (MW) 5.5 31 2.16 28 6 1 63.8

Eacc (MV/m) 17 30 21 28 50 14 100

Energy (MeV) 15 45 6 56 10 2 23

Acknowledgements

RF Sources LinacsI Syratchev (CERN) W Wuensch (CERN)G Burt (Lanc U) G Burt (Lanc U)A Dexter (Lanc U)A Wheelhouse (STFC)

Affordable Linacs, U Amaldi (TERA Foundation)

RF Questions

Accelerator Technologies

RF Sources• Linacs can potentially be driven by Magnetron, Klystron or Solid state

devices - do you have any preferences? Why?• Which accelerator technology is most commonly used?

Linacs• Which accelerator technology is most commonly used • Pro’s/Con’s of the accelerators used for the treatments, what is the most

annoying part of working with the accelerator• List the electron beam energies needed for a cancer treatment• List electron beam current needed for a cancer treatment• Can current generation of LINAC available in hospitals deliver the required

parameters• Linacs based on Travel Wave/Standing waves do you have any

preferences? Why?

Quality

• Electron beam quality i.e. beam dimensions and dispersion?

• Accuracy of beam delivery to the target?

• Electron beam stability over the treatment time?

• Which accelerator technical parameters are the most important for a cancer treatment?

Reliability

• Accelerator stability i.e. how stable it should be and what are the acceptable boundaries of parameters variations?

• Change of the environment and reliability: how stable environment conditions can be provided i.e. cost of running environment stable conditions against the cost of environment robust accelerator?

Size

• Favourable preferable dimensions for the accelerator?

• What is more preferable compact but more expensive accelerator or capital cost to upgrade the hospital available rooms to accommodate the facility?

Second Session – 16:15 – 17:45

16:15 RT Technology Operation Experience, J Van Dyk (Western Univ, London, Canada)

Servicing/Maintenance

Operability

Costs

Services/Maintenance

• Availability of technical personal?

• Availability of mechanical and electrical workshops to fix things locally?

• Stable water and electricity supplies?

• What are servicing requirements, capability available, how modular does system need to be?

Operability

• What is important efficiency criteria – initial costs or operating costs, (is it important to reduce energy consumption by 10% or it would be important to reduce the initial cost of the equipment by 10%)?

• What cooling configurations are deemed appropriate (additional water cooling or well-conditioned room)?

• What level of controls needed – cost implications? Manual but cost reduced system or fully automated but more expensive?

• What are stability requirements – which components need tight control?

Costs

• Capital vs Operating?

• Technology drivers?

• Manufacturing techniques?

Combined Session Summary

• Capture of key points raised– Energy– Frequency– Size– Source technology– Staffing – expertise and training needed– Operability constraints – local infrastruture

• Opportunities for development of RT concepts:– Scope?– Market research?– Technology R&D?