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PSB C04 RF system Consolidation or upgrade? M. Paoluzzi – CERN BE-RF. C02 : 4 cavities in 2 straight sections freq= 0.6-1.8 MHz Vgap=8 kV Rs≈350 Ω seen by the beam C04 : 4 cavities in 1 straight section freq 1.2 3.6 MHz Vgap=8 kV Rs≈350 Ω seen by the beam

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PSB C04 RF system

Consolidation or upgrade?

M. Paoluzzi – CERN BE-RF


C02 : 4 cavities in 2 straight sections

freq= 0.6-1.8 MHz

Vgap=8 kV

Rs≈350Ωseen by the beam

C04 : 4 cavities in 1 straight section

freq 1.2 3.6 MHz

Vgap=8 kV

Rs≈350Ωseen by the beam

C16 : 4 cavities in 1 straight section

freq 6.0- 16 MHz

Vgap=6 kV

Rs≈2 kΩ seen by the beam


  • Consolidation foreseen C02, C16

  • Replacement of ITL, power supplies, cables

  • (rebuilt the systems keeping the cavities and amplifiers)

  • Possibly move AVC and Tuning loops to Low Level

  • Consolidation foreseen C04

  • Same as above but power stage replacement

  • (improve mean available power and current for beam

  • loading compensation)

  • Is it the time to envisage a technology change?


Narrow band

Tuned systems

Highly optimized

Almost no room for Vgap increase

Further reduction of Rs very difficult


  • Finemet LEIR Cavity

  • A single cavity covers the range 0.35÷5 MHz

  • Cavity length 0.5 m

  • Gap voltage 4 kV (tested at 5 kV)

  • No tuning

  • AVC integrated in Low Level

  • But…

  • … diameter incompatible with PSB overlapped rings


  • Finemet in PSB

  • Maximum outer diameter OD=330mm

  • Inner diameter ID=200mm

  • Standard Finemet thickness 25mm

  • Two kind of material:

  • Standard LEIR like : FT3M (data available from small rings)

  • New low loss : FT3L (Thanks to KEK and Chihiro Ohmori for

  • providing data)


  • Air cooling test on small rings (OD=133mm) :

  • Simple blower on each ring side

  • With 500kW/m3 t MAX≈70°C

  • Maximum inside temperature unknown

  • Limit temperature

    • Suggested from Hitachi t MAX≤100°C

    • KEK booster experience t MAX≈100°C

    • J-PARC experience t MAX≈200°C for few hours


Minimum peak voltage

380V for FT3L

300V for FT3M

@ 1 MHz

Note:

f Injection ≈1 MHz with LINAC4

One C04

cavity contains 50 rings

In the range 1÷4 MHz :

VGAP=15÷17 kV with FT3M

VGAP=19÷29 kV with FT3L


Basically working

on a capacitor

Almost no difference with increased number of rings


Alternative approach based: use two rings (FT3L) and 1 gap

Each ring can accept 500pF and still cover the 1÷4 MHz band .

RPmin is ≈100 Ω (per ring)

P≈1500W for 700V across two rings

This can be supplied by a solid-state amplifier

(in PSB solid state amps used since 1987!!!)


Beam current

Sine shape approximation

Beam current

φL , TL

For a pure h1 or h2 beam,

the beam peak current is 22.7 A @ ej

1st rf harmonic : ÎH1 = 9.56 A

2nd rf harmonic: ÎH2 = 6.06 A

w/o acceleration, the h1 bunch length:

φL 138o (2.4 rad or 220 nsh1 @ej.)

Total charges per bunch= 2 E13h1

(sinus shape approx.)

Slide provided by A. Blas CERN BE-RF


MRF157 Mosfet

600W up to 80MHz

To provide 800W

(2 units push-pull)

ID-peak≈32A

ID-DC≈10A

MRF151 Mosfet

150W to 175MHz

To provide 200W

(2 units push-pull)

ID-peak≈12A

ID-DC≈4A


  • Shunt resistance of each gap Rs≈200

  • To get the present 8kV need 12 gaps

  • Total impedance seen by the beam Rstot≈2400 Ω

  • Impedance of present cavities (including FB) ≈350 Ω

  • We must reduce Rstot and compensate beam loading with:

    • ≈20 dB RF feedback seems possible with 10 ns delay in the loop.

  • 1 turn feedback: difficult (nevertheless possible) because revolution time is only ≈500 ns at extraction.

  • Combination of both


The cavity could be used as combiner for push-pull operation and driven by 2 amplifiers similar to the LEIR 1kW drivers.

The total power could easily be

brought to 2 x 2 kW simply

increasing the DC supply by 15%.

The 120W (200W) power module

delay is 12 ns and the 9 ways

combiner 4ns. Both could be

reduced and 10 ns total seems

within reach.


Simulated system response: and driven by 2 amplifiers similar to the LEIR 1kW drivers.

1 Finemet ring driven by 9 combined 200W modules

and feedback including delay .

200W module.

1 ring impedance.

Amplification chain response.


  • Advantages and driven by 2 amplifiers similar to the LEIR 1kW drivers.

  • Modular system.

  • Reduced machine space and/or increased installed voltage.

  • Possibility of installing spare cavities as hot back-up.

  • No tuning loop.

  • Simplified solid-state system.

  • Risks

  • Additional new system at restart with LINAC4.

  • New technology and configuration.

  • Complete new design.


  • How could we proceed… and driven by 2 amplifiers similar to the LEIR 1kW drivers.

  • 2010-2011 Design and produce a first section.

  • … if successful then:

  • 2012 produce and install and test a full set of cavities for the required 8 kV.

    • They should fit in the place of one of the present C04 cavities.

  • 2013 Tests with beam (1 ring and C02 system still in place)

  • … if successful then:

  • 2014-2015 Proceed with full scale construction and

    • C02/C16 renovation

  • 2016 Installation

  • … but for security

  • 2011 Design a first C04 improved RF power amplifier.

  • 2012 Produce and install C04 improved RF power amplifier.

  • 2013 Tests with beam (1 ring)

  • 2014-2015 Depending on 2013 tests start C02/C04/C16 renovation or

    • stop C04 renovation it and proceed with new system.

  • 2016 Installation


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