PSB C04 RF system Consolidation or upgrade?

M. Paoluzzi – CERN BE-RF

04/21/23 1

C02 : 4 cavities in 2 straight sectionsfreq= 0.6-1.8 MHz

Vgap=8 kVRs≈350Ω seen by the beam

C04 : 4 cavities in 1 straight sectionfreq 1.2 3.6 MHz

Vgap=8 kVRs≈350Ω seen by the beam

C16 : 4 cavities in 1 straight section freq 6.0- 16 MHz

Vgap=6 kVRs≈2 kΩ seen by the beam

04/21/23 2

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?

04/21/23 3

Narrow band

Tuned systems

Highly optimized

Almost no room for Vgap increase

Further reduction of Rs very difficult

04/21/23 4

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

04/21/23 5

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)

04/21/23 6

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

04/21/23 7

Minimum peak voltage 380V for FT3L300V 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 FT3MVGAP=19÷29 kV with FT3L

04/21/23 8

Basically working on a capacitor

Almost no difference with increased

number of rings

04/21/23 9

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!!!)

V A C U U M C H A M B E R

G A P

A I R O U T

1 0 - 1 5 C M

F I N E M E T

A I R I N

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Beam current

04/21/23

ejAFTT

ejI

T

eBunchCh

Tdt

d

d

dQ

dt

dQI

eBunchCheBunchCh

ddeBunchCh

peakRFRFRF

LRFRF

L

L

L

L

L

LL

@7.22101377.0

102.3

180138

102106.1@ˆ

arg2ˆmaxmaxˆ

arg2

cos

argˆ

sinˆ)(arg

6613192

2

0

00

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.)

For a pure h1 or h2 beam,the beam peak current is 22.7 A @ ej

1st rf harmonic : ÎH1 = 9.56 A2nd rf harmonic: ÎH2 = 6.06 A

φL , TL

I

Sine shape approximation

11

Slide provided by A. Blas CERN BE-RF

MRF157 Mosfet600W up to 80MHz

To provide 800W(2 units push-pull)

ID-peak≈32AID-DC≈10A

04/21/23 12

MRF151 Mosfet150W to 175MHz

To provide 200W(2 units push-pull)

ID-peak≈12AID-DC≈4A

• Shunt resistance of each gap Rs≈200 Ω• 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

04/21/23 13

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.

04/21/23 14

04/21/23 15

Simulated system response:1 Finemet ring driven by 9 combined 200W modules

and feedback including delay .

Amplification chain response.

200W module.

1 ring impedance.

Advantages

• 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.

04/21/23 16

How could we proceed…• 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

04/21/23 17