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# PEP Super-B High Power RF - PowerPoint PPT Presentation

PEP Super-B High Power RF. Peter McIntosh SLAC. Super-B Factory Workshop in Hawaii 20-22 April 2005 University of Hawaii. Outline. RF Requirements Cavity Limitations Voltage Power Klystrons 1.2 MW 2.4 MW Circulators HVPS System System Configurations Conclusions. RF Requirements.

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### PEP Super-B High Power RF

Peter McIntosh

SLAC

Super-B Factory Workshop in Hawaii20-22 April 2005University of Hawaii

• RF Requirements

• Cavity Limitations

• Voltage

• Power

• Klystrons

• 1.2 MW

• 2.4 MW

• Circulators

• HVPS System

• System Configurations

• Conclusions

• 3 cavity solutions being investigated:

• R/Q = 5, 15 and 30 W (see S Novokhatski’s talk).

• The RF power required for L = 7e35 and 1e36 varies as a function of cavity option as the R/Q impacts primarily the HOM losses:

• As R/Q goes up  cavity HOM losses go up!

• The R/Q also impacts the cryogenic losses which affect the Total AC power required:

• As R/Q goes up  cavity cryogenic losses go down!

• For the cavity options being investigated, the net difference in Total AC power is almost zero!

• Assuming the cavity to be used lies somewhere between 5 – 30 W we can see that ……

Reduced

RF and AC Power (30W)

• To define the number of cavities required, have assumed that 1 MW can be supplied to each RF cavity (see later).

• For L = 7e35 using R/Q = 5 W cavity:

• LER = 21.7 MW

• HER = 16.2 MW

• For L = 7e35 using R/Q = 30 W cavity:

• LER = 22.1 MW

• HER = 16.2 MW

• For L = 1e36 using R/Q = 5 W cavity:

• LER = 39.8 MW

• HER = 24.9 MW

• For L = 1e36 using R/Q = 30 W cavity:

• LER = 42.0 MW

• HER = 25.0 MW

• Cavity HOM losses increase by 2.2 MW in the LER at 1e36.

• Total AC cryogenic power however reduces considerably for the 30 W cavity by 50% for both luminosity options compared to the 5 W cavity.

• Net AC power difference is comparable (to within 2%) for each cavity option at each luminosity.

R/Q=15W Solution

• Practical achievable voltage/cell depends upon:

• Cavity Qo

• Niobium purity

• Cryogenic operating temperature

• For the R/Q = 5, 15 and 30  cavities:

• Required voltage per cell Vc = 1.25 MV, requiring Qo = 3e9, 1e9 and 1e9 respectively.

• For feedback stability R/Q = 5 W preferable  lowest detuning (seeD. Teytelman’s talk)

• For cryogenic reasons R/Q = 30 W preferable (see later).

• Number of cavities required is the same for each @ L =7e35.

• At L = 1e36, the cavity HOM losses in the LER require more RF cavities (2) at R/Q = 30 W.

• What cavity voltage can we expect to reach ….

Cavity Epk and Hpk Parameters

S Novokhatski

Theoretical Quench Limit for Nb (Hpk = 1700 Oe or 135.281 kA/m)

Field Emission Onset (Epk > 10 MV/m)

Theoretical Quench Limit for Nb (Hpk = 1700 Oe or 135.281 kA/m)

Field Emission Onset (Epk > 10 MV/m)

Theoretical Quench Limit for Nb (Hpk = 1700 Oe or 135.281 kA/m)

Field Emission Onset (Epk > 10 MV/m)

• To minimize the number of RF cavities per ring:

• Based on what has been achieved at ~ 500 MHz for both KEK-B and CESR:

• 1 MW total RF input power per cavity has been chosen!

• Cavity will employ dual RF feeds, each providing up to 500 kW.

• RF breakdown investigations need to be performed to identify a system that can meet this power requirement at 952 MHz.

• Coaxial coupler arrangement  more compact.

• Is this power level realistically achievable?

KEK-B (fRF = 508 MHz):

Biased coaxial coupler

Operate typically up to 350 kW

For Super-KEKB hope to reach 500 kW

Tested up to 800 kW (through)

CESR (fRF = 500 MHz):

Aperture waveguide coupled

Operate typically up to 300 kW

Operated up to 360 kW (through)

Cavity Input Couplers

• SLAC already produces 1.2 MW tubes at 476 MHz for PEP-II.

• Tube operates at 83 kV and 24 A with perveance of 1.004.

• Maintaining these beam parameters for Super-B @ 952 MHz would enable the same HVPS system to be used.

• Scale the cavity frequencies, drift tube spacing, gap lengths, drift pipe and beam radii.

• Magnetic field increases by factor of 2  existing 476 MHz tube focus coil adequate.

Gun

Accelerating

Cavities

140.0

RF Output

(WR975)

Collector

(Full power)

• Doubling in RF power means that the existing 2.5 MVA HVPS can no longer be used  now need a 4 MVA HVPS.

• Beam power characteristics increase up to 125 kV and 29.2 A with drop in perveance to 0.6607.

• Higher beam voltage increases cavity spacing and gap lengths  accelerating section ~ 20% longer than the 1.2 MW tube.

• Magnetic field comparable to that of the 1.2 MW tube.

• Suspect will most likely require a dual output to minimize thermal loading at the RF windows.

Gun

Accelerating

Cavities

160.0

RF Output

(WR975)

Collector

(Full power)

* Needs further optimization

1.2 MW @ 476 MHz

83 kV and 24 A

Perveance = 1.004

210.07

1.2 MW @ 952 MHz

83 kV and 24 A

Perveance = 1.004

140.0

2.4 MW @ 952 MHz

125 kV and 29.2 A

Perveance = 0.6607

160.0

Full Reflection!

Klystron would see 2.4 kW in beam abort

x 4 increase c.f. 1.2 MW 476 MHz unit

Circulators Spec

• Originally designed for a depressed collector klystron.

• Existing 2.5 MVA HVPS has a primary SCR-controlled rectifier operating at the existing site-wide distribution voltage of 12.47kV:

• control provides for fast voltage adjustment and fault protection.

• Rectifier configuration prevents the dump of filter capacitor stored energy into the klystron in the event of a klystron arc.

• 12.47kV enters the circuit breaker and manual load disconnect switch and provides a safety lock and tag disconnect for maintenance.

• Remote turn-on and turn-off is by a full, fault-rated vacuum breaker used as a contactor.

• A 12-pulse rectifier reduces power line harmonic distortion to industrial standards.

• 1.2 MW Klystron:

• Existing 2.5 MVA HVPS system compatible.

• 2.4 MW Klystron:

• Same 2.5 MVA HVPS design, with larger transformers to reach 4 MVA:

• Applicable transformers are commercially available.

• Higher voltage required (125 kV):

• Makes HV connections more difficult/expensive.

• Anticipate a 20 – 30% size and cost increase over the existing 2.5 MVA unit.

1.2 MW Klystron

Single

952 MHz

RF Cavity

1.2 MW

Circulator

WR975 Waveguide

Dual

952 MHz

RF Cavities

2.4 MW

Circulator

WR975 Waveguide

System Configuration 2

Circulator

Dual

952 MHz

RF Cavities

2.4 MW Klystron

1.2 MW

Circulator

System Configuration 3

• RF requirements for L=7e35 and L=1e36 identified  need up to 190 MW site AC power!

• Low R/Q cavities needed for stability control.

• Cavity voltage and RF power limits identified  how far can we push these?!?

• High power klystrons (> 1 MW) at 952 MHz look to be achievable.

• High power circulators appear to be available from industry.

• HVPS systems for Super-PEPII klystrons are available now at 1.2 MW, but require development at 2.4 MW.

Watch this space!