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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

PEP Super-B High Power RF

Peter McIntosh

SLAC

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


Outline
Outline

  • RF Requirements

  • Cavity Limitations

    • Voltage

    • Power

  • Klystrons

    • 1.2 MW

    • 2.4 MW

  • Circulators

  • HVPS System

  • System Configurations

  • Conclusions


Rf requirements
RF Requirements

  • 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 ……



Rf and ac power 30 w

Increased

Reduced

RF and AC Power (30W)


Rf and ac power summary
RF and AC Power Summary

  • 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 15 w solution
R/Q=15W Solution


Cavity limitations voltage
Cavity Limitations - Voltage

  • Practical achievable voltage/cell depends upon:

    • Cavity Qo

    • Niobium purity

    • Cryogenic operating temperature

    • Cryogenic load

  • 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 e pk and h pk parameters
Cavity Epk and Hpk Parameters

S Novokhatski


Voltage overhead for 30 w
Voltage Overhead (for 30W)

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

Field Emission Onset (Epk > 10 MV/m)


Voltage overhead for 5 w
Voltage Overhead (for 5W)

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

Field Emission Onset (Epk > 10 MV/m)


Voltage overhead for 15 w
Voltage Overhead (for 15W)

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

Field Emission Onset (Epk > 10 MV/m)


Cavity limitations power
Cavity Limitations - Power

  • 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?


Cavity input couplers

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


Klystrons 1 2 mw
Klystrons – 1.2 MW

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

  • Each powered by a 2.5 MVA DC HVPS.

  • 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.




1 2 mw klystron specification
1.2 MW Klystron Specification

Gun

Accelerating

Cavities

140.0

RF Output

(WR975)

Collector

(Full power)


Klystrons 2 4 mw
Klystrons – 2.4 MW

  • 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.

  • Thermal loading of the output circuit requires more detailed investigation.

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



2 4 mw klystron specification
2.4 MW Klystron Specification

Gun

Accelerating

Cavities

160.0

RF Output

(WR975)

Collector

(Full power)

* Needs further optimization


Klystron option footprints
Klystron Option Footprints

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



Circulators spec

1.7%

1 dry load, 1 water load

Full Reflection!

Klystron would see 2.4 kW in beam abort

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

Circulators Spec


HVPS

  • 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.



Super b hvps options
Super-B HVPS Options

  • 1.2 MW Klystron:

    • Existing 2.5 MVA HVPS system compatible.

    • No development overhead.

  • 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.


System configuration 1
System Configuration 1

1.2 MW Klystron

Single

952 MHz

RF Cavity

1.2 MW

Circulator

WR975 Waveguide


System configuration 2

2.4 MW Klystron

Dual

952 MHz

RF Cavities

2.4 MW

Circulator

WR975 Waveguide

System Configuration 2


System configuration 3

1.2 MW

Circulator

Dual

952 MHz

RF Cavities

2.4 MW Klystron

1.2 MW

Circulator

System Configuration 3


Conclusions
Conclusions

  • 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!




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