ESS RF System Design

Stephen MolloyRF Group

ESS Accelerator Division

SLHiPP24-May-2012

Outline

• Overview of the ESS RF system• System behaviour• System layout• Modulator workshop• Risk & reliability

SYSTEM OVERVIEW

0 50 100 150 2000

100000

200000

300000

400000

500000

600000

700000

800000

900000

1000000

Pow

er (W

)

RF System OverviewNB: Lattice updates will have altered this.

Superconducting linac

RF System Main Components• The RF system for the ESS linac is defined as the system that:

– converts AC line power to RF power at either 352 or 704 MHz – supplies this power to the cavity couplers

• Main components– Modulator

• Converts conventional AC power into pulse power• ESS requires 90 modulators

– RF Power Amplifiers• Converts the modulator’s pulsed power to RF at 352 or 704 MHz• Typically klystrons

– Require ~180 klystrons– 1 MW peak power per klystron (40 kW average)

– RF Distribution• Transports the RF from power amplifiers to cavity coupler couplers • Typically waveguides with other components (circulators, directional couplers, etc…)

– Low Level RF Control• Regulates RF amplitude to 0.5% and phase to 0.5 degrees• Requires both feedback and adaptive feed-forward algorithms

General Requirements

Parameter Value Unit PublisherMaximum Beam Current 50 mA GeneralBeam Current Stability 1 % Ion SourceBeam Current Control 1 % Ion SourceBeam Current Ripple 1 % Ion SourceBeam Current Pulse Length 2.86 mS GeneralBeam Current Pulse Length Stability 1 ppm ChopperBeam Current Pulse length Control 1 ppm ChopperRepetition Rate 14 Hz GeneralCavity Gradient Amplitude regulation 0.5 % Beam PhysicsCavity Gradient Phase regulation 0.5 degrees Beam PhysicsAllowed AC Grid Load Variation (Flicker) 1 % Energy

General Requirements

System RequirementsParameter RFQ Bunchers DTL Spokes Low Beta High Beta Unit PublisherNumber of Couplers 1 2 3 36 64 120 Beam PhysicsAverage Coupler Spacing 0 1 7 2.1 1.8 1.8 meters Cavity DesignMaximum Power Delivered to Coupler 1000 10 2100 245 610 950 kW Beam PhysicsMinimum Power Delivered to Coupler 1000 10 2100 100 50 610 kW Beam PhysicsAverage Power Delivered to Coupler 1000 10 2100 215 400 900 kW Beam PhysicsMaximum Reflected Energy per Pulse 15 0.2 35 60 160 250 J Beam PhysicsMaximum reflected power 1000 10 2100 245 610 950 kW RFFrequency 352 352 352 352 704 704 MHz Beam PhysicsAverage Synchronous phase 0 90 30 15.2 15.9 14 degrees Beam PhysicsLoaded Q 15 15 15 160 640 820 103 Cavity DesignMaximum Cavity Fill Time 50 50 50 400 250 250 uS Cavity DesignLorentz de-tuning coefficient 0 0 0 1 1 1 Hz/(MV/m)2 Cavity DesignLorentz de-tuning Time constant 0 0 0 1 1 1 mS Cavity DesignSlow Tuner Range 100 100 100 100 100 100 kHz Cavity DesignSlow Tuner Slew Rate 1 1 1 1 1 1 kHz/sec Cavity DesignMaximum Slow Tuner Cycles 1 1 1 .1 .1 .1 106 Cavity DesignFast Tuner Range 0 0 0 10 10 10 kHz Cavity DesignFast Tuner Bandwidth 1 1 1 1000 1000 1000 Hz Cavity DesignCavity phase noise (microphonics) 0 0 0 10 10 10 Hz Cavity DesignCavity drift rate 1 1 1 1 1 1 Hz/sec Cavity Design

Requirements

Example Specifications

Parameter RFQ Bunchers DTL Spokes Low Beta High Beta Unit SubscriberRF Regulation Overhead 25 25 25 25 25 25 % System DesignRF Distribution Loss Budget 5 5 5 5 5 5 % LLRFRF pulse Length 2.91 2.91 2.91 3.26 3.11 3.11 mS DistributionNumber of Couplers per Power Source 1 1 1 1 1 1 ModulatorSaturated RF Power per Power Source 1300 15 2750 350 800 1250 kW Power SourceMinimum Efficiency at Operating Power 43 43 43 50 43 43 % Power SourceNumber of Power Sources per Modulator 1 3 1 9 2 2 Power SourceMax. Modulator Stored Energy per Pulse 6.8 0.2 14.5 14.5 9 14 kJ ModulatorModulator Efficiency 85 85 85 97 85 85 % ModulatorTotal Average AC Power to modulator 117 2.3 750 800 3250 13550 kW EnergyTotal Average Cooling Rate 91 0.0 544 459 3199 10983 kW EnergyTotal Average AC power 132 2.3 795 800 4210 15350 kW

Specifications

BEHAVIOUR

Large-scale system response

Required saturated klystron power assuming 25% overhead

+ 5% losses.Drives the scale of the

klystron/modulator systems, cooling requirements, etc.

Steady-state reflected power (i.e. during beam-time) is governed by the R/Q drop at the ends of

each section.Drives requirements of the circulators, loads, etc.

Single coupler design (i.e. QL) for each section, but each cavity detuned to

minimise the reflected power.

Temporal response

Total reflected energy per pulse under nominal conditions.

Dictates the load requirements.

Efficiency of the overall RF system

Efficiency of the overall RF system

LAYOUT

Gallery/Linac integration:Chute Concept

Gallery/Linac integration:Chute Concept

Gallery/Linac integration:Stub Concept

Gallery/Linac integration:Stub Concept

Benefits:1. Fewer (larger) penetrations.2. Wide penetrations allow 90 degree bend.3. No line of sight from tunnel to gallery.4. Freedom to alter cryomodule positions

MODULATOR WORKSHOP

“Intense” Discussions

• Presentations by invited experts• CERN, DESY, FNAL, LANL, RRCAT, SLAC, SNS

• Attendance included manufacturers– No presentations, but strong participation in discussions

• Draft strategy emerged from the meeting• ESS will write the technical specifications

» Does *not* impose a topology

• Call for tender for production of multiple prototypes• Limited call for tender for series production

» Possibility for multiple vendors to be successful

RISK & RELIABILITY

95% availability

• MTBF & MTTR of klystrons is likely to dominate the machine availability

Transformer

Rti=0.99999969

RF Source 1

ModulatorRmi=0.9999

KlystronRki=0.9995

Circulator/load

Rci=0.9995

LLRF

R mi=

0.99

99

KlystronRki=0.9995

Circulator/load

Rci=0.9995

LLRF

R mi=

0.99

99

RF Source <i>RBD

RF Source 3RF Source 2 RF Source 4

Power dist <i>RBD