The RF Power Source for the High Beta Elliptical Cavities of the ESS Linac

K. Rathsman, H. Danared, R. Zeng, ESS, Lund, Sweden

R.J.M.Y. Ruber, Uppsala University, Sweden; C.A. Martins, Laval University, Canada

C. Lingwood, Lancaster University, UK; A.J. Johansson, Lund University, Sweden

Klystron ParametersHigh Power 704 MHz

Parameter Minimum Nominal Maximum Units

RF Frequency 704.42 MHz

Peak Output Power 1.0 1.2 1.5 MW

RF Pulse length 3.3 ms

Pulse repetition rate 14 Hz

DC to RF efficiency 65 %

Perveance 0.55 μPerv

Beam Voltage 102 113 kV

Beam current 18 21 A

RF Power Gain 48 dB

Bandwidth (-1 dB) 4 MHz

Cathode lifetime 100000 h

VSWR Tolerance 1.2:1

Parameter Minimum Nominal Maximum Units

Peak power 1.5 1.8 2.3 MW

Peak voltage 95 102 113 kV

Pulse width 3.5 ms

Pulse repetition rate 14 Hz

Pulse rise time 0.2 ms

Ripple (<100 Hz) & droop 3 %

Ripple (0.1-1 kHz) 1 %

Ripple (>1 kHz) 0.1 %

Pulse reproducibility 99.98 %

Energy in case of arc 10 J

Power efficiency 90 %

Undershoot voltage 10 %

Modulator ParametersHigh Power 704 MHz

Parameter Unit

Average beam power 5 MW

Proton kinetic energy 2.5 GeV

Average macro pulse current 50 mA

Macro pulse length 2.86 ms

Pulse Repetition Rate 14 Hz

Maximum cavity surface field 40 MV/m

Linac Length 392 m

Annual operation period 5200 h

Reliability >95 %

Losses <1 W/m

Elliptical power coupler power <0.9 MW

Linac Parameters

High power 704 MHz

112

High β

Medium power 704 MHz

8

High β

36

Low β

Low power 704 MHz

28

Low β

Low power 352 MHz

28

Spoke

2

DTL

1

DTL

1

RFQ

High power 352 MHz

Klystron Modulator IOT / Solid state

RF Source Scheme

Power to Beam1.0

0.8

0.6

0.4

0.2

0.00 50 100 150 200 250 300 350

Cav

ity

Pow

er (

MW

)

Position (m)

28 Spokes

64 Low β

120 High β

2828

44

112

Calculation by M. Eshraqi, WEPS062

RF Source

Circulator

LLRF

Cavity

loadKlystronModulator

Klystron

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Sustainable ScienceReliable Renewable, Responsible, Recyclable