MAX II RF system100 MHz technology

Lars Malmgren

10th ESLS RF MeetingDortmundSeptember 27-28, 2006

Facts and figures

1.7Rms bunch length [cm]

8Synchrotron frequency [kHz]

3.0Bucket height [%]

93(135)Net power [kW]

90Available power [kW]

35 (50)Beam power @ 250mA [kW]

21 (29)Cu losses [kW]

450 (530)Tot Voltage [kV]

19000Q-value

9.6Tot Rshunt (≡≡≡≡V*V/P) [MΩΩΩΩ]

1.5Tot length of cavities [m]

0.41Cell radius [m]

3No of transmitters

3No of cavity cells

30Harmonic number

99.956Frequency [MHz]

MAX-II

Simple circuit model of the RF-system with beam

LL

ZR coupS ⋅=

0

β

Lcoup L C Rs Ibeam

Zc

n λ/2

Z0

Lcoup << L

LLRZ coupS ⋅=

β0

N2

N=transformer ratio

Zc=cavity impedance

RF-system with beamloading

⋅⋅−⋅+⋅⋅⋅+

⋅=

sc

sDCs

c

sDC

URIQi

URI

ZZφξφ

β

cos2sin21 0

0

2 2

21 sin

2 21 sin 1 1

DC Ss

C

DC C S S beamS beam

C C C

I RUI U R R PPU U P

β φ

β φ

⋅ ⋅= +

⋅ ⋅ ⋅ ⋅= + = + ⋅ = +

A. Matched condition of resistive part: ReZ=Z0

B. Matched condition of reactive part: ImZ=0

SC

sDC

c URIQ

ffQ φξ cos22

00⋅⋅=∆⋅=⋅

A. Defines the coupling factor of the cavityB. Defines the necessary detuning of the cavity

Φs is the phase angle betweenthe synchronous electron andthe zero crossing of the cavityvoltage.

Cavity

A. The main cavities are of the capacity-loaded type.

B. The tuning is made by squeezing the cavity side.

100 MHz cavity100 MHz Capacity-loaded Cavity for MAX-II and -III, F = 100.08323 MHz

C:\LANL\EXAMPLES\RADIOFREQUENCY\PILLBOXCAVITIES\100MHZ.AF 11-10-2005 20:03:50

0

5

10

15

20

25

30

35

40

0

5

10

15

20

25

30

35

40

0 5 10 15 20 25 30 35 40 45 50 55

100 MHz Capacity-loaded Cavity for MAX-II and -III, F = 455.96217 MHz

C:\LANL\EXAMPLES\RADIOFREQUENCY\PILLBOXCAVITIES\100MHZ.AF 11-10-2005 20:16:42

0

5

10

15

20

25

30

35

40

0

5

10

15

20

25

30

35

40

0 5 10 15 20 25 30 35 40 45 50 55

100 MHz cavity profile with fundamental mode E-field lines

E-field lines of the high order mode at 456 MHz

Q-value 19000

Tot. Rshunt 3.2 MΩ

The high order modes are damped by antennas in the endplate. This endplate is convenient to use since the fundamental mode is not affected.

Landau cavity

The Landau cavities are of simple pill-box type. Tuning is doneboth by plunger and temperature.

RF amplifier and feeder line• The generator system consists

of three 30 kW FM transmitters (Itelco T254T) feeding one cavity each

• The power stages are tetrodeamplifiers

• Class C operation for high efficiency

• An integer λ/2 long coaxial 3 1/8” transmission line is feeding the cavity input coupler. The reflected wave will add in phase with the wave at the generator

RF path

φ φ

Main cavity

Frequency tuning loop

Power control loopPhase control loop

SingleSingle stubstub tunertuner100 MHz master oscillator

Power amplifier

The power control makes the cavity to see a matched condition at the generator.A phase control system is used to control the phase difference between the cavities.

Stub matching networkA stub matching network is installed to keep an optimal match of transmitter and cavity for every beam current.

An alternative to a circulator

Tetrode amplifiers

S

Dummy load

Dummy load

Switchlesscombiner

λ/4 +n λ

3 dB hybrid

BPM systemBand pass filter300 MHz

Multiplexer

AnalogSignal

Processing

Demultiplexer

Low pass filter

ADC

ADC

ADC

ADC

Frombuttons

The BPM receivers are working at the third harmonic. This minimizes the risk of 100 MHz leakage from the transmitters.Resolution << 1µm

CONCLUSION• The 100 MHz 90 kW RF system has been in

operation since September 2004. The system is now running at 240 mA with two wigglers at 150 and 200A.

• Beam lifetime I*t=6000mAh with Landau cavity in operation.

• BPM system resolution <<1 µm.• The transmitter tubes must have high anode loss

capability when working without circulator. This is an disadvantage but a solution is presented.