j. teichert, a. büchner, h. büttig, f. gabriel, p. … 1 radiation source elbe mitglied der...

17.03.20051

Radiation Source ELBE

Mitglied der Leibniz-GemeinschaftJ. Teichert

Status of superconducting module developmentsuitable for cw operation: ELBE cryostats

J. Teichert, A. Büchner, H. Büttig, F. Gabriel, P. Michel, K. Möller, U. Lehnert, Ch. Schneider,

J. Stephan, A. Winter Forschungszentrum Rossendorf

Zentralabteilung Strahlungsquelle ELBEPF 510119, 01314 [email protected]



The radiation source ELBE

MeV Brems-strahlung 10-100 keV

Channeling

FEL 1: 3-22 µm

Neutrons

Positrons

FEL 2: 10-150 µm

KlystronsAcceleratorelectronics

FEL user labs

• First beam in April 2001• Nuclear physics experiments are running since January 2002• Channeling radiation since September 2003• FEL 1 since May 2004 • Second Cryomodule since February 2005

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ELBE radio-frequency electron accelerator

Accelerator parameters:40 MeV cw-operation2 modules, each 2 TESLA cavitiesrf frequency: 1.3 GHz10 MeV & 10 kW rf power per cavity average beam current: ≤ 1 mAbunch charge: ≤ 77 pCpulse frequency: 260, 26 … 0.01 MHzvariable pulse trains

74.0,1,250 =βmAkeV7 MeV @ 10 MV/m foroptimum beam capture

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ELBE cryomodule design

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ELBE cryomodule

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ELBE cryogenics

Helium plant 220 W @ 1.8 Kp control with cold compressors CC1, CC2

Cryostat pot heater

T1 T2 T3

CC1CC2

C1-2

VSC

1-3

cryostat

Coldbox

Byp

ass

1.8K 16 mbar

4K 1bar

14K 0.1 bar

293K

12

bar

Now: stable operation of the two cryomodules

Problems at beginning:- pressure instability- interference between

p and He level (valve) controlSolutions:

- increased He flow in CC via bypass,- level control with heater in modulesfeed-forward control from gradients

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ELBE tuning system

Tuning rangemechanical: ±0.37 mmfrequency: ± 116 kHz

Tuning resolutionmechanical: 3 nmfrequency: 1 Hz

Transfer156 nm/motor turn2.3 steps/nm

Maximum load: 3000 N

“slow” spindle/lever system due to cw fast Lorentz-force compensation not needed

Lorentz-force detuning: 50 Hz @ 7 MV/mcompensation “by hand” during gradient ramp up

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RF control

10 kW CPI VKL 7811 ST klystron for each cavity, in cw operation analog low-level rf control, phase & amplitude loop

separate for each cavity:- gradient- phase- power meas. values(tuning)

Safety systemGradient loop error:- detuned cavities- beam loading etc.

microphonicsopen loop: 0.97 deg rmsclosed loop: 0.02 deg rms

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ELBE rf power coupler

LN port

coldwindow

Cu antenna

contactsprings

overheated incoupler testswith 8 kW fullreflection

Coupler design for 10 kW cwusing the TTF conical insulator,T.Kimura/HEPL-Stanford & J.Stephan

three-stub waveguide tuner for BW adjustment

RT planar window in waveguideREXOLITHEposition at E-field waist

conical cold window at 70 Kceramics

Coupling is matched for 1 mAbeam current at 10 MV/m

BW = 114 HzQL= 1.2 x 107



ELBE cryomodule diagnostics

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RF control

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ELBE module - cavity properties

Idealkurve einfügen

cavity operation at ELBE: Gradient limit due to strong field emission

ELBE cavities vertical test at DESY before tank welding etc.:Q0 = 2 x 1010, Eacc = 15... 25 MV/m

TESLA cavities

Pdi

ss/ W

Eacc / MVm-1

Reason: welding, assembling, storage, couplers?

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ELBE module – energy drift

We observed an energy growth with time after switching ongradient set values and pick-up signals are constant

20 40 60 80 100 120 140 160 180 200 220 240 260

7,3

7,4

7,5

7,6

7,7

7,8

7,9

8,0

8,1

8,2

Energy drift of cavity RC01 after switch on

RC11 off RC11 on (8 MV/m)

beam

ene

rgy

/ MeV

time / min

0 50 100 150 200 250 300

950

1000

1050

1100

1150

1200

1250

1300

energy drift after rf on cavity RC01

slope: 1.1 W/min

rf po

wer

(for

war

d) /

Wtime / min

the source is in the module, it is not rf control,temperature increase with the same time scale,connected with cw operation of TESLA cavities at ELBE?

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ELBE cryomodule - summary

• ELBE cryomodules are suitable for cw-operation @ 10 MV/m & 1 mAmost of module parameters better/equal to design specificationscommon He pressure control with cold compressors,separate He level control (heater) in each module,analog phase and amplitude rf control for each cavity,sophisticated coupler/window diagnostics,

• Higher gradients:1. limit due to field emission in cavities, difficult to reach 20 MeV,

extended quality management for next module2. At ELBE: capacity limit of the cryogenic plant,

• Higher current (rf power):1 mA (10 kW) seems near to the limit of the rf power couplers,

• Energy drift:cw-operation causes 1 MeV energy drift within first hours,source is in module (temperature effect) , no rf control

17.03.200515



Acknowledgment

FZ Rossendorf:Module design and assembling:J. Stephan, R. Schlenk, B. Wustmann, A. Winter, M. Freitag, A. Noack, B. ReppeLL RF control: F.GabrielRF and couplers: H. Büttig, R. Schurig, A. BüchnerDiagnostics: D. Pröhl, F. Herbrand, R. Jainsch, J. Claussner, A. SchamlottCryogenic system: Ch. Schneider, Ch. Haberstroh, B. HartmannOperation: U. Lehnert, P. Michel, P. Evtoushenko, J. Voigtländer

DESY Hamburg (A. Matheisen ...), HEPL Stanford, ACCEL, TU Dresden

j. teichert, a. büchner, h. büttig, f. gabriel, p. … 1 radiation source elbe mitglied der...

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