Sievers - Overview of the latest SRF projects at the S-DALINAC

Overview of the latest SRF
projects at the S-DALINAC*

Sven Sievers

TU Darmstadt
Institut für Kernphysik SFB 634

*Supported by the DFG through SFB 634

Outline

• Overview of the S-DALINAC

• SRF at the S-DALINAC

• Vertical bath cryostat

• Latest measurements
• Piezo-Actor
• Oscillating Superleak Transducers

• Test in preparation
• RF power couplers

• Outlook

04. Oktober 2010 | TU Darmstadt | Institut für Kernphysik | Sven Sievers

Overview of the S-DALINAC

Design values: Max. energy: 130 MeV
Energy spread: ±10-4
Max. beam current: 60 µA
Duty cycle: cw

Overview of the S-DALINAC


SRF at the S-DALINAC

Material: Niob (RRR=300) Length: 1m
Frequency: 2.9975 GHz Eacc: 5 MV/m
Mode: TM010,π Q0: 3·109
Temperature: 2K Pdis: 4.2 W


Vertical bath cryostat

Diameter: 35 cm
Depth: 260 cm
Minimum required LHe-level: 150 cm
Maximum LHe-level: 190 cm

D=3
5 cm



Operation characteristics
• Cooldown 300 K → 4 K ~ 1.5 h

• Fill-up to maximum LHe level ~2h

• Pump down to 35 mbar / 2 K ~ 2.5 h

• Stand-by losses of cryostat <1W

Current limitations
• No pressure regulation
→ 35 mbar kept via cryostat heating

• Operation of vertical cryostat not possible while linac is at 2 K
→ Measurements limited to shut downs of the S-DALINAC


First measurements: Piezo Actor

Investigation of the stroke of a piezo-actor @ 2 K to
replace magnetostricitive elements of fine tuning system



Existing tuning system: Fine tuning of cavity with magnetostrictive elements



Required frequency shift:
1000 Hz

Resulting cavity deformation:
2 µm

Required stroke of fine tuner:
5 µm



Required stroke of fine tuner: 5 µm

Stroke of piezo-actor @ 300 K: 90 µm
Predicted stroke @ 4 K*: 22.5 µm

Measurement with simplified tuner set-up

Measured frequency shift @ 4 K in LHe: ~ 1100 Hz
Resulting stroke of piezo-actor: ~ 5.5 µm

Measured frequency shift @ 2 K in LHe: ~ 950 Hz
Resulting stroke of piezo-actor: ~ 4,75 µm

*B. Sahu, G. Chowdhury, S. Ghosh, D. Kanjilal, D. Mathuria, R. Mehta, A. Pandey, P. Patra, A. Rai and A. Roy: Use of Piezo Actuator
to Frequency and Phase Lock a Superconducting Quarter Wave Resonator, Proc. of the 24th Linear Accelerator Conference


First measurements: OSTs

Performance check of the prototypes of an
Oscillating Superleak Transducer (OST)
for quench localisation @ 2 K



OSTs shall be used for the
detection of quench positions
of superconducting cavities

The quench causes a 2nd sound
wave in the superfluid LHe that can
be detected by the OSTs

The location of the quench is
determined by triangulation



R – Moment of the heat pulse
1 – Response of the 1st OST after ~ 2 ms
2 – Response of the 2nd OST after ~ 4 ms

2 R 1 2

1

R

Test in preparation: RF power couplers

Characterisation of new power couplers for the injector upgrade



Planed injector upgrade

• Energy increase in the injector
section from 10 up to 14 MeV

• Increase in current from
60 μA to 150 – 250 μA



Actual power coupler: 500 W Qex = 3·106 - 1·1010


RF power couplers

Actual power coupler: 500 W Qex = 3·106 - 1·1010

Waveguide coupler: 2 kW Qex = 5·106

transition
beam
transfer

transition

Design: TEMF Fabrication: FZ Julich
M. Kunze, W. F. O. Müller

Outlook

• Construction of Quench-Detection-Array

• Development of optical inspection setup

• Further investigations of piezo-actors

• Design of new equipment for the vertical bath cryostat
(Bacholer/Master thesises):
• Measurement of Q-value via decay time
• Design and construction of T-Map-System


Thank you for your attention

Institut für Kernphysik, TU Darmstadt

S. Sievers, U. Bonnes, J. Conrad, R. Eichhorn, F. Hug, M. Konrad,
T. Kürzeder, N. Pietralla, A. Richter


Closed loop for liquid Helium


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