Burkhard, P.

Gütlich, K.

Kowina, P.

Reichert, Thomas

GSI Repository

Cryogenic Tests of Ceramic Feedthroughs for SIS100 BPMT. Reichert1,2, P. Burkhard1, K. Gu¨tlich1, and P. Kowina11GSI, Darmstadt, Germany; 2Goethe Universita¨t Frankfurt, GermanyIntroductionDue to the cryogenic environment in which the BeamPosition Monitors (BPMs) will be used at SIS100 syn-chrotron special attention has to be turned to the BPMs’signal feed-throughs (FT) [1]. Present design considers ti-tanium based, N-Type FTs isolated with Al2O3 ceramicsand welded into CF-16 flange. In a temperature rangebetween room temperature and 4.2 K the requirementsfor the FTs are threefold: i) high mechanical stability,ii) vacuum-tightness even after many cold-warm cycles,iii) good and stable electrical connectivity. These fea-tures were tested in 10 cold-warm cycles in the temperaturerange given above.Methods and ResultsFig. 1 shows the test setup: Five N-type (FT) weremounted to a sixfold CF-16 crosspiece that was installed ina bath cryostat having a volume of 30 l. The free flange ofthe crosspiece was connected via a long stainless-steel pipeto a He leakage detector installed close to the cryostat. AllM4 bolts (A4-80 stainless-steel) used at the flanges werefastened with a final torque of 2.6 Nm. One pair of spa-tially opposing FTs was electrically connected inside thecrosspiece via a titanium rod equipped with spring con-tacts typically used in banana-connectors. This formed a50 Ω transmission line with an intended impedance mis-match in the crosspiece center. The electrical connectionbetween the two interconnected FTs and a Network Ana-lyzer (NWA) was done by semiflex Tensolite coaxial ca-bles. The quality of the electrical connectivity was mea-sured using Time Domain Reflectometry (TDR) based onthe analysis of the synthetic time domain signals measuredby means of NWA [2]. Temperature monitoring was done25Ω heater Tensolitesignal cableto leak detectorthermal shield(Cu- and PS-plates)crosspiece w. feedthroughsheating-wire(Nichrome)NWA port 1port 2E5071CAgilentFigure 1: Cryogenic test setup48505254565860626 8 10 12 14Impedance [Ω]Time [ns](1) : transition between        Tensolitemale to         FT female N-type(3) : diameter change         @ crosspiece center(2) : passage of Al2O3-        insulationT = 299 KT =  4.2 K(3)(2)(1)crosspiece-FT        unit  Tensolite cable       (port 1)  Tensolite cable       (port 2)  Figure 2: TDR signals at room and LHe temperatureby four resistive temperature sensors depicted in Fig. 1 byred boxes. The cryostat was equipped with a 25 Ω resis-tive heater for removing residual LN2 left over from pre-cooling. A Nichrome heating wire wound around the cross-piece was used to accelerate cold-warm cycling so that theaverage duration of a cycle could be reduced to less than2 h. He leak rate monitoring was performed during thewhole test. Since the crosspiece was immersed into LHeany leaks at the FT that could possibly occur should beimmediately registered in the leakage detector. TDR mea-surements were done first at room temperature and havebeen repeated after LHe was filled into the cryostat to cooldown the crosspiece to 4.2 K. Fig. 2 compares two TDRmeasurements made at 299 K and 4.2 K in one of the 10cold-warm cycles. The characteristic points (1), (2) and (3)on the plot correspond to the electrical connections withinthe crosspiece-FT unit. In the crosspiece-FT region bothTDR signals are highly congruent which proves that elec-trical connections between rod and FTs do not change withtemperature. Moreover, this connection is even better ifcompared to the left and right part of the plot, where thecryogenic cables’ passage between the outside and the in-side of the cryostat is strongly effected by the temperaturechanges. Thus, it can be stated that the solution proposedhere results in a stable and reproducible electrical connec-tivity under cryogenic conditions. Comparing Fig. 2 to themeasurements made in the remnant cycles, the pointwisedeviations of the impedance curves are below ±0.05 Ω inthe significant region of the crosspiece-FT unit. Further-more, within ten cold-warm cycles, the crosspiece-FT unitdid not exhibit any leaks maintaining a He leak rate in theorder of 5 × 10−10 mbar · l/s. However, a slight looseningtendency of about 11 % of the initial torque was measuredat the bolts used for flange mounting. The usage of foldablewashers might be necessary.References[1] P. Kowina et al., Proc. EPAC‘06, Edinbourgh, p.1022[2] see e.g. www.home.agilent.com, Application Note 1287-12FG-SIS100-03 GSI SCIENTIFIC REPORT 2013326 doi:10.15120/GR-2014-1-FG-SIS100-03

Cryogenic Tests of Ceramic Feedthroughs for SIS100 BPM

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Cryogenic Tests of Ceramic Feedthroughs for SIS100 BPM

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