User's Manual SRD1000 System
Contents
1. Move the degauss coil slowly starting from about 4 5 cm above the Cryoperm shield downwards and Ta then upwards again see Figure 3 4 a b c d e The total sequence should take about 20 s Re peat the sequence at least one more time SRD1000 _ SRD1000 Do not forget to switch off the DCS 10 after the procedure The supply unit and coil may become a b d B warm after prolonged use This is a normal situa tion Do not cover the supply unit to prevent Figure 3 4 Degauss sequence Cryoperm overheating shield User s Manual SRD1000 System version 06 02 2006 HDL Leiden The Netherlands 3 3 Temperature and width of a refer ence point A reference point is observed by monitoring the output voltage V T of the MIDS 10 electronics as a function of the temperature 7 of the cryogenic sensor Figure 3 5 shows an example of the superconduc tive transition of an Irg2Rhog sample When the temperature is increased the state of the reference sample in the sensor gradually changes from the superconducting state corre sponding to a system output voltage V Vsc toa state of normal conducting with V Vyc In this manual reduced output voltages V rela tive to voltages in the superconducting state are used to present the data of the transitions with V V Vsc The reference point 7c is defined as the tempera ture when 52. At the control unit set the primary current switch 1 to on the filter switch 2 to slow and dis play switch 3 to output This should produce a voltage value at the output terminal 11 as is indicated on the test plug The value displayed on the front panel meter may deviate 1 LSB from this value To test the performance of the front panel meter set the primary current switch 1 to off and turn the offset control knob 4 fully clockwise When the display switch 3 is set to output the meter should read 000 offset it should read 1000 deviation it should read 1000 all indications are 1 LSB An oscilloscope connected to the signal monitor terminal 9 enables the observation of the ampli fied AC signal of the sensor or test plug The signal should be sinusoidal with a frequency of about 977 Hz and its amplitude varies some what due to noise of the preamplifier see Figure 2 14 The sync output terminal 8 provides a square wave Signal to trigger the oscilloscope Figure 2 15 shows a set up for testing the effec tive value of the AC primary current Connect the SRD terminal 1 of the preamplifier to the test box using the black Lemo OB cable supplied with the ACS 10 unit One can measure the current at the primary coil terminal P of the test box with a true RMS type current meter The meter preferably should be powered by a battery and not by the m
3. 2 3 4 Connections from the sensor to the top part of the cryostat For optimal results use 3 separate cables in the cryostat to connect the primary secondary and compensation coils of the sensor Preferably one Should use a shielded twisted pair cable for each connection In the section of the cryostat at tem peratures below 9 K this should preferably be su perconductive cable Ensure proper thermal an choring at various suitable points in the set up Small diameter about 1 mm superconductive or normal conductive shielded twisted pair cable made by Habia is obtainable through HDL Figure 2 4 Similar types are available from other com panies like Lake Shore The DC resistance of each lead of a connection to the sensor should be less than about 50 2 when the cryostat is at cryogenic temperatures 2 3 5 Connections between the cryostat and the electronics The electronics are supplied with 2 black Shielded cables Figure 2 5 for the room tem perature connections to the cryostat 1 mutual inductance cable for connecting the MIDS 10 preamplifier 2 compensation coil cable for connecting the ACS 10 current source Each cable is about 0 75 m long and contains 3 Shielded twisted pair conductors One side is terminated with a 5 way Lemo OB free plug the connector at the other side of the cable has to be selected by the user to fit the connector at the top part of the cryostat Figure 2 6 gives the pin layo
4. fast filter time constant of the system output 11 rear panel is set to slow T 62 5 s or fast T 10 s the normal operation mode is slow The noise level of the signal at the system output at slow is about 0 4 mVpp at fast this is about 0 9 mVpp display output front panel meter shows the voltage Vour mV at the sys switch tem output 11 blue output LED is on offset front panel meter shows the set point of the offset voltage Vorr mV blue output LED is off deviation front panel meter shows the voltage Vper Vout Vorr a ae ne aa at the deviation output 10 blue output LED is off 4 offset control changes the level of the offset voltage Vopr 0 1000 mV _ the level of the offset voltage Vorr 0 1000 mV power switch on off power of the MIDS 10 main unit and preamplifier unit is switched on or off as is indicated by the blue power LED s 9 default setting for normal operation User s Manual SRD1000 System version 06 02 2006 HDL Leiden The Netherlands 23 B3 Control unit rear panel ower in round signal rear phace 4 fe p 3 monitor phase mutual inductance detection system e mail HOLinfo esdall ni serial no MCU web site weaw ssdallnl hdleiden Description Function power in termi power input 8 V 50 mA max 50 60 Hz pin 1 3 or pin 1 2 de nal 3 way male _ pending on the regional voltage of the mains supply only use the socket Bin
5. si i16 4 Residual magnetic field test at low temperatures 18 4 1 Tc shifts due to magnetic fields 18 4 2 Test procedure for residual magnetic fields _ 18 4 2 1 Preparing the ACS 10 19 4 2 2 Tc versus Ipc Measurements __19 Annex A SRD1000 cryogenic sensor 21 A1 The dimensions and connections of the sensor Al Annex B MIDS 10 mutual inductance detection system 22 B1 Features o Y 22 B2 Control unit front panel _ S O 2 B3 Control unit rear panel __ 23 B4 Mains adapter ee 23 B5 Preamplifier unit _ ee _ 24 B6 Test box 24 B7 Connections cable arrangements 25 Annex C DCS 10 demagnetisation coil supply degauss coil 26 C1 Features 26 C2 Front rear view __ S _ 26 User s Manual SRD1000 System version 06 02 2006 HDL Leiden The Netherlands Annex D ACS 10 adjustable current source D1 Features D2 Front rear bottom view i Annex E Symbols and definitions User s Manual SRD1000 System version 06 02 2006 HDL Leiden The Netherlands 27 27 27 28 1 Introduction to the SRD1000 system The SRD1000 system comprises a cryogenic sen sor and related measurement equipment to es tablish a series of reference points for thermome try between approximately 15 mK and 1 2 K The points are realised by observing supercon ductive transitions of a set of samples of refer ence materials using a mutual inductance detec tion technique An overview of the main system components 1
6. Leiden The Netherlands 4 2 1 Preparing the ACS 10 Before using the ACS 10 see Figure 4 2 insert a 9V PP3 battery in the bottom compartment When the on off switch 4 is operated the blue power LED 3 should go on and off if not the battery voltage is too low Connect a DC current meter e g a digital multi meter at the BNC output 6 In order to activate this output set the monitor output switch 7 in the on position To test for the Z component of the residual field connect the compensation coil input C of the cryogenic sensor to the current output 5 at the rear of the ACS 10 see Figure 4 3 a To test for X Y components connect the input marked ACS 10 at the preamplifier unit to the current output 5 at the rear of the ACS 10 using the black cable supplied with the ACS 10 see Figure 4 3 b Remark One can check the performance of the ACS 10 by inserting the test plug see Section 2 5 in output 5 Next switch the unit on and turn knob 2 fully clockwise The current meter Should read 2 mA or 2 MA depending on the position of switch 1 Note that the indication of the ten turn dial has to be multiplied by a factor 2 to find the setting of the output current so for example 500 gives an output of 1 mA 4 2 2 Tc versus I pc measurements To determine the residual field component one has to measure the shift of Tc as a function of the ACS 10 current Ipc in the sensor The A
7. sensor thermometers thermal plate a Make sure that the thermal resistance of the pressed contact between the mounting adapter of Figure 3 1 Set up for thermometry the sensor and the thermal plate is as low as pos with the SRD1000 cryogenic sensor sible Especially at temperatures below 50 mK the heat flow from to the Cryoperm shield of the sensor may otherwise lead to significant time dependent temperature differences between the sensor and the thermal plate and thus to errors in the realisation of the reference points Always clean the contacting surfaces with acetone and alcohol before the joint is made If the thermal plate is not gold plated first remove any oxide layer by gently polishing the contact area 3 2 Degaussing the Cryoperm magnetic shield The strength of ambient magnetic fields at the mounting position of the sensor should be in the order of 100 uT or less the earth magnetic field In order to obtain an optimal shielding perform ance at low temperatures the Cryoperm shield should be degaussed at room temperature using the DCS 10 unit and the degauss coil Figure Figure 3 3 Front and rear view of the 3 2 prior to each low temperature run DCS 10 Proceed by connecting the degauss coil to the DCS 10 supply unit terminal 1 Figure 3 3 7 i Next connect the DCS 10 to the mains supply ws a cable 5 and switch on the unit switch 4 the blue LED 3 is on a bout 5 cm
8. the cryogenic sensor see Figure 2 12 for a typical example It varies from about 550 mV at a tem perature T lt 15 mK to about 850 mV atT gt 1 2 K The ten steps of the staircase pattern are at the ten superconductive transitions of the reference samples The height of a transition step varies between about 5 mV to 100 mV depending on the sample The noise present in the signal is about 0 4 mV peak to peak when the filter of the control unit is set to slow To record the signal with a computer use for ex ample a DVM with a resolution of at least 0 1 mV at a full range of 2 V equipped with a computer interface Please be aware of the influence like heating ef fects that such digital meters and interfaces may produce on low temperature set ups due to the generation of RF energy Whenever possible apply an optical interface be tween the computer and the measuring equip ment to reduce such interference problems 12 0 850 0 800 0 750 0 700 Output voltage V 0 650 0 600 0 550 10 100 1000 Temperature mK Figure 2 12 Output voltage control unit as a function of the temperature of the cryogenic sensor User s Manual SRD1000 System version 06 02 2006 HDL Leiden The Netherlands 2 4 3 Testing the MIDS 10 system In order to test the basic transfer function of MIDS 10 electronics one can connect the test plug to the preamplifier instead of the cryogenic sensor Figure 2 13
9. Tc shifts due to magnetic fields Table 4 1 Shift dTc dB of the reference The Tc value of a reference sample is reduced by mat rials the presence of a magnetic field Tabel 4 1 pre sents estimated values for the shift d c dB of 4 nee eee each type of sample material mK mK pT Experimental work has shown that the magnetic shielding of the sensor sufficiently reduces com mon ambient magnetic fields in a cryostat once 3 the shield is properly degaussed at room tem 4 perature before the start of a low temperature 5 Ir 98 0 09 3 experiment see Section 3 6 P PEENI ee ee 7 owever in order to reproduce the reference points with the highest accuracy one should ver ee 9 2n 850 0 06 B ify that residual fields in the sensor are suffi 10 Ali i80 0 06 1 ciently low 1 J R Schooley et al Temperature Its Control and Measurement in Science and Industry 5 4 2 Test procedure for residual mag p 251 260 1982 netic fields 2 Estimated value based on measurements on Iro2Rhog Samples 3 Figure 4 1 shows the shield and coil configura aad ii al ee on ie o i reference materials Kamerlingh On tions of the cryogenic sensor nes Laboratorium Leiden 2005 An electrical current running in the detector coils green squares will generate a magnetic field in the X Y plane horizontal component A current in the compensation coil red cylinder will result in a magne
10. mains supply and to the control unit terminal 6 11 Figure 2 9a MIDS 10 control unit front panel Figure 2 9b MIDS 10 control unit rear panel Figure 2 10 Grey ca ble with 8 way Lemo 1B connector Figure 2 11 MIDS 10 mains adapter User s Manual SRD1000 System version 06 02 2006 HDL Leiden The Netherlands Switch on the power switch 5 of the control unit the blue power LED s at both the control and preamplifier unit are on Set the primary current switch 1 to off the filter switch 2 to fast and display switch 3 to output blue display LED is on The front panel meter should settle down at about 000 When the cryogenic sensor is at temperatures be low 9 5 K its circuitry is superconducting and one can switch the primary current switch 1 to on The front panel meter should settle at a value be tween 500 and 1000 which equals the system output voltage in mV If the display shows a negative sign reverse the phase switch 13 at the rear of the MIDS 10 unit Set the filter switch 2 to slow for normal op eration at a low noise level the time constant of the system output voltage is about 62 5 s 2 4 2 Output signal versus sensor tempera ture The output signal of the system is a DC voltage at the output terminal 11 located at the rear panel of the control unit The voltage level depends on the temperature of
11. shielding performance Do not try to open the sensor by removing the shield as you may dam age the internal circuitry Do not immerse the sensor directly and quickly from room tempera ture and atmospheric conditions into liquid Nb Always cool and warm it gradually and in a pro tected atmosphere like in the IVC of a dilution refrigerator This will avoid severe internal stress to the reference samples and the detection cir cuitry The electrical connections 5 are not sensitive to electrostatic discharge The resistance of the cir cuitry may be measured using a digital multi meter at ranges equal and below 20 MQ Figure 2 1 The SRD1000 cryogenic sensor 2 2 Mechanical and thermal connections The mounting adapter 2 made of gold plated OFHC copper is attached to a thermal plate in the experimental region of a dilution refrigerator using a stainless steel M3 bolt and washer Prior to mounting remove any oxidation on the ther mal plate when its surface is not gold plated and SRD1000 coil system clean the contacting surfaces thoroughly with Fad acetone and alcohol to reduce the thermal resis compensation ry 4a coil n h 1 in it 4 tance of the joint detector coils with riot reference samples In most cases the filter 3 and the three shielded leads 4 are mechanically and electrically fixed at the same thermal plate as to which the sensor is being attached The thermal conduction of the leads is low at cr
12. 0 of the transition is completed which is at V Tc 0 5 Vne Vsc Relative to the Superconducting state this it at Vce V Tc ViTc Vse 0 5 Vue Vsc For many transitions the most temperature sensitive part occurs when the signal level is be tween approximately 10 and 90 of the inter val Vuc Vsc The corresponding temperature in terval is defined as the width Wc of the transition Wc T Voo T Vio with Voo 0 9 Vyc and Vio 0 1 Vuic The transition of Figure 3 5 shows a width Wc of 0 24 mK and provides a reference point at Tc 65 34 mK with Vc 21 3 mV Annex E gives an overview of the symbols and definitions to present the characteristics of a tran sition 3 4 Staircase patterned temperature sweep In order to observe a transition preferably a staircase pattern is used to increase the tempera ture of the thermal plate see Figure 3 6 This means that each time temperature T is in creased with a step AT next during a stabilisa tion time At the temperature is stabilised at T AT before a next AT step is made The interval At has to be sufficiently long to es tablish thermal equilibrium between all relevant elements at the thermal plate before the data point at T AT is collected 16 V 42 5 mV V 38 3 mV 30 Vi 21 3mV 20 V mV W 0 24 mK 10 Vo 4 3 mV 0 63 64 65 66 67 Tao mk Figure 3 5 Superconductive transition of an Iro2RhN
13. 06 HDL Leiden The Netherlands Method 2 is more time consuming but often eas ier to perform as the demands for the tempera ture stabilisation are easier to meet The goal for each method is to acquire transition data to determine the various Tc values for sev eral settings of Ipc For example start by setting Ipc at O pA and find Tc 0 UA To next set Ipc at 100 UA to find T100 Switch to 100 UA for T io9 next to 200 pA 200 WA etc Analyse the collected data by making a graph of the observed Tc and Ipc values like in Figure 4 5 Find the intersection point of the blue and red lines corresponding to the maximum Tc value Tmax and the current value Ipes One can derive the residual magnetic field Bres near the tested sample by multiplying the value Ires by the material dependent coil constant that can be found in Table 4 2 The coil constants were derived both by calcula tions and experiments Experimental work on the value of the coil constants is still in progress and future results shall be reported to the user Example Figure 4 6 shows an example of a measurement of the shift ATc of an AUAlz sample versus the current Ipc in the compensation coil with ATc Tc Ipc maximum Tc value The po sition of the measured data points marked deviates from the blue and red straight lines for Ipc lt 300 uA The intersection point of the lines is assumed to indicate the Tc value of the sample in zero magne
14. 4 1 Annex B5 8 way grey cable oscilloscope Section 2 4 3 Annex B7 MIDS 10 control unit i Section 2 4 1 Annex B2 3 MIDS 10 O s TOOR O Q mutual inductance detection system MI DS 10 mains adapter Section 2 4 1 Annex B4 digital voltmeter Section 2 4 2 computer optical interface DCS 10 ma gnetisation coil supply User s Manual SRD1000 System version 06 02 2006 HDL Leiden The Netherlands 3 Realisation of the reference points 3 1 Experimental set up mixing chamber id Figure 3 1 shows a set up typical for the realisa tion of the reference points of the SRD1000 cryo genic sensor heat link thermal shield The sensor is attached to a thermal plate to gether with some thermometers The plate is connected to the mixing chamber of a dilution re frigerator with a heat link A heater is attached to the link for temperature regulation In order to reduce thermal gradients within the plate the heater is not positioned at the plate itself One of ea Mas the thermometers is used to provide a PID feedback loop to control the heater power A punches thermal shield surrounding the set up reduces adapter gradients produced for example by thermal ra diation or residual exchange gas
15. HI GHTECH H D L DEVELOPMENT LEI DEN User s Manual SRD1000 System supports precision thermometry on the PLTS 2000 User s Manual SRD1000 System version 06 02 2006 HDL Leiden The Netherlands Contents 3 1 Introduction to the SRD1000 system 5 2 Installation system components 8 2 1 Handling the cryogenic sensor _ S O _ 8 2 2 Mechanical and thermal connections 8 2 3 Electrical connections _8 2 3 1 Signal connections 8B 2 3 2 Signal parameters 9 2 3 3 Requirements for electro magnetic shielding and filtering in the cryostat ___9 2 3 4 Connections from the sensor to the top part of the cryostat 10 2 3 5 Connections between the cryostat and the electronics _ 10 2 3 6 Testing the connections _ S PeR ni 2 4 Measuring the signals iil 2 4 1 Connecting the electronics 11 2 4 2 Output signal versus sensor temperature 12 2 4 3 Testing the MIDS 10 system _ 13 2 5 System map ee 14 3 Realisation of the reference points 15 3 1 Experimental set up COE E 3 2 Degaussing the Cryoperm magnetic shield _ _ _ ALS 3 3 Temperature and width of a reference point l6 3 4 Staircase patterned temperature sweep ____
16. SRD1000 cryogenic sensor The sensor contains a mutual inductance detector array of integrated planar micro coils to which Samples of variouS Superconductive reference materials are attached The detector array and the samples are thermally connected to a gold plated mounting plate at the bottom of the sen sor The temperatures of the superconductive transi tion of the materials depend on the presence of a magnetic field To reduce ambient magnetic fields the sensor is equipped with a cylindrical Cryoperm niobium shield A compensation coil inside the shield surrounding the detector assembly allows for additional test ing and suppression of magnetic fields in the sen sor The signal leads of the sensor are shielded and equipped with a filter to suppress RF interference The user has to attach the sensor to a thermal plate inside the low temperature area of a cryo genic set up and connect it to the room tempera ture MIDS 10 electronics via 3 pairs of shielded twisted conductors Annex A provides information on the dimensions and the electrical connections of the sensor 2 MIDS 10 mutual inductance measure ment system The measurement system drives the cryogenic sensor and provides an output voltage propor tional to the sensor signal to detect the supercon ductive transitions The system comprises the following components a control unit a preamplifier unit to drive current to the pri mary coil in
17. ains sup ply The effective value of the current should be 50 pA 1 977 Hz 13 Figure 2 13 The test plug connected to the preamplifier the control unit displays the value as indicated on the plug Figure 2 14 Sensor and sync signal displayed on an oscilloscope re S preamplifier unit test box E e O F iz control unit true RMS type current meter Figure 2 15 Testing the primary current User s Manual SRD1000 System version 06 02 2006 HDL Leiden The Netherlands 2 5 System map test box Section 2 3 6 Annex B6 xoqusea OT Xa1 ACS 10 Section 4 2 1 Annex D ACS 10 ree Pee 7 oe test plug Section 2 4 3 c LEELEE EEE ees o gt 5 way black cables Annex B7 cryostat connector Section 2 3 5 Annex B7 cryostat system normal conductive shielded twisted pairs thermal anchoring connector T gt 9 K level T lt 9 K level superconductive shielded twisted pairs Section 2 3 4 thermal anchoring cryogenic sensor Section 2 3 Annex A ISRD1000 EMI filter thermal plate 14 mK lt T lt 1 2 K DCS 10 Section 3 2 Annex C 14 resistance meter Section 2 3 6 current meter Section 4 2 1 MI DS 10 preamplifier unit Section 2
18. ble are indicated The mains adapter Pin 1 3 7 3 V input 230 V 50 Hz 7 VA Pin 2 3 8 3 V input 230 V 50 Hz 2 VA Pin 1 2 7 8 V input 115 V 60 Hz 7 VA User s Manual SRD1000 System version 06 02 2006 HDL Leiden The Netherlands 24 B5 Preamplifier unit Description Function sensor terminal 5 to connect the black cable from the cryostat connection to the way Lemo OB fe sensor male socket control unit termi to connect the 5 m grey cable leading to the control unit nal 8 way Lemo 1B female socket power LED indicates the power status of the preamplifier when connected to the main unit the preamplifier unit is switched on off by switch 5 at the control unit ACS 10 input ter refer to Section 4 2 this input is used to connect the black cable minal 5 way Lemo leading to the ACS 10 current source for analysing X Y magnetic OB female socket field components in the sensor 4 mm ground terminal to ground the preamplifier unit grounding is not required socket in most cases B6 Test box Description function input terminal 5 way Lemo OB for the black sensor cable from the cryostat in order to test the electrical connections to the sensor BNC connection to the primary coil section of the SRD connector BNC shield gt Lemo pin 5 I BNC centre pin gt Lemo pin 3 I connecting a resistance meter allows the checking of the primary coil conn
19. der mains adapter that is supplied for powering the MIDS 10 system to type 711 avoid any damage to the electronics 7 ground 4 mm terminal to ground the main unit grounding is not required in most socket cases sync output AC square wave signal 1 Vpp f 976 5 Hz to synchronise an oscil BNC loscope while monitoring the sensor signal 9 signal monitor AC amplified secondary voltage of the sensor f 976 5 Hz to be output BNC monitored on a oscilloscope for diagnoses purposes deviation output DC deviation voltage Vpev Vout Vorr to monitor small changes in BNC the system output voltage 11 relative to the set point of the offset voltage 4 system output DC output Voy 0 1000 mV proportional to the secondary voltage BNC of the sensor preamp terminal to connect the 5m grey cable leading to the preamplifier unit 8 way Lemo 1B female socket phase switch to change the phase of the sensor signal by 180 when the front panel meter shows a negative sign for normal operation select a set ting that will result in a positive sign on the meter note that as Vorr is a positive voltage only a positive Voyr can be fully compensated by Vorr at the deviation output B4 Mains adapter Power supply connection 3 way female socket Binder type 712 nr 99 0406 00 03 Pin lay out front view of the male panel socket or solder contact view of the female cable socket the lead colour codes of the Supply ca
20. ections of the sensor BNC connection to the secondary coil section of the SRD connector BNC shield gt Lemo pin 4 V BNC centre pin gt Lemo pin 2 V connecting a resistance meter allows the checking of the secondary coil connections of the sensor User s Manual SRD1000 System version 06 02 2006 HDL Leiden The Netherlands 25 B7 Connections and cable arrangements Pin layout of the 5 way Lemo OB connector and the composition of the black connecting ca bles Q 4 3 Contact Lead colour Mutual inductance Compensation connection coil connection Front view of the male free plug or rear sol yellow green ground shield ground shield der contact view of the l i white secondary coil V female chassis socket the direction of the pin i Pin layout of the 8 way Lemo 1B connector and the composition of the grey cable between preamplifier and control unit Lead colour Connection blue ground chassis socket or solder con 5 V supply tact view of the male free plug the yellow line indi ground spare cates the direction of the pin amplified sensor voltage number count 7 amplified sensor voltage User s Manual SRD1000 System version 06 02 2006 HDL Leiden The Netherlands Annex C DCS 10 demagnetisation coil supply degauss coil 26 C1 Features tool for degaussing the Cryoperm shielding of the sensor to optimise its magnetic prop erties s
21. ion certificate for more information User s Manual SRD1000 System version 06 02 2006 HDL Leiden The Netherlands HDL DEVELOPMENT User s Manual SRD1000 System
22. its outer dimensions Table A1 Sensor signal connections with general values for the electrical resistance Connection type Function Colour code R 300 K R 77K R lt 9 K 1 P primary coil I red white 180 000 Q 90 000 Q Q 2 S secondary coil S secondary coil coil V Ve V blue white blue white white 700 000 2 700 000 Q 000 Q 350 000 Q 000 Q User s Manual SRD1000 System version 06 02 2006 HDL Leiden The Netherlands Annex B MIDS 10 mutual inductance detection system B1 Features detection electronics to establish the tempera ture reference points of the cryogenic sensor plug and play no adjustments are required for the entire temperature range of the sensor primary current 50 pA 976 5 Hz system voltage output 0 1000 MVpc propor tional to the sensor signal temperature coefficient of the parameters of the electronics lt 50 ppm C design ensures minimal RF heating in ultra low temperature experiments B2 Control unit front panel primary filter n MIDS 10 current Be big mutual inductance detection system Description Position Function primary cur on off primary current 50 HA 976 5 Hz is switched on or off rent switch the off position may be used to diagnose heating effects of the sensor or to monitor possible interference at the system output filter switch slow
23. m temperature the resistance between the primary and secondary circuitry should be higher than a few MQ This also applies for the resis tance between the circuitries and the sensor housing 2 3 2 Signal parameters The signal parameters of the sensor are 1 primary current 50 pA 976 5 Hz produc ing a field of less than 0 4 uT near the refer ence samples 2 secondary voltage 2 nV 2 uV depending on the temperature of the sensor 3 compensation coil current O 2 mA pro ducing a field of about 0 5 uT near the samples 2 3 3 Requirements for electro magnetic shielding and filtering in the cryostat The amplitude of the AC field produced by the sensor detection circuitry is negligible outside the sensor shielding 100 nT The SRD1000 meas urement electronics was designed for use in ultra low temperature set ups and have proved not to cause RF heating or other interference in cryo genic experiments The sensor is equipped with a filter to reduce RF energy penetrating the sensor housing Additional filtering of sensor signal leads in the cryostat may lead to phase shifts and distortions while measur ing the transitions of the device However the effects of small capacitors lt 0 2 nF and ferrite chokes are negligible For specific cases please contact HDL Figure 2 3 The P S and C connectors User s Manual SRD1000 System version 06 02 2006 HDL Leiden The Netherlands
24. og sample 67 0 66 5 65 5 Va m K 65 0 64 5 64 0 0 100 200 300 400 500 time minutes Figure 3 6 Temperature sweep following a Staircase pattern User s Manual SRD1000 System version 06 02 2006 HDL Leiden The Netherlands In order to reproduce a transition with sufficient resolution at least 5 data points are to be meas ured along the most temperature sensitive part of the transition This means that step AT should be smaller than Wc 5 It also means that the stability of the temperature regulation during the sweep should be significantly better than Wc 5 Remark Figure 3 6 shows the staircase pattern of the temperature sweep between about 64 mK and 67 mK that was used during a calibration run to record the transition of Figure 3 5 The size of each AT step of the staircase is about 60 uK and the period At after a step is about 10 minutes Depending on the thermal characteristics of a set up and the desired accuracy level of the repro duction of Tc different settings for AT and At might be used User s Manual SRD1000 System version 06 02 2006 HDL Leiden The Netherlands 17 4 Residual magnetic field test at low temperatures 4 1
25. put of the sensor and amplify the voltage of the secondary coil output a mains adapter for powering the MIDS 10 User s Manual SRD1000 System version 06 02 2006 HDL Leiden The Netherlands a test plug to verify the functioning of the pre amplifier control unit a cable grey 5 m 8 way Lemo 1B connectors to connect the preamplifier with the control unit a cable black 0 75 m 5 way Lemo 0B con nector to connect the preamplifier with the cry ostat connector a test unit TBX 10 which converts Lemo to BNC and thus allows easy testing of the sensor connections Annex B gives additional information on the MIDS 010 system explaining the controls and terminals on the front and rear panels and the pin layout of the cable connections 3 Calibration certificate aa aa wm A calibrated cryogenic sensor and MIDS 10 sys P tem is supplied with a PTB certificate stating the _ _ a temperatures of the reference points Annex E lists the symbols and definitions that are used to present the characteristics of the transi ieee tions ma 4 DCS 10 degauss tools The DCS 10 supply unit with degauss coil enables the demagnetisation of the Cryoperm magnetic shielding of the cryogenic sensor at room tem perature prior to a low temperature run Annex C presents additional information on the DCS 10 describing the items on the front and rear panels 5 ACS 10 cu
26. r than during normal operation Consequently the super conductive transitions are shifted to lower tem peratures The connections can be verified by checking the resistance values of the coils at the Lemo OB s connectors outside the cryostat The TBX 10 test box Figure 2 7 facilitates these checks by converting the Lemo OB connections to BNC terminals clearly marked with primary coil P and secondary coil S 2 4 Measuring the signals 2 4 1 Connecting the electronics The MIDS 10 system is designed for use at room temperature in a laboratory environment Refer to Annex B for more information regarding the system components Position the MIDS 10 preamplifier unit Figure 2 8 near the top of the cryostat and connect the cryogenic sensor to the preamplifier unit using the black interconnecting cable see section 2 3 Ensure that the preamplifier is not too close to a source of electro magnetic interference such as a mains transformer of another instrument Position the MIDS 10 control unit Figure 2 9 at a convenient position to monitor the SRD1000 Signal Connect the preamplifier terminal 2 to the control unit terminal 12 using the 5 m grey cable Figure 2 10 Ensure that the 8 way Lemo 1B connectors at both ends of the grey cable are firmly plugged in all the way a clicking sound is heard when the connector snaps into its mechani cal restraint Connect the mains adapter Figure 2 11 to the
27. rrent source The ACS 10 adjustable current source is used to test for residual magnetic fields in the sensor at cryogenic temperatures The ACS 10 is supplied with a cable black 0 75 m 5 way Lemo OB connector to connect the unit to the compensa tion coil in the sensor to reduce the Z component of a residual magnetic field a cable black 0 75 m 5 way Lemo OB connec tors to connect the unit to the preamplifier to reduce the X Y components of a residual mag netic field User s Manual SRD1000 System version 06 02 2006 HDL Leiden The Netherlands 9 V PP3 alkaline battery to power the current source Annex D gives additional information on the ACS 10 describing the items on the front and rear panels User s Manual SRD1000 System version 06 02 2006 HDL Leiden The Netherlands 2 Installation system components This chapter provides an overview of the installa tion of the system components Please refer to Section 2 5 for a system map The Annexes A to D provide details on the features of the various components Please e mail HDL if you experience any problems during the installation of the SRD1000 system 2 1 Handling the cryogenic sensor Figure 2 1 shows the SRD1000 cryogenic sensor The outer shield 1 of the cryogenic sensor is made of annealed Cryoperm covered with a layer of copper foil for thermal conduction Avoid me chanical stress to this shield as this may reduce its
28. tery User s Manual SRD1000 System version 06 02 2006 HDL Leiden The Netherlands Annex E Symbols and definitions Table El provides an overview of the symbols and definitions that are used in this manual to present the characteristics of a superconductive transition Table E1 Symbols and definitions to characterise a superconductive transition Symbol Definition T2000 Too Temperature along the PLTS 2000 and ITS 90 scales respectively T U To U T2000 90 Reference or transition temperature Tc T Vc O Expanded uncertainty of the determination of the transition temperature Expanded uncertainty of the corresponding temperature scale realisation Output voltage MIDS 10 measurement electronics Vsc Output voltage when sample is sufficiently in the superconducting state v Output voltage relative to superconducting state V V Vse Output voltage relative to superconducting state V V Vsc ro Relative voltage after completing 10 of the total variation Vne Vsc x Relative voltage after completing 50 of the total variation Vne Vsc c oO Relative voltage after completing 90 of the total variation Vyc Vsc Output voltage when sample is sufficiently in a normal conducting state gt O Relative voltage Vyc Vsc which equals the step height of the transition Width of the transition T Voo T Vio i t please refer to a PTB calibrat
29. tic field The shift OT of 39 uK be tween this value and the top of the set of date points is supposed to be caused by the AC detec tion field near the sample which has an ampli tude of about 0 3 uT The Ipcvalue at the inter section point of the lines is close to zero which indicates that the residual DC magnetic field near the sample is negligible 20 awer faes MAX RES S AUTI T J 0 uA a r 100 uA T 100 nA y 100 100 200 lso Al 200 100 0 Figure 4 5 Example of Tc values as a function of applied current Ipc Table 4 2 Coil constants cryogenic sensor W Ir 6 10 2610 AuInz Coil constant Coil constant f ee ae uT pA uT pA w Be Ir Cd Zn OE 1 25 10 Auna cd 610 2 910 Zn 67 39 uK AT mK dT di 0 3uK pA 20 i 800 600 400 200 0 200 400 600 800 ho nA Figure 4 6 Shift ATc of an AuAl sample versus Ipc in the compensation coil measurements by the PTB institute User s Manual SRD1000 System version 06 02 2006 HDL Leiden The Netherlands Annex A SRD1000 cryogenic sensor 21 A1 Dimensions and connections of the SRD1000 cryogenic sensor Cryoperm shield with copper foil internal niobium shield compensation coil coil system with reference samples 63 mm I a a a a a 8 mm gold plated OFHC copper mounting adapter Figure A1 The sensor and
30. tic field in the Z direction vertical component Cryoperm cylinder shield Niobium shield The ACS 10 current source is a tool which allows an adjustable DC current to run e ther in the de tector coils Superimposed on the AC primary cur rent to analyse the horizontal X Y component or in the compensation coil to analyse the vertical Z component Please note that the ACS 10 does not provide for testing a combination of the hori zontal and vertical components at the same time Compensation coil SRD copper body SRD detector coil on chip I detector coil Experimental work proved that in most cases due to the geometry of the shielding the X Y components are significantly smaller than the Z component Thus analysing only the Z component will generally suffice for the residual field test i compensation coil Figure 4 1 Shield and field configurations By varying the strength and the sign of the cur of the cryogenic sensor rent while operating the cryogenics sensor and observing a transition one can find a value for the current at which a residual magnetic field near the samples is reduced or compensated Please note that connecting the ACS 10 current source to the sensor circuitry should only be done for an occasional field test For standard opera tion to reproduce the reference points it is ad vised to disconnect the ACS 10 User s Manual SRD1000 System version 06 02 2006 HDL
31. ty level Description function polarity switch to change the sign of the output current ten turn control to set the level of the DC output current between 0 2000 pA note that the setting of the dial needs to be multiplied by a factor 2 to find the value of the output current so for example 500 equals a current output of 1000 HA power LED is on indicates that the power is switched on and that the battery voltage is OK Replace the internal battery in the bottom compartment 8 if the LED is off when the power switch 7 is on Operating the ACS 10 with low battery voltages may result in unstable currents Use 9 V PP3 alkaline type batteries only switch on off for power and output current current output terminal 5 way Lemo OB to drive the sensor compensation coil or de tector coils refer to Section 4 2 monitor output BNC to connect an external current meter to monitor the output cur rent 0 2000 UA the meter is connected in series with the current flow when the meter is not connected switch 7 should be set to the off position 7 monitor output on of switch to shunt the monitor output 6 and to disconnect the BNC terminal from the current circuitry 8 battery compartment at the bottom of the unit for one 9 V PP3 alkaline type battery battery compartment at the bottom battery compartment at the bottom of the unit for one 9 V PP3 alkaline type battery the unit for one 9 V PP3 alkaline type bat
32. uAl transition is well suited for these meas urements The transition at about 145 mK is lo cated in a temperature region where most dilu tion refrigerators work well and where tempera ture control is often easy The transition is also Smooth and narrow and the midpoint is easily determined Two methods are possible each requiring differ ent skills from the operator 1 stabilise the temperature to reach the mid point of the transition apply a current Ipc and ad just the temperature of the thermal plate so that the midpoint is indicated again then go for the next current setting adjust the temperature etc 2 make various temperature sweeps staircase patterned like in Figure 3 6 through the mid point each time for a different current setting Ipc Figure 4 4 shows an example for each Ipc setting a Tc value is found at V Ve 19 a adjustable DC current source polanty level preamp MIDS 10 preamp control unit control unit Figure 4 3 Connecting the ACS 10 see the text I 0 0 mA T 142 98 mK 0 5 mA T 142 87 mK I 1 0 mA T 142 72 mK 2 0 mA T 142 44 mK 510 V mV 500 490 480 142 0 142 5 143 0 143 5 T mK Figure 4 4 Example of an AuAl gt transition observed for various currents settings User s Manual SRD1000 System version 06 02 20
33. upply provides 1 7 A 50 60 Hz to drive the degauss coil input 230 240 V 50 Hz model a or 115 V 50 60 Hz model b max 10 W C2 Front rear view DCS 1 0 demagnetisation coil supply output fuse wr Function AC current output to connect the degauss coil 5 way female socket Binder type 711 fuse holder contains 2 AT glass fuse 20 x 5 mm to limit the output current blue power LED is on indicates that the output circuitry is on When the degauss coil is not connected the LED shines bright it dims when the coil is connected power on off switch mains input 115 or 240 V 50 60 Hz depending on the model 10 W max User s Manual SRD1000 System version 06 02 2006 HDL Leiden The Netherlands Annex D ACS 10 adjustable current source D1 Features battery powered precision current source for compensating residual fields in the cryogenic sensor E o DC output current adjustable between 0 pA and ACS 10 adjustable DC current soiree 2000 pA with a polarity selection for the sign of the output current the compliance voltage is about 3 V temperature coefficient electrical parameters smaller than 50 ppm C the low load capacitance allows direct superim posing of the DC output current on the AC pri mary current of sensor output to monitor the current powered by one 9V PP3 battery indication of low battery voltage D2 Front rear bottom view polari
34. ut for the Lemo con nector and Table 2 2 shows the connection scheme of the cables The shields of the cables are to be connected to the ground chassis of the cryostat Table 2 2 Lemo OB lead colour 10 Figure 2 4 Cryogenic shielded twisted pair cable Figure 2 5 Black cable with 5 way Lemo OB connector 1 ground O em 3 I C 5 I C 4 v Figure 2 6 Pin layout of the 5 way Lemo OB connector front view of the male free plug or rear solder contact view of the female chassis socket The yellow line indicates the direction of the pin number count mutual inductace connection 1 compensation coil connection 2 ground shield ground shield secondary coil V J primary coil I secondary coil V J primary coil_I User s Manual SRD1000 System version 06 02 2006 HDL Leiden The Netherlands 2 3 6 Testing the connections After the installation of the sensor and the signal leads it is important to verify that all connections are made correctly before the sensor circuitry be comes superconducting If for example the connection to the primary coil is accidentally interchanged with the one to the secondary coil the sensor may seem to operate correctly at low temperatures However in this case the primary current is running in the secon dary coil producing a magnetic field near the ref erence samples that is a factor 10 highe
35. yogenic temperatures as the r shield of the leads is made of phosphor bronze mesh and the internal conductors are of NbfTi The leads are already thermally anchored inside the sensor body 2 3 Electrical connections EMI filter las a LZ 2 3 1 Signal connections H The sensor contains a set of mutual inductors the red and blue coils in Figure 2 2 to detect the transitions of the reference materials A compen sation coil the green coil allows reduction of re sidual magnetic fields in the sensor shield Figure 2 2 The sensor circuitry and connections User s Manual SRD1000 System version 06 02 2006 HDL Leiden The Netherlands The coils are connected through 3 shielded super conductive leads These are about 20 cm long and each one contains a twisted pair of insulated conductors A filter reduces spurious EMI signals entering the sensor through the leads Each lead is terminated with a 2 way connector pin spacing 2 56 mm 0 1 see Figure 2 3 which fits into a standard type IC socket e g a SIL socket connector The colour of the tubing indicates the type of connection P primary coil red S secondary coil blue C compensa tion coil green Table A 1 in Annex A summarizes the connections and lists general values for the electrical resis tance of the coils at 300 K 77 K and atT lt 9K The label on the transport box of the sensor gives the specific values At roo
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