Agapov, V

Gorchenko, V

Khodzhibagiyan, H G

Kirichenko, A E

Kovalenko, A

Kulikov, I I

Romanov, S

Sveshnikov, B N

Vasilishin, B V

Volkov, V

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CONTROL SUBSYSTEM FOR NUCLOTRON CRYOGENICSB. Vasilishin#, V. Agapov, V. Gorchenko, G. Khodgibagian, A. Kirichenko, A. Kovalenko,I. Kulikov, S. Romanov, B. Sveshnikov, V. Volkov, JINR, Dubna, RussiaAbstractThe Nuclotron, a superconducting synchrotron was putinto operation in March 1993 at the Laboratory of HighEnergies, Joint Institute for Nuclear Research. Thecryogenics subsystem of the Nuclotron Control System[1] is described in this paper. The subsystem providestemperature measurements of the Nuclotron elements atmore then 600 control points. The measurement range isfrom 4 to 300 K with a resolution of 25 mK at atemperature of 4 K. Carbon resistors are used astemperature sensors. The subsystem  measures:- helium pressure in both supply  and return lines- helium and nitrogen levels in the separators- helium and nitrogen pressure in the separators andstorage tank- the mass vapour content of helium in the supplyheaders. The subsystem has been implemented utilizing hardwareinterface is CAMAC and PC.1  INTRODUCTIONThe superconducting synchrotron named Nuclotron [2]was put into operation at the LHE JINR in 1993. It’spurpose is to accelerate nuclei and heavy ions. Themaximum energy of particles with the charge to mass ratioZ/A=1/2 is 6 GeV /u. The 250 meter ring of the Nuclotroncomprises 96 dipole magnets and 64 quadrupole lenses,forming the FODO lattice with 32 periods. There are nodipoles in every 4-th period , i.e. the Nuclotron structureforms 8 superperiods with two free spaces in each. Atpresent the slow extraction system is being commissionedalmost for all the Nuclotron energies. The plannedextraction duration is 0,5…10 s.The cryogenic system [3] (see Fig.1) consists of twosubsystems. Each of them is supplied with a separaterefrigerator connected to its half-ring and operatesindependently. Liquid helium entering the supply headerof the half-ring cryostat, is distributed over the coolingchannels of parallel connected individual units (magnetsand lenses). In each unit, the two-phase helium flowsthrough the cooling channels of the superconductingbuses, the windings and the iron yoke. Each subsystemcontains a nitrogen channel for  cooling  the 490-mmdiameter shield surrounding the structure elements of theNuclotron ring.___________________# Email: vasilish@sunhe.jinr.ru2  GENERAL DESCRIPTIONThere are more than 600 of measurement points in thecryogenics subsystem. The structure dipole andquadrupole magnet sensors are placed at the inlet andoutlet of the windings and at the entrance of the returnheader. The other sensors are placed in the inflectorseptum-magnet, on the nitrogen shield and in somenonstructural elements of the ring.It is necessary to shield the cabling  fromelectromagnetic noise because of the  considerabledistance of the sensors from the measuring equipment(50-100 m) and their proximity to RF sources.Figure 1: General scheme of the Nuclotron cryogenics:1 - vacuum shell; 2 - heat shield; 3 - supply header;4-return header; 5-dipole magnet; 6 -quadrupole magnet;7-subcooler; 8 - separator; 9 - helium flow from therefrigerator; 10- return helium flow to the refrigerator;A measurement accuracy of ≈ 1K is tolerable at thebeginning of the cooling process, when the temperature ofthe cooled elements is about ≈ 290 K. Under  operatingconditions at the cryogenic temperature the measurementaccuracy is 0.05K. Commercial  carbon resistors TVO [4]of ∼1 kOhm at room temperature and ∼4 kOhm at thecryogenic temperature are used as temperature sensors.International Conference on Accelerator and Large Experimental Physics Control Systems290International Conference  Accel rator and L rge Experim ntal Physics Control Systems, 1999, Trieste, ItalyThe resistance dependence on element temperature isdescribed  by the 7-th power polynomial. To obtain thecoefficients of the polynomial, 8…10 calibration pointswere taken  over a temperature interval of 4…300 K forevery sensor.3  MEASUREMENT SCHEMEThe cryogenics control system of the Nuclotron is basedon an industrial PC computer from ADVANTECH,connected to the Nuclotron local area network. Themeasuring and auxiliary electronics utilizing PC andCAMAC is  located in the data acquisition room at thecenter of the LHE accelerator complex approximately∼ 50 m from the temperature sensors.All the temperature sensors are divided into10 independent measuring circuits. The sensors of eachcircuit are connected in serial and supplied with separatecurrent sources with the output impedance 1011 Ohm. Acurrent of 10 µA is used to minimize sensor heating.Ten integrating 16 bit AD1170 ADCs with a20 ms conversion time are used for digitizing sensorsignals. The ADCs are mounted on two PC boardsdeveloped and manufactured at LHE. The system isdivided into 10 subsystems. Each subsystem contains 64resistors (60 thermoresistors and 4 calibration resistors),one 64 channel multiplexer and one ADC. An acceptablesignal to noise ratio is achieved with sensor signalamplitudes of 10…50 mV. The CAMAC 64-channelmultiplexer has an output differential amplifier with80 dB common mode rejection and a gain of 100.Each subsystem  includes 4 precise resistors connectedin series with the thermoresistors. This allows anautomatic calibration of the measurement system in everycycle of the Nuclotron.4  MEASUREMENT AND DATAPROCESSINGThe system software consists of two C++ programs. Thefirst, performs measurement of cryogenic systemparameters, processing of information, and the storing ofresults on the network server disk. The second programallows current and archive information to be displayed onany Nuclotron local area network computer.As the measuring time is 1.4 s, the measurements canbe performed between Nuclotron magnetic cycles. Thisresults in reduced noise pickup from the NuclotronRF system.Under operating conditions, temperature measurementsexceeding 9 K for the helium sensors and 90 K for thenitrogen sensors causes an alarm signal and prohibition ofthe Nuclotron cycle.To optimize the cryogenic system operation, it isnecessary to measure other parameters of the system. Thesubsystem  measures:- helium pressure in both supply  and return lines- helium and nitrogen levels in the separators- helium and nitrogen pressure in the separators andstorage tank- the mass vapour content of helium in the supplyheaders.Absolute and differential manometers are used fortemperature measurements. These sensors are read by a13 bit integrating ADC. Helium levels and mass vapourcontent measurement is accomplished using a resonantcircuit where the resonant frequency changes based on thedielectric permeability of the medium being measured.The measurement results are written to a current datafile on the network server disk located in the centralNuclotron control room. Every 30 minutes, data is writtento an archive file on the server disk. The operator can savedata to an archive file at any time.In a special “express-mode” the measurements areperformed with period of 50…100 ms  for a few sensors .The operator select the sensors to be monitored from thefront end computer keyboard. In the “express-mode” theselected measurements are displayed on the front endcomputer screen.Fig.2: Measuring results for 3 sensors in the “express-mode”.Fig. 2 illustrates the system operation in the “express-mode”. The dipole  magnet winding was heated  for ∼10 sat the inlet of the winding. Sensor T1 is located near to thepoint of heating, T2 is  further along the helium flow atthe winding outlet and sensor T3 is located at  the returnheader.5  DATA DISPLAYAfter data processing and transfer to server disk, theinformation is displayed on the front end computer screen,and  is broadcasted to different Nuclotron services usingthe ICTM  interface  developed at LHE.  The  programcycle time is ≈5 s.Any Nuclotron local area network computer can displaythe measurement result. The LAN computer also has291access to all the archive files from previous Nuclotronruns. Data display is controlled with the help of a dialoguemenu in this program.Fig.3: Temperature change for 4 sensors during theNuclotron run.Fig 3 shows the temperature change of 4 sensors duringNuclotron run in May-June 1995. The sensor8D4 N T3 shows the nitrogen shield temperature near oneof the lenses D; the other 3 sensors are located in thecooling channel of one of the dipole magnets. Thetemperature distribution along the Nuclotron ringelements  24 hours after  beginning cool down is shown inFig. 4. The Nuclotron operating conditions are met whenthe temperatures of all the elements reach≈ 4.5 K. The total cool down time  is ≈ 80 hours.Fig. 4. Temperature distribution along the Nuclotron ring(24 hours from the beginning of run).6  CONCLUSIONThe  cryogenics control subsystem has been operatingsince the first Nuclotron run in March 1993, and has beenimproved continuously. In 1999  temperaturemeasurement of the extraction system elements –electrostatic septum (ES) and two Lambertson magnets(LM1 and LM2) were added.7  REFERENCES[1] V.Andreev et. al., Proc. 1997 Part. Accel. Conf., p. 2452.[2] A.M.Baldin et. al., IEEE Trans. Nucl. Sci. 1983, p. 3247.[3] A.M.Baldin et. al., Cryogenics of the new superconductingaccelerator Nuclotron. E8-95-65, Dubna, 1995.[4] V.I.Dackov et. al., JINR, 10-81-200, Dubna, 1981.292

Control Subsystem for Nuclotron Cryogenics

Control Subsystem for Nuclotron Cryogenics

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