Galbraith, Peter

Henrichsen, K N

Jansak, L

Kvitkovic, J

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27 November 1995 OCR OutputGeneva, Switzerland* Slovak Academy of Sciencespresented. A resolution of 0.0001 mT was obtained.from a remanent field of 0.5 mT up to the maximum field of 112.5 mT areevaluated. The measurement method is described and results in the rangereasons, a system based on NMR measurements in flowing water wasmeasurement range causes a problem in these low field magnets. For thesedisadvantage of being sensitive to ionizing radiation. Also its limitedbased on NMR (Nuclear Magnetic Resonance) is used. It has, however, thein two bending magnets in the machine tunnel. Measurement equipmentseries with the bending magnets of the machine. The field is also measuredobtained by measuring the magnetic field in a reference dipole connected in(Large Electron-Positron Collider). One of the parameters for this exercise isutmost importance for the physics experiments being carried out in LEPThe determination of the precise value of particle momentum is ofL. ]ansal<*, ]. I<vitl<ovic*P. Galbraith, K.N. HenrichsenFlowing Water NMR Measurements in the LEP DipoleQU;- 2/LEP2 Note 95-asCERN`AT`95‘5°CERN Aww (MA) /lllllllllllllllllllllllllIIUIIIIMIIIIICERN LIBRARIES, GENEVAEUROPEAN ORGANIZATION FOR NUCLEAR RESEARCHEEFigure 3: LEP dipole hysteresis curve OCR OutputFigure 2: LEP dipole magnetization curveFigure 1: Measurement principleTable 1: Measurement resultsAnnexes:5. References4. Concluding remarks3. Measurement results2. Measurement principle1. IntroductionCONTENTSmeasuring a magnetic field of 8.445 T in the superconducting NMR spectrometer. A OCR Outputstability and frequency step 0.01 Hz, Sheng [9] achieved an accuracy of the order of 10*range of magnetic field 0.05-10 T. Using a frequency synthesizer with extremely highNMR magnetometer in flowing water and arrived at the precision of 3.10*5 in themeasuring a magnetic field of 1.8 mT. Simonov et al. [8] developed the wide rangeflowing water developed by Pendlebury et al. [7] has reached the precision of 10·7 whenmeasure magnetic field using this effect. The precise NMR magnetometer usingtime in 1951 by Suryan [4]. Later, Sherman [5] and Zhernovoy [6] found a method toNuclear Magnetic Resonance (NMR) in flowing water was observed for the first2. Principle of operation of the NMR using flowing watermeasurement in environments of ionizing radiation as in particle accelerators.equipment is not yet commercially available. In addition, it provides a method ofBratislava. It fills the gap in the measurement range up to 0.045 T, for which NMRwas developed at the Institute of Electrical Engineering, Slovak Academy of Sciences,measurements in flowing water. The measurement equipment described in this noteFor these reasons it was suggested to evaluate a system based on NMRwhere the bending field is about 0.05 T.should be noted that the Z bosons are produced at beam energies around 45 GeV,Also its limited measurement range causes a problem in these low field magnets. ItThe disadvantage of the present system is its sensitivity to ionizing radiation.two NMR systems in bending magnets in the machine tunnel.accuracy better than 10 ppm. The system was later completed with the installation ofCommercially available instruments measure fields in the range from 0.045 T with ancalibration, this method provides an ideal tool for precise measurements.measurements was added to the reference magnet. As an absolute standard forresolution were increased, equipment for NMR (nuclear magnetic resonance)magnets installed in the machine [3]. As the requirements for measurementloop which is a one turn induction coil embedded in the lower pole of all bendingcalibrated periodically by a direct measurement of flux variations in the so-called fluxseries with the bending magnets of the machine [2]. This reference magnet isthe magnetic field (in the range of 0.045 to 0.12 T) in a reference dipole connected inPositron Collider) [1]. One of the parameters for this exercise is obtained by measuringimportance for the physics experiments being carried out in LEP (Large ElectronThe determination of the precise value of particle momentum is of utmostthe signal of NMR absorption on the oscilloscope screen. The amplitude of this signal OCR OutputEven if, in the probe MP, the NMR conditions are not fulfilled, one can observefield. These signals are connected to the Y and X inputs of an oscilloscope OSC.component of the magnetization vector) and a signal proportional to the modulatinganalyzer output provides a signal proportional to the polarization of the water (the Zthe sweep generator SG with a saw-tooth current at a frequency of about 15-30 Hz. Thepolarizer AM. This field is modulated by the twin coils MC, which are excited fromflow coming from the probe MP and is placed in the permanent magnetic field of theand amplifier. The oscillator coil AP is wound onto a glass tube inserted in the waterThe analyzer AD consists of a marginal oscillator with detector, feedback loopprotons in H20.where K = 42.575857 MHz / T, is a constant derived from the gyro magnetic ratio of thef = K . B0 (1)FG is:detects the nuclear spin magnetization change when the frequency of the generatorgenerator can be used. Finally, the water goes through the analyzer probe AP, whichmagnetic field. For low magnetic fields, e.g. the Earth magnetic field, an audiofrequency-meter FM. The range of its output frequency is related to the measuredthe output of an RF generator FG, the frequency of which is measured by theon the homogeneity of the measured magnetic field BO. The probe coil is connected to(40 turns). The number of the turns is not critical, it can vary from 5 to 100 dependingfield to be measured, BO. This probe consists of a glass tube with a single layer coilThe water then flows to the measurement probe MP, which is placed in the magneticnormal water = 2 s). This condition corresponds to a water flow rate of about 8 ccm / s.(50 ccm) for a minimum of 6 seconds (3 x T1 - where T1 is the relaxation time of themagnetization of the water of about 90%, it must stay in the polarizer volumeVp, where it is polarized by the field of the permanent magnet PM (0.7 T). To obtain aThe water flows from the tap, through a plastic tube, to the polarizer volumeFig. 1, is explained as follows:this paper. The operation of the NMR magnetometer using flowing water, shown inA similar system was constructed and used for the measurements described inhas been used for Hall probe calibration.Electrical Engineering, Slovak Academy of Sciences, Bratislava in 1981. Since then itmagnetometer using NMR in flowing water was developed in the Institute of- 2frequency of about 2 kHz. We therefore consider the method as a possible solution to OCR Outputto detect the Earth magnetic field outside the magnet, corresponding to an excitationit very suitable for absolute measurements at low fields. In fact, it was even possibleThe remarkable sensitivity and resolution of this measurement method makes4. Concluding remarksthe magnet.ratio of the detector output. This was perhaps due to the field gradient which exists indifficult to perform than the half-level method, due to the rather low signal to noiseIn practice, the zero—crossing measurement, described above, was slightly morewhere k = 0.0241455 T / kA and Bmm is the remanent field of the dipole shown in Fig. 3.AB=B-Bmm-k*Iand Fig. 2. A blow-up of the hysteresis curve,reproducibility was observed. The results of the measurements are shown in Table 1remanent field of 0.5 mT, up to the maximum field of 112.5 mT and a correspondinglaboratory instruments. A resolution of 0.0001 mT was reached in the range from thefeasibility of this method. The measurements were carried out with standardThe full excitation curve of the LEP dipole was measured in order to prove the3. Measurement resultsTable 1.maxima. For our measurements we used both methods with results as shown indetermine the frequencies where the amplitude of the signal is one half of theratio is relatively small, instead of measuring the zero-crossing frequencies, one canEq. 1 the unknown measured magnetic field can be calculated. When the signal / noisefrequency of the two zero-crossings gives the exact resonance frequency and usingresonance frequency which corresponds to the maximum inverted signal. The meanmaximum value as before, out of the resonance. There are two ways to establish theinverted signal. It then diminishes again, passes through zero and finally reaches theoscilloscope diminishes, passes through zero, then increases and reaches a maximumis approaching the resonance frequency, the amplitude of the signal on thegenerator FG connected to the probe AP (placed in the magnetic field to be measured)oscillator level as well as by the feedback parameter. When the frequency of theseconds. These conditions must be achieved by proper adjustment of the marginaldepends on the water flow rate. At zero water flow the signal disappears after a few- 3field", }. Appl. Phys., 57, p. 3830 (1985) (Abstract). OCR Output[9] Ye Sheng, "Method of the super-highly precise measurement of strong magnetic(Russian), 10, p. 76 (1975).[8] V.M. Simonov, G.K. Yagola, "A wide range proton teslameter", Measur. Tech.Sci. Instr., 50, pp. 535-540 (1979).averaging NMR magnetometer for low and high fields, using flowing water", Rev.].M. Pendlebury, K. Smith, P. Unsworth, G.L. Greene, W. Mampe, "Precision fieldprotons", Instr. and Exp. Tech., pp. 664-666, No. 5 (1957).stabilization of weak magnetic fields on the basis of the magnetic resonance of[6] A. I. Zhernovoi, Iu. S. Egorov, G. D. Latyshev, "The measurement andfield over an extended path in space", Rev. Sci. Instrum., 30, pp. 568-575 (1959).[5] C. Sherman, "High-precision measurement of the average value of a magnetic[4] G. Suryan, Proc. Indian Acad. Sci., A33, p. 107 (1951).Conference, San Francisco, USA, pp. 2122-2124, (May 1991).momentum in LEP from precise magnet measurements", 1991 Particle Accelerator[3] ]. Billan, ].P. Gourber, K.N. Henrichsen, "Determination of the particleAccelerators, 29, pp. 215-220, (1990).forecast of beam momentum and betatron frequencies in LEP", Particle[2] ]. Billan, ].P. Gourber, K.N. Henrichsen, L. Walckiers, "Field display system for theenergy calibration of LEP", Phys. Lett. B, 307, pp. 187-193, (1993).ALEPH, DELPHI, L3 and OPAL, "Measurement of the mass of the Z boson and the[1] L. Arnaudon et al., The Working Group on LEP Energy and the LEP collaborationsReferences:dipoles.might then be possible to install this type of equipment directly in the acceleratorrequired, further development of the related detection equipment will be needed. Itsome measurement problems in the LEP tunnel. However, if automatic operation is- 4NMR WF macmetometerSG OCR OutputFMOSC XFGADMPAP MCAMOCR OutputOCR OutputPMOCR Output(uu) mam OCR Output

Flowing water NMR measurements in the LEP dipole

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