Magnetic fields of moderate strength may cause errors of order 0.5% in measurements made with magnetostrictive spark chamber readouts.
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The fringe magneticfi eld surroundingm omentum-is the linearm assd ensitya)F. or practicapl urposetsh e analyzingm agnetsw ill alter the velocity,a mplitude velocityc anbe considerefdr equencyin dependennt;o and shape of the output pulses of magnetostrictived ispersiown asn oticedo vert hel engtho f the half meter spark chamberr eadoutslo catedn ear thesem agnets. delay line used for thesem easurements. Thesee ffectsa rea lwaysa dverseto the properd igitizing The variationi n pulse velocity( Av/v) with an ex-of spark chamberc oordinatesT.h e behavioro f the ternalm agnetifci eld or an externaslt ressw as of order pulses dependso n the directiona nd strengtho f the +0.5% for our samplesA. n increasein velocityw ith ambientm agneticfi eld at the send and intermediate an increasein field was observedin the "Remendur" areas of the magnetostrictivdee layline and on the that had been annealeda; decreasein velocityw ith intrinsicc haracteristicosf the line. an increasein field was observedfo r the "Remendur" The effecto f ambienmt agnetifci eldso n the received that had not beena nnealedT.h e magnitudoef the de-amplitudeo f longitudinal-modpeu lsesh as previously pendencew as similar for all samples;t he velocity been reportedf or severalf erromagnetimc aterials1). changew as approximatel1y0 times more dependent The currentm easurementasls, o for longitudinal-modeo n the magnitudoef the longitudinafli eldthan on the pulsese, xtendth isd ataf or a commonly-usemda gneto-magnitudeo f the transversfeie ld and independenotf strictivea lloyto includee xternaslt ressa s an additional the sign of eitherfi eld.For both longitudinaaln dtrans-parametearn dp ulsev elocitya nds hapea s observables. versef ieldsthe velocityd ependencoen field was ap-Since this magnetostrictivmea terialhas properties proximatelyli near-at least for the fields of up to which vary considerablfyro mb atcht o batch,e mphasis severakl ilogaussw hichwe were able to produceT. he is placed on the qualitativee ffectsw hich occur and velocityc hangefo r our samplesd id not dependo n the the order of magnitudoef thesee ffects. previouss tressh istoryo f the delayl ine. Figs. 1 and 2 The sampleso f "Remendu''r2 ) which we evaluated indicatet he dependencoef the delayc haracteristicosf were derived from two independenbta tchesm anu-the magnetostrictilvinee on the externafli eld.M easure-facturedto similars pecificationesx, ceptth atone batch mentsw erem adeb y varyingb oththe appliedfi eldand was annealeda t 550°C while the other was not an-the lengtho f delayl ine. The resultsb y both methods nealed.T he delay lines all measured0 .004"×0.015".a greew ith the plottedc urves. The magnetostrictipvuel sesw erep roducedb y a single The effecto f tensiono n velocityf or both samples turn of wire wrappeda roundt he" Remendurl"in e and was of the sames ign as the effecto f an externafli eld. driven by a spark gap at approximatel5y kV; the We found that for any tensiont hatmight actuallyb e receivec oil was 200 turns of no. 50 wire wound on a encountereind a magnetostrictisvpea rkc hamberre ad-plasticd ie approximate1ly m mwide and 2 mm in dia-out the velocityd ependencoen tensionf or delayl ines meter,m ountedc oncentricalloyn the delay line. The up to severaml etersl ong was less than the error in outputo f the coil was displayedd irectlyo n an oscillo-discriminatioonn the signalp eak( about1 00n sec).B y scope.T he externasl tresso n the "Remendurr"i bbon using large externatle nsions( morethan 500 newton/ was appliedt hrougha hangingw eightarrangement. mm2),t hev elocityc hangec anbe madet o exceed0 .5%. The velocity of the longitudinalm agnetostrictive The shapeo f the pulseo utputb y the receivec oil on strainp ulse in our sampleso f "Remendurw" as 5.4 a magnetostrictidveel ayl ine with neithere xternafli eld 4-0.1 mm/pseca t room temperaturwei th no external nor tensionis proportionatlo the secondt imederiva-magneticfi eld or stresso n the ribbon.T he velocityis tive of the spark send pulse3).T he observeds hape equal to (E/p) ~ whereE is Young's modulusa nd p showni n fig. 3a approximateths es econdd erivativeo f * Supported by the U.S. Atomic Energy Commission. a gaussian.
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