Granetz, R.

Gwinn, D.

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OBSERVATION OF NEUTRON AND X-RAY SAWTEETH IN ALCATORDavid Gwinn, Robert GranetzJune 1978MIT Plasma Fusion Center Report RR-78-8OBSERVATION OF NEUTRON AND X-RAY SAWTEETH IN ALCATORDavid Gwinn, Robert GranetzMassachusetts Institute of TechnologyCambridge, MassachusettsU.S.A.ABSTRACTSawtooth oscittations in the themonuctea& neutton ptoductionAate have been ob.erved in AtcatoA. They axe coAtelated with oscdJationsin zoit x-ay emizzion 6'Lom the p&a.ma and indicate tavge (>15%) o6cifta-tion4 o6 centWaL ion tempexatue.Soft x-ray emission from the Alcator plasma has been observedusing a multi-diode imaging apparatus built by Petrasso et al [1]. Thex-ray flux exhibits the characteristic sawtooth behavior first noted byVon Goeler [2]. In addition, similar fluctuations have now been seen inthe emission of D-D fusion neutrons (Figure 1). The strong temporal cor-relation between these two diagnostic signals indicates that similar pro-cesses affect both the electron and ion temperatures during the internaldisruption. This would follow if present theories of the disruption processare correct [3, 4].The rapid growth of magnetic islands from the q=1 surface and re-connection of magnetic field lines is a process which should affect boththe electron and ion radial temperature profiles. We have developed a quan-titative picture by fitting temperature profiles to the experimental dataand studying the effects of the disruptions on -the calculated x-ray andneutron emission.Prior to the internal disruption, the temperature profiles areapproximated by Gaussian functions [5]. The peak electron temperature isdetermined by matching the measured x-ray flux with that calculated usinga computer code developed here [6]. The code takes into account the spe-cialized geometry of the detectors and aperture, the transmission effectsof various x-ray filters, and the assumed density, temperature, and im-purity...profiles. The electron temperature c'alculated by this method isin excellent agreement with temperatures determined by Thompson scattering [7].Immediately after the disruption, it is assumed that the tempera-ture profile becomes flattened in the central section of the plasma whileremaining constant elsewhere (Figure 2). By requiring conservation oftotal energy (both kinetic and magnetic) during the internal disruption,we can relate the radius of flattening to the temperature of the flattenedregion, thus leaving only one independent parameter to vary. This parameterwas determined by again matching the measured x-ray signal with the computermodel.In a disruption, we theorize that the ion temperature profile isperturbed in essentially the same manner as the electron temperature profile.Previous experimental measurements [8] indicate that the ion temperature inAlcator is lower than the electron temperature by an amount which is relatedto the ion-electron thermal equilibration time. Therefore, prior to the dis-ruption, the ion profile is assumed to be Gaussian but with a peak tempera-ture 70 eV below the electron central temperature. During the disruptionit is postulated that the ion profile flattens out to the same radius asthe electron profile. Since the time scale for this process is so short(<20 usec), the electron-ion energy transfer can be neglected; therefore,energy conservation requires that the ion temperature drop be about the sameas the electron drop, or approximately 130 eV for the discharge in Figure 1.1Given these temperature profiles, the change in the neutron production ratewas calculated and was found to agree with that which is observed.Additionally, the fitted electron temperature profiles were usedto calculate the current density immediately before and after the internal1The neutron signal is averaged with a time constant of 0.5 msec, resultingin the apparent difference in the shape of the neutron and x-ray sawteeth.disruption. The resulting current density profiles (which are quite flatin the central region due to inductive effects) were then used to deterMinesafety factor profiles, q (r) (Figure 3). The results are in good agreementwith theory.ACKNOWLEDGMENTThe authors are grateful to S.H. Chen for the loan of the highsensitivity neutron detectors used for this work.REFERENCES[1] PETRASSO, R., SEGUIN, F.A, A Versatile High-Sensitivity X-Ray ImagingSystem for the Alcator Tokamak, American Science and Engineering,Inc., Report ASE-4107-1 (1977).[2] VON GOELER, S., STODIAK, W., SAUTOFF, N., Physics Review Letters33 (1974) 1201.[3] JAHNS, G., SOLER, M., WADDELL, B., CALLEN, J., HICKS, H., NuclearFusion 18 (1978) 585.[4] ARA, G., BASU, B., COPPI, B., LAVEL, G., ROSENBLUTH, M., WADDELL, B.,Magnetic Reconnection and m=1 Oscillations in Current Carrying Plasmas,Massachusetts Institute of Technology, RLE Report PRR - 77/8 (1977).[5] APGAR, E., COPPI, B., GONDHALEKAR, A., HELAVA, H., KOMM, D., MARTIN,F., MONTGOMERY, B., PAPPAS, D., PARKER, R., OVERSKEI, D., in PlasmaPhysics and Controlled Nuclear Fusion Research (Proc. 6th Int. Conf.Berchtesgaden, 1976) 1, IAEA, Vienna (1977) 247.[6] GRANETZ, R., Numerical Code for Calculating Soft X-ray Fluxes inAlcator, MIT Plasma Fusion Center Report TR-78-1 (1977).[7] GONDHALEKAR, A., Massachusetts Institute of Technology, privatecommunication (1978).[8] PAPPAS, D., PARKER, R., Thermonuclear Neutron Production in AlcatorDeuterium Plasmas, MIT Plasma Fusion Center Report RR-78-5 (1977).F I GUBE............... ................................ ................................ ................................ .................NEUTBONS............................. .........................  ........ ................................................ ..................   ......... .................. ..... ... ...........  ..... X-BRYS::....................................................................................................................... ................................ .. .................... .. .......... .......... ........... .   ISHOT .21 3 9/78NO=7X.10"' /(M3: .................... .. .   ..  ..........B=60 hG.................. . .. ...... .. .. ...... .. .. ...... ... ................ .   .. .... .X-RRYS.................. . ...... .. ...... ..........  .......  U E U T R O N -S. ... .................... ............ .. . . ...... . ................. .............  .28 5bMSEC125 1 0 115lio 115 120 i125 I1 30105MSEC8.0CHANGF IN K-RRY 5IGNAL:............ .............. ...... ......................  ............. e ....... ...................................... ...... ....... ................... ......'EX-RE-R-1-MEM ...............--------- ---------ALCOLATED:................... ..... ............ .. ........ ........................ ......................... ..... . ...... .... ....... - * --------- ------a6.0 8.0F I GURE-Lif .0 -2 1 .0 0 1 a 2. 1 0RADIB (CM)-6.0 -4.0 -2.0 0.0 2.'o 4. i 0DETECTOR CHORD INTERCEPT (CM)2In0 -6. 0C)cuC)C)--, IC)crcoC)WC3cr C --D coWo0-crLnzc)(D C: -L)w.-jwc)ClPROFILES FI:T-TED TOSAWTobTH DI:SBUPTION................... ..... ...... ....... ....................... .. ...... .. . .................. .....RIGR TO................... ...... ..... . ...... ....... .. ......  . 0................... ...... % ........   ..................   ............ ......R F 'E'" R-:DISRUPTION...................................... ................ ........ ................ .. ......... ......... ......................... ........... ................................... ................  ...................  .......................  . ............ ..... .  .......................... . .. ...... .. ...... . ................ ............................ ... .. ...... .. ...... .. ...... .. .  ..............0c_C)c_Z:LDCf) C)ccC)c)LLI CD-4LLJi4.0 i6.0D:I SBUPTBRDIUS (CM)LnCuC3C3M CVX:L)CLX: cocrmLnLLJC3-c3c3-4=3C3IL-31 SiLnA 2RROWS (CM1C3.3GROWTH OF CUBRENTPROFJ LE DURINGSAWTOOTH:.............. ............ .............. ................... ...... . . .. . .. ......... ............................. ........................................................... ......................... ......................... ............................................................... ....... .............................. ................................ ............. ........................... .............................................. ........................................................ ............. ........... ................ ............................. ............... ..... ...... .... . .. .................. ....... ....... ....... .......I OR TO DISRUPTION*:10OEMC)V--L)ccU-0u-CCCO C30. Q8 P.-6 10F I GUBEQ-PRDFILES......................:AFTER

Observation of neutron and x-ray sawteeth in Alcator

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Observation of neutron and x-ray sawteeth in Alcator

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