F1-CN-64/A2-5 T I

STVDY OF TIFTR D-T NEUTRON SBECTRA USING NA$URAL DIAMOND DETECTORS

A.V.KRASILNIKOV~. ALROQUEMORE~, N.N.GORELENKOV~, and R.V.BWNY2

~Troirslc Institute of Innovating and Fusion Resmhes, 142092 TRINITI, Troitsk, Moscow region, Russia %inceton Plasma Physics Laboratory, P.O.Box 451, Princeton, NJ , 08543-0451, USA

Abstract

Three Natural Diamond Detector (NDD) based spectrometers have been used for neutron specua measurements during Deuterium-Tritium @-T) experiments wing high power Neutral Beam Injection (NBI) and Ion Cyclotron Resonance Heating (ICRH) on the Tokamak Fusion Teet Reacmr cTT;IR) in 1996, A 23% cnergy resolution coupled with the high radiation re~iStancc of NDD8 (5*1014&rn2) makes them ideal far mcasUring the D-T neutron spectra in tfie high radiation environment of TFI'R tritium experiments.

' ?he compact size of the NDD made it possible m insert one of the detectors into one of lhe center channels of &he "FIR multichannel neutron collimator to provide a venical view perpeadicatar to the vessel midplane, lho other detectors werc placed inside shields in TFTR test cell and provide measurements of the neutrons having angles of emission of 110-180° and 0-1200 with respect to the direction of the plasma c m t . By using a 025 ps swing time of the Onec 673 spectroscopy amplifier we were able M accumulate useful spectrometry date at countram up io 1 9 1 0 3 counLgszc.

To model the D-T neutron spectra rncfisureA by each of thrcc NDD's the Neutron Source post TRANSP ( N S T ) code and semi-analytical model were developed. A set of D-T and D-b plnwas IS ~ I I ~ Y J L J L E ill= JylldlkLis af D-P neutron apeettdl breadeninE €or oaoh of thmo NDD cones of view. The application of three NDD bawd TI-T neutron specmmcter m a y demonstrated the anisotropy of the ion disuibution function, and provided a meawre of thc dynamics of the effective ion temperatures for cach detector view, and determined the tangential vclocity of resonsnt tritons during ICRH.

1. INTRODUCTION

During the last three years Deiiterium-Tririum @-T) experiments using high power Neutral Beam Injection (NRT) and Ion Cyclotron Resonance Heating (ICRFI) have been canied out on the Tokamak Fusion Teat Reactor

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(mTR). During this experimental phase, up to six NBI sources were aimed in the counter-direction and six in co-direction. with a total power of 36 MW of 105 keV D-T injection. Up to 3 MW of rf ower at 30 MHz was injected with

current) during ICRH at the fundamental triton cyclotron frequency. The high flux of 14 MeV neutrons during high power deuterium and tritium NBI and ICRH experiments on the TFTR has made it possible to use neutron spectrometry to study the ion distribution under reactor-like conditions. The TITR ion distribution function during NBI, as calculated by the 2-dimensional transport code, TRANSP [ 11, is non-Maxwellian and anisotropic. ' M a anisotropy is directly reflected in the D-T neutmn energy and angular emission distributions so that a measure of its dynamics provides information about the ion eaexgy distribution, transport, confinement and slowing down time of high energy particles and alpha-particle binti erieryy didLiLtibi\. In the CBSC af ICRH it shows the efficiency of heating by the resonant particles.

wave phasing 600 (counter), 1800 (n), and s OO'J (co with respect to the plasma

2. DIAGNOSTIC ARRANGEMENT

Three neutron spectrometers based on Natural Diamond Detectors (NDD) were developed in Russia [a-41 and have been used for D-T neutron spectra measurements during NBI and ICRH on TFTR in a variety of locations \J]. The 14 MeV peak of the NDD pulse height spectra arising from the 2C(n,a~)9Be reaction possesses a 2-38 energy resolution. Such high resolution

cuupled w i h llir; Id$ ~diat ia~i Ftsktancc 6f diamonds (5* lO%/omZ) make0 the NDD ideal for measuring the D-T neutron spectra in the high radiation environment of TFTR tritium experiments. The sensitivities of the detectors and the speed of the signal processing electronics drive the location and shielding required for each detector 151. The compact size of the NDD housing (-1 c d ) allowed the detectors to be inserted into the TFTR multichannel neumn collimator and fusion gamma shield without interfering with other detectors operating there. The first detector (NDD1) was placed inside a central channel of the TPTR vertical neutron collimator to provide a view perpendicular to the plasma ciimnt nxis [5], During the 1996 expeximenta a second detector (NDD2) was placed inside the TFTR fusion gamma shield and measured neutrons with emission angles in the range of 110 - 1800 with respect to the plasma current [5]. l l ic third dctcctm (NDD3) wa3 plaood inoido a omall epecially designed shield in the TFTR test cell 11 rn from the plasma axis and provided measurements of the spccnal broadening of 14 MeV neutrons having angles of emission of 60-1200 with respect to the plasma current [5].

The signal from each of the NDDs is fed into a standard Ortec spectroscopy electronics. By using a 0.25 ps shaping time and employing the pilemap rejectinn fmnire, nf the Oltec 673 rpecaosccrpyplifier we were able to accumulaf useful spectrometry data in the lzC(n,ao) Be peak at count rates

The full width at half-maximum (FWHM] of the 12C(n,a)%e line of the NDD pulse height spectriirn is a measure of the broadening of the energy

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up to l.S*IO B countdsec.

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distribution of thc D-T neuttons [4] that leave the plasma along the detector viewing cone and contains information about the cmsponding mean effective ion temperature Teff.

3.ru36aTS AND ANALYSIS

For a Mwwellinn DmT plasma with ion tempmmire! T, rhc anrtlyticrll salarlllcieao 16) giold n D T noutaon opouum iriith n rJaiicrian ~ h 9 p -

rw = x GAP (-(L-<E+)2/ 2 a, 1 ) (1) 6- whmc fin a i s the, sffindant Afiviatinn. The, I;'wHM Lq given by &= mq~, For plasmas with ion temperatures in the range 30-50 keV,

(2) A& = 180 dTdf (where &&and dT,lcfin keV [7]). The ion component in l l T R contains both thermal and hot beam ions.

The sources of thermal ions are gas puffing, emission from the walls and limiter. rncluding a few percent of T in the hydrogen Influx, and rhermnllzation of beam ions. The emitted neutrons resalt from three channels: beam-plasma. (5S73%>, beam-beam (0-208) and tticmd i~uu~lwrrv (lO-SO%e). TG aidel die D-T neutron spectra measured by each of the three NRDs the Neutron Source post TRANSP (NST) code was developed. This code utilizes TRANSP [I J to calculate deuterium and tritium plasma densities and temperatures as well as 13 and T beam distribution functions and applies fusion moss sections to derive the neutron emission spectra using well known [S J hi~uulaiiuii . !3ytdI a1 broadening of D-T neutrons escaping from the TFTR l a m a with emission angles of 900, 110-1800 and 60-1200 was obsemd by &e NDDl, NDD2 and NDD3 respectively. These measurements were made with NBI power of between 17 - 36 MW, ICRH power up to 3 MW and demonstrated thc anisotropy of the ion distribution function in TFTR. The dynamics of the Tcff ,~ measured by NDDl during 22 MW NBI and modeled by the NST code are in good agreement and are shown in Fig. 5 of ref.7 ,

In addition to the NST code we deveIoped relatively simple semi- analytical model 171 for calculations of D-T neutron spectra for plasmas with anisotropic deuteron and triton distribution functions. We consider each deuterium and tritium (beam or plasma) component to be a displaced Maxwellian with effective perpendicular and parallel temperatures and having a certain directed parallel velocity, which can be found from the actual J l s L l L u t i ~ v Ly a v ~ a g L ~ g U V ~ A dr; ,clacilj space. AccMding te this model w6

approximated the D-T neutron distribution function at dif€erent an les (arccosx) between the direction of the neumn emission and plasma current % y a Gaussian (see q u a r i m (1)) with the standard deviation:

OCT 81 '96 01:1@PP1 TRINITI FUSIQti

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where:

Q is the nuclear energy release of the reaction, <v\lDi> and *lmj> ZKG &vw&g& over the disbibution function velocities of deuterons and tritons, mn. mD. m ~ , mar are masses of corresponding particles, and i and j refer to beam and plasma.

An example of the measurements versus modeling is shown in Fig. 1. In this case, 18 Mw of balanced tritium NBI was injected into a deuterium plasma. The tangend& detector showed large broadening of the neutron spectm due to the momentum of beam tritons in the tangential direction. NST calculates the total contributions From beam-plasma and plasma-plasma interactions and fits the resulting data with a Gaussian. The semi-analytical model, based on equations (3)-(6) was also applied to the neutron spectra calculations, and the derived spectrum is shown in Rg.1 by the dashed curve. The values of Tilai, Tmiq Timi, T L ~ . C V I I ~ ~ and e l m j > were determined by averaging over deurer~n and triton distribution functions calculated by TRANSP. Fusion reactivity was calculated in accordance with reference [8]. The neutron soutces in the caw of anisompic plasma is:

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Good agreement is seen between measurements, NST and the semi-analytical model.

The system of three NDD based D-T nmtmn spectrometers was used to stud the dynamics of D-T neutron distribution functions and fluxes during TFT il fundamental tritium ICRH experiment. During these experiments plasmas with major radius 277 cm (with Shafranov shift), minor radius 96 cm were heated d d n 1 second (from 2.1 s to 3.1 s) by 17 Mw NBJ. and durin 0.8 second (from 8 .3 s to 3.1 s) with up to 3 MW ICRH at a frequency of 3 MHa with the wave phasing 600 (counter) 1800 (E) or 3000 (co with respect ta dw y l a w ~ b cui'tmt). The rcsbnancc layer #or rhc first hamoniu uf triturie wac L L ~ major radius 235 cm far wave phasing of 1800 and moved in the range 221 - 249 em in accordance with the wcll known condition for single particle resonanca Q - kli YII = W, , where co- wave frequency, kll - tangential wavenumber, vii - tangential component of triton velocity, w, - triton cyclotron resonance frequency. Figure 2 shows the dynamics of Teff as measured by three NDD based neutron spectrometers during experiments with NBI power of 17 MW and ICRH power of 2 MW. The FWHM of the neutron energy distributions for pe endicular and tangential emission (with respect to plasma

majority of the neumns fmm TFTR are from beam-plasma and beam-beam interactions [l], The FWHM is a function not only of the pIasma ion temperature but also of the average energy of the beam ions along the detector viewing cone which in turn is 8 function of the electron density. 7 % ~ decrease ia the effective tangential temperature (Fig.2, curve 1) and increase in effective perpendicular temperature (Fig.2, curve 2 and 3) during the first half of the beam phase ate functions of the change of beam penetration due to the increase of plasma density, The difference between cuwa 3, and 3 illustrates the increase in perpendicular energy of the tritons due to ICRH. The niton slowing down time was estimated from the decrease of tangential effective tempexatwe (Fig.2, curve I) after deuterium and tritium beams were turned off. The derived value of about 100 ms is in reasonable agreement with calculations,

Figure 3 shows the difference in dynamics of perpendicular effective temperature measured in experiments with the same NBI power but without ICRH (curve l), with 2 MW ICRH and high (-25%, curve 2) and low (-lo%, curve 3) triton concentrations. These measurements demonstrated the highest heating of tritons occured in experiments with lower triton concentration.

ICRH is usually considered to cause dispersion only in VI. However as shown by T.Wx (91 during ICRH quasi-linear diffusion in velocity space directed along the! circles v12 f (VI! - w / ku )a = consc and in &e case of co or counter wave phasing resonant particles should receive some velocity in tangential direction also. In the case of the TFTR tritium ICRH experiments in accordance with (6) this should cause a shift in average energy of the D-T neutrons emitted from the plasma along the tangential direction. These shifts far w and counter phasing of ICRH waves were measured by the NDD2 and are

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aumnt mitt) @re dif 7) went due to the anirompy of the hot hqm inn8 since the

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Time (sec) Time (aec)

R$.2. raaprttial (curve 1) and perpendicular Fig.3, Petpendicular aimon effective temperature (curve 2 and 3) triton offeotive mrnpemture during hiton ICRH experirnentir without XCRH during tritium ICRH expcrirnenrs. NBI (curve 1). with 2.1 MW ICRW and high (-75 %) pow@ - 17 MW. ICRH poww - 2 MW viton concentradon (curve 21, and with 2.4 M W (curves 1 and 2) and wirhout ICRH ICRH and Iow (- 1096)ttitonconcentration ( c m e 3). (curve 3)

Time (sec) ICRH Power (Mw)

Fig.4. Peak energy of tangential neutrons energy dirtdbution during tritium ICRH experiment8 with countcr (curve I) and co (curve 2) wave phasing.

Fig.5. Perpendicular ( c u m 1) and tangential (curve 2) effectbe ion rcmpcrature of plasma with few % of aitium due to gas puffing during 16.8 MW deuterium NBI and ICRH with IC (1.2 MW) and counter (1.5 MW) wave phasing.

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shown in Fig.4. During the first half of the heating time the mewred shift corresponded to averaged triton tangential velocities of +/-lo7 c d s and during second half to +/-7*106 cm/s. The decrease in the averas triton tangential velocities can be explained by the increase of plasma density during NBI.

Energetic banana particles in a tokamak can hit the wall M Urnitex and are thus in the "lass region" of kinetic space. During TFTR tritium ICRH experiments the resonance Iayer crosses the plasma at major radius 235 cm, SO we calcularc thc loss region boundaries for magnetic surface with minor radius 0.4*a. These calculations were produced in accordance with the model suggested by J. Rome [lo] and gave for coordinates of loss-region peak values & 4 5 0 keV and arcC6SX& = - SGO- This means that m~ tcgotlant counter- moving tritons with ener higher than 150 keV can be lost during TFTR off-

efficiency is shown in Fig.5. NBI in these experiments was pure deuterium. Tritium was injected into the plasma by gas puffing. Both the tangential and perpendicular ion temperature measured by NRP2 and NDD1 spectrometers are i1lgltr;l dit ur ICPII w l z ~ l db p~,aa;,ls a l , ~ yuww 1.a lifllf LI~A.~ ICRII with counter phasiag and power 1.5 MW.

n-T ncirtrnn f l u x dynamics measured (in parallel wirh ~ p e c ~ ~ m e f r y ) during four shots by NDD2 are shown an Fig.6. These shots wcre with almost balanced 17 M W NBI of six deuterium sources and one tritium source directed in co- (shots 93332 and 93335) and counter (shots 93336 and 93337) directians and 2 MW ICRH with co (shots 93335 and 93336) and counter (shots 93332 and 93337) wave phasing. The D-T neutran flux decreased in the case of oounter wava phsaing or countcr tritium injection when more uitons c8n reach the loss region during ICRH.

axis Piton ICRH. The in %x uence of the triton first orbit lasses on the ICRH

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P;g.G. Dynamiea of D-T ncuaan fluxea mwsurcd by dimand dwotor during ahocn with dmact balanced 17 MW NBI with six deuterium sources and one tritium t~oun?e. Tha tritium source wag directed in co- (curves 1 and 2) and counter (curves 3 and 4) dklians. In addition, 2 MW of ICRH WBS iaecred with co (curva 1 and 3) and counter (curves 2 and 4) wave phasing.

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4. CONCLUSION AND DISCUSSION

Natural Diamond Detectors based spectrometers have successfuuIly measured the dynamics of both pe endicular and tangential ID-T neutron spectra during 'ITTR experiments wixhigh power NBI and ICRH. The results of these measurements and simulations using NST code and semi-analyticd model yields information about the effective ion temperature, averaged perpendicular and tangential b e m ion energies, triton sIowing down time and averaged tangential velocity of resonant mtons during ICRH with co- and counter wave phasing. Spectrometry and flux measurements made using NRDs show the decreases of effective temperatures and D-T neutron fluxes during ICRH with counter triton neutral beam injection or counter wave phasing. This can he cxptaind hy the, inmeme, nf the r f - driven velocity space difusicm of tritpm nnta 1ms orhip The excellcnr energy resdutivn! high rWpvn resistance (5*1014/crn ) and very small size (detector housing - 1 cm ) of Nnns make them nna nf the hest choices for neutran spectrometry in future burning plasma experiments auck as the Intmnational Thormonualonr Experimental Reactor (ITER),

ACKNOWLEDOMENT

We are grateful to Drs, EAAzizov, V.S.Khrunov. R.M.Young, D.W.Johnson, S.von Goeler, S,J,Zweben, R.Majeski and D,S.Dmow for useful discussions, and for the support for this work which was done 8s a pan of the PPPL-TRINITI collaboration under U.S. DOE contract DE-AC02-76-CHO- 307 3.

[l] BUDNY R.V., et al., Nuclear Fusion 35, (1995), 1497. [a] KONOROVA E.A., et. al., Sov.Phys,Semiconductors 4, (1971), 1600. [3] LUCHANSKII A.E., et al., Sov. Atomic Energy 63, (19871,639. [4] KRASILNIKOV A.V., in "Diagnostics for Experimental Thermonuclear Fusion Reactor" ed. by P.B.Stott, et. al., Plenum Press, New York and London (1995), 435. [5] KRASILNIKOV A.V., et. al., to be published in Rev. Sci. Instrum. (1997). [q BRYSK H., Plasma Physics, 15, (1973), 611. [?] KRASILNIKlV A V , er a1 , tn he. piihlishPd in Cnnrmlled Firlsinn and Plasma Physics (Proc. 23th EPS Conference, Kiev, 1996). (81 PUWINSKIJ S,V., Reviews of Plasma Phys. 18. 191 STM T.H., Nuclear Fusion 15, (1973,737 . [IO] ROME J.A., et. al., Nuclear Fusion 16, (1976). 55.

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty, express or implied, or assumes any legal liabili- ty or respondbility for the accuracy, completeness, or usefulness of any information, appa- ratus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commerad product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessar- ily state or reflect those of the United States Government or any agency thereof.