摘要:

This paper describes the hardware, performance, and physics results achieved with the TFTR ICRF system in 1992 and the system modification and experiments planned for TFTR’s D‐T phase in 1993. (AIP)

ISSN:0094-243X    

DOI:10.1063/1.44970

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

ASDEX Upgrade is equipped with an ICRH system consisting of 4 generators of 2 MW power each and 4 double loop antennas. The generators, tuneable in frequency from 30 to 120 MHz, cover several heating scenarios over a wide range of magnetic fields (1 T<Bt<3.9 T): minority heating of H and He3and second harmonic heating of H and D. ICRH‐heated discharges in ASDEX Upgrade were so far carried out mainly at 30 MHz and a magnetic field of 2 T (H minority in D and He). Peak powers of 2.4 MW and pulse length up to 2.5 s were achieved (total energy 3.75 MJ). In L‐mode, the density on turn‐on of the ICRH stays constant, or even decreases. The ratio of radiated power to total input power is unchanged (60% in an unboronized machine, 30% in a freshly boronized machine) between Ohmic and ICRH phases. The electron temperature increases with 0.9 MW from 1 to 1.25 keV, the loop voltage drops. Transitions to the H‐mode were easily and reliably achieved with ICRH alone (necessary ICRH power as low as 0.9 MW) and the length of the ELMy H‐mode phases was limited only by the applied ICRH pulse length (ELMy H‐mode phases of up to 2 s were achieved). The paper presents further results on heating and confinement in L and H‐mode, antenna and edge studies and on divertor measurements. Preliminary experiments, performed with a combination of H minority heating (30 MHz) and H second harmonic (60 MHz) in 600 kA He and D discharges (H minority in the 5 to 20% range) at 2 T, and with non‐resonant heating (30 MHz and 60 MHz at 1.35 T) are briefly discussed.

ISSN:0094-243X    

DOI:10.1063/1.45015

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

For a given ICRF power, the sawtooth‐free period duration increases with plama density. This trend, correlated with an increasing soft X‐ray inversion radius, clearly shows a better stabilization by hot ions at higher density. A tentative explanation is given through a full modeling of the hot ion anisotropy using a Fokker Planck code coupled with a 1/2 D power balance code simulating experimental data. A linear stability analysis of the kink/tearing m=1 mode, in terms of a MHD kinetic functional, shows that the anisotropy of the distribution function may amplify the effect of the hot ion pressure gradient. A two‐fold lengthening of the sawtooth‐free period is obtained when applying LHCD to ICRF heated plasmas. Analysis of polarimetric data shows that, instead of the continuous decrease of the central safety factor observed when using ICRF alone, the q value ‘‘freezes’’ when LHCD power exceeds 3 MW. This demonstrates a current profile control effect opening the way towards steady‐state stabilization. Working with both ICRH and LHCD on the same target plasma allows thorough comparisons of transport with different power deposition profiles and coupling mechanisms. The energy stored in electrons is the same although the electronic temperature gradients are quite different. Nevertheless, due to better ion heating, the energy life time (discarding hot ions contribution) is always higher with ICRH. Local transport analyses allow comparisons between both heating schemes for different confinement situations.

ISSN:0094-243X    

DOI:10.1063/1.45005

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The synergism observed between NBI and ICRH is theoretically interpreted for the interaction at the second and third ion cyclotron harmonic. It is also shown that the performances of supershot‐like discharges obtained with balanced injection can be substantially improved by beam‐RF interaction both at 2 &ohgr;CDand 3 &ohgr;CD.

ISSN:0094-243X    

DOI:10.1063/1.45017

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

ICRF heating experiments have been conducted in a variety of conditions on the TFTR tokamak. Power levels up to 11.4 MW have been applied. During NBI driven supershot discharges the central electron temperature has been increased from 9 kev to 13 kev via3He minority heating with 6 MW of RF power. This temperature increase leads to a 70% increase in the projected alpha energy slowing down time. In gas fueled L‐mode discharges the energetic hydrogen minority tail is observed to strongly influence the MHD stability of the discharges. Besides the stabilization of the sawtooth instability previously reported, the destabilization of both the m=1 fishbone and the TAE (toroidal Alfven eigenmode) instabilities have been observed. The TAE instability is accompanied with significant (∼10%) loss of high energy ions and degradation in global confinement time.

ISSN:0094-243X    

DOI:10.1063/1.45006

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Modifications have been made to allow two of the ICRF antennas (bays L and M) on TFTR to operate at either of two frequencies, 43 MHz or 64 MHz. The two frequency operation will allow a combination of3He‐minority and H‐minority heating at near full field on TFTR. Distributing the RF power between different ion species is expected to result in lower energy minority ions which have better confinement and better energy coupling to the bulk plasma. The higher frequency, 64 MHz, may also be useful in direct electron heating and current drive experiments at lower toroical fields. The two frequency capability was accomplished by lengthening the resonant loops (2&lgr; at 43 MHz, 3&lgr; at 64 MHz) and replacing the conventional quarter wave impedance transformers with a tapered impedance design. The other two antennas (bays K and N) will operate at a fixed frequency, 43 MHz. Models of the antenna, resonant loops, and impedance matching system are presented.

ISSN:0094-243X    

DOI:10.1063/1.44973

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Detailed comparisons between the calculated ICRF power deposition profiles and measured quantities for TFTR are presented. (AIP)

ISSN:0094-243X    

DOI:10.1063/1.45007

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Direct electron heating experiments were carried out in two regimes: BT=4.6 T with D+supershots; and BT=2.3 T with3He majority. The electron power deposition profiles measured with modulation of RF power are found to be strongly peaked in the core with the total volume‐integrated power of up to 80% of the modulated power. The magnitude and profile shape agree well with those predicted by a full‐wave code.

ISSN:0094-243X    

DOI:10.1063/1.44933

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Extension of an operation range for the sawtooth stabilization by a second harmonic minority ion ICRF heating is being pursued in JT‐60U. The sawtooth stabilization is obtained at relatively high density (n¯e∼3.8×1019m−3) and low‐q (qeff=4 at Ip=2.4 MA) for OH target plasmas with only 2.8 MW of ICRF power. The sawtooth stabilization is thus obtained at high ⟨ne⟩/Ptotvalue of 0.8×1019m−3mW−1, which is notably larger than the value achieved on JET, where fundamental resonance minority ion heating is employed. Another peculiar effect of the second harmonic heating is that stabilization occurs only after the inversion radius expands sufficiently, i.e., rinv/a≥0.26. The sawtooth stabilization by ICRF heating becomes easier with NBI‐heated target plasmas (longest stable period up to 1.7 sec), while it tends to be difficult with the LHCD target plasmas.

ISSN:0094-243X    

DOI:10.1063/1.44934

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Alcator C‐MOD tokamak (R=0.67 m, &agr;=0/21 m,@g‘1.8,B≤9 T,I≤3 MA) will start operating in April 1993. Initially 2 MW of rf power at 80 MHz will be available, which will be upgraded to 4 MW by early 1994. Additional 2–4 MW of 40–80 MHz tunable power may be installed in 1996 in collaboration with PPPL. With the 80 MHz transmitters, He3minority heating atB=7.9 T and H minority heating at 5.3 T are the main heating scenarios, with possibilites of He3and H second harmonic minority heating (at 3.9 T and 2.6 T, respectively) and direct electron heating by ELD/TTMP. The tunable transmitter will enable fundamental He3and H minority heating at lower fields, and Alfve´n wave heating below the ion cyclotron frequency at fields above 4 T in H plasmas. Advanced tokamak scenarios with high bootstrap current fraction and high normalized beta can also be studied in combination with pellet fueling and 4.6 GHz LHCD under TPX‐like conditions (B∼4 T,n¯e≲1×1020m−3) for pulse lengths exceeding the L/R time.

ISSN:0094-243X    

DOI:10.1063/1.44935

出版商:AIP    

年代:1994

数据来源: AIP