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Journal ArticleDOI

Parametric instabilities and plasma heating in an inhomogeneous plasma

01 Apr 1976-Nuclear Fusion (IOP Publishing)-Vol. 16, Iss: 2, pp 269-278
TL;DR: In this article, experimental studies of plasma heating due to microwave irradiation of the magnetically confined plasma column in the Princeton L-3 device are presented, and detailed measurements of electron heating rates are presented and compared with collisional heating rates.
Abstract: Experimental studies of plasma heating due to microwave irradiation of the magnetically confined plasma column in the Princeton L-3 device is presented. X-band (10.4 GHz) microwave power, both in the ordinary and the extraordinary modes of propagation, is used in these experiments. Plasma heating is observed to occur simultaneously with the occurrence of parametric decay instabilities. The mode structure of the pump wave and the decay ion wave dispersion have been measured with high frequency probes. Detailed measurements of electron heating rates are presented and compared with collisional heating rates. In addition, production of suprathermal electrons and ions is also observed and measured. A comparison is made with recent laser-pellet interaction experiments.

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  • This requires either sufficiently high temperatures and/or sufficiently collision-. . less plasmas, and electromagnetic waves incident onto an inhomogeneous plasma from'the outside.
  • The density gradient scale length is typically.

An example of P=

  • In order to verify that the low frequency decay waves were ion acoustic waves, the authors carried out interferometrkc measurements somewhat above threshold using band-pass filters.
  • The authors see that the heating rate increases roughly linearly with input power.
  • Thus, the authors conclude that for input powers a factor of five or more above threshold the main body electron temperature is heated anomalously fast due to the simultaneously occur.ing (and localized in the same radial position) parametric,instabilities.
  • Finally, the authors should mention that they have also attempted to measure the possible presence of anomalous reflection and/or absorption directly, using directional couplers 'in the waveguide (placed just before the .incident microwave horn).
  • These measurements showed only 7% reflection, almost independent of incident power.

Pe

  • In Fig. 12 the authors .show the electron distribution function due to the parametric decay.
  • The authors see that both main body and :tail . . heating occurs, and that the results are quite similar to.
  • For longer pulse lengths ionization took place, and no measurements were taken.

We have studied excitation of parametric instabilities

  • During microwave heating of a magnetized plasma.
  • Since the magnetic field was weak (i.e., R < o ) the heating observed we.
  • The importance of some of these effects have been discussed recently [15] .
  • The local threshold (near the critical layer) for these instabilities was comparable with the predictions of uniform plasma theory (well within anaorder of magnitude) in both the .
  • Ordinary and the extraordinary modes of propagation.

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OCTOBER
I975
-
PARAMETRIC INSTABI LIT1
ES
AND
PLASMA
HEATING
IN
AN
INHQMOGENEOUS
PLASMA
Ma
PORKOLAB,
Vm
ARUNASALAM,
Nn
C,
LUHMANN
JR,,
AND
Jn
Pa
Ma
SCHMITT
PLASMA PHYSICS
LABORATORY
-
[
PRIN-cEToN
UNIVERSITY
I
PRINCETON,
NEW
JERSEY
This
work
was supported
by
U.
S.
Energy Research and Development
Administration Contract
E
(11-1)
-3073.
Reproduction, translation,
publication, use and disposal,
in whole or in part,
by
or for
+he
United States Government is permitted.

DISCLAIMER
This report was prepared as an account of work sponsored by an
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makes any warranty, express or implied, or assumes any legal
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Portions of this document may be illegible in
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from the best available original document.

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ernment. Neither the United States nor the
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.
PARAMETRIC INSTABILITIES AND PLASMA HEATING
IN AN INHOMOGENEOUS PLASMA.
*
..
.
I
M.
PORKOLAB,
'V.
ARUNASALAM,
N.'
C. LUHMANN JR. ,+'and
J.
P.
M.
SCHMITT~.
Plasma Physics Laboratory, Princeton university
princeton, New Jersey
08540
USA
-
NOTICE
I
their
employ@,
\
ABSTRACT
>..
-
Experimental studies of plasma heating due to
microwave irradiation of the magnetically confined
plasma column in the Princeton L-3 device is presented.
X-band
(10.4
GHz)
microwave power, both in 'the ordinary
'and the extraordinary modes of propagation, is used in
these experiments. Plasma heating is observed to occur
simultaneously with the occurance of parametric decay
instabilities. The mode structure of the pump wave and
the decay ion wave dispersion has been measured with
high frequency probes. Detailed measurements of electron
heating rates are presented and compared with
collisional
heating rates. In addition, production
of
suprathermal
electrons and ions is also observed and measured. A
\
b
comparison is made with r.ecent
laser-pellet'inte%action
\<<
\
experiments.
'
\
t
Pro~cnt
address:
bepartment of Electrical Sciences,
university
of
California, Los Angeles, California.
d
Present addrcsa: Laboratoire Be Physique des Milieux ~onises,
Ecole Polytechnique, Palaiseau, France.
.
.
f

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TL;DR: A review of experiments and theory of electron cyclotron resonance heating (ECRH) and current drive (ECCD) is presented in this article, where the basic linear theory of wave propagation and absorption is given and compared with experimental results from many devices.
Abstract: A review of experiments and theory of electron cyclotron resonance heating (ECRH) and current drive (ECCD) is presented. An outline of the basic linear theory of wave propagation and absorption in the electron cyclotron range of frequencies and their harmonics is given and compared with experimental results from many devices. The experimental data base on quasilinear and nonlinear physics as well as on parametric wave decay is reviewed and compared to theory. Experiments and theory on doppler shifted absorption either by bulk or tail electrons (which can be created by other means) are discussed. ECRH provides means for controlled plasma breakdown and current ramp up in tokamaks and plays a key role in net current-free stellarator research. Start-up was investigated in many tokamaks and stellarators and the results are discussed in the light of the present day theoretical understanding. The role of ECRH to improve the understanding of both particle and energy confinement is described and special heating correlated features, such as 'density pump out' during ECRH are discussed. The application of modulated ECRH for perturbative heat wave studies and the comparison with both sawtooth heat pulse propagation and the steady state power balance analysis is presented. Electron cyclotron current drive is a possible method for current profile and MHD control in tokamaks and provides means for bootstrap current compensation in stellarators. The basic theory of electron cyclotron current drive is presented and compared to experiments in both tokamaks and stellarators. Experiments on sawtooth stabilization and MHD control by ECRH or ECCD are discussed and compared to theory. An increasing number of fusion devices is equipped with ECRH for bulk heating and sophisticated plasma physics investigations. A remarkable extension of the accessible plasma parameter range became possible by the recent development of sources with high power (1 MW) and frequency (110-160 GHz). Particular emphasis is given to new experiments and the refinement of theory incorporating plasma phenomena and the mutual impact on the wave physics.

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TL;DR: The theory and present experimental status of parametric instabilities in CTR oriented magnetized plasmas is reviewed in this paper. And the most recent non-linear theory is summarized in a compact form.
Abstract: The theory and present experimental status of parametric instabilities in CTR oriented magnetized plasmas is reviewed. Both linearized theory and the most recent non-linear theory are summarized in a compact form. The regimes of upper hybrid frequency, lower hybrid frequency, ion cyclotron frequency, Alfven wave, and TTMP are covered. In each case the important parametric processes are discussed, including some work on the coupling to drift waves. Then recent experimental results which indicate the importance of parametric phenomena are presented.

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TL;DR: In this article, a suprathermal electron beam is injected parallel to vector B in a low-..beta.. plasma, and the sharp space-potential drop across the surface of the beam generates a strong cross-field current which in turn drives a modified two-stream instability at the lower hybrid frequency.
Abstract: A suprathermal electron beam is injected parallel to vector B in a low-..beta.. plasma. The sharp space-potential drop across the surface of the beam generates a strong cross-field current which in turn drives a modified two-stream instability at the lower hybrid frequency. Intense stochastic ion heating is observed with the onset of the instability, and the heating rate is found to be proportional to the wave energy.

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TL;DR: In this paper, a comparative study of X-and O-mode high field side launch for electron cyclotron heating breakdown and startup of tokamak plasmas has been performed.
Abstract: A comparative study of X- and O-mode high field side launch for electron cyclotron heating (ECH) breakdown and startup of tokamak plasmas has been performed. It is found that X-mode power is not absorbed at the cyclotron resonance but uniquely at the upper hybrid resonance, displaced to the low field side of the cyclotron resonance. O-mode power, however, is absorbed at the cyclotron resonance as well. The displacement of the upper hybrid resonance to the low field side with O-mode launch is significantly smaller than that with X-mode launch because of the lower densities produced by O-mode launch at the same microwave power level. The result is a more central and less localized breakdown with O-mode launch. The breakdown characteristics of X- and O-mode launch are seen to affect the position of the initial plasma current centroid in the poloidal cross-section. There is a strong correlation between the initial current ramp rate and the initial plasma current position which is most likely due to the dependence of the plasma inductance, toroidal electric field and field line connection lengths on the plasma major radius. O-mode launch starts the plasma more centrally than X-mode launch and results in higher current ramp rates. X-mode startup occurs further to the low field side where current ramp rates are observed to be poor

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Journal ArticleDOI
B. Grek1, H. Pepin1, T.W. Johnston1, J.N. Leboeuf1, H.A. Baldis 
TL;DR: In this paper, an attempt is made to carry out a global series of measurements and interpret them in the light of currently available theory, including absorption, reflection, ion and X-ray emission (line and continuum) and in considerable detail the infra-red emission spectra of the plasma in the vicinity of the incident 10.6?m radiation as well as its harmonics were measured.
Abstract: Experimental results of the interaction of short (1.5 ns) CO2 laser pulses with solid targets at a flux reaching 1013 W/cm2 are presented. An attempt is made to carry out a global series of measurements and interpret them in the light of currently available theory. The absorption, reflection, ion and X-ray emission (line and continuum) and in considerable detail the infra-red emission spectra of the plasma in the vicinity of the incident 10.6 ?m radiation as well as its harmonics were measured. From the emission spectra the existence of the parametric decay and the stimulated Brillouin backscatter instabilities was identified. Furthermore, the energy and angular dependence of the reflected-light calorimetry in addition to the X-ray and ion emission results are found to be consistent with the hypothesis that the interaction of high power CO2 lasers with plasmasis dominated by non-linear effects such as the parametric decay instability.

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References
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TL;DR: In this article, the theory of the three-wave parametric instability for weakly inhomogeneous media is derived with an application to laser pellet irradiation and applied to laser beamforming.
Abstract: The theory of the three-wave parametric instability for weakly inhomogeneous media is derived with an application to laser pellet irradiation.

496 citations

Journal ArticleDOI
Kyoji Nishikawa1
TL;DR: In this paper, the coupling of two waves due to the presence of a third wave with large amplitude is studied on the basis of simple model equations, and the conditions for excitation of the first two waves are discussed for the following three cases: i) ω 1, ω 2 are large compared with their frequency shift.
Abstract: The coupling of two waves due to the presence of a third wave with large amplitude is studied. On the basis of simple model equations, the conditions for excitation of the first two waves are discussed for the following three cases: i) \(\omega_{1}+\omega_{2}{\risingdotseq}\omega_{0}\) and ω 1 , ω 2 are large compared with their frequency shift, ii) \(\omega_{1}{\ll}\omega_{2}{\lesssim}\omega_{0}\) and iii) \(\omega_{1}{\ll}\omega_{0}{\lesssim}\omega_{2}\), where ω 1 , ω 2 are the unperturbed frequencies of the two waves under consideration and ω 0 is the frequency of the incident large amplitude wave. In the first two cases, the excited wave is found oscillatory, while in the third it is found non-oscillatory. The threshold power of the incident wave for the onset of excitation, the frequency shift at the threshold and the growth rate above threshold are calculated in each case.

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TL;DR: In this paper, magnetic fields in the megagauss range have been observed in the laser-produced plasma near the focus of a high-power laser pulse, and faraday-rotation measurements utilizing the light of a probing beam and the specularly reflected laser light both show the presence of these large fields.
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TL;DR: In this article, the threshold ac electric field required for the excitation of the purely growing "oscillating two-stream" and decay instabilities is found to increase when the density gradient scale length H becomes less than the mean free path.
Abstract: The threshold ac electric field required for the excitation of the purely growing “oscillating two‐stream” and decay instabilities is found to increase when the density‐gradient scale length H becomes less than the mean free path. For a plasma with no magnetic field, the threshold field is given by E2/4πnTe≈2(k‖H)−1, where k‖≲(1/4)D−1 is the wavenumber of the instability in the direction orthogonal to the density gradient. (D is the electron Debye length.) Qualitative arguments suggest that this result should hold in the presence of a magnetic field. Recent experimental measurements of the threshold field agree well with these theoretical calculations. The reason for the threshold field increasing is that, in an inhomogeneous plasma, the unstable region has a finite extent spatially and energy (in the form of electron plasma waves) can propagate out of this region, thus creating an energy loss not found in uniform plasmas.

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