Author: Artur Niemczewski
Publisher:
ISBN:
Category :
Languages : en
Pages : 290

Get Book Here

Book Description

Author: Artur Pawel Niemczewski
Publisher:
ISBN:
Category :
Languages : en
Pages : 290

Get Book Here

Book Description

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 4

Get Book Here

Book Description
Recently, much effort has been dedicated to understanding the bifurcation involved in the transition from a low to high confinement regime. While several theories have been brought forward, many factors remain to be elucidated, one of which involves the role played by neutral particles in the evolution of a transport barrier near the edge of the plasma. Alcator C-Mod is especially well suited for the study of neutral particle effects, mainly because of its high plasma and neutral densities, and closed divertor geometry. Alcator C-Mod employs ICRF as auxiiiary heating for obtaining a high confinement regime, although ohmic H-modes are routinely obtained as well. The neutrals can enter the edge dynamics through the particle, momentum and energy balance. In the particle balance, the source of neutrals has to be evaluated vis-8-vis the formation of the edge density pedestal. It is widely believed that plasma rotation is an important factor in reducing transport. In this case, neutrals could act as a momentum sink, through the charge-exchange process. That same process can also modify the energy balance of the plasma near the edge by increasing the cross-field heat flux. These effects are quite difficult to measure experimentally, in large part because neutral particle diagnosis is not an easy task, and because of the inherent 3-dimensional aspect of the problem. Consequently, the neutral s spatial and energy distributions are usually not well known. In Alcator C-Mod, we recently implemented a series of diagnostics for the purpose of measuring these distributions. They include measurements of the neutral pressure at many locations around the tokamak, and spatially resolved measurements of Lyman-a and charge-exchange power emission. A high-resolution multichord (20 channels) tangential view of neutral deuterium emission (Lyman-a) has been recently installed near the midplane. The viewing area covers approximately 4 cm across the separatrix, with a nominal 2 mm radial resolution. Standard Abel inversion techniques give the local Lyman-a emission. In conjunction with electron density and temperature, we can infer the local ionization rate and neutral density profiles. Two types of bolometer arrays (16 channels each), one being sensitive and the other insensitive to power carried by neutrals, view the plasma cross-section, tangentially at the midplane of the tokamak. By Abel inverting the difference between the 2 measurements, we infer the local power emissivity carried by neutrals[11].

Author: D. P. Stotler
Publisher:
ISBN:
Category :
Languages : en
Pages : 11

Get Book Here

Book Description

Author: A. Niemczewski
Publisher:
ISBN:
Category :
Languages : en
Pages : 11

Get Book Here

Book Description

Author: D. P. Stotler
Publisher:
ISBN:
Category :
Languages : en
Pages : 11

Get Book Here

Book Description

Author: Maxim V. Umansky
Publisher:
ISBN:
Category :
Languages : en
Pages : 131

Get Book Here

Book Description

Author: Aaron Craig Bader
Publisher:
ISBN:
Category :
Languages : en
Pages : 220

Get Book Here

Book Description
In this thesis we discuss measurements and modeling of minority heated fast-ion distributions in the Ion Cyclotron Range of Frequencies (ICRF) on the Alcator C-Mod tokamak. Analysis of fast-ions >100Te is important for both ITER and a future fusion reactor as both will have a significant population of 3.5 MeV alpha particles generated in fusion reactions. Fast particles in this energy range can drive unstable modes such as Toroidal Alfvén Eigenmodes (TAEs) and Reversed Shear Alfvén Eigenmodes (RSAEs). Furthermore, energetic ions may display plasma properties that differ from the bulk plasma. It is crucial to benchmark current simulation codes with measurements from highly energetic fast-ions on current devices. This thesis will focus on measurements of the fast-ion distribution made on C-Mod with an upgraded Compact Neutral Particle Analyzer (CNPA). Measurements of the fast-ion distributions will reveal strong dependences of the fast-ion effective temperature on both electron density and plasma current. For further analysis, we use the simulated distributions generated by the coupled full-wave spectral solver AORSA, with the zero orbit-width bounce-averaged Fokker-Planck code CQL3D. A new synthetic diagnostic integrated into CQL3D is used to make direct comparisons with the CNPA. We find that for plasmas that have a steady-state fast-ion distribution (df /dt = 0) the simulation and the experiment have good agreement. However, in simulations where the fast-ion distribution is evolving in time (df/dt =/ 0) we find a discrepancy between the simulation and the experimental results. The simulation is seen to evolve much slower than the experiment. Various reasons for the discrepancy are explored, including the possibility of a violation of the quasi-linear theory used in CQL3D.

Author: Earl S. Marmar
Publisher:
ISBN:
Category :
Languages : en
Pages : 16

Get Book Here

Book Description

Author: Cindy R. Christensen
Publisher:
ISBN:
Category :
Languages : en
Pages : 184

Get Book Here

Book Description