M. Santala

Fusion alpha-particle diagnostics for DT experiments on the joint European torus

JET equipped with ITER-like wall (a beryllium wall and a tungsten divertor) can provide auxiliary heating with power up to 35MW, producing a significant population of α-particles in DT operation. The direct measurements of alphas are very difficult and α-particle studies require a significant development of dedicated diagnostics. JET now has an excellent set of confined and lost fast particle diagnostics for measuring the α-particle source and its evolution in space and time, α-particle energy distribution, and α-particle losses. This paper describes how the above mentioned JET diagnostic systems could be used for α-particle measurements, and what options exist for keeping the essential α-particle diagnostics functioning well in the presence of intense DT neutron flux. Also, α-particle diagnostics for ITER are discussed.

Novel ion detector for fusion plasma diagnostics

A novel thin silicon detector for the neutral particle analyzers (NPA) of the joint European Torus (JET) is introduced for studying plasma characteristics during the fusion experiments. The new ion detector would replace the presently used very thin scintillator - photomultiplier tube combination. The proposed new NPA detector is based on direct conversion of charge in silicon and approximate matching of the detector thickness with the ranges of the observed ions. A thin silicon detector is only weakly sensitive to photon and neutron backgrounds but detects highly ionizing ions efficiently. Even high energy gammas deposit only little energy in the thin detector allowing effective background discrimination through pulse- height-analysis. Thin silicon strip detectors have been fabricated by using the silicon-on-insulator (SOI) technology. Fabricated detectors have 6 or 26 mum thick high resistive silicon bonded on a conductive silicon support. The thinner detectors are designed to be used for the low energy NPA and the thicker ones for the high energy NPA. The presentation comprises a short introduction to the fabricated detector structures, TCAD simulations and results of the electrical and spectroscopic characterizations.

Error estimation and parameter dependence of the calculation of the fast ion distribution function, temperature, and density using data from the KF1 high energy neutral particle analyzer on Joint European Torus

Joint European Torus high energy neutral particle analyzer measures the flux of fast neutrals originating from the plasma core. From this data, the fast ion distribution function f(i)(fast), temperature T-i,perpendicular to(fast), and density n(i)(fast) are derived using knowledge of various plasma parameters and of the cross section for the required atomic processes. In this article, a systematic sensitivity study of the effect of uncertainties in these quantities on the evaluation of the neutral particle analyzer f(i)(fast), T-i,perpendicular to(fast), and n(i)(fast) is reported. The dominant parameter affecting n(i)(fast) is the impurity confinement time and therefore a reasonable estimate of this quantity is necessary to reduce the uncertainties in n(i)(fast) below 50%. On the other hand, T-i,perpendicular to(fast) is much less sensitive and can certainly be provided with an accuracy of better than 10%

N=2 ICRH of H majority plasmas in JET-ILW

Heating single ion species plasmas with ICRF is a challenging task: Fundamental ion cyclotron heating (w = wci) suffers from the adverse polarization of the RF electric fields near the majority cyclotron resonance while second harmonic heating (w = 2wci) typically requires pre-heating of the plasma ions to become efficient. Recently, w = 2wci ICRF heating was tested in JET-ILW hydrogen plasmas in the absence of neutral beam injection (L-mode). Despite the lack of pre-heating, up to 6MW of ICRF power were coupled to the plasma leading to a transition to H-mode for PICRH>5MW in most discharges. Heating efficiencies between 0.65-0.85 were achieved as a combination of the low magnetic field adopted (enhanced finite Larmor radius effects) and the deliberate slow rise of the ICRF power, allowing time for a fast ion population to gradually build-up leading to a systematic increase of the wave absorptivity. Although fast ion tails are a common feature of harmonic ICRF heating, the N=2 majority heating features mo...

Silicon radiation detector development at VTT

VTT has two decades experience on the manufacturing and design of the silicon radiation detectors. The activities cover a range of industrial devices as well as the devices for the physics experiments. The paper gives an overview on the new solid state detector development activity at VTT that comprise advanced X-ray photo diodes, through wafer interconnections for the photo diode arrays, thin silicon strip detectors, active-edge strip and pixel detectors with different biasing schemes, and full 3D 1 mm thick active edge silicon detectors.

ICRH for core impurity mitigation in JET-ILW

Ion cyclotron resonance frequency (ICRF) heating has been an essential component in the development of high power H-mode scenarios in JET-ILW. The steps that were taken for the successful use of ICRF heating in terms of enhancing the power capabilities and optimizing the heating performance in view of core impurity mitigation in these experiments will be reviewed.

Development of RF Tools and Scenarios for ITER on JET

The improvement of LH coupling with local puffing of D2 gas, which made operation at ITER relevant distances (10 cm) and with ELMs a reality, has been extended to ITER‐ like plasma shapes with higher triangularity. With ICRF, we developed tools such as (1) localized direct electron heating using the 3He mode conversion scenario for electron heat transport studies, (2) the production of 4He ions with energies in the MeV range by 3 ωc acceleration of beam injected ions at 120 keV to investigate Alfven instabilities and test α diagnostics, (3) the stabilisation and destabilisation of sawteeth and (4) ICRF as as a wall conditioning. Several ITER relevant scenarios were tested. The (3He)H minority heating scenario, considered for the non‐activated start‐up phase of ITER, produces at very low concentration energetic 3He which heat the electrons indirectly. For n3He/ne > 2%, the scenario transforms to a mode conversion scenario where the electrons are heated directly. The (D)H minority heating is not accessible ...