17th TM on Research Using Small Fusion Devices Overview of recent ISTTOK results Presented by: C. Silva Association Euratom/IST on behalf of the ISTTOK

17th TM on Research Using Small Fusion Devices

Overview of recent ISTTOK results

Presented by: C. Silva

Association Euratom/IST on behalf of the ISTTOK Team

Collaborations:


Outline

ISTTOK brief description Test of the liquid metal limiter concept Control and data acquisition Development of diagnostics Plasma physics studies Summary


Tokamak ISTTOK

Circular cross-section

Poloidal graphite limiter

R = 46 cm

a = 8.5 cm, rvess= 10 cm

BT = 0.3-0.6 T

Ip = 4-8 kA

<ne>= 3-6x1018 m-3

D = 40 ms


ISTTOK aims

ISTTOK has been very important for the creation and consolidation of the Portuguese fusion research team

Provide basic experimental formation in fusion-oriented plasma physics and technologies to young physicists and engineers PhD, MSc, BSc, High school students programmes

Provide a test-bed for new diagnostic techniques as well as new digital instrumentation and systems

Allowing to carry out a tokamak physics programme


Liquid Metal Limiter concept


Liquid Metal Limiter concept

Motivation The high power loads may be responsible for reducing the

lifetime of the plasma facing components The use of liquid metal flow may provide an efficient mean

to exhaust heat produced in the core plasma

Free flying Ga jet Gallium: better thermal properties

than Li (ebullition point much higher) but higher Z

Jet breaks in droplets to avoid currents (jxB forces)

Stable jet successfully developed with required specifications (length ~ 13 cm for 2.3 mm nozzle)

R. Gomes: OP2


LML results on ISTTOK

LML does not affect significantly plasma behavior No significant increase in the

radiated power Jet is not an efficient limiter -

small area (2.3 mm thick) Ga emission local - No plasma /

machine contamination Gallium jet compatible with

tokamak operation but heat removal capabilities not assessed

R. Gomes, FED 07

Collaboration with Latvia

Installation on FTU (Italy) being assessed


Control and data acquisition


Control and data acquisition

Upgrade of the ISTTOK control and data acquisition system Migrate data acquisition from VME to PCI Production of new switched power supplies for

plasma position control Development of a real-time controller for the plasma

position Development of a cooperative software for shared

tokamak operation and remote data access tools Development of Videoconference tools


PCI acquisition boards (TR-512)

Number of channels: 8 (differential, galvanically isolated), 14 bits, 2 MSPS

Storage capabilities 512 MB of registered SDRAM DIMM (maximum).

Processing capabilities Processor: DSP TMS320C6415T @ 600 MHz FPGA: Xilinx® Spartan™ 3 series

M. Correia, FED 04


Real-time plasma position control

PCI-TR-512 calculates/controls the corrections fields needed for plasma position stabilization

Each power supply controls their current output to match the set-point given by PCI-TR-512

D. Valcárcel, P26

B. Carvalho, OT18D. Valcárcel, FED 06


A Standard Data Access Layer for Fusion Devices

Each laboratory uses different data store schemes To solve these problems a common software layer between

end-users and laboratories has been developed The library allows data retrieval using the same methods for

all laboratories (tested in some of the most common data analysis programs such as MatLab and IDL)

The system is already being used in ISTTOK and CASTOR/CR, ETE (particularly relevant for working groups as ITM where data access to different databases is essential)

To be extensively used during the ISTTOK JE

A. Neto, FED 07


FireSignal – user interface for data acquisition and control

FireSignal is a highly generic system for data control and acquisition

Main features: Remote hardware configuration, Shot launching, Data sharing between users, Unified user-interface for acquisition devices

FireSignal is a plugin based system. Database, data viewers and the security system are some examples of what can easily be changed and adapted to the target machine’s needs.

FireSignal is currently being used to control the ISTTOK/PT and CASTOR/CR tokamaks (started to be implemented on ETE)


Diagnostics


3 linear 10-pixel detectors Optimization of the reconstruction

methods to be used in real time Comparison of Fourier-Bessel and

Neural Network methods

Bolometer tomography

Collaboration with HAS and IPP Greifswald

P. Carvalho, P13


Retarding field energy analyser Allows the measurement of the edge ion temperature Based on the retardation of charged particles by bias

potentials applied to a number of grids Rather compact and robust (1423 mm2) The derived ion temperature (Ti = 14 eV) is ~2xTe - in

agreement with the results of the SOL models.

I. Nedzelskiy, RSI 06To be installed on TJ-II (Spain) spring 2008


Mechanical force sensor

Novel mechanical probe to measure the plasma pressure directly

Consists of two pendulums whose heads are exposed to plasma, while the deflection is measured by semi-conductor strain gauges

The plasma pressure was successfully measured Its value is in good agreement with that derived from the electrical probe data (1–10 Pa)

T. Lunt, PPCF 07

Collaboration with Ciemat and Humboldt-Universitat, Berlin


Other recent diagnostic developments

Development of a multichannel time-of-flight technique for plasma potential profile measurements by heavy ion beam diagnostic (I. Nedzelskiy, OT13)

Plasma spectroscopy in ISTTOK (J. Figueiredo, P15)

MCAD

Cs+

Stop Start

Modulator

Cs2+

Primary detector

Sample volumes Plasma


Plasma physics studies


Relevant features Emissive electrode (j=20 A/cm2) Rake probe (4mm radial resolution) Gundestrup and TTP probes

Emissive Electrode

Control of turbulence by electrode biasing

Clear improvement in particle confinement only observed for negative bias

F. Figueiredo, RSI 04C. Silva, NF 04


Edge radial profiles

In the region just inside the limiter position the magnitude of the ExB flow shear is larger for negative bias.

The ExB flow shear necessary to suppress turbulence is 3x105 s-1. For negative bias the ExB flow shear exceeds largely that value while for positive bias this is only clearly true for r-a>-2 mm.

This difference may explain the distinct behaviour of the particle confinement for positive and negative bias.


Bias effect on edge fluctuations

Edge plasma biasing strongly modifies edge fluctuations

Strong reduction in Isat and Vf fluctuations and ΓExB.

Observations consistent with a reduction of the anomalous particle flux, as a result of a reduced electrostatic turbulence.

C. Silva, PPCF 06


Fluctuations poloidal structure

Poloidal array of probes 7 pins: 3 mm long, 0.75 dia. Δθ = 1.5 mm

Correlation length ~ > 9 mm Correlation time 10 µs Poloidal velocities 1-2 km/s Evidence of multi-scale

structures with different properties

To be studied in detail during the ISTTOK Joint Experiments


Other IST contributions

Time scale analysis of the ISTTOK probe data (R. Coelho, P14)

New approach to plasma facing materials in nuclear fusion reactors (V. Livramento, OT20)


Summary

ISTTOK achievements Provide basic experimental formation in fusion-oriented

plasma physics and technologies (4 PhD, 6 MsC) Provide a test-bed for new diagnostic techniques (HIBD, RFA,

force sensors, fast tomographic reconstruction,…) as well as new digital instrumentation (PCI) and systems (real-time control, remote data access tools) This ISTTOK upgrade allowed the achievement of AC

operation Allowing to carry out a tokamak physics programme

(characterization and control edge turbulence, study of the MHD activity)

Materials for plasma facing components (Ga liquid metal limiter and development of nano-structured materials, W-nD, Cu-nD)

Documents

17th TM on Research Using Small Fusion Devices Overview of recent ISTTOK results Presented by: C. Silva Association Euratom/IST on behalf of the ISTTOK