Fast ion collective Thomson scattering (CTS) principle

Introduction

Examples of TEXTOR fast ion CTS results from previous campaign

Slowing down of fast ions after switching off the heating

NBI & ICRH

Sawteeth

NB

I &

IC

RH

V resolved

Sawteeth and fast ions

Shot 89510

NBI(D) 1500 kW

ICRH(H) 1000 kW

V resolved

R = 1.63 m

NBI & ICRH

CTS geometry

Ion velocity distribution over timeIon velocity density as a function of time. The colours of the lines correspond to the sectional cuts in the ion velocity distribution graph above.

Velocity / m/s

( , )/vv t

dv dt

Calculated ion velocity slowing down time.

Ion velocity density distribution as a function of the velocity before and after the heating switch off.

Spectral power density.

CTS spectra 90 time slices 4 ms resolution.

In magnetically confined fusion plasmas

Thermal bulk ions and electrons have temperatures of 10 – 20 keV (100 – 200 MK)

Fast ions come from:

•Fusion processes

•Ion Cyclotron Resonance Heating (ICRH)

•Neutral Beam Injection (NBI)

Fast ions:

•have highly non-thermal populations with energies 0.1 – 5 MeV

•have relatively low density: nfast / nbulk 1 %

•may carry 1/3 of the plasma kinetic energy.

Collective fluctuations k D < 1

an upper limit of the probe

frequency an upper limit on the

scattering angle  (ki, ks).

D

Collective Thomson scattering (CTS) diagnostic systems for measuring fast ions in TEXTOR and ASDEX Upgrade are described on this poster. Both systems use millimeter-waves generated by gyrotrons as probing radiation and the scattered radiation is detected with heterodyne receivers having 40 spectral channels at TEXTOR and 50 spectral channels at ASDEX Upgrade. The antenna patterns of probe and receiver, both steerable, determine size and location of the measuring volume, and the direction of there solved fast ion velocity. The alignment of the transmission line is aided by laser beams relayed by small optical mirrors, inserted in the quasi-optical mirrors.

Related presentations :B31(H.Bindslev et. al.), B24 (F.Meo et. al.) and B35 (J.Egedal et. al.)

Fast ions are nearly invisible but their wakes give them away.

Fast ions draw a wake in the electron distribution, detectable by Collective Thomson Scattering (CTS). And at scales larger than the Debye length ion wakes are the dominant cause of microscopic fluctuations

Fast Ion

1Association EURATOM-Risø National Laboratory, DK-4000 Roskilde, Denmark

2MIT Plasma Science and Fusion Center, Cambridge, MA 02139, USA

Theoretical CTS scattering function

Fast ions can be studied from

νδ= νs - νi ~ 1 GHz

Received scattered radiation

k

Incident radiation

ks

ki

Resolved fluctuations

Scattering volume

In front of the horn on the receiver box there is a wire grid, to remove the unwanted polarisation.

There is also a chopper mirror which can be inserted when the system is calibrated.

The upgraded CTS system for TEXTOR

Blue parts: upgraded components

Receiver

The CTS system has been upgraded. The major changes are:

• A new quasi-optical transmission line and a motorized steerable mirror

• A universal polarizer

• Updates in the receiver system: extra amplifiers and a the diplexer which splits the central part of the spectrum from the upper sideband.

• A new DAQ system operating 40 channels at 100 k samples/s with a dynamic range of 24 bit.

Quasi-optical transmission line for CTS diagnostic

CTS quasi-optical transmission line Container with liquid N2

CTS cabinet with electronics

CTS portSteerable mirror

Universal polarizer

Scattering volume

CTS receiver

Alignment of the quasi-optical mirrors

Diode laser Scalar horn

Small optical mirrorPolarizers

Millimeter Wave CTS Diagnostics on TEXTOR andS. Michelsen1, 2, H. Bindslev1, J. Egedal2, J. A. Hoekzema3, S. B. Korsholm1,2, F. Leuterer4, F. Meo1, P. K. Michelsen1, S.K.Nielsen1, E. L. Tsakadze1, E.Westerhof5 and P. Woskov2

Supported by EURATOM and U.S. DoE Email: susanne.michelsen@risoe.dk Web page: www.risoe.dk/euratom/CTS

3Association EURATOM-Forschungszentrum Jülich GmbH, Institut fur Plasmaphysik, 52428 Jülich, Germany

Alignment of the system is first done with a diode laser as illustrated on the graph.

In this case the polarizer's are covered with a plate containing a small mirror.

Measurement Calculation

Test of the polarizer plates Power measured with the detector for different polarizer angles

: min power, : max power.

Detector

A detector can be used to measure the antenna patternThe Beam comes from the horn and toward the first mirror

Antenna HornNotch Filter

APadding

AttenuatorNotch Filter

B

Combined RF VCVA switch & variable attenuator

TTL controlpulses from gyrotron control

Mixer

100.5 GHz LO

Triplexer

50

30dB10dBm.

30dB10dBm

40dB23dBm

To 1st bank of 80MHzCTS monitors

To 2nd bank of 80MHzCTS monitors

To low frequency

(< 108.6GHz)

ECE monitors

30dB10dBm.

2-waypower

splitter

To high frequency

ECE monitors

J1

J3

J4

J2

Quasi-optical transmission line

18-40 GHz

2-8 GHz

8-18 GHz

Diplexer

(> 111.1GHz)

10.68-18 GHz

8-10.68 GHz

35dB15dBm 24dBm

35dB

Outline of the future receiver layout

Design and manufacture of the quasi-optical mirrors at Risø

Cloud of points

CATIA drawing

CNC Cutting tools

Final quasi-optical mirror

Surface characterization

Transmission line calculated in Matlab

Beams

Mirror

In-vessel mirrors

Steerable mirror

Corrugated waveguide

Left: The CTS operation is illustrated, since the mirror is moved into the transmission line.

In front of the horn on the receiver box there is a wire grid, to prevent standing waves. There is also a chopper mirror which can be used during calibration of the system.

Right: The switching between CTS and gyrotron operation of the beam line is done by a moveable quasi-optical mirror.

MOU box supporting frames

Quasi-optical CTS transmission line

Towards the tokamak

CTS receiver and electronics cabinet

CTS operation

Moveable mirror is in the CTS operation mode

ECRH operation

Moveable mirror is in the neutral position

Left: For calibration of the receiver the chopper mirror is used. The black body signal emitted from EchoSorb submersed in liquid N2 is compared with the black body signal at room temperature.

Right: An example of the difference in signal for one channel when the chopper mirror is in or out.

Right: The RF part, the IF part, and the filter bank of the receiver for the ASDEX Upgrade CTS system. The RF part consists of notch filters, band pass filter, wideband switch, isolators and a down-converter shifting the centre frequency from 105 GHz to 9.5 GHz. A triplexer divides the signal into three bands: 4.5 – 9.0 GHz, 9.0 – 10.0 GHz, and 10.0 – 14.5 GHz.

After a two-step amplification of 70-80 dB the signal enters the 50 channel filter bank.

ASDEX Upgrade CTS system

At ASDEX Upgrade, the ECRH system is being upgraded.

The CTS system rely on one dual frequency gyrotron at 105 GHz, with 1MW power and a pulse length of 10s.

By inserting a moveable mirror in the MOU box, of the other gyrotron, the scattered signal can be redirected into the CTS receiver box. When this mirror is inserted the gyrotron can not be used.

This modification of one MOU boxes gives optional use between CTS or gyrotron operation.

Modified transmission line for CTS

Calibration setup

Receiver

Summary

The filter bank and the receiver are located in an aluminium box on top of a cabinet containing DC amplifiers, power supplies, and the data acquisition system, similar to the one at the new TEXTOR CTS system.

Present status:

The CTS system was installed at ASDEX Upgrade in December 2003

The CTS system for TEXTOR is being upgraded and tested at Risø

Future:

Commissioning of the CTS systems

Physics exploitation of fast ions from NBI and ICRH etc.

Design of CTS on ITER is in progress (see posters B31, B24 and B35)

ASDEX Upgrade

5FOM-Institute for Plasma Physics Rijnhuizen,Association EURATOM-FOM, Trilateral Euregio Cluster, The Netherlands

4Max-Planck-Institut fur Plasmaphysik, EURATOM Association, 85748 Garching, Germany

Chopper mirrorHorn support

Container with liquid N2

T E C