power neutral beam on rfx-mod: design and mission

RFP Workshop Stockholm 9-11 / 10 / 20098

Power Neutral Beam on RFX-mod:Design and Mission

M Valisa, M Gobbin, L Grando, L Marrelli, S Martini, R Piovan, A Rizzolo, P. Zaccaria and the RFX team Consorzio RFX

Y. Hirano, S. Kiyama, H. Sakakita AIST Tsukuba


OUTLINE

- Mission : to study physics of energetic particles on RFX

- Design status :

1. Issues to be solved to connect the AIST beam on to RFX-mod

2. Diagnostics to be implemented for the beam exploitment

Outline


• Advanced scenarios have been reached in Tokamaks by controlling the current profile. Methods include use of neutral beams and radio frequency injection

• As in Tokamkas, auxiliary power can be used in RFP’s to optimize plasma control and performance and widen the physics studies.

• MST ( Madison, Wisconsin) is testing - Lower Hybrid & Berstein waves & Neutral Beam Injection for current drive and heating (25keVx40A)

•TPE-RX (Japan) has developed a 1.2 MW neutral beam injector.

Motivation


TPE-RX (*) has been dismantled (Jan 2008) .

Unique opportunity to loan their Neutral Beam.

Beam characteristics

Positive Ion source (filament type)Energy : 25 keVIon Current : 50 APulse Duration : 30 ms

The TPE-RX beam is available

(*) AIST – Tsukuba Japan


Strong focussing: 4 cm of minimum waist Suitable to fit the existing RFX-mod ports( 100 - 150 mm)

The TPE-RX beam

0

20

40

60

80

100

120

1000 1200 1400 1600 1800 2000 2200

beamradZ (-) Z (+) Y (-) Y (+)

Bea

m r

adiu

s, r

(m

m)

Distance from electrode, X (mm)


The TPE RX Neutral Beam Injector

Source

Expansion chamber


The TPE RX Neutral Beam Injector


The power supply


• Plasma heating

• Momentum injection

• Current drive

Control of MHD dynamo and tearingactivity.

• Fast particle confinement, beta and instabilities. ( Alfven mode excitation by fast ions. In particular, mediation of energytransfer to thermal ions)

• Core particle source

Scientific objectives


On RFX only radial injection possible


•The initial pitch of the particle is zero (but for the beam divergence): the initial velocity is mainly perpendicular to the field ( apart from the large divergence term).

• Particles ionized on the Low Field side are deeply trapped.• Particles ionized beyond the axis are passing.

Current and momentum drive is low

Detailed simulation of the experiment to be done shortly evaluate best position for diagnostics

Consequences of the radial injection

R, cm

Z, cm

(ORBIT simulation by M. Gobbin)


0

0,2

0,4

0,6

0,8

1

1,2

0 0,2 0,4 0,6 0,8 1

E_BEAM =25 keVNormailzed Attenuation

ne=5e19 m-3 (NORM_extrap)ne=1e19 m-3 (NORM_extrap)

r (m)

Because of the 25 keV, shine-through issuesare not severe for the RFX densities

Beam attenuation

(ADAS data / flat density profile)

In RFX a(minor radius) = 0.459 m


Heating

• 1 MW of injected power in standard discharges is marginal to be sizeable on top of the typical RFX input power > 10 MW.

• Slowing down time is 40-60 ms, against a confinement time of approx 3 ms, so that heat release is diluted in time. Heating efficiency will be low

• Perhaps some effect during enhanced confinement regimes (QSH, PPCD, OPCD..) with reuced input power .

2 MA

From P. Innocente et alRFP workshop 2008, Stockholm


Fast Ion Physics

Relevance:

Sufficient confinement of fast ions (MeV) is a mandatory requisite of burning plasmas.

Collective modes excited by fast ions can enhance energy and momentum losses and cause wall damage

Long time-scale non linear processes are expected from interaction of collective modes and fast ion dynamics as well as between drift waves and turbulent transport

Fast Ion Physics


- In MST 25 keV particles have exp. confinement times ( 30 ms)!

Fiksel G. et al 2005 Phys. Rev. Lett. 95 125001

Fast Ion Physics

>Neutron emission in MST after beamshort pulse

MST


Estimated Slowing down timein RFX-mod ~ 40-60 ms (Simulations in progress including main losses mechanisms, i.e. mg perturbations, ripple, CX etc.)

Gobbin et al Nucl. Fusion 48 (2008) 075002

Fast Ion Physics


Design and construction of a new mechanical interface

(expansion chamber and stand).

Is a Residual Ion Dump necessary?

Design of a new magnetic shield for the source and the neutralizer

(higher stray fields on RFX than on TPE)

Design of the power supply layout and connection to the beam

Procurement and installation of ancillary equipment (cooling, gas valve PS etc)

Integration in the RFX timing sequence

Personnel training (Collaboration from TPE RX expected )

Development of kinetic models for simulation and interpretation

(Colalboration with MST would be helpful)

Development of diagnostics

Installation on RFX not trivial


Max filed tolerated in

ion source ~ 0.5mT

neutralizer ~ 1mT

Sourceneutralizer

Screening mg fields

Filaments are ON 30 sec before pulseTherefore must stand the field generated by the magnetizing windings (60 mT) during charging time( few sec.s) before the RFX-mod discharge

Screen must not perturbe the RFX field .

ongoing work


NBI diagnostics

An NPA diagnostic presently being procured for general Ti

measurements on RFX-mod will also be used to study fast ions produced by the power NBI

Development/ procurement of a Fast Ion Losses Diagnostic (FILD) to directly study the losses due to instabilities.

Neutron diagnostic only if D operation will be permitted

CERS will be expanded to the power beam.

Diagnostics


Currently discussing about the use of the old NPA of RFX ( originally built for JET in the early 80’s) and the loan of a ACORD model (IOFFE Institute) from Greiswald (IPP COLLABORATION) in view of (possibly) the procurement of a Compact NPA ( IOFFE)

NPA

IOFFE INSTITUTE http://www.ioffe.rssi.ru/ACPL/npd/npahtml/00/00.htm

Old JET NPA efficiency vs neutr. pressure ( high –top – and low – bottom energies)


Fast Ion Losses Diagnostic

• FILD allows to directly study the losses due to instabilities.

• Scheme as in JET and ADEX-U: magnetic spectrometer disperses fast ions onto a scintillator, the strike point depending on gyroradius and pitch angle.

• Detector head: 3-dimensional ion collimator, stainless steel plate coated with scintillator powder and a graphite cap.

• Collimator geometry to be optimized by simulating typical particle trajectories of interest.


Alternatively: Faraday cup collector

• Alternatively FILD realized with Faraday foil collectors:

• Charged particles penetrate a stack of conducting foils, separated by insulating foils.

• Number of foils passed before being stopped and generating a current signal depends on their energy .


Timeline

Delivery Autumn 2008

Installation Winter 2008 /Spring 2009

( various steps during RFX ordinary

maintainance periods)

Commissioning/connection to RFX Summer/Autumn 2009

Installation of related diagnostics Autumn/Winter 2009

Operation Winter 2009 / early 2010

Timeline (Temptative

power neutral beam on rfx-mod: design and mission

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