powerful rf ion sources for fusion - agenda (indico)€¦ · powerful rf ion sources for fusion...

Ursel Fantz for the IPP-NNBI Team

IPAB2016, Legnaro (Padova) March 14-15, 2016

Towards 40 A Negative Hydrogen Ion Beams for Up to 1 hour

Powerful RF Ion Sources for Fusion

Max-Planck-Institut für Plasmaphysik

The half size ITER source at the ELISE test facilty

Ursel Fantz, p. 2 IPAB2016: March 14-15, 2016

Neutral Beam Injection (NBI) for ITER

~ 25 m

Beam line

RF ion source and

MAMuG accelerator

neutralizerRIDcalorimeter

gate valve

bellows

~ 25 m

Beam line

RF ion source and

MAMuG accelerator

neutralizerRIDcalorimeter

gate valve

bellows

Diagnostic beam (100% IN)

3 MW 3 s every 20 s, 100 keV Hydrogen

Heating beams (50% EU, 50% JA)

33 MW injected power from 2 injectors 3600 s, 1 MeV Deuterium

15 m beam line based on

negative hydrogen ions

An international project that aims to demonstrate that fusion is an energy source for the future!

Bellows Gate valve

Calorimeter Residual ion dump Neutralizer

RF ion source Accelerator

Ion generation Acceleration Neutralisation Transport


Ion sources in present NBI systems: Example ASDEX Upgrade

40 cm

Beamline 1 Arc sources: H 85 A, 55 kV, 7.2 MW D 75 A, 65 kV, 10 MW

Beamline 2 RF sources: H 62 A, 72 kV, 5.6 MW D 62 A, 93 kV, 10 MW

Sources for positive ions (> 60% H+) at low pressure ( ~1 Pa) and high power (~100 kW)


Ion sources – Two concepts

High-current

tungsten filaments

RF

coils

Faraday shield

Inductively driven source

RF power supply ( 100 kW)

RF frequency 1 MHz

Long lifetime

Arc sources RF sources

AUG sources

Hot cathodes (2000 – 3000 K)

DC voltage ( 100 V)

Arc current (1000 A)

Regular maintenance


Positive or negative hydrogen ions?

Question answered by requirements on beam energy needed for heating and current drive

ITER: 1 MeV (D) for substantial CD

Negative ions

Fragile objects

(binding energy: 0.75 eV)

Co-extracted electrons

Accelerated electrons damage electrodes ! Deflection of electrons by a magnetic field in the 2nd grid, the extraction grid, keeps heat load below tolerable amount.

Low current densities

j(H¯) 0.1 j(Hx+)

ITER: 40 A D¯

for 16.5 MW power

ITER: electrons / ions < 1

Large sources


How to create negative hydrogen ions?

Volume process

Dissociative attachment

Vibrational excitation

e- + H2 → H2(B,C) + e- → H2(v) + e- + hn

e- + H2(v) → Hˉ + H

hot electrons

cold electrons

High electron density and high pressure

Plasma Generation

„hot“ electrons

Expansion

ChamberMagnetic FilterDriver

2He fast

*

2He fast eH *

2

eHH

eVTe 5 eVTe 1

H

H

e

„cold“

electrons

Plasma Generation

„hot“ electrons

Expansion

ChamberMagnetic FilterDriver

2He fast

*

2He fast eH *

2

eHH

eVTe 5 eVTe 1

H

H

e

„cold“

electrons

Concept of a tandem source

Problems:

High co-extracted electron current

Pressure and thus

Stripping losses in accelerator

Low ion current at low pressure

Hˉ + H2 H + H2 + e

ITER: p 0.3 Pa 30% losses


How to create sufficient negative hydrogen ions at 0.3 Pa?

Volume process dissociative attachment

e- + H2(v) → Hˉ + H jH- 4 mA/cm2 je/jH- > 30

Surface process

Cs layer low work function

H, Hx+ + surface e- Hˉ Cs evaporation

much higher jH- much lower je/jH-

Destruction: volume processes

Survival length of Hˉ few cm

Electron stripping

Mutual neutralisation

Hˉ + e- H + 2e-

Hˉ + H+ H + H

Hˉ + H H2 + e-

or H + H + e-

Associative detachment

(non-associative)

0

50

100

150

200

250

20 40 60 80 1001201401601800.1

1

10

100Ca

l. c

urr

ent

den

sity [

A/m

2]

0.37 Pa

0.5 Pa

0.85 Pa

1.4 Pa

0.4 Pa

no Cs

H

RF power [kW]

0.4 Pa

1.4 Pa

Ele

ctr

on t

o io

n r

atio

no Cs

0.37 Pa

0.5 Pa

0.85 Pa

RF source (2005)


The RF ion source concept for negative hydrogen ions

- -

N

S

- -

- -

(magnets turned by 90º)

e

e

Source on high potential Current density measurements

Electrical: je, jion

Calorimeter: jion, beam profile

Co-extracted electrons

Plasma grid: ~ -20 kV pos. bias: ~ 15 V

bias plate

Grounded grid

Extraction grid : ~ -15 kV

Hˉ

Cs oven

water cooled Faraday screen

Al2O3 ceramic

gas feed

Filter field

N

S

Driver Expansion Extraction

H2

e

Hx+

H

Hˉ

RF coil

10 mT

In 2007 chosen as ITER NBI reference source.


The RF ion source for ITER NBI

Prototype source

Driver

0.52 m

2 m

1 m

8 RF drivers with 4 RF generators of 180 kW power each

1.9

m

RF Driver

Extraction area 0.2 m2

1280 apertures in 16 groups

Iex = 57 A (Dˉ), Iex = 66 A (Hˉ)

jD > 28 mA/cm2, jH- > 32 mA/cm2

je/jD- < 1 (co-extracted electrons)

Stable for 1 hour

Uniform (d<10%)

p ≤ 0.3 Pa

Requirements


Achievements at test facilities: Status 2011

BAvarian Test MAchine for Negative Ions

BATMAN

Physical parameters

jH- > 30 mA/cm2

jD- > 20 mA/cm2

je/jD- < 1

0.3 Pa

(4 s)

1/8 area of ITER source, 1 driver, body 3259 cm2

* stopped operation in 2011 MANITU*

Multi Ampere Negative Ion Test Unit

Long pulse extraction

3600 s

Dˉ operation

(Hˉ)

at reduced parameters

1/2 area ITER source, 4 drivers body 7680 cm2

RADI* Former RADIal Injector of W7-AS

Size scaling

Scalability

Plasma uniformity

80 cm

okay

Tasks achieved BUT NOT SIMULTANEOUSLY IN ONE LARGE SOURCE

Task of ELISE within the F4E roadmap towards ITER NBI


The intermediate step: ELISE

8 driver, 800 kW 1.9 x 0.9 m2

Extrapolation to large ITER source within the F4E roadmap towards ITER NBI

Intermediate step: ELISE

Extraction from a Large Ion Source Experiment

1 driver, 100 kW 0.52 x 0.26 m2

IPP prototype source

Heating & Diagnostic beam European NBTF (Italy)

4 driver, 360 kW 1.0 x 0.9 m2

4 x

2 x

ITER reference source since 2007

Neutral Beam Test Facilities


The ELISE test facility

Parameter and targets

Isotope H-, D-

RF power = 2 x 180 kW in 4 drivers

Aex = 1000 cm2, uniformity > 90%

Iion,acc = 20 A, Ie/Iion < 1 at 0.3 Pa

Utot = 60 kV, Uex < 12 kV

Plasma: 3600 s Beam : 10 s every 120 - 150 s (HV)

1 m

ELISE test facility with a ½-size ITER source

Provide input for design, commissioning and operation

of ITER NBI systems and European test facilities

Demonstrate ITER parameters in large sources

Extracted currents (ions and electrons)

Beam homogeneity

Develop most efficient

source operation scenarios

Gate Valve Ø 1.25m

Main insulator

Ion source

Extraction system

Tank

Cryopumps

Diagnostic calorimeter

Beam


The ELISE test facility

ELISE test facility with a ½-size ITER source

Provide input for design, commissioning and operation

of ITER NBI systems and European test facilities

Demonstrate ITER parameters in large sources

Extracted currents (ions and electrons)

Beam homogeneity

Develop most efficient

source operation scenarios

Parameter and targets

Isotope H-, D-

RF power = 2 x 180 kW in 4 drivers

Aex = 1000 cm2, uniformity > 90%

Iion,acc = 20 A, Ie/Iion < 1 at 0.3 Pa

Utot = 60 kV, Uex < 12 kV

Plasma: 3600 s Beam : 10 s every 120 - 150 s (HV)

Source opening after 2 years of experimental phase


0

50

100

150

200

250

300

350

10 20 30 40 50 60 70 800 900.1

1

10

j ion

,ex [A

/m2]

ITER req.

ITER req.

electrons

ions

Ele

ctr

on / ion r

atio

RF power per driver [kW]

ELISE 3.8 mT BATMAN

Deuterium, 0.3 Pa

0

50

100

150

200

250

300

350

10 20 30 40 50 60 70 800 900.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

ions

j ion

,ex [A

/m2]

ITER req.

electrons

ITER

req.

BATMANELISE 2.2 mT

Ele

ctr

on / ion r

atio

Hydrogen, 0.3 Pa

RF power per driver [kW]

ELISE test facility – Short pulse operation

Size scaling: ELISE source performance compared to prototype source at BATMAN

20 s plasma, 10 s beam

Similar dependencies Lower Cs consumption than expected

Less magnetic filter field needed 80 kW/driver should be sufficient


ELISE test facility – Towards long pulses

0 100 200 3000

50

100

150

200

jion

jionjion

je

jeje

Extr

acte

d c

urr

ent density [

A/m

2]

Time [s]

40 kW

30 kW

40 kW

30 kW

0.0

0.7

1.4

2.1

2.8 Hydrogen at 0.35 Pa

40 kW/driver

30 kW/driver

Cs e

mis

sio

n [a.u

.]

0 50 100 150 2000

20

40

60

80

100

120

jionjion

je

je

Extr

acte

d c

urr

ent density [

A/m

2]

Time [s]

0.0

0.2

0.4

0.6 Deuterium at 0.30 Pa

20 kW/driver

Cs e

mis

sio

n [a.u

.]

Stable ion currents (within 5%) but high dynamics of co-extracted electrons

Co-extracted electrons limit source performance, in particular in deuterium !

je/jion < 1 je/jion > 1

Cs release by back-streaming ions


ELISE test facility – Towards long pulses

Record-setting one hour pulse at 0.3 Pa in hydrogen

Best 3600 s pulse up to now

ion = 9.3 A, je/jion < 0.4

(20 kW/driver)

1500 1600 1700 1800 1900 2000 21000

2

4

6

8

10

Time [s]

Ie,bottom

Ie,top

Curr

ent [A

]Iion

0 600 1200 1800 2400 3000 36000

20

40

60

80

100

je/jion

je

Extr

. curr

ent density [A

/m2]

Time [s]

jion

0.0

0.4

0.8

1.2

1.6

2.0

Ele

ctro

n / io

n ra

tio

H¯ beam on the calorimeter


ELISE test facility – Beam diagnostics

Grid system

Advanced beam diagnostics

To determine beam divergence and beam homogeneity

Diagnostic calorimeter with thermocouples,

water calorimetry and IR data analysis

Beam Emission Spectroscopy (BES with 20 LoS)

Tungsten wire calorimeter

Grounded grid


ELISE test facility – Beam diagnostics

5 10 15 20 25

0

2

4

6

8

Div

erg

en

ce / (

°)

Normalized Perveance / (%)

LOS #18

Beam Emission Spectroscopy

Advanced beam diagnostics

To determine beam divergence and beam homogeneity

Diagnostic calorimeter with thermocouples,

water calorimetry and IR data analysis

Beam Emission Spectroscopy (BES with 20 LoS)

Tungsten wire calorimeter

In perveance optimum: divergence between 1° and 2° and homogeneity better than 90 %

Grid system


Towards 20 A Negative Hydrogen Ion Beams for Up to 1 hour

Achievements of the ELISE Test Facility

Experience in operation of large RF beam sources

2½ years of successful operation

Inspection and maintenance

Similar dependencies as in prototype source

Less Cs consumption as expected

Lower magnetic filter field needed

80 kW/ driver should be sufficient

Beam homogeneity better than 90%

SPIDER, 2017+ ELISE, 2012+ MITICA, 2021+

NBTF in Padua, Italy

Important step within the European roadmap for ITER NBI

ITER NBI

Iion,ex Pulse Power/driver

25.5 A 20 s 52 kW

18.3 A 400 s 45 kW

9.3 A 1 h 20 kW

Hydrogen, 0.3 Pa, e/ion < 1

Co-extracted electrons limit source performance, in particular in deuterium !

powerful rf ion sources for fusion - agenda (indico)€¦ · powerful rf ion sources for fusion...

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