ESS | A Preliminary Feasibility Assessment of Power Converters and Magnets for Beam Raster System| 2012-03-14| Carlos A. Martins, ESS

Preliminary Feasibility Assessment of Power

Converters and Magnets for Beam

Raster System

Carlos A. MartinsESS, Accelerator Division

1

ESS | A Preliminary Feasibility Assessment of Power Converters and Magnets for Beam Raster System| 2012-03-14| Carlos A. Martins, ESS

The (APT) Concept

Features:- 4 Horizontal Dipole Magnets; 4 Vertical Dipole Magnets (in principle all identical);- 8 independent power converters (modulators), all identical;- Magnet technology: Ferrite cores, water cooled copper windings;- Power converter technology: IGBT based H-bridges (600V, 100A);- Continuous (CW) operation;

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Cables(coaxial or tri-axial)

Power converters/current generators (triangular current waveforms)

4 H + 4 V fast AC dipole magnets

ESS | A Preliminary Feasibility Assessment of Power Converters and Magnets for Beam Raster System| 2012-03-14| Carlos A. Martins, ESS

ESS Raster systemFeatures:- 4 Horizontal Dipole Magnets; 4 Vertical Dipole Magnets (in principle all identical);- 8 independent power converters (modulators), all identical;- Pulsed Linac (duty-cycle = 5%) -> PULSED RASTER SYSTEM;- Magnet technology: Ferrite cores, Air cooled copper windings (Litz wire to reduce eddy

currents);- Power converter technology: IGBT based H-bridges (<1kV, <1kA);- Ceramic vaccuum chamber (< 1m length/section) with metallic RF coating (thickness: <

1 μm ??)

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< 1 m

Raster Dipole magnets

Side view of the raster beam line

Vaccuum chamber (ceramic) section

flange

ESS | A Preliminary Feasibility Assessment of Power Converters and Magnets for Beam Raster System| 2012-03-14| Carlos A. Martins, ESS

Main Parameters of the Raster System(*)

(source: Heine Thomsen – Aahrus University)- Number of magnets (H+V):

4+4;- Total beam deflection (H & V)(*):

1.81 mrad;- Beam deflection, per magnet (H & V)(*):

0.453 mrad;- Beam rigidity:

11 T.m;- Field accuracy (H & V):

1 %;- Max. raster frequency (H & V)(*):

20 kHz

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Beam spot trajectory (example)

time

time

Bx

0 1 2 3 4 5 6 7 8 9

Bxmax

-Bxmax

By

Bymax

-Bymax

Magnetic field waveforms in H (x) and V (y) dipoles

(*) x and y deflections considered identical for simplicity(square raster footprint)

x

y

xmax-xmax

ymax

-ymax

0 1

2

3

4

5

6

7

8

9

raster footprint

ESS | A Preliminary Feasibility Assessment of Power Converters and Magnets for Beam Raster System| 2012-03-14| Carlos A. Martins, ESS

Characteristics of Raster MagnetsFrom the former Main Parameters table:

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“Double-C” core

I : coil current;N: number of turns;g : height of the air gap;wc : width of the air gap core;wg : width of the flux in gap (wg=1.3*wc);l : magnetic length (3rd dimension);Bg : Field density in the gap;L : Magnet inductance:

“C” core

g

wc

wgN

I

I

l

vacuum chamber

Magnetic core

winding

ESS | A Preliminary Feasibility Assessment of Power Converters and Magnets for Beam Raster System| 2012-03-14| Carlos A. Martins, ESS

Analytical Dimensioning of Raster Magnets(from Heine Thomsen inputs)

From the former Main Parameters table:- Magnetic length, (H & V): 300 mm;- Magnet air gap height, (H & V): 100 mm; (80 mm chamber inner

diameter)- Magnet air gap width (H & V): 100 mm; (80 mm

chamber inner diameter)- Field amplitude, Bxmax/Bymax (H & V) (*): 17 mT (compatible w/ ferrite

core);

- Magnet current amplitude, peak: 440A;- Magnet coil number of turns: 3;- Effective magnet air gap cross section: = 1.3*0.1*0.3 = 0.039 m2;- Magnet inductance: 4.45 μH;- Cable inductance: 6 μH; (20m distance)- Magnet coil cross section: 11 mm2;- Magnet coil length: 2.4 m;- Magnet coil resistance: 4 mΩ;- Magnet coil losses during pulse flat-top: 388 W;- Magnet coil losses (average, 5% duty-cycle): 19.4W; (compatible w/ air cooling, Litz

wire)6

Note: All calculations are in magneto-static conditions; effect of eddy currents neglected;

ESS | A Preliminary Feasibility Assessment of Power Converters and Magnets for Beam Raster System| 2012-03-14| Carlos A. Martins, ESS

Characteristics of Power ConvertersFrom the former Main Parameters table:

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DRIV

ER

DRIV

ERCAPACITORCHARGER

COAX CABLEVC

+

-

DRIV

ER

DRIV

ERCAPACITORCHARGER

COAX CABLEVC

+

-

X 8

time

IImax

-Imax

time

VVC

-VC

Control flexibility:- Adjust Vc, i.e. the dI/dt (slope);- Choose all switching instants;

(choose frequency and current amplitudes)

But:- Positive slope = negative slope;- Impossible to adjust the slopes inside a beam

pulse, but possible from one pulse to the next one;

ESS | A Preliminary Feasibility Assessment of Power Converters and Magnets for Beam Raster System| 2012-03-14| Carlos A. Martins, ESS

Dimensioning of Power Converters

From the Magnets & cable parameters table:- Output voltage (peak): = (Lmag+Lcable)*dI/dt =

+/- 370 V;- Output current (peak): +/- 440A;- Max. switching frequency: 20 kHz (3.5ms / 14

Hz);

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- Straightforward design;- Dimensions: 19” rack, 3U height, 600mm depth;- Cost per power converter: < 5 kEURO (*);- Cost of the entire power supply system (including controls): < 50 kEURO (*);

(*): does not includes development costs

ESS | A Preliminary Feasibility Assessment of Power Converters and Magnets for Beam Raster System| 2012-03-14| Carlos A. Martins, ESS

Conclusions

Technical:- Effect of the vacuum chamber coating thickness on the field distortion;- Controls of the power converters, assuring raster pattern quality;- Interlocks (Beam interlocks, field interlocks, current interlocks);- Redundancy ? If yes, how to manage it ?

Organizational:- Prototyping ? Testing without beam / with beam ?- Development plan ?

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Open points

- Power converters and raster magnets seem feasible at moderate costs;- Use of ceramic vacuum chambers (< 1m) would be preferable wrt vacuum tanks;- 2 raster magnets per chamber section leads to total length = ~ 4 m (optimization still

possible);- Power converters should be placed in a place such that cable lengths to magnets < 20 m;