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;