klystron modulators for 1) – the lp-spl and for 2) – the hp-spl

CERN

Klystron modulators for: 1) LP-SPL ; 2) HP-SPL 1

Klystron Modulators for1) – the LP-SPL

and for2) – the HP-SPL

Carlos DE ALMEIDA MARTINS

CERN – AB / PO

Pulsed and High Voltage Power Converters Section

11 Dec 2008

CERN


Summary

1 – Modulators for the LP-SPL @ 2 Hz

• Selected topology. Advantages

2 – Modulators for the HP-SPL @ 50 Hz

• Why not the same topology as the LP-SPL ?

• The SNS modulator, by LANL. Design key points

• Proposed topology. Advantages

• Preliminary theoretical studies

11 Dec 2008

CERN

11 Dec 2008 Klystron modulators for: 1) LP-SPL ; 2) HP-SPL 3

1. Modulators for the LP-SPLMain parameters

Cathode power supply- Pulse width: 2.3 ms- Flat-top duration 2 ms- Precision at flat-top: < 1%- HF ripple at flat-top: < 0.1%- Repetition rate: 2 Hz- Nominal voltage: 110 kV (*)- Nominal current: 91 A (*)- Nominal power (peak): 10 MW (*)- Rise/fall times (99% / 1%): 300µs- Cooling: Air (natural or forced)- Maximum energy in case of arc: < 20 J

No Anode Mode terminal

Pulse width

Rise time fall time

timeFlat-top

(*) to be confirmed, taking the new klystrons design into consideration

CERN


1. Modulators for the LP-SPLSelected topology.

Same as Linac 4 and ~same as 3 MeV Test Stand Simplified schematics

Description• Capacitor bank charged via a standard commercial power converter, PS1;• Pulses formed by solid state medium-voltage switches;• Step-up pulse transformer with oil insulation;• Droop compensation system, PS2;• Commercial filament power converters, PS4;• No CROWBAR needed in the HV line for klystron arc protection

PULSE TRANSFORMER

(OIL TANK)

Main solid state switches

C

1:30

Ca

pa

cit

or

ba

nk

ch

arg

er

po

we

r c

on

ve

rte

r, P

S1

C - Collector;K - Cathode;F - FilamentVout

Droop compensation power converter or “bouncer”, PS2

5 mFCapacitor discharge

system

VPS1

VPS2

4.5 kV

-110 kV

K1

A

DRIVER DRIVER

K

F

KLYSTRONhead

KLYSTRON(OIL TANK)

Filament (floatting)power supply, PS4

11 Dec 2008

CERN


Cathode ratings: 100 kV, 20A, pulsed 2 Hz, flat-top: 600 s

A global klystron supply solution:( Cathode, Anode, Filament power supplies in one system )

Prototype for the 3 MeV Test Stand.

Flat-top width: 30% of the LP-SPL;

Peak power: 20% of the LP-SPL;

Average power: 16 % of the LP-SPL;

11 Dec 2008

CERN


Load Voltage

-20

0

20

40

60

80

100

120

0.E+00 2.E-04 4.E-04 6.E-04 8.E-04 1.E-03 1.E-03

time (s)

Vk

(k

V)

Cathode voltage

Thyratron Firing

Cathode Voltage(20kV/div)

Cathode Current (4A/div)

Earc (65kV)=0.44JEarc (100kV)~1J200µs

Normal Operation Arc protection(short circuit with Thyratron)

Load Voltage (Zoom)

95

97

99

101

103

105

107

-2.E-04 0.E+00 2.E-04 4.E-04 6.E-04 8.E-04

time (s)

Vk

(k

V)

With bouncer

Without bouncer

< 1%

Cathode voltage (zoom at flat-top)

Test of the prototype in a dummy load


11 Dec 2008

CERN


Normal Operation at nominal

Test of the prototype with the LEP klystron


Ch4:Anode Voltage to ground(10 kV/div)

Ch3:Cathode Current(4A/div)

Ch2: Cathode Voltage to ground(20 kV/div)

Ch4:Anode Voltage to ground(1 kV/div)

Ch3:Cathode Current(0.8A/div)

Ch2: Cathode Voltage to ground(2 kV/div)

1.2%

1%

< 1%

Zoom at flat-tops

11 Dec 2008

CERN


1. Modulators for the LP-SPLAdvantages of this topology.

Advantages• Simple and reliable;• All active electronic components on transformer primary side

(medium voltage);• Easy to control and interlock;• Straightforward path from design to practical results;

11 Dec 2008

CERN


2. Modulators for the HP-SPLWhy not the same topology as LP-SPL?

Cathode power supply LP-SPL HP-SPL- Pulse width: …………………… 2.3 ms …………………. 2.3 ms- Flat-top duration ………………… 2 ms ……………………….. 2 ms- Precision at flat-top: ……………. < 1% ……………………….. < 1%- HF ripple at flat-top: ……………. < 0.1% ……………………… < 0.1%- Repetition rate: ………………… 2 Hz ………………………... 50 Hz- Nominal voltage: ………………… 110 kV ……………………... 110 kV- Nominal current: ………………... 91 A ………………………… 91 A- Nominal peak power: ………….. 10 MW ……………………… 10 MW- Nominal average power: ……. 46 kW ……………………… 1.15 MW- Rise/fall times (99% / 1%): …….. 300µs ……………………… 300µs- Cooling: …………………………… Air (natural or forced) ……. Water- Maximum energy in case of arc: .. < 20 J ……………………… < 20 J

Practical limitations of the LP-SPL topology• Relies on two SPECIAL components (solid state HV switch and pulse transformer);• The whole power has to pass through these two crucial components;

- A pulse transformer for 1.2 MW average power, 50Hz, has never been built: -demagnetization of the core during “off-time” requires high negative voltages;

- A HV solid state switch for 1.2 MW average power has never been built;• A modular approach, by placing several LP-SPL systems in parallel to increase power is

possible, however very expensive and less reliable for klystron protection in case of arc;

11 Dec 2008

CERN


The SNS modulator, by LANL

The Oak Ridge Nat Lab (SNS) type modulator, Bill Reass and Al. Los Alamos Lab

140 kV, 70A, 1.6ms, 60 Hz(9.8 MWpk, 940 kWav)

AC/DC input converter not shown

11 Dec 2008

CERN


The SNS modulator, by LANLAdvantages

Advantages• All active electronic components on transformer primary side

(medium voltage);• Semiconductor switches of standard commercial types

(multisource);• Transformers are not of “pulsed type”. Traditional High

Frequency transformer design and construction techniques can be applied;

• Flat-top closed loop regulation through the IGBT controls;• Intrinsic voltage shut-down in case of klystron arc, due to the

resonance technique (De-Qing);

11 Dec 2008

CERN


The SNS modulator, by LANLDesign keypoints

Hard points• Construction of the HF transformers:

- Mechanical stress due to pulsed operation;- High Frequency (20 kHz) bandwidth with High

Voltage insulation (110 kV at worst point);• Assure “soft-switching” of the IGBT’s in all operating

points -> safe interlocking if not;

• Thermal management;• Mechanical layout (reliability);

11 Dec 2008

CERN


2. Proposed topology for the HP-SPL

110 kV, 91A, 2.3ms, 50 Hz (10 MWpk, 1.15 MWav)

Pulse former:- Modular topology (4 or 5 independent modules in parallel/series);- Easier imposition of “soft switching” in all operating points (no coupling between modules);- However, former hard points related to the transformers, thermal management and mechanical layout remain.

Pulse former: In the tunnelCapacitor charger: In surface building

AC

DC

+

-DC-link

CR

Linear HFtransformer

LR Lf

Cf

+

HVOutput

CR


LR Lf

Cf

CR


LR Lf

Cf

-

1

2

n

11 Dec 2008

CERN


Studies based on simulation(Jonas BAKKEN, Tech. Univ. Trondheim, NO)

Soft switchingSimulated circuit

Cathode pulse

zoom

Intrinsic current limitation in case of arc

11 Dec 2008

CERN


Conclusions

• The acronym SPL is meaningless for modulator discussions. Always specify: LP-SPL or HP-SPL;

• The LP-SPL topology will be the same as the Linac 4 one. New design and prototyping needed for higher ratings (longer flat-top and peak power);

• The HP-SPL modulator project will be a unique project in this domain, at the ultimate technology frontier:

- Only one (known) realization in solid state was done worldwide;- Several difficulties to get it working at nominal ratings;

• A new topology has been studied (simulation), based on a modular approach. It solves some of the former difficulties but others remain;

• A prototype construction and validation at CERN is possible in the medium term only and requires advanced preparation.

11 Dec 2008

klystron modulators for 1) – the lp-spl and for 2) – the hp-spl

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