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CERN
Klystron Modulators for
1) – the LP-SPL
and for
2) – the HP-SPL
Carlos DE ALMEIDA MARTINS
CERN – AB / PO
Pulsed and High Voltage Power Converters Section
11 Dec 2008
Klystron modulators for: 1) LP-SPL ; 2) HP-SPL
1
Summary
CERN
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
Klystron modulators for: 1) LP-SPL ; 2) HP-SPL
2
CERN
1. Modulators for the LP-SPL
Main parameters
Cathode power supply
- Pulse width:
- Flat-top duration
- Precision at flat-top:
- HF ripple at flat-top:
- Repetition rate:
- Nominal voltage:
- Nominal current:
- Nominal power (peak):
- Rise/fall times (99% / 1%):
- Cooling:
- Maximum energy in case of arc:
2.3 ms
2 ms
< 1%
< 0.1%
2 Hz
110 kV (*)
91 A (*)
10 MW (*)
300µs
Air (natural or forced)
< 20 J
Rise time
fall time
Flat-top
time
Pulse width
(*) to be confirmed, taking the new
klystrons design into consideration
No Anode Mode terminal
11 Dec 2008
Klystron modulators for: 1) LP-SPL ; 2) HP-SPL
3
1. Modulators for the LP-SPL
Selected topology.
CERN
Same as Linac 4 and ~same as 3 MeV Test Stand
Capacitor bank charger
power converter, PS1
Main solid state
switches
PULSE
TRANSFORMER
(OIL TANK)
4.5 kV
DRIVER
Simplified schematics
-110 kV
K1
KLYSTRON
(OIL TANK)
DRIVER
Vout
VPS1
C - Collector;
K - Cathode;
F - Filament
K
5 mF
Capacitor
discharge
system
1:30
A
KLYSTRON
head
F
VPS2
Droop compensation power
converter or “bouncer”, PS2
C
Filament (floatting)
power supply, PS4
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
11 Dec 2008
Klystron modulators for: 1) LP-SPL ; 2) HP-SPL
4
CERN
Prototype for the 3 MeV Test Stand.
Cathode ratings: 100 kV, 20A, pulsed 2 Hz, flat-top: 600 ms
Flat-top width: 30% of the LP-SPL;
Peak power: 20% of the LP-SPL;
Average power: 16 % of the LP-SPL;
A global klystron supply
solution:
( Cathode, Anode, Filament
power supplies in one system )
11 Dec 2008
Klystron modulators for: 1) LP-SPL ; 2) HP-SPL
5
Test of the prototype in a dummy load
CERN
Cathode ratings: 100 kV, 20A, pulsed 2 Hz, flat-top: 600 ms
Normal Operation
Arc protection
(short circuit with Thyratron)
Load
Voltage
Cathode
voltage
120
100
Thyratron
Firing
Vk (kV)
80
60
200µs
40
Earc (65kV)=0.44J
Earc (100kV)~1J
20
0
-20
0.E+00
2.E-04
4.E-04
6.E-04
8.E-04
1.E-03
1.E-03
Cathode Current
(4A/div)
time (s)
Load Voltage (Zoom)
Cathode
voltage
(zoom at flat-top)
Load Current
Cathode Voltage
(20kV/div)
107
25
Without bouncer
105
20
Vk (kV)
Vk (kV)
103
< 1%
15
101
With bouncer
10
99
97
5
95
0
-2.E-04
-5
0.E+00
11 Dec 2008
0.E+00
2.E-04
4.E-04
6.E-04
8.E-04
time (s)
2.E-04
4.E-04
6.E-04
time (s)
8.E-04
1.E-03
1.E-03
Klystron modulators for: 1) LP-SPL ; 2) HP-SPL
6
CERN
Test of the prototype with the LEP klystron
Cathode ratings: 100 kV, 20A, pulsed 2 Hz, flat-top: 600 ms
Normal Operation at nominal
Ch2:
Cathode
Voltage to
ground
(20 kV/div)
Ch3:
Cathode
Current
(4A/div)
Zoom at flat-tops
< 1%
1%
1.2%
Ch4:
Anode
Voltage to
ground
(10 kV/div)
11 Dec 2008
Klystron modulators for: 1) LP-SPL ; 2) HP-SPL
Ch2:
Cathode
Voltage to
ground
(2 kV/div)
Ch3:
Cathode
Current
(0.8A/div)
Ch4:
Anode
Voltage to
ground
(1 kV/div)
7
CERN
1. Modulators for the LP-SPL
Advantages 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
Klystron modulators for: 1) LP-SPL ; 2) HP-SPL
8
CERN
2. Modulators for the HP-SPL
Why not the same topology as LP-SPL?
Cathode power supply
……………………
- Flat-top duration …………………
- Precision at flat-top: …………….
- HF ripple at flat-top: …………….
- Repetition rate: …………………
- Nominal voltage: …………………
- Nominal current: ………………...
- Nominal peak power: …………..
- Nominal average power: …….
- Rise/fall times (99% / 1%): ……..
- Cooling: ……………………………
- Maximum energy in case of arc: ..
- Pulse width:
LP-SPL
HP-SPL
2.3 ms
………………….
2 ms ………………………..
< 1% ………………………..
< 0.1% ………………………
2 Hz ………………………...
110 kV ……………………...
91 A …………………………
10 MW ………………………
46 kW ………………………
300µs ………………………
Air (natural or forced) …….
< 20 J ………………………
2.3 ms
2 ms
< 1%
< 0.1%
50 Hz
110 kV
91 A
10 MW
1.15 MW
300µs
Water
< 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
Klystron modulators for: 1) LP-SPL ; 2) HP-SPL
9
CERN
The SNS modulator, by LANL
The Oak Ridge Nat Lab (SNS) type modulator, Bill Reass and Al. Los Alamos Lab
AC/DC input
converter not
shown
140 kV, 70A, 1.6ms, 60 Hz
(9.8 MWpk, 940 kWav)
11 Dec 2008
Klystron modulators for: 1) LP-SPL ; 2) HP-SPL
10
CERN
The SNS modulator, by LANL
Advantages
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
Klystron modulators for: 1) LP-SPL ; 2) HP-SPL
11
CERN
The SNS modulator, by LANL
Design 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
Klystron modulators for: 1) LP-SPL ; 2) HP-SPL
12
CERN
2. Proposed topology for the HP-SPL
110 kV, 91A, 2.3ms, 50 Hz
Capacitor charger: In surface building
(10 MWpk, 1.15 MWav)
Pulse former: In the tunnel
Linear HF
transformer
LR
1
+
AC
DC
Cf
CR
Linear HF
transformer
LR
2
-
+
Lf
Lf
Cf
CR
HV
Output
DC-link
Linear HF
transformer
LR
n
CR
Lf
Cf
-
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.
11 Dec 2008
Klystron modulators for: 1) LP-SPL ; 2) HP-SPL
13
CERN
Studies based on simulation
(Jonas BAKKEN, Tech. Univ. Trondheim, NO)
Simulated circuit
Soft switching
Cathode pulse
Intrinsic current
limitation in case of arc
zoom
11 Dec 2008
Klystron modulators for: 1) LP-SPL ; 2) HP-SPL
14
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) LP-SPL ; 2) HP-SPL
15