Modulators for magnetrons Mark Iskander - PAEN 2014

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Cleopatra Cook
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1 Modulators for magnetrons Mark Iskander - PAEN 2014 Page 1

2 Modulators for magnetrons Introduction Modulator types Switch The thyratron Features and advantages e2v solid state modulator Page 2

3 Modulators types Types of pulse modulator commonly used to drive magnetrons Basic Modulator circuits Hard Switch modulators Line type modulators Marx modulators Page 3

4 Modulators types Types of Switch used in magnetrons modulators Hard Switch modulators Closing Spark gaps Thyratron Semiconductor etc. Thyristor Closing and Opening Tubes Triode Tetrode Semiconductor Field Effect Transistors (FET) Insulated-gate bipolar transistor (IGBT) Integrated Gate-Commutated Thyristor (IGCT) Page 4

5 Basic circuit for discharging pulser Load Directly driven magnetron Pulse transformer driven magnetron Page 5

6 Basic hard-tube pulser Load Directly driven magnetron Pulse transformer driven magnetron Page 6

7 Basic line-type pulser Load Directly driven magnetron Pulse transformer driven magnetron Page 7

8 Basic marx pulser Load Directly driven magnetron Page 8

9 Thyratrons > What is a Thyratron? High peak power electrical discharge switch that now uses ionised hydrogen gas as the switching medium Thyratron initially developed in US 1941, as a method to drive magnetron based radar systems. Development of the thyratron at the then English Electric Valve Company (e2v Ltd.) commenced in 1948 under the sponsorship of the Marconi Wireless Telegraph (MWT) Company, first produced by e2v in the early 1950s. Page 9

10 Thyratrons > Used worldwide in various applications such as: Kicker magnet switching, Over-voltage damage prevention via Crowbar mechanism, Radar, Lithotripsy shock wave generation, high energy Gas Laser switching and Medical, Scientific and Industrial Linac operation Page 10

11 Thyratron > What is a Thyratron? High peak power electrical discharge switch that uses ionised hydrogen gas as the switching medium Page 11

12 Thyratrons > e2v product lines : Glass Envelope > Up to 35kV Voltage hold-off capacity > Oxide Cathode > Low average Current capability up to 1.5A Ceramic Envelope > Up to 100kV Voltage hold-off capacity > Oxide Cathode > Medium average Current capability up to 6A Ceramic/ metal Envelope > High peak and average powers achievable simultaneously 10kA and 50kV > Barium Aluminate Cathode Page 12

13 Traditional PFN Line Type Operation Peak Voltage KV Operating point b a Load line 410 Ohms Dynamic impedance = a/b, moves away from a given point on the load line, along a given voltage line as set by the electro magnet. Static impedance, is at a given operating point and moves along the load line = Peak Voltage / Peak Current. Peak Current Page 13

14 AMM > Key modulator type differentiators Line type Solid State Pulse Transformer type Hard Switch type Simple Solid State switch is at lower voltage Pulse shape is maintained across full operating magnetron current range Advantages Cheap Solid state switch is not required to be in insulating medium Pulse width can be easily altered Change of pulse duration like hard tube, switching at low voltage Wide range of mismatch permissible Page 14

15 AMM > Key modulator type differentiators Line type Solid State Pulse Transformer type Hard Switch type Good operation at a single operating point Higher current rating of switch components Higher voltage rating of switch components Disadvantages Voltage can overshoot Limits pulse width operation External network required to shape pulse Pulse shape not maintainable across full operating magnetron current range Higher stored energy Pulse shape Complex pulse transformer required Size. (PFN & Pulse Transformer) Page 15

16 How AMM works > The Solid State Modulator Although there are a number of modulator types, e2v s modulator is a hard switch type. Page 16

17 How AMM works > The Solid State Modulator Although there are a number of modulator types, e2v s modulator is a hard switch type. Page 17

18 How AMM works > The Solid State Modulator Although there are a number of modulator types, e2v s modulator is a hard switch type. Page 18

19 How AMM works > The Solid State Modulator Although there are a number of modulator types, e2v s modulator is a hard switch type. Page 19

20 How AMM works > The Solid State Modulator Although there are a number of modulator types, e2v s modulator is a hard switch type. Page 20

21 AMM System Features > Key operating parameters > Pulse rise time and flatness is tailored for optimal magnetron switching characteristics. > Magnetron current pulse flatness maintained across all operating levels. > No external network required. I V I V AMM1 AMM2 V Line Type I Page 21

22 AMM2 Functionality > Magnetron Heater Management: > Two key functions: > Initial warm up. > Cutback during pulsing. > Magnetron Arc Management : > Arc conditions detected and pulse truncated. > System managed based on arc count. Page 22

23 AMM > What is AMM? (Active Magnetron Modulator) > Compact range of solid state modulator systems to drive the e2v range of linac magnetrons. > Medium Power System - 130A Pulse Current, 54kV > High Power System 260A Pulse Current, 60kV Page 23

24 How AMM works > Modulator switch stacks > AMM1 MOSFET Stack > 75 series stage boards > AMM2 IGBT Stack > 22 series stage boards Page 24

25 AMM2 Functionality > Key System Features > Diagnostic Data > Available on a pulse by pulse basis. > Data can be monitored real time or stored for later analysis. > Pulse amplitude > Regulated on magnetron current. > Digital Magnetron Current control loop. > System configuration > System is configurable through parameter tables. > Determines magnetron operating conditions. Page 25

26 Testing an AMM1 into a short circuit Page 26

27 > End Of Presentation. Page 27

REVIEW OF SOLID-STATE MODULATORS

REVIEW OF SOLID-STATE MODULATORS E. G. Cook, Lawrence Livermore National Laboratory, USA Abstract Solid-state modulators for pulsed power applications have been a goal since the first fast high-power semiconductor