Transcript PULSED THERMIONIC GUN

R.F.AND HIGH VOLTAGE SYSTEMS FOR
IR-FEL (CUTE FEL) IN INDIA
Umesh Kale
Beam Physics & FEL Lab
Raja Ramanna Centre for Advanced Technology,
Indore 452 013
INJECTOR For CUTE FEL
Pre-buncher
@ 476MHz
Pulser
+ Power supplies
50kW , 476MHz
RF Source
buncher
@ 2856MHz
PWT
@ 2856MHz
10MW,2856MHz
RF system
LLRF & HPM
Undulator
Pulsed thermionic
GUN
Terahertz FEL
Wave length region : 80 um , 10ps pulses
Peak power : 1MW, Average power 1W
Beam Energy : 10MeV
Already made
Under way
MODULATOR
Beam Dump
INJECTOR For CUTE FEL
Pre-buncher
@ 476MHz
Pulser
+ Power supplies
50kW , 476MHz
RF Source
buncher
@ 2856MHz
PWT
@ 2856MHz
10MW,2856MHz
RF system
LLRF & HPM
Undulator
Pulsed thermionic
GUN
Terahertz FEL
Wave length region : 80 um , 10ps pulses
Peak power : 1MW, Average power 1W
Beam Energy : 10MeV
MODULATOR
Beam Dump
•PWT LINAC: 2856MHz
•BUNCHER : 2856MHz
•PRE BUNCHER :476MHZ
•GUN :
36.6 MHz
Pre - Buncher
• A single cell re-entrant type pill box cavity with nose cone at 476MHz. It
prebunches the beam to minimize current loss.
• RF power for the pre-buncher : ~ 30kW @ 476MHz
•Cavity developed put in the beam line.
• Procurement of Planner triode based multistage amplifier is underway.
(JPAW,USA)
Buncher
• A 4-cell PWT ( Plane wave transformer) LINAC developed indigenously .
• Around 3MW RF power @ 2856MHz for ~4MeV energy gain.
• 10MW RF system @ 2856MHz delivers power to both Buncher &
Accelerator.
Accelerator
•A 8-cell PWT ( Plane wave transformer) LINAC developed indigenously .
• Around 8MW RF power @ 2856MHz for 7.5MeV energy gain.
• RF system for Buncher & Accelerator ready.
PULSED THERMIONIC GUN ( CCR, USA InC.)
• Thermionic gun with grided dispenser cathode
• Beam energy : 90keV , Charge : 1nC & Pulse width : 1ns FWHM
•Pulse separation : 27.3 ns ( @ 36.615MHz) dictated by the one round trip time of the optical pulse in
4.1m long optical cavity.
•Normalized emittance : 15 pi-mm-mrad ( rms) & Energy spread : <1%
• Macro-pulse duration : 10us @ 10Hz ( Max)
• Operating cathode voltage is -90kV, grid is negatively biased with -150V and a fast pulser applies
200V to drive 1A peak micro pulse current.
• Spellman make -130kV,0.1mA HVDC power supply with 1nF intermediate energy storage capacitor
bank supply 1A peak current.
•A isolation transformer supply power to Filament P/S , BIASING P/s & pulser floating at -90kV .
• Employed a crow bar system for the protection Gun in events of arcing. (maximum energy that can be
dumped in the event of arc is 1J ). But stored energy is 4J.
• COMMISSIONING IS UNDERWAY.
LLRF ( Low level RF )
• Synchronized operation of GUN , modulator & low power RF
• SG1 operated with internal in-built 10MHz source & SG-2 operated
from SG-1 externally.
•SRS delay generator triggers the SG-1 ,gun controller & modulator.
• Pulse modulation of 2856MHz done internally in SG-1.
• Pulse modulated low power RF pulse is set inside the high voltage
pulse in flat portion to avoid false triggering, any phase change.
• Complete system is operated remotely.
TTL, 10us @ 1-10Hz
SG-1
VA1
2856MHz
36.615MHz
GUN
controller
SG-2
TTL, 10us @ 1-10Hz
DG 535
90kV
thermionic
gun ( procured
from CCR Inc.
,USA)
Modulator
TTL, 10us @ 1-10Hz
Low power RF line for present set up ( pre-buncher
is not energized)
RF System & Modulator
Specification of 10MW klystron
Specification of 25MW line type modulator
Circulator
High power RF
• WR284 based transport line.
•Presently RF transport line is pressurized with N2 at 4 bar.
• Circulator has provision for installing arc detector. (AFT make)
• Each line has one circulator , phase shifter and dual directional
coupler for protection,phase adjustment and power measurement.
Chiller
Micro -controller
Analog/Digital
control
High power RF line
L2
L1 30H
D1
L3
L3
L3
R3
C3
R
1
0
2
Y
1
0
2
B
1
2
U4
HVDC P/S,
EHT xmer,
12 pulse
rectifier
+ LC
filter
R1
C3
C1
R2
C2
N
0
Interlocked for
Low flow
Droor interlock
Scram
Ref 0-10V
0
TTL from SRS delay generator
Driver
0
0
TX4
0
Reservior
Heater
Core bias P/s
Filament
Heater
Micro -controller
Analog/Digital
control
Modulator Block diagram
Filament P/s
Features
•
Line type modulator , PFN with mutual inductance
•
Resonant charging through charging inductor .
•
15kV, 1A HVDC power supply , reg. <1%, Ripple <1%
•
HVDC power supply has two 6 pulse rectifier in series forming 12 pulse
rectifier with LC filter.
•
15 section PFN with mutually coupled inductors of 6 Ohm characteristic
impedance. Total capacitance : 0.8 uF
•
E2V make 40kV, 10kA thyratron switch ( CX2609) used for discharging PFN.
•
Pulse transformer ( ratio 1:6 ) with reset core employed.
•
Provision to power filament through transformer secondaries.
•
Remotely operated using distributed control architecture 8 bit micro
controllers placed locally using supervisory PCs in control room.
•
Lab-view based GUI
•Interlocks for experimental hall door ,Vacuum of klystron, wave guide arcing,
scram, low flow provided. All safety interlocks are relay based.
• PFN voltage, klystron filament current, HVDC voltage are monitored remotely.
• Modulator tested with klystron and dummy water load up to 7MW peak
power. Modulator is operational since 2002.
• Preliminary acceleration trials with 4-cell PWT performed. Electron beam
form 2us,40keV DC thermionic gun accelerated up to 3.5MeV consuming ~
4MW of RF power.
Typical wave shape across the klystron
Using the existing set up we have done the following experiments

Conditioning of 4 cell buncher.
 Acceleration up to 4MeV using 4 cell PWT and a 2us DC thermionic gun.
 Transmission through undulator experiment. ( 60 % transmission measured)
Problems encountered during commissioning
 Ringing on flat top of pulse due to stray inductance, capacitance. ( eliminated
by putting an RC network across Pulse Transformer. However rise time
affected)
 Damaging spikes through ground path. ( all components insulated from cabinet
then grounded to ensure single point grounding), used MOVs, filters , faraday
shield transformer for the electronics)
 Cabinet door with RF contact fingers helped in reduction of EMI generated
noise.
 Tuning of PFN is difficult with this design.
• These power supplies are basically SMPS buck converters with
100ppm stability developed in RRCAT
Some photographs
Pulse transformer
25MW Pulse Modulator
Brazed components of PWT3
GUN
THANKS