LCLS Energy Jitter Reduction
Modulator 21-1(L1-S) HVPS Upgrade
Minh Nguyen
October 30, 2013
Scope of modulator 21-1 upgrade
• Install a low power, high voltage power supply (HVPS) inverter in
parallel to the existing high power, resonant charger to provide fine PFN
voltage regulation
• Install a PFN voltage regulator chassis to provide voltage regulation for
both the resonant charger and the new HVPS inverter
• Install and modify other components to improve the overall klystron
beam voltage stability
• Tail clipper: to minimize PFN voltage variations due to random thyratron recovery
and to protect the klystron from high PIV
• Negative bias thyratron grid 2: to promote thyratron consistent recovery
• Thyratron grid drive circuit: to minimize turn-on time jitter
Modulator HVPS Upgrade AIP
2
Modulator upgraded circuit (in red lines)
Modulator Output: 360 kV, 420 A , 151 MW peak, 91 kW ave. @ 120 Hz
Modulator HVPS Upgrade AIP
3
Some upgraded components
Inhibit signal
monitor
120Vac input
PFN voltage
monitor
Tail Clipper Assembly
De-Q SCR
trigger
On/Off
switch
HVPS
control
Vref input
PFN Voltage Regulator Chassis
Modulator HVPS Upgrade AIP
PFN voltage
feedback
SCRTD with -75Vdc Bias
4
Upgraded components installed
Ross Divider
5000/1
HVPS Charging
Resistors
HVPS Reverse
Voltage Protection
Diode
Tail Clipper
Assembly
Power Transformer 3-Phase
600Vac In, 208/120Vac Out
PFN Voltage
Regulator Chassis
(mounted outside of
modulator cabinet)
TDK 50kV HVPS
Modulator HVPS Upgrade AIP
208 and 120Vac Circuit Breakers
5
Modulator 21-1 performance after HVPS upgrade
Typical PFN voltage stability at 120Hz: 101uV/8V = 13 ppm (RMS)
Zoom –in
PFN regulated voltage
(50V/div)
HVPS
regulation
Modulator HVPS Upgrade AIP
Resonant charging
voltage (10kV/div))
De-Q’ing
regulation
Thyratron
fire
6
Modulator 21-1 performance after HVPS upgrade
Typical beam voltage stability at 120Hz: 2.63mV/64V = 41 ppm
Modulator HVPS Upgrade AIP
7
Klystron modulator 21-1 before and after upgrade
Before Upgrade
PFN voltage stability=739uV/8.8V= 84 PPM (RMS)
Zoom –in PFN Voltage
Regulated by de-Q only (50V/div)
Modulator HVPS Upgrade AIP
After Upgrade
PFN voltage stability=106uV/8V= 13 PPM (RMS)
Zoom –in PFN Voltage
Regulated by HVPS (50V/div)
8
Modulator 21-1 performance after HVPS upgrade
Typical PFN voltage stability in a 10-minute period
15
Stability (ppm)
14
13
12
11
1
2
3
4
Modulator HVPS Upgrade AIP
5
6
7
8
9
10
11
12
Intervals (30sec)
13
14
15
16
17
18
19
20
9
BVLT and BCUR 24-Hr stability
Long term drift (~ 0.3%) is consistent with other modulators
Modulator HVPS Upgrade AIP
Tail clipper performance
Klystron backswing voltage before and after tail clipper installation
BV scale: 50kV/div
PFN volt scale: 5kV/div
Modulator HVPS Upgrade AIP
11
Thyratron control-grid voltage
-- 75Vdc bias
Modulator HVPS Upgrade AIP
~ 1nS time jitter
12
L1-S after modulator upgrade
Typical RF phase and amplitude jitter at 120Hz beam rate
Modulator HVPS Upgrade AIP
13
Remaining task
• Implement EPICS remote control and status monitor of
TDK-Lambda HVPS through either CAMAC or modulator
MKSU Interface chassis
Modulator HVPS Upgrade AIP
14