TS01 Klystron Modulator
Beam Voltage Stability Improvements
Minh Nguyen
May 20, 2014
TS01 current modulator status
• TS01 modulator has been running without PFN voltage
regulation. Klystron beam voltage stability measures ~
1000 ppm (rms) at 300kV, 120Hz
• Restore existing de-Q’ing regulation chassis #1 and #2
and measure PFN voltage and beam voltage stability at
various voltage levels and pulse repetition rates
• 30, 33, 35, 38, and 41kV (PFN from Ross HV divider)
• 240, 260, 280, 300, and 320kV (Beam voltage)
• 10, 30, 60, and 120Hz
2
Stability measuring device
7 ppm resolution
3
TS01 stability at 120Hz PRR
300
250
Stability (ppm)
200
BV
150
PFN
100
50
0
220
240
260
280
300
320
340
Beam Voltage (kV)
4
TS01 short-term PFN/BV stability
PRR (Hz)
120
120
120
120
120
41/320kV
38/300kV
35/280kV
33/260kV
30/240kV
60
60
60
60
60
Beam Voltage
30
30
30
30
30
PFN Voltage
10
10
10
10
10
0
50
100
150
200
250
300
Stability (ppm)
5
Motivation for TS01 improvements
• Klystron beam voltage stability is mainly dependent on
modulator PFN voltage stability and thyratron operating
conditions
• PFN voltage with original de-Q’ing regulation circuitry is stable
within 120 – 150 ppm (rms)
• Fine PFN voltage regulation can be achieved by the use of a
low power, high frequency capacitor charger (HVPS) in
conjunction with existing high power resonant charger. The
HVPS charges and regulates PFN capacitor voltage - on top
of the resonant voltage – up to 0.5% target voltage
• Two previously upgraded modulators in the Linac 21-1 and 248 have shown to improve beam voltage stability to < 100 ppm
6
Scope of TS01 modulator upgrade
• Install a new 50kV TDK-Lambda HVPS to charge the PFN
capacitors in parallel to existing resonant charger
• Install new PFN voltage regulator chassis and Ross HV divider
to provide voltage regulation for both the resonant charger and
the TDK-Lambda HVPS
• Install and modify other components to improve the beam
voltage stability
• Tail clipper to reduce klystron backswing voltage
• SCR thyratron driver to provide negative bias on thyratron grid 2
• Thyratron grid drive circuit to minimize trigger rise and delay time
• Replace the thyratron if necessary after assessing the
performance of the upgrade
7
Upgraded modulator circuit diagram (in red lines)
Modulator Output: 360 kV, 420 A , 151 MW peak, 91 kW ave. @ 120 Hz
8
Some upgraded components
120Vac In
Inhibit signal
monitor
PFN voltage
monitor
TDK-Lambda 50kV Capacitor Charger
(402-OEM series w/ blank front panel)
De-Q SCR
trigger
On/Off
switch
HVPS
control
Vref input
PFN voltage
feedback
PFN Voltage Regulator Chassis
Tail Clipper Assembly
Modified SCR
Thyratron Driver
9
Upgraded Linac modulators
Ross Divider
TDK Charging Resistors
TDK Reverse Voltage
Protection Diode
Power Transformer 3-Phase
600Vac In, 208/120Vac Out
Tail Clipper
PFN Voltage Regulator
Box (Outside of Cab 3)
TDK 50kV HVPS
Circuit Breaker 208Vac / 20A
10
Mod 21-1 PFN voltage stability measurements
Before Upgrade
PFN voltage stability=739uV/8.8V= 84 ppm (rms)
Zoom –in PFN Voltage
Regulated by de-Q only (50V/div)
After Upgrade
PFN voltage stability=106uV/8V= 13 ppm (rms)
Zoom –in PFN Voltage
Regulated by HVPS (50V/div)
11
Mod 21-1 Beam voltage stability measurements
Before Upgrade
BV stability: 10mV/69.9V= 143 ppm (rms)
After Upgrade
BV stability: 2.63mV/64V= 41 ppm (rms)
12
Mod 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
5
6
7
8
9
10
11
12
Intervals (30sec)
13
14
15
16
17
18
19
20
13
Tail clipper performance
Klystron backswing voltage before and after tail clipper installation
Effects of thyratron
random recovery on
beam and PFN voltages
BV scale: 50kV/div
PFN volt scale: 5kV/div
14
Thyratron grid 2 voltage after upgrade
Beam voltage
Trig rise time
after
Trig rise time
before
-- 75Vdc bias on grid 2
~ 1nS time jitter
15
TS01 upgrade schedule
•
TDK-Lambda 50kV HVPS purchase requires 14wks of lead time. To meet the
UED@ASTA project schedule, we have to borrow/move this HVPS and other
upgraded components as needed from Linac modulator 24-8
16
TS01 cost estimate
M&S (not including new thyratron)
Engineering (Electrodynamics, APSE, and TestLabs Dept)
Coordination
APSM and TestLabs Technicians
Cost Total
$25,000
200
$22,000
16
$1,760
160
$13,600
$62,360
17