ts01 klystron modulator - stanford university · 7 scope of ts01 modulator upgrade • install a...
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TS01 Klystron Modulator
Minh NguyenMay 20, 2014
Beam Voltage Stability Improvements
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
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Stability measuring device
7 ppm resolution
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TS01 stability at 120Hz PRR
Beam Voltage (kV)
Sta
bilit
y (p
pm)
4
0
50
100
150
200
250
300
220 240 260 280 300 320 340
BV
PFN
TS01 short-term PFN/BV stability
Stability (ppm)
PR
R (H
z)
41/320kV38/300kV35/280kV33/260kV30/240kV
5
0 50 100 150 200 250 300
1010101010
3030303030
6060606060
120120120120120
Beam Voltage
PFN Voltage
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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 24-8 have shown to improve beam voltage stability to < 100 ppm
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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
Upgraded modulator circuit diagram (in red lines)
Modulator Output: 360 kV, 420 A , 151 MW peak, 91 kW ave. @ 120 Hz
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Some upgraded components
PFN Voltage Regulator Chassis
De-Q SCR trigger On/Off
switchVref input
PFN voltage feedback
120Vac In PFN voltage monitor
Tail Clipper Assembly
Inhibit signal monitor
HVPS control
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TDK-Lambda 50kV Capacitor Charger(402-OEM series w/ blank front panel)
Modified SCR Thyratron Driver
Upgraded Linac modulators
Ross Divider
TDK Charging Resistors
TDK Reverse Voltage Protection Diode
Tail Clipper
PFN Voltage Regulator Box (Outside of Cab 3)
TDK 50kV HVPS
Power Transformer 3-Phase600Vac In, 208/120Vac Out
Circuit Breaker 208Vac / 20A
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Mod 21-1 PFN voltage stability measurements
Zoom –in PFN VoltageRegulated by de-Q only (50V/div)
Zoom –in PFN VoltageRegulated by HVPS (50V/div)
Before Upgrade After Upgrade
PFN voltage stability=739uV/8.8V= 84 ppm (rms) PFN voltage stability=106uV/8V= 13 ppm (rms)
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Mod 21-1 Beam voltage stability measurements
BV stability: 2.63mV/64V= 41 ppm (rms)BV stability: 10mV/69.9V= 143 ppm (rms)
Before Upgrade After Upgrade
Mod 21-1 performance after HVPS upgrade
Typical PFN voltage stability in a 10-minute period
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12
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14
15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Stab
ility
(ppm
)
Intervals (30sec)
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Tail clipper performance
BV scale: 50kV/divPFN volt scale: 5kV/div
Klystron backswing voltage before and after tail clipper installation
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Effects of thyratron random recovery on beam and PFN voltages
Thyratron grid 2 voltage after upgrade
-- 75Vdc bias on grid 2 ~ 1nS time jitter
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Beam voltageTrig rise time after
Trig rise time before
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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
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TS01 cost estimate
M&S (not including new thyratron) $25,000
Engineering (Electrodynamics, APSE, and TestLabs Dept) 200 $22,000
Coordination 16 $1,760
APSM and TestLabs Technicians 160 $13,600
Cost Total $62,360