TS01 Klystron Modulator

Minh Nguyen

May 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

2

Stability measuring device

7 ppm resolution

3

TS01 stability at 120Hz PRR

Beam Voltage (kV)

Sta

bilit

y (p

pm)

4

220 240 260 280 300 320 3400

50

100

150

200

250

300

BV

PFN

TS01 short-term PFN/BV stability

Stability (ppm)

PR

R (

Hz)

41/320kV38/300kV35/280kV33/260kV30/240kV

5

10

10

10

10

10

30

30

30

30

30

60

60

60

60

60

120

120

120

120

120

0 50 100 150 200 250 300

Beam Voltage

PFN Voltage

6

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

7

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

8

Some upgraded components

PFN Voltage Regulator Chassis

De-Q SCR trigger On/Off

switchVref input

PFN voltage feedback

120Vac InPFN voltage monitor

Tail Clipper Assembly

Inhibit signal monitor

HVPS control

9

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

10

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)

11

12

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

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 2011

12

13

14

15

Intervals (30sec)

Sta

bil

ity

(pp

m)

13

Tail clipper performance

BV scale: 50kV/divPFN volt scale: 5kV/div

Klystron backswing voltage before and after tail clipper installation

14

Effects of thyratron random recovery on beam and PFN voltages

Thyratron grid 2 voltage after upgrade

-- 75Vdc bias on grid 2 ~ 1nS time jitter

15

Beam voltageTrig rise time after

Trig rise time before

16

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

17

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