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TS01 Klystron Modulator Minh Nguyen May 20, 2014 Beam Voltage Stability Improvements

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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

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Stability measuring device 7 ppm resolution 3

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TS01 stability at 120Hz PRR Beam Voltage (kV) Stability (ppm) 4

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TS01 short-term PFN/BV stability Stability (ppm) PRR (Hz ) 41/320kV 38/300kV 35/280kV 33/260kV 30/240kV 5

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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

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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

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Upgraded modulator circuit diagram (in red lines) Modulator Output: 360 kV, 420 A, 151 MW peak, 91 kW ave. @ 120 Hz 8

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Some upgraded components PFN Voltage Regulator Chassis De-Q SCR trigger On/Off switch Vref input PFN voltage feedback 120Vac In PFN 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

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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-Phase 600Vac In, 208/120Vac Out Circuit Breaker 208Vac / 20A 10

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Mod 21-1 PFN voltage stability measurements Zoom –in PFN Voltage Regulated by de-Q only (50V/div) Zoom –in PFN Voltage Regulated by HVPS (50V/div) Before UpgradeAfter Upgrade PFN voltage stability=739uV/8.8V= 84 ppm (rms)PFN voltage stability=106uV/8V= 13 ppm (rms) 11

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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 UpgradeAfter Upgrade

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Mod 21-1 performance after HVPS upgrade Typical PFN voltage stability in a 10-minute period 13

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Tail clipper performance BV scale: 50kV/div PFN volt scale: 5kV/div Klystron backswing voltage before and after tail clipper installation 14 Effects of thyratron random recovery on beam and PFN voltages

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Thyratron grid 2 voltage after upgrade -- 75Vdc bias on grid 2 ~ 1nS time jitter 15 Beam voltage Trig rise time after Trig rise time before

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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

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17 TS01 cost estimate M&S (not including new thyratron)$25,000 Engineering (Electrodynamics, APSE, and TestLabs Dept)200$22,000 Coordination16$1,760 APSM and TestLabs Technicians160$13,600 Cost Total$62,360

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