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