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3-CELL TEST RESULTS & 9-CELL PLAN Howie Pfeffer 11/13/13. LINAC LOW ENERGY MODULATORS. 3-cell test set-up. 2-stage diagram. 900 V/cell, 8.3 ohm load – no problem?!. 3-Cell test. Turn-on Ringing, cells switching within 600ns. 3-cell test. Run just 2-cells - simplify

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## LINAC LOW ENERGY MODULATORS

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**3-CELL TEST RESULTS & 9-CELL PLAN**Howie Pfeffer 11/13/13 LINAC LOW ENERGY MODULATORS**900 V/cell, 8.3 ohm load – no problem?!**3-Cell test**Turn-on Ringing, cells switching within 600ns**3-cell test**Run just 2-cells - simplify**Bottom (ground-level) cell switching in 2nd place – measurements easier. Isolated charging circuits with high-value resistors – eliminate other possibilities. Still had oscillations when spaced less than 600 ns. investigating**Turn-on Ringing, cells within 600ns**2-cell testing**After various failures, started to suspect problem due to**diode turn-off before diode is fully on. Seen similar problems with FETs – turning them off shortly after turning them on. If so, then problem should go away if diode is at higher current during turn-off. Possible explanation?**Switching at 300 amps**2-cell**Switching at low currents**2-cell**“ON” time is important**2-cell**3-cell switching at 100 amps**3-cell**No problems with 3-cell operation as long as initial turn on**timing is done properly. Simultaneous turn-on yields 2700 volts with 250 ns rise time (10% - 90%). 9-cell construction under-way 3-cell testing conclusions**Modulator requirements**Pulse rep rate: 15 Hz Maximum Output: 35 kV Maximum step size: 1.5 kV Load Resistance: ~100 ohm Beam Length/Time: 110 usec Load (Tube) Voltage 40-Cell Marx Output Beam Top Tilt (Adj.): +/- 5 kV Beam Voltage Step : 15 kV/usec Flattop/Beam Reg.: +/- 25 V Repeatability: +/- 10 V Max. sparkEnergy: < 5 Joules 12-Cell Reg. Output**Nine steps up to 8 kV**• Load = 100 ohms. • First step on for 2 us before subsequent steps. • One step followed by 8 cells simultaneously. • Uses existing driver electronics. • Delays between control edges and outputs. • Short circuit protection • Delay turn-off by 8 us after receiving trip signal. This allows overcurrent circuits on gating boards to turn off slowly. 9 – cell testing**Interleaved Regulator operation**• Uses Matt’s circuit. • Doesn’t require ultimate resolution. • Pulse one cell ON, then make 4 kV 8-cell interleaved pulse. • 1 us spacing, 2 us minimum time, 8 us cycle, 96 us pulse length. • Filter circuit? • Short circuit response • Freeze signals for 8 us then turn OFF. 9 – cell testing (cont.)**9-cell test waveforms**Program Voltage Triangle Square Wave Load Voltage**Pwm filter**Filtered Unfiltered**Short circuit testing**• Critical function – there will be arcs • Charging diode transients during pulse • Diode Qrr results in reverse current during turn-off • Charge inhibit function • Ensure charge switch and main switch are never on at the same time - disaster Special concerns**Short circuit concerns**SPARK CURRENT AND ENERGY WITH NO CURRENT LIMITTING 55 Joules (50 volt arc) 37,000 amps 18 usec**Importance of charge inhibit**Main Switch Capacitor Charged to 950 volts Charging Switch Current**9-Cell construction on-going**• All 9 cells individually tested • Controls for ramping complete • Regulation mode controls being designed • Goal: start system testing in late January Conclusions, 9-cell testing

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