3-CELL TEST RESULTS & 9-CELL PLAN Howie Pfeffer 11/13/13

 900 V/cell, 8.3 ohm load – no problem?!

 Turn-on Ringing, cells switching within 600ns

 Run just 2-cells - simplify  Bottom (ground-level) cell switching in 2 nd place – measurements easier.  Isolated charging circuits with high-value resistors – eliminate other possibilities.  Still had oscillations when spaced less than 600 ns.

 Turn-on Ringing, cells within 600ns

 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.

 Switching at 300 amps

 Switching at low currents

 “ON” time is important

 3-cell switching at 100 amps

 3-cell simultaneous turn- on at 300 amps.

 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

Beam Top Tilt (Adj.):+/- 5 kV Beam Voltage Step :15 kV/usec Flattop/Beam Reg.:+/- 25 V Repeatability:+/- 10 V Max. spark Energy:< 5 Joules 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 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.

 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  F reeze signals for 8 us then turn OFF.

Program Voltage Load Voltage TriangleSquare Wave

UnfilteredFiltered

 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

SPARK CURRENT AND ENERGY WITH NO CURRENT LIMITTING 37,000 amps 55 Joules (50 volt arc) 18 usec

Main Switch Charging Switch Capacitor Charged to 950 volts 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