Linac RF Modulators New Specifications Trevor Butler Oct
Linac RF Modulators New Specifications Trevor Butler Oct 26 th 2011, 10: 30 am – 11: 00 am
PIP – Linac 200 MHz Modulator Working Group New Modulator Specifications WG • • • Started: 07/20/2011 Complete: 10/03/2011 Working Group members • • AD/EE Support • Dan Wolff • Howie Pfeffer AD/PS/Linac • Trevor Butler (chair 09/21 – now) • Fernanda G. Garcia (chair 07/20 – 09/21) • Johnathan Walters Consultant • 2 Larry Allen Trevor Butler 9/24/2021
LE Linac Modulators Overview These modulators use vacuum switch tubes to provide pulsed voltage to the anode of the Burle 7835 power amplifier. • • Original design contracted by Continental Electronic (Dallas TX) in the late 60’s. • Minor upgrade in the early 80’s to replace 2 vacuum tube (Y 631) video driver to solid state (2 SK 183 V) FET video driver. • The main series regulator tube, (F 1123) was discontinued 10 years ago. • Other typical accelerator RF systems use direct feedback, driving the RF input to the main power amplifier (PA) to regulate the cavity field. • Since in our application, the 7835 is run grounded grid (cathode driven), the PA is unstable with low or no RF drive, so the anode/plate voltage is modulated instead of the RF drive amplitude to regulate the cavity accelerating field. • The modulator requires linear operation of the F 1123 “switch” tubes to set the accelerating field anywhere from 0. 5 to 4 MW. • The LLRF system, upgraded a few years ago, uses a feed-forward loop to drive the modulator with an additional ‘boost’ pulse to compensate for beam loading. 3 Trevor Butler 9/24/2021
LE Linac Modulators Block Diagram 4 Trevor Butler 9/24/2021
LE Linac Modulators Present Situation • Modulators are a major source of downtime in the Linac • 57 % of downtime over the past 10 years • DC Power supplies – Built directly to the frame and need to be repaired in place, which leads to long downtimes. A modular power supply system would be more efficient in diagnosing and repairing the modulator • Switch Tubes – The main power “switch” tubes in the modulator are no longer manufactured. • Fiber-optic TX / RX – Equipment is also discontinued should be upgraded to a modern instrumentation-grade analog data link system. • Relays & Interlocks – Most relays are not long manufactured. Few spares • FET keyer module – The first stage amplifier after the fiber-optic data link is discontinued, although an amply supply is currently on hand. • Diagnostics – Lack of reliable diagnostics equipment. Troubleshooting the modulator is very difficult since the equipment runs at high voltage and most measurements need to be observed when at full voltage and full loading 5 Trevor Butler 9/24/2021
LE Modulator Electrical Schematic CPI F 1123 CPI-Eimac “Switch” Tubes ML-6544 operated as Power Triode linear amplifiers • Maximum (20 k. V, 75 Amp, 1 k. W ) • 2. 8 k. V Typical • Uses 2 per modulator and 1 per driver screen modulator (5+1 Stations) • 18 tubes total • High Production Tube for CPI • Used in multiple radar and science applications • 50 k. V Standoff ~100 Amps each ~350 Amps Total Manufactured by Westinghouse, ITT, Richardson, Varian, CPI, now nobody • Use 3 per station (5+1) = 18 total • Series-pass regulator between the capacitor bank and Burle 7835 Power Triode anode • No replacement part available • Rebuilt by Kennetron & Econco* – Can’t Rebuild Grids Not expected to be discontinued anytime soon 6 • *Problem – Bad grids are a typical type of failure in these tubes. Therefore, they need two tubes (one as a donor) to rebuild a tube with a bad grid Trevor Butler 9/24/2021
LE Linac Modulator Waveform Description 7 Trevor Butler 9/24/2021
LE Linac Modulator Specifications 8/73 Trevor Butler 9/24/2021
LE Linac Modulator Specifications Id Specification Current 1 Pulse Repetition Rate 15 2 Rise Time 150 3 Fall Time 4 New Max Units 15 Hz 50 150 μs 50 70 150 μs Flat Top Time 150 50 160 μs 5 Beam Length/(Adjustable) 62 110 μs 6 Beam Time Delay (Adjustable) 72 100 μs 7 Peak Voltage Time (Adjustable) 125 35 150 μs 8 Output Voltage (Adjustable) 40 8 35 k. V 9 Output Current 350 375 Amps 10 Beam Voltage Step Size 3 -8 5 10 k. V 11 Flat Top Voltage Regulation/Slope (Within 150 usec) 80 -25 25 V 9 Trevor Butler New Min 9/24/2021
LE Linac Modulator Specifications Id Specification Current New Min New Max Units 12 Flat Top Repeatability (Pulse to Pulse) 200 -25 25 V 13 Flat Top Resolution 15 -5 5 V 14 Beam Top Repeatability -10 10 V 15 Beam Top Tilt +/- 3 -5 5 k. V 16 Slew Rate (Beam Voltage Step) 20 15 17 Slew Rate (Rising Edge) 0. 25 1. 00 k. V/usec 18 Slew Rate (Falling Edge) 0. 50 k. V/usec 19 Step Size (Rising or Falling Edge) 1. 5 k. V 20 Modulator Emergency Turn off (<2 usec in pulse) 500 400 Amps 21 Modulator Emergency Turn off (<2 usec out of pulse) 150 100 Amps 22 Linearity +/- 20 % 23 Gain 10000 10 Trevor Butler k. V/usec 10000 9/24/2021
LE Linac Modulator Specifications Id Specification Current 1 Pulse Repetition Rate 15 2 Rise Time 150 3 Fall Time 4 New Max Units 15 Hz 50 150 μs 50 70 150 μs Flat Top Time 150 50 160 μs 5 Beam Length/(Adjustable) 62 110 μs 6 Beam Time Delay (Adjustable) 72 100 μs 7 Peak Voltage Time (Adjustable) 125 35 150 μs 8 Output Voltage (Adjustable) 40 8 35 k. V 9 Output Current 350 375 Amps 10 Beam Voltage Step Size 3 -8 5 10 k. V 11 Flat Top Voltage Regulation/Slope (Within 150 usec) 80 -25 25 V 11 Trevor Butler New Min 9/24/2021
1) Pulse Repetition Rate • Current – 15 Hz • New – 15 Hz • Booster limitation on RF • Operations standard for 40+ years 12 Trevor Butler 9/24/2021
LE Linac Modulator Specifications Id Specification Current 1 Pulse Repetition Rate 15 2 Rise Time 150 3 Fall Time 4 New Max Units 15 Hz 50 150 μs 50 70 150 μs Flat Top Time 150 50 160 μs 5 Beam Length/(Adjustable) 62 110 μs 6 Beam Time Delay (Adjustable) 72 100 μs 7 Peak Voltage Time (Adjustable) 125 35 150 μs 8 Output Voltage (Adjustable) 40 8 35 k. V 9 Output Current 350 375 Amps 10 Beam Voltage Step Size 3 -8 5 10 k. V 11 Flat Top Voltage Regulation/Slope (Within 150 usec) 80 -25 25 V 13 Trevor Butler New Min 9/24/2021
2&3) Rise Time & Fall Time • Present – 150 us rise time & 50 us fall time • New – adjustable from 50 -150 us on both rising and falling edges • Currently, the rise and fall times are dependent on the characteristics of the Linac modulator RF feedback loop topology, most notability, the cavity overcoupling. • Studies performed in ADS RF simulation software show the effect of reducing or increase the rise time on both the falling and rising edges 14 Trevor Butler 9/24/2021
Cavity Field Simulation Parameters 15 Trevor Butler 9/24/2021
Cavity Field Simulation No Feedback 16 Trevor Butler 9/24/2021
Cavity Field Simulation No Feedback 17 Trevor Butler 9/24/2021
Cavity Field Simulation With Feedback 18 Trevor Butler 9/24/2021
Cavity Field Simulation With Feedback 19 Trevor Butler 9/24/2021
LRF 3 LE Linac Modulator Waveforms LRF 3 – No Beam 20 LRF 3 – With Beam Trevor Butler 9/24/2021
Cavity Field Simulation (Feedback) • The cavity fields must be settled before beam arrives. • Without feedback, or some form of active feedforward, the cavity fields can take up to 150 us stabilize to <1% (4 -5 time constants) • We know from earlier calculations that the cavity time constant is around 35 us. • With feedback, this can be reduced that to < 65 us (about 2 cavity time constants) • Therefore, feedback will be necessary in order to stabilize fields before the natural response of the system, with a minimum of about 40 us between peak time and beam time. • The next question: What if we reduce the rise time and increase the fall time? Will this have and effect on the reverse power peaks? 21 Trevor Butler 9/24/2021
Cavity Field Simulation (Feedback) 22 Trevor Butler 9/24/2021
Cavity Simulation Reverse Power 23 Trevor Butler 9/24/2021
LRF 3 LE Linac Modulator Waveforms LRF 3 – No Beam 24 LRF 3 – With Beam Trevor Butler 9/24/2021
Cavity Simulation Reverse Power 25 Trevor Butler 9/24/2021
2&3) Rise Time & Fall Time • The current system runs at 150 us rise & 50 us fall times. • The data shows that we could accept a faster rise time of about 50 us, and would run better with a slower fall time of about 150 us. This will be helpful since we need to overshoot the modulator to keep the gradient settling time acceptable • These limitations on rise and fall time need to be independent of the feedback topology that is chosen, whether it is point to point feedback or using waveform sampling to modify points on the desired waveform shape. This mean that we might need a different feedback topology & desired gradient waveform shapes than currently used to achieve lower reverse power. Final Specification • Rise Time & Fall Time (50 -150 us) of acceptable range 26 Trevor Butler 9/24/2021
LE Linac Modulator Specifications Id Specification Current 1 Pulse Repetition Rate 15 2 Rise Time 150 3 Fall Time 4 New Max Units 15 Hz 50 150 μs 50 70 150 μs Flat Top Time 150 50 160 μs 5 Beam Length/(Adjustable) 62 110 μs 6 Beam Time Delay (Adjustable) 72 100 μs 7 Peak Voltage Time (Adjustable) 125 35 150 μs 8 Output Voltage (Adjustable) 40 8 35 k. V 9 Output Current 350 375 Amps 10 Beam Voltage Step Size 3 -8 5 10 k. V 11 Flat Top Voltage Regulation/Slope (Within 150 usec) 80 -25 25 V 27 Trevor Butler New Min 9/24/2021
4) Flat Top Time • Present – 150 us rise time • New – adjustable from 50 -160 us • This parameter is ultimately limited by the flattop time of the HE klystron RF systems (~125 us on modulator voltage (about 80 us of RF with present settings) • The flat top time needs to be long enough to account for the maximum beam length and the settling time of the RF cavity fields. • Assuming a maximum beam length of 110 us, a settling time of 40 us, and at least 10 us of stable field after beam exits for LLRF calculations, a final specification of 50 -160 us was decided. 28 Trevor Butler 9/24/2021
LE Linac Modulator Specifications Id Specification Current 1 Pulse Repetition Rate 15 2 Rise Time 150 3 Fall Time 4 New Max Units 15 Hz 50 150 μs 50 70 150 μs Flat Top Time 150 50 160 μs 5 Beam Length/(Adjustable) 62 110 μs 6 Beam Time Delay (Adjustable) 72 100 μs 7 Peak Voltage Time (Adjustable) 125 35 150 μs 8 Output Voltage (Adjustable) 40 8 35 k. V 9 Output Current 350 375 Amps 10 Beam Voltage Step Size 3 -8 5 10 k. V 11 Flat Top Voltage Regulation/Slope (Within 150 usec) 80 -25 25 V 29 Trevor Butler New Min 9/24/2021
5) Beam Length / Time • Present – 62 us • New – adjustable up to 110 us • Was increased to 110 us for the final specification to provide overhead for future linac injectors (RFQ, etc. ) 30 Trevor Butler 9/24/2021
LE Linac Modulator Specifications Id Specification Current 1 Pulse Repetition Rate 15 2 Rise Time 150 3 Fall Time 4 New Max Units 15 Hz 50 150 μs 50 70 150 μs Flat Top Time 150 50 160 μs 5 Beam Length/(Adjustable) 62 110 μs 6 Beam Time Delay (Adjustable) 72 100 μs 7 Peak Voltage Time (Adjustable) 125 35 150 μs 8 Output Voltage (Adjustable) 40 8 35 k. V 9 Output Current 350 375 Amps 10 Beam Voltage Step Size 3 -8 5 10 k. V 11 Flat Top Voltage Regulation/Slope (Within 150 usec) 80 -25 25 V 31 Trevor Butler New Min 9/24/2021
6) Beam Time Delay • Present – 72 us • New – up to 100 us • Assuming the modulator runs with a flat top time of 160 us, and beam was up to 60 us in length, that would give a maximum delay of about 100 us. • This parameter is important since there needs to be a delay before beam enters the cavity to give the fields time to stabilize. 32 Trevor Butler 9/24/2021
LE Linac Modulator Specifications Id Specification Current 1 Pulse Repetition Rate 15 2 Rise Time 150 3 Fall Time 4 New Max Units 15 Hz 50 150 μs 50 70 150 μs Flat Top Time 150 50 160 μs 5 Beam Length/(Adjustable) 62 110 μs 6 Beam Time Delay (Adjustable) 72 100 μs 7 Peak Voltage Time (Adjustable) 125 35 150 μs 8 Output Voltage (Adjustable) 40 8 35 k. V 9 Output Current 350 375 Amps 10 Beam Voltage Step Size 3 -8 5 10 k. V 11 Flat Top Voltage Regulation/Slope (Within 150 usec) 80 -25 25 V 33 Trevor Butler New Min 9/24/2021
7) Peak Voltage Time • Current – 100 -125 us • New – 35 -150 us • Depending on the age of the 7835, this parameter currently varies to keep gradient stable by increasing the power to the tube during turn-on. • This parameter will not exist on any direct RF feedback topology. 34 Trevor Butler 9/24/2021
LE Linac Modulator Specifications Id Specification Current 1 Pulse Repetition Rate 15 2 Rise Time 150 3 Fall Time 4 New Max Units 15 Hz 50 150 μs 50 70 150 μs Flat Top Time 150 50 160 μs 5 Beam Length/(Adjustable) 62 110 μs 6 Beam Time Delay (Adjustable) 72 100 μs 7 Peak Voltage Time (Adjustable) 125 35 150 μs 8 Output Voltage (Adjustable) 40 8 35 k. V 9 Output Current 350 375 Amps 10 Beam Voltage Step Size 3 -8 5 10 k. V 11 Flat Top Voltage Regulation/Slope (Within 150 usec) 80 -25 25 V 35 Trevor Butler New Min 9/24/2021
8) Output Voltage • Current – 11 to 24 k. V flattop voltage [plus up to 10 k. V extra for beam (11 -34 k. V)] for LRF 1 -5 at nominal operating gradients. • New – 8 to 35 k. V of range • Some stations had voltage peaks up to 32 k. V, and this number can approach 34 when a 7835 tube gets old and needs maximum voltage to get the required RF energy out. • Series Pass Regulator • Current modulators can’t produce more than 34 k. V • Switch tubes can only hold of about 42 k. V • Most switch tubes can only drop a minimum of about 8 k. V across them at full power. • The 7835 cavity sockets break down at >35 k. V. • The final specification was set to be 8 -35 k. V operating range, with typical stations (LRF 2 -5) running at 25 -30 k. V 36 Trevor Butler 9/24/2021
LE Linac Modulator Specifications Id Specification Current 1 Pulse Repetition Rate 15 2 Rise Time 150 3 Fall Time 4 New Max Units 15 Hz 50 150 μs 50 70 150 μs Flat Top Time 150 50 160 μs 5 Beam Length/(Adjustable) 62 110 μs 6 Beam Time Delay (Adjustable) 72 100 μs 7 Peak Voltage Time (Adjustable) 125 35 150 μs 8 Output Voltage (Adjustable) 40 8 35 k. V 9 Output Current 350 375 Amps 10 Beam Voltage Step Size 3 -8 5 10 k. V 11 Flat Top Voltage Regulation/Slope (Within 150 usec) 80 -25 25 V 37 Trevor Butler New Min 9/24/2021
9) Output Current • Current – 350 Amps max • New – 375 Amps max • The output current is entirely dependent on the impedance of the 7835 Power Amplifier (PA). • The tube can range from 80 -120 Ohms during typical forward powers between 2 -3 MW. • This impendence can drop below 80 ohms during the voltage ramp up, and to higher than 120 ohms during the voltage ramp down because the energy in the cavity is feedback into the tube, reducing it apparent impedance. 38 Trevor Butler 9/24/2021
9) Output Current 39 Trevor Butler 9/24/2021
LE Linac Modulator Specifications Id Specification Current 1 Pulse Repetition Rate 15 2 Rise Time 150 3 Fall Time 4 New Max Units 15 Hz 50 150 μs 50 70 150 μs Flat Top Time 150 50 160 μs 5 Beam Length/(Adjustable) 62 110 μs 6 Beam Time Delay (Adjustable) 72 100 μs 7 Peak Voltage Time (Adjustable) 125 35 150 μs 8 Output Voltage (Adjustable) 40 8 35 k. V 9 Output Current 350 375 Amps 10 Beam Voltage Step Size 3 -8 5 10 k. V 11 Flat Top Voltage Regulation/Slope (Within 150 usec) 80 -25 25 V 40 Trevor Butler New Min 9/24/2021
10) Beam Voltage Step Size • Measured between ~3 -8 k. V of beam voltage step on LRF 1 -5. This number is dependent on the beam energy gain per station which varies. • It also depends on the age of the 7835 PA, which can increase this amount of voltage needed to get enough RF out of the tube to accelerate the beam to the proper energy. • The final specification was set to 10 k. V maximum step size • Most tubes run around 5 k. V during normal operation with a 7835 in optimal condition. 41 Trevor Butler 9/24/2021
LE Linac Modulator Specifications Id Specification Current 1 Pulse Repetition Rate 15 2 Rise Time 150 3 Fall Time 4 New Max Units 15 Hz 50 150 μs 50 70 150 μs Flat Top Time 150 50 160 μs 5 Beam Length/(Adjustable) 62 110 μs 6 Beam Time Delay (Adjustable) 72 100 μs 7 Peak Voltage Time (Adjustable) 125 35 150 μs 8 Output Voltage (Adjustable) 40 8 35 k. V 9 Output Current 350 375 Amps 10 Beam Voltage Step Size 3 -8 5 10 k. V 11 Flat Top Voltage Regulation/Slope (Within 150 usec) 80 -25 25 V 42 Trevor Butler New Min 9/24/2021
11) Flat Top Voltage Regulation • • Current – 80 Volt maximum variation • Measured on LRF 1 -5 for a 150 us pulse flat top length. • This would be reduced to ~50 Volts for a 100 us pulse. New – The final specification was set to +/-25 Volts of regulation. 43 Trevor Butler 9/24/2021
LE Linac Modulator Specifications Id Specification Current New Min New Max Units 12 Flat Top Repeatability (Pulse to Pulse) 200 -25 25 V 13 Flat Top Resolution 15 -5 5 V 14 Beam Top Repeatability -10 10 V 15 Beam Top Tilt +/- 3 -5 5 k. V 16 Slew Rate (Beam Voltage Step) 20 15 17 Slew Rate (Rising Edge) 0. 25 1 k. V/usec 18 Slew Rate (Falling Edge) . 5 0. 5 k. V/usec 19 Step Size (Rising or Falling Edge) 1. 5 k. V 20 Modulator Emergency Turn off (<2 usec in pulse) 500 400 Amps 21 Modulator Emergency Turn off (<2 usec out of pulse) 150 100 Amps 22 Linearity +/- 20 % 23 Gain 10000 44 Trevor Butler k. V/usec 10000 9/24/2021
12) Flat Top Repeatability • Measured 200 Volts maximum on LRF 1 -5 • Measured during time when gradient feedback loops where disabled and during line voltage fluctuations. • Decided on a final specification of +/- 25 Volts 45 Trevor Butler 9/24/2021
LE Linac Modulator Specifications Id Specification Current New Min New Max Units 12 Flat Top Repeatability (Pulse to Pulse) 200 -25 25 V 13 Flat Top Resolution 15 -5 5 V 14 Beam Top Repeatability -10 10 V 15 Beam Top Tilt +/- 3 -5 5 k. V 16 Slew Rate (Beam Voltage Step) 20 15 17 Slew Rate (Rising Edge) 0. 25 1 k. V/usec 18 Slew Rate (Falling Edge) . 5 0. 5 k. V/usec 19 Step Size (Rising or Falling Edge) 1. 5 k. V 20 Modulator Emergency Turn off (<2 usec in pulse) 500 400 Amps 21 Modulator Emergency Turn off (<2 usec out of pulse) 150 100 Amps 22 Linearity +/- 20 % 23 Gain 10000 46 Trevor Butler k. V/usec 10000 9/24/2021
13) Flat Top Resolution • Current – Measured between 15 -40 Volts resolution between LRF 1 -LRF 5. • New – Decided on the final specification of +/-5 Volts • Set by the bits of resolution of the D/A module used to create the voltage steps used in the feedback loop • This makes sense, since we desire 0. 1 % accuracy, assuming 25 k. Volts for LRF 2 -5, we have 25000*0. 1% = 25 Volts. For LRF 1, which has historically run as low as 10 k. V to get nominal gradient regulation, this number can be as low as 10 Volts = 10000*0. 1% 47 Trevor Butler 9/24/2021
LE Linac Modulator Specifications Id Specification Current New Min New Max Units 12 Flat Top Repeatability (Pulse to Pulse) 200 -25 25 V 13 Flat Top Resolution 15 -5 5 V 14 Beam Top Repeatability -10 10 V 15 Beam Top Tilt +/- 3 -5 5 k. V 16 Slew Rate (Beam Voltage Step) 20 15 17 Slew Rate (Rising Edge) 0. 25 1 k. V/usec 18 Slew Rate (Falling Edge) . 5 0. 5 k. V/usec 19 Step Size (Rising or Falling Edge) 1. 5 k. V 20 Modulator Emergency Turn off (<2 usec in pulse) 500 400 Amps 21 Modulator Emergency Turn off (<2 usec out of pulse) 150 100 Amps 22 Linearity +/- 20 % 23 Gain 10000 48 Trevor Butler k. V/usec 10000 9/24/2021
14) Beam Top Repeatability • Current – We were not able to measure directly since we always activate the auto gradient regulation loop when running beam. • New – Specification of +/- 10 Volts • It can be assumed that this regulation must be good enough to keep beam energy stable to less than 0. 5%. • If we have 5 k. V for a beam voltage typical step size, and we have a resolution of +/- 10 Volts, we have 20/5000 = 0. 4% regulation repeatability, which could be regulated down further with the LLRF feedback loop 49 Trevor Butler 9/24/2021
LE Linac Modulator Specifications Id Specification Current New Min New Max Units 12 Flat Top Repeatability (Pulse to Pulse) 200 -25 25 V 13 Flat Top Resolution 15 -5 5 V 14 Beam Top Repeatability -10 10 V 15 Beam Top Tilt +/- 3 -5 5 k. V 16 Slew Rate (Beam Voltage Step) 20 15 17 Slew Rate (Rising Edge) 0. 25 1 k. V/usec 18 Slew Rate (Falling Edge) . 5 0. 5 k. V/usec 19 Step Size (Rising or Falling Edge) 1. 5 k. V 20 Modulator Emergency Turn off (<2 usec in pulse) 500 400 Amps 21 Modulator Emergency Turn off (<2 usec out of pulse) 150 100 Amps 22 Linearity +/- 20 % 23 Gain 10000 50 Trevor Butler k. V/usec 10000 9/24/2021
15) Beam Top Tilt • Current – Measured up to 7 k. V of tilt on the modulator voltage pulse during beam. • New – Specification of +/- 5 k. V • This is primarily due to the current feedback loop in the modulator and the roll of frequency to keep the modulator for oscillating. • In an ideal modulator, with ideally square beam, and a 7835 running below anode voltage saturation level, this pulse would be a perfect square. • Exception - The beam pulse is not ideally square on NTF pulses • Although the amount of slope on the RFQ beam is currently unknown, it is expected to have be large enough tilt to require the modulator to have tilt to compensate. • It was decided to leave a beam tilt of +/- 5 k. V in order to compensate for any, or all, of the non-ideal characteristics of either the RF system or Ion Source 51 Trevor Butler 9/24/2021
LE Linac Modulator Specifications Id Specification Current New Min New Max Units 12 Flat Top Repeatability (Pulse to Pulse) 200 -25 25 V 13 Flat Top Resolution 15 -5 5 V 14 Beam Top Repeatability -10 10 V 15 Beam Top Tilt +/- 3 -5 5 k. V 16 Slew Rate (Beam Voltage Step) 20 15 17 Slew Rate (Rising Edge) 0. 25 1 k. V/usec 18 Slew Rate (Falling Edge) . 5 0. 5 k. V/usec 19 Step Size (Rising or Falling Edge) 1. 5 k. V 20 Modulator Emergency Turn off (<2 usec in pulse) 500 400 Amps 21 Modulator Emergency Turn off (<2 usec out of pulse) 150 100 Amps 22 Linearity +/- 20 % 23 Gain 10000 52 Trevor Butler k. V/usec 10000 9/24/2021
16) Slew Rate (Beam Voltage Step) • Current – The original specification of the modulator was designed to be 20 k. V/usec. • New – Specification of 15 k. V/us • Measured 5 -10 k. V/usec on LRF 1 -5. • This parameter is important since the beam current rises in greater than 1 usec, and the modulator needed to be able to jump up to 10 k. V to compensate for the energy taken from the DTL cavity. • A final specification of 15 k. V/us was set. 53 Trevor Butler 9/24/2021
16) Slew Rate (Beam Voltage Step) 54 Trevor Butler 9/24/2021
LE Linac Modulator Specifications Id Specification Current New Min New Max Units 12 Flat Top Repeatability (Pulse to Pulse) 200 -25 25 V 13 Flat Top Resolution 15 -5 5 V 14 Beam Top Repeatability -10 10 V 15 Beam Top Tilt +/- 3 -5 5 k. V 16 Slew Rate (Beam Voltage Step) 20 15 17 Slew Rate (Rising Edge) 0. 25 1 k. V/usec 18 Slew Rate (Falling Edge) . 5 0. 5 k. V/usec 19 Step Size (Rising or Falling Edge) 1. 5 k. V 20 Modulator Emergency Turn off (<2 usec in pulse) 500 400 Amps 21 Modulator Emergency Turn off (<2 usec out of pulse) 150 100 Amps 22 Linearity +/- 20 % 23 Gain 10000 55 Trevor Butler k. V/usec 10000 9/24/2021
17&18) Slew Rate (Rising and Falling Edge) • Current – Rising Edge 0. 25 k. V/usec & Falling Edge 0. 50 k. V/usec • New Spec – Rising Edge 1. 00 k. V/usec & Falling Edge 0. 50 k. V/usec • It was determined that a slew rate limitation would be needed on the rising and falling and rising edges to reduce the reverse power spikes that occur during those times. • From both simulations and tests performed on LRF 2 (next slide), we showed that if we increase the fall time, we reduce the peak of reverse power. • This reduction is important to reduce the risk of sparking from reverse power spikes that could be created if the modulator is designed with voltage steps. • A final specification of 1 k. V/us on the rise and 0. 5 k. V/us on the fall time was chosen. 56 Trevor Butler 9/24/2021
17&18) Slew Rate (Rising and Falling Edge) 57 Trevor Butler 9/24/2021
17&18) Slew Rate (Rising and Falling Edge) 58 Trevor Butler 9/24/2021
LE Linac Modulator Specifications Id Specification Current New Min New Max Units 12 Flat Top Repeatability (Pulse to Pulse) 200 -25 25 V 13 Flat Top Resolution 15 -5 5 V 14 Beam Top Repeatability -10 10 V 15 Beam Top Tilt +/- 3 -5 5 k. V 16 Slew Rate (Beam Voltage Step) 20 15 17 Slew Rate (Rising Edge) 0. 25 1 k. V/usec 18 Slew Rate (Falling Edge) . 5 0. 5 k. V/usec 19 Step Size (Rising or Falling Edge) 1. 5 k. V 20 Modulator Emergency Turn off (<2 usec in pulse) 500 400 Amps 21 Modulator Emergency Turn off (<2 usec out of pulse) 150 100 Amps 22 Linearity +/- 20 % 23 Gain 10000 59 Trevor Butler k. V/usec 10000 9/24/2021
19) Modulator Step Size • Current – Does not exist • New – 1. 5 k. V • If the modulator puts out power in steps, the cavity acts as a short/open and returns all of the forward power. • Assuming that 30 k. V maximum is needed to power the 7835 PA to 3 MW, then, we can calculate that 10 k. V steps yield 1 MW jumps of reverse power. • With steps of 1. 5 k. V, we would have reverse power spikes of < 150 k. W, which would be acceptable on both the rising and falling edges. • A reduction of 150 k. W in reverse power is possible when reducing the fall time from 50 us to 150 us, which is the falling edge time specification 60 Trevor Butler 9/24/2021
Modulator Step Size 61 Trevor Butler 9/24/2021
Modulator Step Size 62 Trevor Butler 9/24/2021
LE Linac Modulator Specifications Id Specification Current New Min New Max Units 12 Flat Top Repeatability (Pulse to Pulse) 200 -25 25 V 13 Flat Top Resolution 15 -5 5 V 14 Beam Top Repeatability -10 10 V 15 Beam Top Tilt +/- 3 -5 5 k. V 16 Slew Rate (Beam Voltage Step) 20 15 17 Slew Rate (Rising Edge) 0. 25 1 k. V/usec 18 Slew Rate (Falling Edge) . 5 0. 5 k. V/usec 19 Step Size (Rising or Falling Edge) 1. 5 k. V 20 Modulator Emergency Turn off (<2 usec in pulse) 500 400 Amps 21 Modulator Emergency Turn off (<2 usec out of pulse) 150 100 Amps 22 Linearity +/- 20 % 23 Gain 10000 63 Trevor Butler k. V/usec 10000 9/24/2021
20&21) Modulator Emergency Off • Current – 500 Amps in Pulse & 150 Amps out of Pulse • New Spec – 400 Amps in Pulse & 100 Amps out of Pulse • Under fault conditions, the modulator needs to drop to zero voltage in less than 2 usec. • Fault condition included the RF drive turning off, the 7835 RF cavity sparking, the 7835 internally sparking, the transmition line sparking, or the DTL cavity sparking. • There is an out of pulse specification since the 7835 will oscillate in grounded grid mode without RF drive on the tube. 64 Trevor Butler 9/24/2021
LE Linac Modulator Specifications Id Specification Current New Min New Max Units 12 Flat Top Repeatability (Pulse to Pulse) 200 -25 25 V 13 Flat Top Resolution 15 -5 5 V 14 Beam Top Repeatability -10 10 V 15 Beam Top Tilt +/- 3 -5 5 k. V 16 Slew Rate (Beam Voltage Step) 20 15 17 Slew Rate (Rising Edge) 0. 25 1 k. V/usec 18 Slew Rate (Falling Edge) . 5 0. 5 k. V/usec 19 Step Size (Rising or Falling Edge) 1. 5 k. V 20 Modulator Emergency Turn off (<2 usec in pulse) 500 400 Amps 21 Modulator Emergency Turn off (<2 usec out of pulse) 150 100 Amps 22 Linearity +/- 20 % 23 Gain 10000 65 Trevor Butler k. V/usec 10000 9/24/2021
22&23) Linearity & Gain • The current specification on linearity was choosen to be +/- 20% to match the previous specification • The current LLRF system has a typical voltage range or 5 Volts, requiring a gain of at least 10000 66 Trevor Butler 9/24/2021
LE Linac Modulator Summary • The present modulator is the major source of downtime in the Linac, creating over 50 % of the downtime in last 10 years. • The main power tubes in the modulator, the F 1123 switch tubes, are no longer manufactured, along with most of the relays, power supplies, diagnostics, and interlocks circuits, relying on the present system for the next 15 years of operation is unrealizable. • Phase 1 – Specificiation Stage is now complete • Phase 2 – This phase will involve sending the new specifications to interested companies working in high power modulator design for evaluation and prototype cost estimate. • • Currently do not have any numbers as to cost and time In-House design under consideration by AD/EE Support Dept. (ESTIMATE!) • Prototype $520 k in Materials (with 20% contingency) ~ (7*$520 k = 3640 k$ for complete build) • 3 years? total development time for one prototype 67 • 1 year of EE Support Engineering Time for design and prototype (~2000 hrs) • ~5 years [$520 k with 20% contingency] of EE Support Tech. Support time (~10000 hrs) Trevor Butler 9/24/2021
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