department of physics and astronomy - diva...

FREIA Report 201 /07 201

Department of Physics and Astronomy

. , R. Wedberg, K. Gajewski

Department of Physics and Astronomy Uppsala University P.O. Box 516 SE – 751 20 Uppsala Sweden

Papers in the FREIA Report Series are published on internet in PDF- formats. Download from http://uu.diva-portal.org

FREIA Department of Physics and Astronomy

Uppsala University

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Itelco-Electrosys 400 kW RF Station Site Acceptance Test M. Jobs, R. Wedberg, K. Gajewski

Uppsala University, Uppsala, Sweden

Figure 1. Installed Itelco-Electrosys 400 kW Station at FREIA

Abstract

The manufactured and delivered Itelco-Electrosys 400 kW RF station was tested on site at FREIA, in Uppsala August 31 through September 4 2015. The station could successfully deliver continuous pulse-trains with a power-level up to 400 kW. Each of the stations 200 kW tetrode based amplifier sections were mounted with TH-595 tetrode tubes from Thales and tuned for optimal performance. The gain of the tetrode amplifiers were roughly 15 dB with some variation between the two amplifier sections and the overall gain was approximately 85 dB maximum.

Some droop and phase distortion on the combined output pulse was measured caused primarily by a limited response time of the screen-grid power supply.


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1. 00Introduction The following section includes some general characteristics and remarks. The data presented within this report provides the test results for acceptance of the Site Acceptance Test of the Itelco-Electrosys RF -station.

1.1 General station characteristics

1. Dimensions of the power station: 4884 mm long 1158 mm width 2550 mm high (incl.combiner)

2. Documentation: Massive 3 folders. 1.2 Response to FAT remarks

The following remarks were made during factory acceptance test and have now been responded to

1. “One series switch has to be replaced, broken” a. Series switch replacement provided by Astrol and installed on site

2. “Complete test for EMC/CE compliance are to be done before shipping and must have passed acceptance values before shipping” a. Full EMC/CE documentation provided

3. “Elimination of software small bugs found during test” a. Multiple bugs removed and corrected, see Section 5.

4. “Full control via EPICS (some parameters setting by remote is not available in the current software version)” a. Remote interface updated, See section 5.

5. “Synchronization of history log data-base via SNMP” a. Remote interface updated, See section 5.

6. “The station emergency stop must be equipped with under-voltage protection. At the time of the test the power supply for the emergency switch had broken and stopped all functionality in the emergency switch. The station should not be able to run if the emergency stop is not working.” a. Station installed with properly functioning emergency switch

7. “The ability to remotely enable/disable the driver gain control feedback loop. The drivers has a built in gain feedback loop with a few seconds settling time which might interfere with any external feedback loops used to control the station. If this would be the case it must be possible to disable the internal loops to gain full control of the station.” a. AGC is now available to enable/disable at will

8. “When running at 28 Hz the stations internal power measurement shows a discrepancy in the measured values. When outputting 200 kW 1 ms pulses the stations measured value was roughly 150 kW. It was theorized that this might be related to the short pulse duration and would be further investigated by Electrosys.” a. Internal component values updated by Itelco-Electrosys to solve issue


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2. 00Key Parameters Tender Comparison The following list describes the correspondence of the measured station parameters during the on-site acceptance test and its correspondence with those specified in the tender. Green markings indicate better or equal to tender specifications, yellow indicate slight deviation and red indicate major deviations.

Parameter Tender Specification HPA1 HPA2 Station Out

Frequency of operation 352.21 MHz 352.21

MHz 352.21

MHz

Output power ≥ 175 kW 200 kW 200 kW

3 dB bandwidth ≥ 250 kHz ≥ 2.5 MHz ≥ 2.5 MHz Pulse width 3.5 ms 3.5 ms 3.5 ms

Frequency of pulses 14 Hz 14 Hz 14 Hz

Input power from driver ≤ 10 kW 6.0 kW 6.9 kW Gain ≥ 14.5 dB 15.6 dB 14.9 dB

Anode Efficiency ≥ 65 % 65% 60%

Class of operation AB AB AB Harmonics < -35 dBc < -40 dBc

Spurious < -60 dBc < -60 dBc Linearity1 ± 0.5 dB ± 1.25 dB ± 1.25 dB ± 1.25 dB Gain amp. stability (time >5 μs) ± 1 dB ± 0.3 dB

Gain phase stability (time >5 μs) ± 5degrees ± 1.5

degrees Driver Gain2 ≥ 70 dB 69.5 dB 70 dB Driver amp. stability (time >5 μs) 3 ± 0.2 dB ± 0.25 dB ± 0.1 dB

Driver Phase Linearity ± 5degrees ± 0.5

degrees 1: Primarily caused by deviation in linearity in the <50 kW range 2: Controlled by station, could be modified by if required 3: Some minor discrepancy of gain control in HPA1


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3. 00Power Supplies The RF station power supplies were thoroughly evaluated as part of the on-site acceptance test. The performance both during idle operation as well as in the output power range 40kW to 400kW were recorded and are presented in the following sections.

3.1 Station Idle Set Values After mounting of the two tetrode tubes the screen and control grid supplies were set for class AB operation. The bias of the control grid voltages were set so that the idle anode currents were 40mA. The input water flow and pressure as well as the serial numbers of the tetrode tubes were recorded and are given below. The main tests were performed using 3.5 ms long pulses at 14 Hz repetition rate and the carrier frequency was set to 352.21 MHz.

Pulse Settings: 3.5 ms 14 Hz Carrier Freq: 352.21 MHz

Power Supplies Idle Control Grid Voltage [V] HPA1 HPA2 Screen Grid Voltage[V] HPA1 HPA2

Operating Voltage -215 -250 Operating Voltage 900 900 Blanking Voltage -249 -282

Cooling Water: Water Conduct. Water Flowrate [l/min] Pressure [bar] Average [μS/cm] 0,4 Station In 195 Station In 2,55 Log Exist Load In 60 Station Out 0,35

Water Temp [Celsius] HPA1 HPA2 Water Temp [Celsius] Station In 22° 20° Load In 21,3° Station Out 22° 21° Load Out 24,8°

Tube A Serial Nr: 755305 Tube B Serial Nr: 753397


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3.2 Supplies – Station Read Values

The following values were recorded using the stations built in current and voltage meters at a total output power ranging from 40 kW to 400 kW. These should be read in comparison with the actual measured voltages given in Section 3.3 and 3.4.

HPA1 Station P. Out [kW] 0 40 80 120 160 200 240 280 320 360 400 I_anode [I] 4,93 6,98 8,66 10,1 11,35 12,55 13,47 14,52 15,87 17,46 V_anode [kV] 16,3 16,28 16,33 16,33 16,38 16,38 16,43 16,43 16,45 16,5

Filament Current [I] 182 182 182 182 182 181 181 181 180 180 Filament Voltage [V] 8 8 8 8 8 8 8 8 8 8

G1 Current [I] 0 0,03 0,15 0,32 0,47 0,63 0,73 0,89 1,13 1,52 G1 Voltage [V] -216 -216 -217 -217 -218 -219 -219 -220 -221 -222

G2 Current [I] 0,023 0,03 0,072 0,08 0,096 0,117 0,14 0,175 0,24 0,357 G2 Voltage [V] 899 902 910 924 929 934 935 938 942 947

HPA2 Station P. Out [kW] 0 40 80 120 160 200 240 280 320 360 400 I_anode [I] 4,88 6,95 8,59 10,08 11,35 12,5 13,62 14,62 15,79 17,31 V_anode [kV] 17,14 17,16 17,21 17,24 17,26 17,28 17,31 17,33 17,36 17,38

Filament Current [I] 172 172 172 172 171 171 171 171 170 169 Filament Voltage [V] 8 8 8 8 8 8 8 8 8 8

G1 Current [I] 0 0,05 0,22 0,41 0,58 0,74 0,92 1,1 1,35 1,78 G1 Voltage [V] -251 -251 -252 -253 -254 -255 -255 -257 -258 -260

G2 Current [I] 0,026 0,062 0,073 0,083 0,097 0,12 0,155 0,197 0,264 0,415 G2 Voltage [V] 899 925 926 927 930 932 935 938 945 957


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3.3 Control Grid Voltage and Current The voltage and current variation of both the control grid supplies were measured during the pulse for the complete power range of 40 kW to 400 kW. In order to measure the voltage and current of the control grid power supplies a Rigol DS4054 scope was connected to the stations BNC connectors included for measurements of control grid voltages and currents. A drop in voltage as a function of increased output power can be seen in Fig. 2 and Fig.3. However, the response time of the control grid supplies seems adequate as only a minor initial drop of control grid voltage is visible when the RF pulse is applied at full power.

Figure 2. HPA1 control grid voltage as a function of total output power.

Figure 3. HPA2 control grid voltage as a function of total output power.


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The measured current over the control grid supplies shows an increase in grid current in the initial 1 ms of the output pulse at full (400 kW) power. This is, however, not currently thought of as being attributed to the performance of the control grid supply. The variation in grid current is instead thought of as being an effect of the limited response time of the screen grid power supply (see Section 3.4).

Figure 4. HPA1 control grid current as a function of total output power.

Figure 5. HPA2 control grid current as a function of total output power.


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3.4 Screen Grid Voltage The screen grid power supplies were measured in the power range of 40 kW to 400 kW. The measurements seen in Fig. 6 through Fig. 10 show that the screen grid supply experience an initial droop. This indicates that the response time of the screen grid power supplies is long enough to cause distortion of the output pulse. As is presented in Section 4.4 and section 4.8 this causes a distortion on both the amplitude of the output signal as well as a phase-shift.

Figure 6. HPA1 screen grid voltage as a function of total output power.

Figure 7. HPA2 screen grid voltage as a function of total output power.


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In order to be able to measure the output current of the screen grid power supply direct probing of the built-in measurement boards were necessary. No external BNC connectors for voltage or current measurements were available on the station. For voltage measurements a high-voltage T-connection were connected to a high-impedance, high-voltage probe placed between the power supply and the tetrode cavity screen voltage connector. Fig. 8 shows the probe location on the board for measuring the screen-grid current.

Figure 8. Current measurement probe location on board.


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Figure 9. HPA1 screen grid current as a function of total output power.

Figure 10. HPA2 screen grid current as a function of total output power.


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3.5 Station Efficiency Evaluation

Both overall station efficiency (wall to RF) was evaluated in the range 0 to 400kW as well as the anode efficiency of both running tetrodes. The voltages and currents delivered to the station through the three-phase mains were measured using FREIA facilities built in monitors for the used three phase lines. Only a minor amount of measurement equipment was connected on the same three phase lines making the read values correspond well to the power consumption of the overall station.

Station P. Out [kW] 0 40 80 120 160 200 240 280 320 360 400 Voltage – L1 231 232 232 232 232 233 230 230 230 230 230 Voltage – L2 233 233 233 233 233 233 231 232 231 231 231 Voltage – L3 233 232 233 233 233 233 231 231 231 231 231

Current – L1 16 33 39 43 48 51 54,5 57 60,5 67 72,5 Current – L2 17 34 40 44 49 52 55 58 61 67,5 73 Current – L3 15 31 41 41 46 50 53 56 59 64,5 72,2

Power Avg [kW] 10,4 21 24 27 30,5 32 34 36 37 40,8 45

Figure 11. Total station efficiency calculated from mains line to RF out.


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The efficiency of both tetrodes was calculated using the measured values of anode voltage and current consumption in relation to the RF power generated in the corresponding tetrode.

Figure 12. Calculated HPA1 tetrode anode efficiency.

Figure 13. Calculated HPA2 tetrode anode efficiency.


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3.6 Crowbar Test

Test of crowbar by crowbar test buttons. No remarks.

3.7 Series Switch Installation & Test

When the station was delivered to FREIA, Uppsala one of the series switches was missing due to being damaged before shipping. A replacement switch had been ordered from Astrol and was installed in time for the on-site test. During initial installation it was discovered that the switch response to the trigger wire (clearly seen in red in Fig. 14) was inverted in relationship to the previous switches. Astrol was contacted and admitted to the replacement switch having been manufactured in this way and the response also told that Astrol would be more stringent in future manufacturing to make sure each switch is manufactured identically. Due to this effect the series switches installed in the station uses mirrored connection of the trigger line, as is seen in Fig. 14.

Figure 14. Installed anode power supply series switches from Astrol. Red cables are trigger signal.


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The series switch used in the station was tested as follows

Test set up:

Figure 15. Schematic of series switch test setup.

The performance of both series switches and crowbar was evaluated using a short circuit wire tester. The setup used can be seen in Fig. 16 and Fig. 17. The station successfully passed the short circuit wire test with the anode power supply voltage set to 18 kV.

Figure 16. Short circuit wire tester connected to station anode high voltage power supply.

C154uF

C254uF

C354uF

0

F1

FGAIN = 1

dI/dt current transformerCrowbar test

R1

4.7

R2

4.7

R3

4.7

R4

4.7

L1

10uH

U10

1

2

0

R5

4.7

R6

4.7 U2

01 2

L3

220uH

Dbreak

D1 F2

F GAIN = 1

Pulse current transformer

F3

FGAIN = 1

LEM Current sensor

Series switch

Crowbar

R8

R9

0

U30

1

2

0

dV/dt detectorWiretester


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Figure 17. Short circuit wire tester setup connected and boxed off to provide security.


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3.8 Tube Installation

After verification of all non-RF operation of the station (including power-supplies idle voltages, control logic and water flow) both HPA1 and HPA2 were fitted with Thales TH-595 tubes. Both tubes were installed and checked to verify that the seals for the liquid anode cooling were leak free.

Figure 18. Tetrode cavity with anode coolant lines (red) disconnected in preparation for tube insertion.


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3.9 Modulator

In order to run the station in pulsed mode a blanking pulse synchronized to the input RF pulse was required as well. Also, the rise time of the input RF pulse should be limited to approximately 20 us in order to make sure no overshoot appears on the output pulse. Both these parameters were included by the use of a custom modulator loaned to FREIA by Itelco-Electrosys. The modulator used was only intended for station testing as custom modulator system will be used at FREIA during normal operation but was not yet fully realized at the time of the on-site acceptance test.

Figure 19. Blanking pulse generator and RF modulator provided by Itelco-Electrosys.

3.10 Interlock Settings

The following settings were used for the interlocks a. Anode power limit 800 kW b. Peak anode power average rms 40 kW. c. Screen grid power max 400 W. d. Anode peak current 30 A. e. Screen grid peak current 800 mA. f. Anode overvoltage 18 kV. g. Anode minimum voltage 10 kV. h. Control grid voltage window 150 – 350 V i. Control grid peak current 4 A.(Sink) j. Control grid max source current 0.5 A.


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4. RF Characteristics The RF characteristics of the station were evaluated for the complete total power range of 40 kW to 400 kW. Measured parameters were primarily measured using a Rigol DS4045 Oscilloscope and a Rigol DSA815 spectrum analyzer. The measured results are presented below.

4.1 Power Measurement Setup

When measuring the performance of the RF station the built in directional couplers were used. The corresponding coupling values of all built in directional couplers is listed below.

Directional Couplers

Value [dB] Value [dB] Driver A Output [dBm] Driver B Output [dBm]

Forward -57,6 Forward -57,6 Reverse -47,6 Reverse -46,6

Value [dB] Value [dB] Tetrode A Output [dBm] Tetrode B Output [dBm]


Value [dB] Value [dB] Station Out [dBm] Dummy Load [dBm]


When measuring the output pulse using the built in directional couplers the insertion loss of the cable used to connect between the couplers and the measurement equipment was characterized using a Keysight FieldFox network analyzer and is given below.

Cable Losses

Spectrum Analyzer Cable S21 -1,2 dB


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Fig. 20 shows measured transmission coefficient of the low-pass filters mounted on the station. At 352.21 MHz the insertion loss was 0.2 dB and was used to calibrate the power meter used to measure the absolute power output of the station.

Figure 20. S21 measurements on low-pass filters provided with station.

Fig. 21 shows the relationship between set values used to obtain a specific power level and the actual power level measured. The plotted difference between designated and measured values are <0.2dB and is considered to be below the total combined measurement accuracy of absolute power measurements with the equipment used.

Figure 21. Relationship between designated power and measured power.


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4.2 Cavity Tuning Measurements After mounting the tubes the cavity output was tuned at low power levels using a Keysight FieldFox network analyzer. Fig. 22 shows the measured transfer function of HPA1 before tuning and Fig. 23 shows the transfer function after tuning. The measured bandwidth after tuning was 11.4 MHz. The same procedure was carried out for HPA2 and the -3 dB bandwidth measured to 12 MHz.

Figure 22. S21 measurements on installed tetrode HPA1 at low power before tuning.

Figure 23. S21 measurements on installed tetrode HPA1 at low power after tuning.


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4.3 Gain & Linearity Measurements

The gain and linearity of both the complete station as well as that of tetrodes and drivers were measured and evaluated for the total output power range of 40 kW to 400 kW and is presented below.

Combined Station Station P. Out [kW] 0 40 80 120 160 200 240 280 320 360 400 Power - In [dBm] -6,8 -4,8 -3,62 -2,65 -2,02 -1,22 -0,67 -0,08 0,48 1,29 Power - FWD [dBm] 0,3 3,48 5,07 6,37 7,15 8,22 8,92 9,57 10,06 10,47 Power - Out [dBm] 75,7 78,88 80,47 81,77 82,55 83,62 84,32 84,97 85,46 85,87 Gain [dB] 82,5 83,68 84,09 84,42 84,57 84,84 84,99 85,05 84,98 84,58

Figure 24. Total measured gain of station for all output power levels.

Driver Section A Station P. Out [kW] 0 40 80 120 160 200 240 280 320 360 400 Power - In [dBm] -9,8 -7,8 -6,62 -5,65 -5,02 -4,22 -3,67 -3,08 -2,52 -1,71 Power - FWD [dBm] 0,37 2,5 3,78 4,75 5,41 6,3 6,89 7,48 8,08 8,95 Power - Out [dBm] 59,17 61,3 62,58 63,55 64,21 65,1 65,69 66,28 66,88 67,75 Gain [dB] 68,97 69,1 69,2 69,2 69,23 69,32 69,36 69,36 69,4 69,46


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Figure 25. Measured gain of driver HPA1 for all power levels.

Driver Section B Station P. Out [kW] 0 40 80 120 160 200 240 280 320 360 400 Power - In [dBm] -9,8 -7,8 -6,62 -5,65 -5,02 -4,22 -3,67 -3,08 -2,52 -1,71 Power - FWD [dBm] 1,38 3,35 4,49 5,53 6,16 7,02 7,58 8,18 8,72 9,6 Power - Out [dBm] 60,18 62,15 63,29 64,33 64,96 65,82 66,38 66,98 67,52 68,4 Gain [dB] 69,98 69,95 69,91 69,98 69,98 70,04 70,05 70,06 70,04 70,11

Figure 26. Measured gain of driver HPA2 for all power levels.


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Amp Section A Station P. Out [kW] 0 40 80 120 160 200 240 280 320 360 400 Power - In [dBm] -9,8 -7,8 -6,62 -5,65 -5,02 -4,22 -3,67 -3,08 -2,52 -1,71 Power - FWD [dBm] 1 4,2 5,84 7,02 7,83 8,82 9,51 10,12 10,65 11,08 Power - Out [dBm] 72,8 83,8 77,64 78,82 79,63 80,62 81,31 81,92 82,45 82,88 Gain [dB] 82,6 91,6 84,26 84,47 84,65 84,84 84,98 85 84,97 84,59

Figure 27. Measured gain of HPA1 for all power levels.

Figure 28. Measured gain of tetrode HPA1 for all power levels.


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Amp Section B Station P. Out [kW] 0 40 80 120 160 200 240 280 320 360 400 Power - In [dBm] -9,8 -7,8 -6,62 -5,65 -5,02 -4,22 -3,67 -3,08 -2,52 -1,71 Power - FWD [dBm] 0,75 3,82 5,4 6,81 7,56 8,71 9,41 10,07 10,55 10,95 Power - Out [dBm] 72,55 75,62 77,2 78,61 79,36 80,51 81,21 81,87 82,35 82,75 Gain [dB] 82,35 83,42 83,82 84,26 84,38 84,73 84,88 84,95 84,87 84,46

Figure 29. Measured gain of HPA2 for all power levels.

Figure 30. Measured gain of tetrode HPA2 for all power levels.


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4.4 Droop Measurements

Droop measurements of the output pulse were performed at 400 kW output power. A total combined output RF power droop of 0.3 dB was recorded and is presented in Fig. 31 through 35. In measurements of both the combined output pulse as well as the individual tetrode outputs an amplitude distortion can be seen in the first half of the pulse corresponding in time to the measured response time of the screen grid power supply.

Figure 31. Measured amplitude and droop of combined output pulse for full pulse at 400 kW.

Figure 32. Measured amplitude and droop of HPA2 output pulse for full pulse at 400 kW.


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Figure 33. Measured amplitude and droop of HPA1 output pulse for full pulse at 400 kW.

Figure 34. Measured amplitude and droop of HPA1 driver output pulse for full pulse at 400 kW.


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Figure 35. Measured amplitude and droop of power delivered to load for full pulse at 400 kW.


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4.5 Bandwidth at 400 kW

The station bandwidth at 400 kW output power was measured by using a Rigol DSA815 spectrum analyzer with a 10 MHz span set to maximum hold. The input frequency was varied in the range of +/- 2.5 MHz and the output power recorded. The resulting output power measured on the built in directional coupler can be seen in Fig. 36. As can be seen the station exhibited minimal gain variation in the set frequency range. Any variations shown is attributed to the fact that the measurement required a frequency sweep with maximum hold and some variation due to synchronization issues of the swept points to the input RF pulses. In the figure 10.5 dBm corresponds to an output power of 400 kW.

Figure 36. Bandwidth measurements of combined station output at 400 kW for +/- 2.5 MHz range

4.6 Harmonics

Harmonics were measured at 400 kW and are listed below in conjunction with the output power measured at 351.21 MHz

Frequency [MHz] 352,2 704,4 1057 Output [dBm] 85,86 35,1 33,2

4.7 Spurious

Using the Rigol DSA815 spectrum analyzer with the maximum frequency span of 1.5 GHz no spurious signals in excess if the tender specified -60 dBc was recorded.


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4.8 Phase Stability

The phase stability of the output pulse was measured by sampling the complete output pulse using a Rigol DS4054 Oscilloscope using a sample-rate of 2 GSa/s. The recorded .wfm traces were imported in Matlab and the phase calculated using a FFT of the recorded traces. The measured results are presented below.

Figure 37. Phase-shift between station input and station output relative to initial value at 400 kW.

Figure 38. Phase-shift between station input and HPA1 tetrode output relative to initial value at 400 kW.


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Figure 39. Phase-shift between station input and HPA1 driver output relative to initial value at 400 kW.

Figure 40. Phase-shift between station input and station output relative to initial value at 200 kW.


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Figure 41 Phase-shift between station input and HPA1 tetrode output relative to initial value at 200 kW.

Figure 42. Phase-shift between station input and HPA1 driver output relative to initial value at 200 kW.


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5. Epics Interface The remote control from Epics has been tested during the last day (Friday). The first three days have been used by Stefano Dilio to test the bug fixes and additions made in the new firmware. The test has been done on the spare Central Control Unit (CCU) not connected to the power station.

The new features added to the firmware as compared to the firmware that came installed in the CCU in the power station:

1. Added status bit for Automatic Gain Control

2. Added remote command to reset IP communication buffers

3. Added possibility (only from local control panel) to specify the period for automatic reset of IP communication buffers. Setting the period to 0 disables the automatic resets.

The improvements and bug fixes done during the acceptance tests:

1. Fixed some pointer reference error (the SNMP object pointed to the wrong hardware)

2. Fixed SNMP Agent status indication

3. Improved the response time for the Epics commands by tuning some parameters for inter-processor communication over RS-232 line in the CCU.

During the tests all acquisition values and status bits have been compared with the local display and nodiscrepancies have been found. The observed update rate for all parameters is about one second and is limited by the Power station’s internal communication architecture. This update rate is often delayed by a few seconds after sending the commands/settings to the station.

All commands and settings have been tested and worked properly.

However, there are some limitations on sending the remote commands and settings. The most serious is that it does not work to send the setting for two or more parameters at the same time. Only value for one parameter is accepted and there is no feedback (other than by checking the read-back value) that the rest is silently ignored.

The second limitation is that the commands/settings can’t be accepted more often than every few seconds (recommended by Itelco-Electrosys delay is 5 s).

These limitations don’t cause serious problems during a normal operation of the station at FREIA but might be unacceptable at ESS.


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6. 00Open Issues & Remarks During the acceptance test of the station a few issues and remarks were noted which related to either the Epics interface of the station or to the electrical/physical performance of the station. Any remarks or issues are listed below with the corresponding proposed cause of action. Itelco-Electrosys has shown a positive attitude towards working on these long-term improvements. The Epics improvements can be done just by updating the firmware without any need for changing the hardware. Uploading of the new firmware to the CCU can be easily done by FREIA staff. All issues listed below are considered minor issues and does not negatively affect the overall operation of the station at FREIA

Description Type Scope Part Action Replacement switch provided by Astrol had inverted trigger cable connection compared to previous switch

Remark Long Term UU/IE Astrol has noted the issue and future manufactured switches will be properly standardized

Response time of screen grid power supplies are a bit long causing slight distortion of output pulse amplitude and phase

Issue Long Term UU Investigate if current supply could be improved or find a suitable replacement

Linearity of the power station is slightly of out the tender specification due to variation in gain for lower output power levels (<100 kW combined output)

Remark Long Term UU

Find exact limitations of tetrodes (linearity vs efficiency tradeoff) and determine feasibility of current specifications

Some variation of control grid bias settings between HPA1 and HPA2 Issue Long Term UU

Switch tubes between HPA1 and HPA2 to determine if tube related, if not further investigation might be required

Anode efficiency of HPA2 slightly below specified requirements (<65%) at full power, currently reaching roughly 60%

Remark Long Term UU Determine cause of anode efficiency difference and propose solution

Risetime of RF input pulse needs to be externally limited to be no less than 20 μs

Remark Long Term UU Investigate if overshoot due to fast risetimes can be reduced

No status bit for "Crowbar Fired" Issue Short Term UU Add a status bit for “Crowbar Fired” (new firmware)

MIB file documentation/comments should be updated

Remark Short Term UU Update the MIB file (only the documentation/comments part)


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HPA.1 and HPA.2 PIB Water Conductivity Alarm and Warning mask timer settings

Issue Short Term UU

Increase HPA.1 and HPA.2 PIB Water Conductivity Alarm and Warning mask timer when the system is powered (from 20 to 36 secs)

MIB capacitor Charge Power not reliably measured Issue Short Term UU Delete from MIB capacitor

Charge Power

Description of dependencies/permissives for all commands and settings not available

Remark Short Term UU Documentation updated – already done

Delays in communication when sending commands/settings to the station

Issue Long Term UU/IE Improve the inter-processor communication in the CCU

Cannot process all incoming commands/settings in one burst Issue Long Term UU/IE Add a FIFO buffer for

incoming commands/settings


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7. 0Conclusions The 400 kW RF station delivered by Itelco-Electrosys to FREIA, Uppsala University performed well during on-site acceptance tests. A few smaller remarks have been made as pointed out in Section. The station fulfills all major tender specifications apart from a few minor deviations as noted in Section 6.

Following the on-site acceptance test initial further investigations will focus on the performance of the screen-grid supplies as well as further characterization of the station.

Some unbalance in bias conditions between HPA1 and HPA2 TH-595 bias voltages were recorded and test including a switch between the tubes mounted in HPA1 and HPA2 has been proposed to verify that the difference in bias conditions stems from difference in tube characteristics and not from the power supplies, power meters and control logic in the respective stations.

The station will also be interfaced with the proper modulator system in development in FREIA and the temporary modulator provided by Itelco-Electrosys will be shipped back to their facilities.

Further work will also be performed in improving the EPICS interface, including trying to reduce the delay times in the CCU.

Overall the station has been considered to pass the on-site acceptance test and start operations within FREIA.

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