LCLS X-Band RF System
The LCLS beam is run off crest on the RF in order to set up a particle position verses energy
correlation. The correlation is used to compress the bunch when it is run through a chicane. The
RF waveform is a sine shape and the correlation set up by running the bunch off crest has a large
second order component, it’s not very linear. The X-band RF station, with higher frequency, has
a much larger curvature in RF voltage verses time. The beam is run on the decelerating crest in
order to remove most of the second order, nonlinear, part of the correlation. The required 22MV
of peak accelerating gradient will require a klystron power output of 24MW. More information
can be found in the CDR Chapter 7, by Paul Emma. Results of the beam energy vs. position
correlation and how the X-Band station takes out the curvature are shown in figure 1.
Figure 1. X-Band Station to Linearize Energy Position Correlation - P. Emma
Accelerator Structure The accelerating structure is the H60VG3N-C structure from NLC. The structure is a 60cm long
5π/6 which has been tested at NLCTA to 65MV/m. LCLS operation requires 32MV/m with a
peak input power of 21MW. The structure has a dual feed at the input and output. The output of
the structure goes to two independent RF loads one of which has a WR90 directional coupler in
between the structure and load. This is used to measure the output power and RF phase of the
structure. The input feeds come from each arm of a magic-T. There is a WR90 direction coupler
at the input to the magic-T to measure the input power and RF phase to the structure.
Water flow through the accelerator is about 0.3GPM. The average power into the structure is
only 126W at 30pps 200nS. The structure's temperature coefficient is 36 degX/degC and the
structure is tuned for 45degC. The nominal water settings at 30Hz is 111degF for accelerator
water in the gallery. The water flow required to raise 1.1degC with 126W of power input is
126W/(4.2J/(cc-degC)x 1.1degC)= 30cc/sec = 1.8l/min = 0.47GPM
High Power Waveguide
The XL4 klystron is powered by modulator 21-2 in the klystron gallery. There is about 6ft of WR90 at the output of the klystron before it reaches a window assemble. The window assembly uses 2 mode converters to go from WR90 to circular waveguide where the window is mounted and then back to WR90. The WR90 is routed above penetration 21-3 where a mode converter changes to WC293. This over-moded circular waveguide runs 35feet through penetration 21-3 into the tunnel. In the tunnel a mode converter changes from WC293 to WR90. The WR90 is routed over to the accelerator structure. A diagram of the system is shown in figure X.
Figure X, X-Band waveguide layout.
XL4 Klystron and modulator
The XL4 klystron was designed to output over 50MW of X-Band power. The beam power to achieve this is 410kV at 350A, 144MW. XL4 klystrons have been run reliably at NLCTA for thousands of hours at over 50MW of output at a 1.6uS pulse width and 60Hz. LCLS requires 24MW at 200nS and 120Hz. The tube is expected to run reliably at these levels.
The standard 5045 15:1 pulse transformer was changed to a 17:1 transformer to achieve higher voltages at the tube from a standard 5045 modulator. The 5045 modulator PFN was redesigned for a short pulse. The pulse shape from the modulator is Gaussian with the 200nS RF pulse at the top. The modulator has an SCR front end control and uses a dequing circuit to regulate the PFN voltage.
As of August 2008, the klystron has been in operation at 30Hz, 22MW at 200nS for the last 2 commissioning runs. The klystron beam is at 372kV at 250A, 93MW.
XL4 Klystron Magnet Power Supplies
There are three coils in an XL4 klystron, as shown in figure X, a upper and lower focus coil and a bucking coil. The upper and lower focus coils each take 2 power supplies in parallel to get up over 300 amps. The current for each circuit is run through shunts which are connected to meters with interlocking capability. Windows are set for each circuit. The modulator is shut off through the MKSU if the current goes outside the window. There are Klixons and water circuits that will shut off the magnet power supplies if they trip.
Figure X, Klystron Magnet Power Supplies
XL4 Klystron Water Circuits
Flow rates for the three klystron water circuits follow:
1. Klystron Body, 2GPM, trip at 1GPM
2. Klystron Collector, 8 to 10GPM, trip at 6GPM
3. Klystron Tank and Magnet, 8 to 10GPM, trip at 6GPM
The water circuits interlock the modulator through the MKSU. The klystron tank and magnet water circuit shuts off the magnet power supplies if tripped.
Station Vacuum Interlocks
The new station gauge interlocks and an ion pump PLC interlock is run into the interlocking summing chassis. The output of interlock summing chassis connects to the MKSU station gauge vacuum interlock. The interlocking summing chassis takes inputs from the vacuum gauges before and after the X-Band window assemble. The PLC monitors ion pump power supplies and is connected to the interlocking summing chassis to be able to turn off the modulator if ion pump currents are above a set threshold. The EPICS L1X vacuum panel show a diagram in figure X. The black bar between W200 and W220 is the X-Band window assembly.
Figure X, EPICS L1X Vacuum panel.
Saturated drive levels for different XL4s are listed in table 1. LDF2-50, 3/8 inch Heliax, is used
to go from the drive amplifier to the tube input. Ten feet of LDF2-50 Heliax has a loss of 1.5dB.
The drive power coupler, KRYTAR 1824, has an insertion loss of 0.7dB. An HP X362A Low
Pass Filter, loss less than 1dB, is at the input of the klystron. Total loss from the drive amplifier
to the klystron is about 3.2dB. 400W of power at the klystron requires 840W of power out of the
drive amplifier. If lower loss is required the Heliax can be replaced with WR90 waveguide. At
11.424GHz 10ft of copper WR90 has a loss of about 0.04dB. This would reduce the drive
amplifier power requirement from 840W to 600W.
XL4 Tube Number Saturated Drive Power
2C 362 3A 400 5D 145 6A 400 7B 800 8A 400 9A 400 12A 400 13A 400 Table 1. Saturated Drive Powers for XL4 Tubes. Data taken from tube folders.
LLRF Control System
A diagram for the X-Band RF system is shown in figure X.
25.5MHz fromPADRF HUTTUNNEL2830.5MHz LO Gen380-208-60LKG-2821-J5J5LKG-2827J26AccOutJ242856MHz fromCH1380-208-51LOX-Band+2dBmAccInJ22RF Reference380-208-50J16LO GeneratorCH0LKG-2730-J104 X MultiplierCLK+2dBmJ816dBm11398.5MHz6dBm In9dBmJ3J616dBm-2dBmCH311424MHzJ76dBm9dBmLKG-283616dBmJ4LKG-2830J9+2dBmJ27MonitorJ15J5Panel380-208-21J14J12CLK DistributionLKG-2608LKG-2718J7
+2dBmKF-21-2B28MKSU16dBmJ24J9J12J13J23KLYS BEAMPADKlystronKlystronCH2LO+2dBmReflectedDriveForwardJ16J27Power380-208-60CLKCH3ControlX-Band CouplerKF-21-2B15J8J26CH0CH1J22Chassis?dBKF-21-2B33380-208-5613dBm-20dBFP J3MonitorMonitor FilterJ7 Couplers10dBAttenuator Diode detectors-2dBm13dBmJ13J5J10J11MIXERCLKTWT AmplifierPACLORF714-107INOUTJ15J14IFKF21-2B39380-208-40?dBKLYSTRONKF21-2B3610dB
Klystron Station 21-2
RF INRF OUT
Figure X, X-Band system diagram
X-Band 4X Multiplier
The X-Band reference RF is generated in the RF Hut. The X-Band 4X Multiplier chassis, figure
X, uses 2856MHz from the RF reference system and multiplies it by 4 to get 11424MHz. The
11424MHz outputs of the multiplier chassis feeds the X-Band LO Generator, the PAC at linac
station 21-2, and is monitored by channel 3 of the X-Band PAD in the RF Hut.
J12856MHz Mon FP N
4 X MultiplierMidwest Microwave2856MHz INMarki AQA-1933K10dBCPL-5215-10-SMA-790dBm RP N J320dBmJ511.4GHz RP N 10dB Coupler +5dBm In +10dBm Out11.4GHz RP SMAJ610dB Coupler Pulsar+5VDC 200mACIAO CA1112-343Pulsar11424MHz BPFPS2-19-450/8SCS20-05-436/10Gain = +20dBP1dB = +27dBm 11.4GHz Mon RP SMAJ4NF = 5dB PulsarIP3 = 35dBm J211.4GHz Mon FP NPS2-19-450/8S+15VDC 600mA
Figure X, X-Band 4X Multiplier Chassis SD-380-208-50-C0
X-Band LO Generator
The X-Band LO Generator uses the 11424MHz from the multiplier and the 25.5MHz from the S-
Band LO Generator chassis to Single Side Band, SSB, generate 11398.5MHz LO frequency for
the Phase and Amplitude Detectors, PADs. A diagram for the X-Band LO Generator Chassis is
shown in Figure X.
25.5MHzREAR PANEL NJ7 25.5MHz2 S1+13dBm out of 2830.5LO chassis ZFSC-2-2ZFSC-2-2REAR PANEL NREAR PANEL NJ6 +7dBm225.5MHz InJ5 S +23dBm+20dBmF5SLP-301
+V15V4123+ - 15V 4mAJ4-VREAR PANEL N -15V11.424GHz In
10dB10dBMarkiFRONT PANEL NJ1IQ0714LXP11.3985GHz0dBm+10 to +13dBmREAR PANEL NIF11.3985GHzJ9LORF 13dBm-6dBm PULSAR REAR PANEL N J8LORF11.3985GHz PULSARCS10-12-435/1 IFCAIO15V3CS10-12-435/1CA1112-441PULSAR11.424GHz to 11.3985GHz SSB IQ ModulatorPS2-19-450/8S
J3DIODECIAO CA1112-441DC 0 to ? VoltFRONT PANEL BNCPULSARDETECTORGain = +30dBIn Diode DetCS10-12-435/1P1dB = +30dBm
NF = 3.4dBFRONT PANEL N+15VDC 900mA11.424GHzJ2
Figure X. X-Band LO Generator Chassis
X-Band Coupler Chassis
The X-Band Coupler Chassis is used to interface control of the drive power to the MKSU. It is
also used to couple down high power RF signals for monitoring. Detector diodes change the
klystron forward power, reflected power, and drive power into video signals which are connected
to the MKSU for monitoring by the control system. The coupler chassis and connections are
shown in figure X.
PACMKSUDRIVEFORWARDREFLECTEDFP NFP N testFP N testOUTTo PAD CH1J13J3J2J1IPA13dBmCouplerConnectorto PADX-Band-20dBCH0-20dB-20dBCouplersRP BNCLP Filter 10kHzJ5Drive6dBmChassisAttenuator 17dBKRYTAR0-28mA0-200mA10dBModel 182416dBm33dBm380-208-56-20dB-20dB?dBFP BNCTestVideoAmp-20dBJ4
M8-0412NZMIXER 17dBmBNC to239-025-20dB-20dBMKSUJ6RFLOIF
J7J8J9J10J11J120dBmN toBNC toBNC to10dBPADMKSUMKSUCH3IN 10dBm MAX
-20dBHP X362A LPFOUTTo Accelerator-53dBTWTKLYSTRONKRYTAR714-107CouplerXL4Model 1824-20dB
Figure X, X-Band Coupler Chassis 380-208-56 and connections.
The X-Band PAC chassis uses the same control board as the other PAC chassis. The control
board puts out 2 preset waveforms on a trigger pulse to drive I and Q of the IQ Modulator. The
diagram of the PAC board is in figure X.
EXTERNALTRIGGERTRIGGERMonitor TTL120HzSSSBSSSBFP BNC60nS NIMGate MonitorChassisCLOCKRP BNCFP BNCRP 15 Pin D119MHzRF OUTPUTRF INPUTRF OUTPUTRP NTo TWT AmpI MONITORQ MONITORMonitorMonitorRP NFP BNCFP BNCFP NFP N+13dBm Out
H9H10J2P5H7J3H6SSSBTrigRF ModuleTTLVLFX-80 Low Pass17 to 30uS10dB11.424GHz Ref-10dB CouplersRP NPulsar-2dBm In16bit DATA3CS10-12-435/116 bitETHERNETJ5-10dB AmpI&Q MODULATORDATAIIAmpCLKXILINXCONTROL /1 -10dBMAX5875LOJ4RF2SPARTAN 3Arcturus uC5282 2 X 16 bit DAC-10dB119MHz ClockFPGAMicrocontroller Module16bit DATAQCS/ (1MHz to 200MHz)IQ0714MXPETHERNETwith 10/100 EthernetCLK4COMQ13 to 16dBmCLKVLFX-80 Low Pass10dBRAW
AD8099 Diff AmpControlControlH12CIAO CA1112-343Gain = +20dBTemperatureP1dB = +27dBmRF INPUTNF = 5dBMonitorMonitor TemperatureIP3 = 35dBmDiodeSLOW ADCstMonitor+15VDC 600mAFP BNCPAC TemptIQ TempSSSB TempSSSB P-FWDSSSB P-RFLSSSB PWR+5V-12VControl Board
Figure X, X-Band PAC Chassis FS-380-208-40-C0
The PAD Chassis down mixes the 11424MHz with 11398.5MHz to a 25.5MHz IF frequency on
3 channels, 0, 1, and 3. Channel 2 is connected to a coupler and an input transformer before
being digitized. The coupler, Minicircuits ZFDC-10-6-S+, 0.005MHz to 20MHz limits the
bandwidth of the signal before it reached the digitizer board. On the digitizer board, the standard
input transformer, Minicircuits TC4-1T, 0.5 to 300MHz, is replaced by Minicircuits TT1-6-
KK81, 0.004MHz to 300MHz to give a total bandwidth of 0.005MHz to 20MHz. This signal is used to measure the beam voltage to the klystron from the MKSU.
CHAN 025.5MHz IFFP BNC - J1 4 X 16 bit ADCControl Board102MHz ClockLTC2208CHAN 0Transformer Coupled Inputs IF BoardRF INPUTMIXER M80412NZRP N16bit DATA16 bitDATAFIFO IFChan. 0WCLKLORF64k words10dBCONTROL /VLFX-80 MinicircuitsFILTER 25.5MHz BPCHAN 1Arcturus uC528216bit DATACS/Chan. 125.5MHz IFWCLKFIFO Microcontroller ModuleCLKFP BNC - J3+12VDCwith 10/100 Ethernet64k wordsCHAN 1 J14RF INPUTETH1TESTCIAO CA1112-34316bit DATARP N714-114-50-R3Gain = +20dBFIFO P1dB = +27dBmWCLK NF = 5dB64k wordsIFIP3 = 35dBm OUT16bit DATAIF Board+15VDC 600mA1MIXER M80412NZ WCLK10dBm2FIFO 3IFLO INPUT 64k words4LORFJ15RAW J13 11.4GHz +2dBm10dBVLFX-80 MinicircuitsFILTER 25.5MHz BPCOMETH25ControlRP N +15VDCChan. 2TESTLO1+12VDCCPLDTEST PORT714-114-50-R3IFChan. 3FP N - J95VDCOUTQSPI0.8A x 2 AnalogCLK INCLK OUTTRIG 5VDC20 pin ribbonCLOCK INCLOCK MonTRIG InCHAN 2TRIG Mon0.5A Digital102MHz102MHz120HzTestFP BNC - J12RP NFP N - J11RP BNCFP BNC - J5 QSPICHAN 2RF INPUT 24Bit ZFDC-10-6-S+RP N0.005 to 20MHz11.3dB couplingAnalog CHAN 3TestInputFP BNC - J7 CHAN 3BoardRF INPUTRP NANALOG INANALOG INTEST IF BoardMIXER M80412NZ10dBPAD UsageCh0 - LO PowerIFIFCh1 - RF Head TempOUTLORFCh2 - ADC BRD TempVLFX-80 MinicircuitsFILTER 25.5MHz BPCh3 - +12VDC714-114-50-R3Ch4 to Ch7 external temps+12VDC
Figure X, X-Band PAD Chassis FS-380-208-60-C0
The PAD chassis in the RF Hut measures the input and output RF for the accelerator structure on channel 0 and channel 1 respectively. Channel 2 is not used and Channel 3 measures the reference RF from the multipler. The PAD chassis at the klystron station measures the PAC output on channel 0, the drive amplifier output on channel 1, the klystron beam voltage on channel 2, and the klystron output on channel 3. The RF Hut X-Band PAD panel is shown in figure X. Since the fill time of the structure is only 100nS and the RF pulse width is only 200nS the window to look at the structure is only 12 points, or 118nS at 102MSPS.
Figure X, RF Hut X-Band PAD Panel