CWRF2014 May 13-16, 2014

RF Upgrades & Experience At JLab

Rick Nelson

CWRF2014 May 13-16, 2014

Outline

• Background: CEBAF / Jefferson Lab• History, upgrade requirements & decisions• Progress & problems along the way• Present status• Future directions & concerns

CWRF2014 May 13-16, 2014

CEBAF at Jefferson Lab• Design

– 4 GeV, 200 uA• 3 Experimental Halls

• Present (pre-upgrade)– 6 GeV, 200 uA

• 3 Experimental Halls• Upgrade

– 11 GeV, 200 uA• 3 Experimental Halls

– 12 GeV, 200 uA• 4th Hall D only

CWRF2014 May 13-16, 2014

CHL-2

Upgrade magnets and power supplies

Upgrade Existing Halls

From 6 to 12 GeV

CWRF2014 May 13-16, 2014

RF + Upgrades

• Original– 42.5 cryomodules/338 SC cavities – 340 klystrons: 5 to 6.5 kW CW, 1497 MHz

• Incremental upgrades to C50 ongoing• C25, C50 cryomodules

• Upgrade– 10 cryomodules, 80 SC cavities– 80 klystrons: 13 kW CW, 1497 MHz

• New designs for klystrons, power supplies, circulators, controls

CWRF2014 May 13-16, 2014

Key RF Requirements 10 new zones of RF power for new accelerating structures:

•1497 MHz•Operating Gradients Required• >17.5 MV/m

•RF Power per cavity•13 kW saturated

•Regulation requirements•(table)

•Cavity QL• ≥ 2x107

Superconducting Cavity

8

High Voltage Power Supply

Klystron

LLRFControls

EPICS IOCEthernet

Ethernet

MasterOscillator

Fast ( <1sec)

Slow (>1sec)

Phase Stability

(rms)0.5º 3.0º

Amplitude(rms) 4.5x10-4 NA

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

-600 -500 -400 -300 -200 -100 0

Detuning (Hz)

Ener

gy C

onte

nt (N

orm

.)

Cavity de-tuning curve

CWRF2014 May 13-16, 2014

1 per cavity (existing configuration)Minimum impact of failures

1 per zone or 1 per linacLarger impact on faultsHigh power splittersHigh power amplitude and phase control required with high precision.

Additional controls and high power modulators found to be more $$ than individual RF sources.

How Many RF Sources?

Single LINAC upgrade shown

CWRF2014 May 13-16, 2014

Parameter Old Spec

New Spec

Actual Units

Power 5 to 8 13 13 KW

Center frequency 1497 1497 1497 MHzBandwidth, -1dB 5 5 5+ MHzBandwidth, -3 dB 6 6 6+ MHz0.5 dB incremental gain at 4 10 meets kWEfficiency (at rated power) 32 >50 50.9 %Gain 38 >42 >50 dBHarmonics -20 -20 meets dBcBeam voltage 11.6 <16 14.5 kV DCHeater voltage 7.3 7.3 7.0 typ V DCModulating anode Yes Yes YesIsolated collector Yes Yes YesCavities/Resonators 4 5 5Focus PM EM ~900 Watts

CEBAF Klystrons Compared

CWRF2014 May 13-16, 2014

• Each system powers 8 klystrons (as before) • Resonant mode switcher design (15-20 KHz)• 4 separate supplies. Each feeds 2 klystrons

– Minimizes klystrons taken offline due to power supply failure

– Controlled as a “unit”• Each adjustable to -15kV • 15 A total• Design adapted from electrostatic

precipitator application (higher volts/lower amps & in oil) 1000+ units in the field at award

• Highly tolerant to load faults• Lower stored energy than T-R, fast

turn off on fault, series resistor limits output current (no crowbar)

HV DC Power Supply

CWRF2014 May 13-16, 2014

Additional Views

Rear View

HV Deck (4 per system, on rollers)

CWRF2014 May 13-16, 2014

Typical RF Installation

All zones installed and commissioned with beam

CWRF2014 May 13-16, 2014

Tunnel Connections

Waveguide installation

CWRF2014 May 13-16, 2014

RF Commissioning Selected Data

Zone/Cavity Gradient Cryomodule

Energy GainBeam

CurrentZone/Cavity Gradient Cryomodule

Energy GainBeam

Current

SL24 SL231 15 100 1 20.4 NA2 13.9 100 2 18.4 NA3 13.4 100 3 19.4 NA4 15.4 100 4 18 NA5 19 100 5 21.4 NA6 20 100 6 20.6 NA7 17.7 100 7 22.2 NA8 14.7 100 8 15.8 NA

Total 129.1 90.37 100 Total 156.2 109.34

SL25 SL221 19.5 465 1 12 NA2 20.5 465 2 21.2 NA3 18.7 465 3 18.5 NA4 20.5 465 4 20.2 NA5 19 465 5 18.7 NA6 20.1 465 6 20.7 NA7 17.5 465 7 20.2 NA8 18.5 465 8 20 NA

Total 154.3 108.01 Total 151.5 106.05

Commissioned w/ Beam Commissioned w/o Beam

CWRF2014 May 13-16, 2014

Good Times / Bad Times• Everything according to plan?• Delivery delays on several key components

• Klystron & general WG close to schedule with no problems• HOM filters, isolators, solenoid power

– Revisions and rework for problem areas– One contract cancellation– Multiple installation delays with starts & stops

• Largely from budget constraints• Resulting in reassignment of workforce• Inefficient to change tasks to often

CWRF2014 May 13-16, 2014

Isolator Requirements• 13 kW CW, full reflection• 0.2 dB insertion loss• 21 dB isolation (any phase & power)• Water cooled• PM only - no TCU • Operates adjacent to others• Awarded to Ferrite (also supplied 350+ units for original

CEBAF)• Full power testing at JLab

– Vendor test capabilities missing– Several rounds of testing with sliding short

• Using FA klystron at L-3• At JLab using 2 x 6.5 kW and 13 kW klystron

CWRF2014 May 13-16, 2014

Events

• Initial tests looked OK and first lots were installed• Tests into WG shorts not as good• Results not repeatable/consistent with similar test

connditons• And, performance varied based on phasing (Distance

to short)– Two rounds of measurements & adjustments to

understand the fix– Tried to characterize performance and make

adjustments before next production batch– Next production units still variable

CWRF2014 May 13-16, 2014

Testing

CWRF2014 May 13-16, 2014

Sensitive to Match & Phase• Isolation affected by

– Ferrite temperature– Magnetic field strength

• Could be adjusted to maintain good performance• Less field needed at higher temperature• Other solutions include TCU, active field control

(VSWR)• “Automatically” handled in small units

– Reflected phase– Match (all ports)

• 2 of 3 need to be good for high isolation• Load OK, short bad, klystron needs to be good (but

not easily measured)

CWRF2014 May 13-16, 2014

Early Test Results

0 2 4 6 8 10 1210

15

20

25

30

35

11.5" short iso

Iso-J1223 11.5"Iso-J1196Iso-J1204iso 1210iso 1229Iso-J1219Iso-J1217-10"Iso-J1217-11.5"Iso-J1199-11.5"Iso-J1209-10"Iso-J1209-11.5"

CWRF2014 May 13-16, 2014

Early Test Results

CWRF2014 May 13-16, 2014

Isolation vs. Short Position

0 1 2 3 4 5 6 7 8 9 10 11 1210

15

20

25

30

35

40

Iso-J1612-11"Iso-8.5"Iso-10"

Forward Power (kW)

Isola

tion

(dB)

CWRF2014 May 13-16, 2014

Temperature• Initial measurements done steady-state

– Find position for lowest isolation (worst case, run plots)

• Changes then observed at turn-on– Concerns for off-resonance conditions at turn-

on• Must avoid tripping on high reflected

power at turn-on• Must work under varying conditions due to

differing distances to cavities

CWRF2014 May 13-16, 2014

Isolation vs. Heating/Time

00:00.0 00:08.6 00:17.3 00:25.9 00:34.6 00:43.2 00:51.8 01:00.5 01:09.140

45

50

55

60

65

70

75

15

17

19

21

23

25

27

forward-0reverse-0isolation-0

Elapsed time (seconds)

pow

er (d

Bm)

• RF heating of ferrite resulted in significant changes over (short) time

CWRF2014 May 13-16, 2014

Adjusting Magnetic Fields

00:00.0 00:08.6 00:17.3 00:25.9 00:34.6 00:43.2 00:51.8 01:00.5 01:09.110

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

Isolation response at 10+ kW vs Magnet Count

isolation-0isolation-1isolation-2Isolation-3isolation-4

CWRF2014 May 13-16, 2014

Isolator

CWRF2014 May 13-16, 2014

Tuning

CWRF2014 May 13-16, 2014

Resolution• Vendor reworked dome – new domes, improved

cooling, full rebuild all units• … results were still variable• LL tuning abandoned in favor of full power setup at JLab

– 100% re-tested at power • Some adjustment to requirements allowed – lower isolation at

lower power• Reflected power well below threshold for klystron damage or

performance degradation• Final solution meets operational needs including credible fault

conditions• All 84 units modified, tested, reinstalled• Considerable extra work -- all units were handle multiple

times installed/removed/reinstalled.

CWRF2014 May 13-16, 2014

Isolation vs. Short Position

7 8 9 10 11 12 130

5

10

15

20

25

30

35

Iso-J1612

Iso-J1612

Short Position (inches)

Isola

tion

(dB)

CWRF2014 May 13-16, 2014

HOM Filters– Uncertainty of need, though requirements known– Originally not needed, later added back in– Belief was only 2 of 8 cavities would require HOM filter– Normal procurement process

• 2 vendor offers• Final units essentially identical to what we had from

multiple purchases– Performance met, cost lower though alternate proposal was more

robust• Small tweaks to reduce fundamental absorption• Manufacturing relied on external shops (as before)

– Vendor a small concern, limited resources & staff– Fabrication subcontracted (metal fab, Iridite, dip brazing)

• Dummy spool pieces installed in other positions• Had expected this to come in last

CWRF2014 May 13-16, 2014

Klystron HV PS• Performance has been good overall

– Switcher design and controls work well - good reliability• DSP-based controls with hardware safety interlocks• Code changes needed to address timing issues

– 1 unit tested OK, but all 4 might trip external breaker– Extended step-start to deal with high inrush & breaker trips

• Possible race condition for contactor control vs. status reporting (several contactors changed but seem to be OK)

– Control transformers (480:120) shorted out– Loose connections/loosening connections

• Contactors, IGBT– Suggestion: check connections…

• No similar problems with old supplies, but a lot less connections– DC power guys regularly check transistor connections

• New doesn’t mean perfect -- especially after x-country trips• A couple noticeable events

CWRF2014 May 13-16, 2014

Flash, Boom – Tripped 3 Breakers

CWRF2014 May 13-16, 2014

Cause & Effect

CWRF2014 May 13-16, 2014

IGBT Connection• Another loose

connection• IGBT overheating &

short circuit• Checked torque on all

connections, all systems

• No early signs noted – just tripped

CWRF2014 May 13-16, 2014

Problem Procurements• Isolator (discussed)• HOM filter (discussed)• Klystron solenoid PS

– Offer looked good on paper• Major design effort resulted in delays and

cancellation– FA looked like a lab prototype – and didn’t work

long– Test results failed to meet their results (tried 3

ways)– Ultimately cancelled and purchased from Sorensen

CWRF2014 May 13-16, 2014

We Didn’t Buy This One

• Liberal use of RTV to insure components didn’t shift during shipping…

• Kluge board• Not First Article class• Order cancelled

CWRF2014 May 13-16, 2014

Installation Challenges• Funding shortages resulted in work

reassignments & delays• Techs reassigned to dismantle other

systems(multi-month delays)• Start/stop/start not efficient and required

relearning• (In spite of this RF finished on time and

below budget)

CWRF2014 May 13-16, 2014

A Wet Year• Brazing issues and water leaks

– Multiple new components, nuisance problems– Both believed to be of similar origin – but

different suppliers– Pressure tested (but not long enough)– Trapped flux dissolved out resulted in small

leaks on a few pieces• Circulator load assemblies

– New loads built, and testing refined• Solenoid leaks on plumbing

– Longer pressure testing with hot water

CWRF2014 May 13-16, 2014

Ongoing Circulator (old style)• Reliable for a lot of years,

but load failures becoming more frequent

• LC DI water• 15 years+ erosion and

leaching• Self-rebuilding w/o

retuning – Same load back to its

circulator• New circulator loads

won’t experience this failure mode

CWRF2014 May 13-16, 2014

Water Flows Downhill• All LCW was turned off during extended down

(~1 year)• Circulator load seals lost their seal• Water in select waveguides (not our selection)• HOM filters soaked

Water level – horizontal run

Bleed hole was for air…

CWRF2014 May 13-16, 2014

Maintenance Issues

• New systems to be learned and maintained

• New systems to be re-checked• Old systems getting older• Spares needed for new (and old alike)• Major PM efforts planned for summer

– Pushed off many times already

CWRF2014 May 13-16, 2014

20 Year Old Transformers

CWRF2014 May 13-16, 2014

Summary• All new LINAC RF has been installed and

commissioned, though not without issues along the way

• Operating requirements met• Staff still learning operational

maintenance differences from old systems• Maintenance activities scheduled for

summer down – old and new systems• Lobby to purchase spares with new

equipment

CWRF2014 May 13-16, 2014

12 GeV Timeline• 2009 12GeV Upgrade construction starts in May with ground breaking

ceremony at the Hall-D site.• 2011 First C100 installed in the 2L23 slot in CEBAF, July.• 2012 C100 module successfully operated at design specifications: 108MeV

of energy gain with 465μ A of beam loading on May-18.• 2013 North and South Linac 2K LHe operations established, Dec-09 for the

first time with two CHL's plants connected to a "split CEBAF".• 2013 12GeV CEBAF Beam Commissioning begins Dec-13.• 2014 Beam successfully transported to the 2R dumplette with 2.2GeV/pass

energy gain on Feb-05. Establishing RF capability to support 12GeV 5.5pass operation with greater than 50% availability.

• 2014 Injector achieves 12GeV design energy of 123MeV on Mar-10• 2014 3-pass beam established to Hall-A Mar-20. Multi-pass capability

established in the 12GeV era. • 2014 3-pass beam with E>6GeV established to Hall-A on Apr-01 and

beam-target interactions recorded. First time beam transported to an end-station with energy that exceeds maximum energy set during the 6GeV CEBAF era.

• 2014 10.5GeV 5.5 pass beam established to Hall-D Tagger dump on May-07.

• 2014 First RF separated beams in 12GeV era on Oct-??. Establishes multi-beam capability in the 12GeV era.

CWRF2014 May 13-16, 2014

Thank You!