Design and Operating Experience with SNS Superconducting Linac

  • Slides: 71
Download presentation
Design and Operating Experience with SNS Superconducting Linac FNAL September 30, 2010 Sang-ho Kim

Design and Operating Experience with SNS Superconducting Linac FNAL September 30, 2010 Sang-ho Kim SCL Area Manager SNS/ORNL

Accumulator Ring: Machine layout Compress 1 msec long pulse to 700 nsec Front-End: Produce

Accumulator Ring: Machine layout Compress 1 msec long pulse to 700 nsec Front-End: Produce a 1 -msec long, chopped, H-beam H- stripped to p Linac; 1 Ge. V acceleration 402. 5 MHz DTL 2. 5 86. 8 805 MHz CCL SRF, b=0. 61 SRF, b=0. 81 186 387 PUP Liquid Hg Target 1000 Me. V mini-pulse Current 945 ns Chopper system makes gaps 2 Managed by UT-Battelle for the U. S. Department of Energy Current 259 m 1 ms 1 ms macropulse FNAL Visit, September 30, 2010

SNS SCL History and initial design concerns • SNS baseline change from NC to

SNS SCL History and initial design concerns • SNS baseline change from NC to SC in 2000, relatively late in the project • RF frequency; followed that of the NC CCL (from LANSCE) • SRF Cavity designs were mainly driven by two constraints – Power coupler; maximum 350 k. W (later increased to >550 k. W) – Cavity peak surface field; 27. 5 MV/m field emission concerns • Later increase to 35 MV/m for HB cavities by adapting EP • With one FPC to cavity; HB cavity 6 cell • Long. Phase slip at low energy; MB cavity 6 cell 3 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

SNS SCL Components Cryomodule and all internal components developments ; done by JLAB including

SNS SCL Components Cryomodule and all internal components developments ; done by JLAB including prototyping • Power coupler; scaled from KEK 508 MHz coupler • HOM coupler; scaled from TTF HOM coupler • Mechanical tuner; adapted from Saclay-TTF design for TESLA cavities • Piezo tuner; incorporated into the dead leg for possible big LFD (later on) • Cryomodule; similar construction arrangement employed in CEBAF • Nb material RRR>250 for cells and Reactor grade Nb for Cavity end- group 4 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

SNS Cavities and Cryomodules look; b=0. 81 Specifications: Ea=15. 8 MV/m, Qo> 5 E

SNS Cavities and Cryomodules look; b=0. 81 Specifications: Ea=15. 8 MV/m, Qo> 5 E 9 at 2. 1 K b=0. 61 Specifications: Ea=10. 1 MV/m, Qo> 5 E 9 at 2. 1 K Medium beta (b=0. 61) cavity High beta (b=0. 81) cavity Helium Vessel Field Probe Fast Tuner HOM Coupler Slow Tuner Fundamental Power Coupler 5 Managed by UT-Battelle for the U. S. Department of Energy 11 CMs FNAL Visit, September 30, 2010 12 CMs

SNS SCL, Operations and Performance • The first high-energy SC linac for protons, and

SNS SCL, Operations and Performance • The first high-energy SC linac for protons, and the first pulsed operational machine at a relatively high duty • We have learned a lot in the last 5 years about operation of pulsed SC linacs: – Operating temperature, Heating by electron loadings (cavity, FPC, beam pipes), Multipacting & Turn-on difficulties, HOM coupler issues, RF Control, Tuner issues, Beam loss, interlocks/MPS, alarms, monitoring, … • Current operating parameters are providing very stable and reliable SCL operation – Less than one trip of the SCL per day mainly by errant beam or control noise • Proactive maintenance strategy (fix annoyances/problems before they limit performance) • Beam energy (930 Me. V) is lower than design (1000 Me. V) due to high-beta cavity gradient limitations (mainly limited by field emission) • No cavity performance degradation has occurred to Oct. 09 6 Managed by UT-Battelle for the U. S. Department of Energy – Field emission very stable FNAL Visit, September 30, 2010

Machine Performances Design Individually achieved Highest production beam Beam Energy (Ge. V) 1. 01

Machine Performances Design Individually achieved Highest production beam Beam Energy (Ge. V) 1. 01 0. 93 Peak Linac Beam current (m. A) 38 42 42 Average Linac Beam Current (m. A) 1. 56 1. 1 Beam Pulse Length (ms) 1000 825 60 60 60 Beam Power on Target (k. W) 1440 1100 Linac Beam Duty Factor (%) 6. 0 4. 8 1. 5 x 1014 1. 55 x 1014 1. 1 x 1014 81 80 80 Parameters Repetition Rate (Hz) Beam intensity on Target (protons per pulse) SCL Cavities in Service 7 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Cavity Specifications Frequency 805 MHz N. of cells 6 Cell-to-cell k [%] Geom. b

Cavity Specifications Frequency 805 MHz N. of cells 6 Cell-to-cell k [%] Geom. b 0. 61 0. 81 Epk [MV/m] 27. 5 35 Lorentz KL < -2 ± 1 (static) Q (2. 1 K) 5 109 [Hz/(MV/m)2] 8 >1. 5 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Cavity Shape Design Geometry optimization; Pretty well understood and straightforward (scan parameter space) Ex.

Cavity Shape Design Geometry optimization; Pretty well understood and straightforward (scan parameter space) Ex. b=0. 61, 805 MHz Ep/Eo. T(bg) For fixed a, Rc, Ri Slope angle ( ) R Dome (Rc) R Equator (Req) 2 b 2 a k Iris aspect ratio (a/b) R Iris (Ri) Bp/Eo. T(bg) For circular dome (Elliptical dome cases are same) Rc, Ri, a, one of (a/b, a, b) ; 4 controllable parameters Req (for tuning) 9 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010 Rs. Q ZTT Now, a/b is dependent parameter

Cell Shape optimization-criteria dependent Scanning all geometry space (systematic approach)-Example 4. 0 Ex. b=0.

Cell Shape optimization-criteria dependent Scanning all geometry space (systematic approach)-Example 4. 0 Ex. b=0. 61, 805 MHz at the slope Angle=7 degree Bp/Ep=2. 0 (m. T/(MV/m)) KL=4 KL in Hz/(MV/m)2 KL=3 3. 6 k=2. 5 % Ep/Eo. T(bg) Bp/Ep=2. 2 k=2. 0 % 3. 2 Bp/Ep=2. 4 k=1. 5 % 2. 8 2. 4 Bore Radius=50 mm Bore Radius=45 mm Bore Radius=40 mm 2. 0 10 30 Managed by UT-Battelle for the U. S. Department of Energy 32 34 36 FNAL Visit, September 30, 2010(mm) Dome Radius 38 40

End Cell design and Qex Increase magnetic volume Qex estimation is quite accurate even

End Cell design and Qex Increase magnetic volume Qex estimation is quite accurate even for the high Qex system (Also alignment error analysis is available) ; Measured ; Calculated 11 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Beam, Qex, RF, margins (design) Early stage of SNS; forhigh bothbetas with 11 MB

Beam, Qex, RF, margins (design) Early stage of SNS; forhigh bothbetas with 11 MB 14(15) Final SNS; 36 m. A, 26 m. A, Epk=27. 5 Epk=35 for with 11 MB CMCM +12+HB CM Highly non-linear region Control margin, dynamic detuning Qb Qex +/- 20 % 12 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Dynamic Mechanical Behavior of Elliptical Cavities -in design stage Many groups have done series

Dynamic Mechanical Behavior of Elliptical Cavities -in design stage Many groups have done series of analysis with FEM codes. Static properties; we can find pretty accurately Mode, damping, modal mass findings; Strongly depends on boundary condition, especially finding damping degree for each mode very difficult Analysis before having experimental results statistical like any other resonance issues Relative comparisons 13 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Dynamic detuning But, a few cavities show bigger resonance phenomena Observed detuning agrees with

Dynamic detuning But, a few cavities show bigger resonance phenomena Observed detuning agrees with expectations as higher repetition rate Medium beta cavity (installed cavity) KL: 3~4 Hz/(MV/m)2 16. 5 MV/m 14 High beta cavity (installed cavity) KL: 1~2 Hz/(MV/m)2 17 MV/m The 2 k. Hz components shows In this example the accelerating gradient is resonances 12. 7 MV/m. (high beta cavity) Managed by UT-Battelle at higher repetition rate for the U. S. Department of Energy FNAL Visit, September 30, 2010 in some of medium beta cavities

AFF learning At beginning AFF fully learned While learning 15 Some cavities need ~>25

AFF learning At beginning AFF fully learned While learning 15 Some cavities need ~>25 % more RF at the beginning of AFF Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

At the present operating condition RF power at 26 m. A average current In

At the present operating condition RF power at 26 m. A average current In steady state Qb Qex 16 • Overall concerns between peak field, operating gradient, inter-cell coupling, RF margin, detuning, Qex (fixed or variable), cost, and system stability Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Cavity Gradient Limiting Factors (60 Hz Operation) One does not reach steady state mechanical

Cavity Gradient Limiting Factors (60 Hz Operation) One does not reach steady state mechanical vibration 1 cavity is disabled CM 19 removed and repaired CM 12 removed and found vacuum leaks at 3 HOM feedthroughs (fixed) 17 -Dominated by Electron Loading (Field Emission & Multipacting) -~14 cavities are limited by coupler/end-group heating (MP), but close to the limits by radiation heating -Operating gradients are around 85~95% of Elim Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Interactions between systems/cavities (collective effects) • Cavity radiation/cold cathode gauge interaction • Helium flow

Interactions between systems/cavities (collective effects) • Cavity radiation/cold cathode gauge interaction • Helium flow in one cavity creates “vapor lock” in another heating of coupler’s outer conductor • Multipacting triggers radiations • Electron activity in one cavity triggers cold cathode gauge in another • Field emission in one cavity heat up beam pipe in another(s) depending on relative phase and amplitude 18 – creates difficulty in finding proper op. gradient for all ranges of phases – Main limiting factor in SNS Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Electron Loading and Heating (Due to Field Emission and Multipacting) Source of electrons ·

Electron Loading and Heating (Due to Field Emission and Multipacting) Source of electrons · Multipacting; secondary emission – resonant condition (geometry, RF field) – At sweeping region; many combinations are possible for MP · Temporally; filling, decay time · Spatially; tapered region · Non-resonant electrons accelerated radiation/heating – Mild contamination easily processible ● Field Emission due to high – But poor surface condition surface electric field Result processing is very difficult in an operating cryomoduleburst End group heating/beam pipe heating + quenching/gas Easy to remove with DC biasing 19 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

End Group Heating & Partial quench Analysis for end group stability ; >4 -5

End Group Heating & Partial quench Analysis for end group stability ; >4 -5 W (overall) or ~1 W local can induce quench At partial Quench (Measured data) FE at OC Electron activity (Field emission, non-procesible MP)induced end group quench: Large temperature rise (24 K) at beam pipe. Quench leads to semi-stable intermediate state condition: Qo~ 2 -3 x 105 20 Managed by UT-Battelle for the U. S. Department of Energy Low RRR & long path to thermal sink Thermal margin is relatively small, P Forward Cavity Field Results in thermal quench FNAL Visit, September 30, 2010

We don’t have MP induced radiation at op. gradient, if any, very small. Basically

We don’t have MP induced radiation at op. gradient, if any, very small. Basically running in the field emission regime. MP Surface condition Radiation onset FE onset Eacc Radiation (arb. Unit) Measurements of Radiation during RF Pulse Radiation (in log, arb. Unit) SNS Cavity Operating Regime 21 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010 Time

Back to Cavity performances in VTA test Typical high beta cavity MP FE More

Back to Cavity performances in VTA test Typical high beta cavity MP FE More precisely this MP indication is MP induced radiation. We observed MP starting from 3 MV/m in both medium and high beta cavities. In general MP can be processed and does not hurt operation that much. A few cavities are showing a symptom of non-processible multipacting 22 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

HOM; in design stage • No Beam dynamics issue • Centroid error, f spread

HOM; in design stage • No Beam dynamics issue • Centroid error, f spread & location of cavities were in question • When Q>105, 106, there’s a concern. – HOM power ~ fundamental power dissipation – but the probability is very low even under the conservative assumptions • Extra insurance – SNS is the first pulsed proton SC linac – Any issues were treated in a very conservative way • Ex. Piezo tuner; we’ve never used them 23 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Problems while running RF only Any electron activity (multipacting, burst of field emitter, etc)

Problems while running RF only Any electron activity (multipacting, burst of field emitter, etc) Destroy standing wave pattern (or notching characteristics) Large fundamental power coupling Feedthrough/transmission line damage (most of attenuators were blown up) Irreversible damages could happen statistically Electric Field 16 Mv/m CCG Df or tau Eacc Magnetic field 24 Managed by UT-Battelle for the U. S. Department of Energy Conditioning after removing feedthrough; Large electron activities around HOM couplers were observed ranging from ~3 MV/m up to 16 MV/m. FNAL Visit, September 30, 2010

Fundamental mode thru HOM coupler HOMA Fundamental mode coupling High 1010~ 1012 ; much

Fundamental mode thru HOM coupler HOMA Fundamental mode coupling High 1010~ 1012 ; much less than a few W during pulse HOMB Normal waveform of fundamental mode from HOM ports (y-axis; log scale) 25 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Abnormal HOM coupler signals (RF only, no beam) ~’ 0’ coupling and rep. rate

Abnormal HOM coupler signals (RF only, no beam) ~’ 0’ coupling and rep. rate dependent signals 1~5 Hz 10 Hz 30 Hz Electron activities (MP & discharge; observations under close attention) 26 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Leak, severe MP, contamination, large coupling, … 27 Managed by UT-Battelle for the U.

Leak, severe MP, contamination, large coupling, … 27 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

HOM in SNS • Availability & Reliability; Most Important Issue – HOM couplers in

HOM in SNS • Availability & Reliability; Most Important Issue – HOM couplers in SNS have been showing deterioration/failure as reported – Reliability & availability of SNS SRF cavities will be much higher w/o HOM coupler • More realistic analysis with actual frequency distributions measured. – Probabilities for hitting dangerous beam spectral lines are much less than expected. – Beam amplitude fluctuation is also very small • Future Plan – HOM feedthroughs will be taken out as needed – PUP cryomodule 28 • Will not have HOM couplers FNAL Visit, September 30, 2010 Managed by UT-Battelle for the U. S. Department of Energy SNS beam (FFT)

Turn-on difficulties Vacuum Interlock 6 days Vacuum Gradient early 2006; After a long shut-down,

Turn-on difficulties Vacuum Interlock 6 days Vacuum Gradient early 2006; After a long shut-down, some cavities showed turn-on difficulties. Gradients were lowered down or turned-off in order to reduce the down time. Severe contaminations in coupler surfaces or cavity surfaces ? ? ? 29 Managed by UT-Battelle Erratic behavior due to the erosions of electrode; no responses or too much for the U. S. Department of Energy FNAL Visit, September 30, 2010

Turn-on and High power commissioning · First turn on must be closely watched and

Turn-on and High power commissioning · First turn on must be closely watched and controlled (possible irreversible damage) - Initial (the first) powering-up, pushing limits, increasing rep. rate (extreme care, close attention) · Aggressive MP, burst of FE possibly damage weak components · Similar situation after thermal cycle (and after long shut down too) behavior of the same cavity can be considerably different from run to run · Subsequent turn-ons (after long shut-down) also need close attention: behavior of the same cavity can be considerably different from run to run gas redistribution · Cryomodules/strings must be removed and rebuilt if vented/damaged 30 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Individual limits & collective limits CM 19; removed Design gradient Large fundamental power through

Individual limits & collective limits CM 19; removed Design gradient Large fundamental power through HOM coupler Average limiting gradient (collective) Field probe and/or internal cable (control is difficult at rep. rate >30 Hz) Average limiting gradient (individual) 31 • Operating gradient setting in SNS are based on the limiting gradients achieved Managed UT-Battelle • by. Operational stability is the most important issue for the U. S. Department of Energy FNAL Visit, September 30, 2010

Current Operating Condition • 1105 us RF (250 us filling + 855 us flattop)

Current Operating Condition • 1105 us RF (250 us filling + 855 us flattop) at 60 Hz – Flattop duty; 5. 1 % • Eacc setpoints; about 85 % of collective limits in average – Average gradient; ~12. 5 MV/m – 925 Me. V + 10 Me. V (energy reserve) • Stable operation; < 1 trip/day (<5 min. /day) mainly by errant beam, control noise 32 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Stable Operation of SCL • Better understanding of: – underlying physical phenomena (outgassing, arcs,

Stable Operation of SCL • Better understanding of: – underlying physical phenomena (outgassing, arcs, discharges, radiation, field emission, beam strike, dark current etc. ) – components response (arc detectors, HOM couplers, Cold Cathode Gauges, coupler cooling, end group heating) – controls (LLRF logic, programming, choice of limits and stability parameters) • Improve performances and ultimate beam power by: 33 – Optimizing gradients, modulator voltages/configuration, matching of klystrons to cavities, circulator settings, available forward power for beam loading, cryomodule Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Status of components and parts • FPC; very stable/robust • HOM coupler; vulnerable component

Status of components and parts • FPC; very stable/robust • HOM coupler; vulnerable component especially during conditioning • Cavity – MP; about 25 cavities show MP, not a showstopper – Field emission; very stable; not changed, main limiting factor – Errant beam could degrade cavity performance (had 2 events) • Tuner; vulnerable component (both piezo and mech. ) 34 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Performance degradation by errant beam • First time in 5 -years operation + commissioning

Performance degradation by errant beam • First time in 5 -years operation + commissioning • Limiting gradient of two cavities; 14. 5 MV/m due to FE Partial quench at 9 MV/m • Beam between MPS trigger and beam truncation off-energy beam much bigger beam loss at further down-stream gas burst redistribution of gas/particulate changes in performance/condition • Random, statistical events; made HOM coupler around FPC worse Cavity field Forward power Partial quench 35 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

At errant beam condition; MPS • MPS – If RF field regulation becomes bad,

At errant beam condition; MPS • MPS – If RF field regulation becomes bad, RF/beam truncation – If BLM signal touches the threshold, beam truncation – MPS; supposed to be less than 20 -30 us • Had performance degradations with 2 cavities claimed that errant beam is too frequent and MPS delay looks long • Measured all MPS delay in the linac; 50 -300 us – Caps, some open collector circuit 36 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Errant beam from the source MPS truncation <30 us Before improvements of MPS (50~300

Errant beam from the source MPS truncation <30 us Before improvements of MPS (50~300 us) 37 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Tuner • Pressure incidents, 2 -4 -2 K transition, or just short life time

Tuner • Pressure incidents, 2 -4 -2 K transition, or just short life time about 10 tuners are replaced. – Harmonic driver, piezo stack (and/or motor) failure – Worn out in progress, loosen connection, slips; unstable mechanical boundary; irregular detuning Motor & Harmonic Drive Piezo Actuator (2 X) Flexure Connection to Cavity 38 (2 X) Flexure Connection to Managed by UT-Battelle Helium Vessel for the U. S. Department of Energy Connection to FNAL Vessel Visit, September 30, 2010 Helium

Irregular dynamic detuning (9 b) Eacc Tuner motion 39 Managed by UT-Battelle for the

Irregular dynamic detuning (9 b) Eacc Tuner motion 39 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Cryogenic loads (I) Dynamic load estimation; provide constant load condition to cryogenic system for

Cryogenic loads (I) Dynamic load estimation; provide constant load condition to cryogenic system for reliable 2 K operation Static loss (20~25 W/cryomodule) total ~500 W Thermal radiation from fundamental power coupler static; without RF dynamic; with RF estimation 20~50 W to 2 K circuit at 1 MW beam operation Cavity surface dynamic loss (design parameter Qo > 5 e 9 at 2. 1 K) BCS resistance (~6. 5 n. Ohm at 2. 1 K, 805 MHz) Qo~1. 1 e 10 (MB) residual resistance (10 n. Ohm) Qo~1. 3 e 10 (HB) Other heating; FE, MP, pure Q-deacy Ex. at 6. 5% duty at 60 Hz & at design gradient Pbcs(6. 4 n. Ohm)+Pres(10 n. Ohm)=130 W, Pother=210 W Qo=5 e 9, 40 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Cryogenic loads at the present operating condition RF off RF on Helium pressure; ~0.

Cryogenic loads at the present operating condition RF off RF on Helium pressure; ~0. 04 atm Total heater power; 1750 W Helium flow rate; ~105 g/s Total heater power; 1490 W Turned off all SRF cavities 41 • Overall Qo~4. 5 e 9 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Operation temperature 4. 6 K 4. 4 K Best SNS with the existing SNS

Operation temperature 4. 6 K 4. 4 K Best SNS with the existing SNS cryo-plant at the SNS SCL layout Relatively low frequency, low field, high static loss, field emission ; 2 K is not optimum 42 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Operational efficiency w/ existing SNS cryo-plant ~30 Hz operation very marginal Duty= 0. 08

Operational efficiency w/ existing SNS cryo-plant ~30 Hz operation very marginal Duty= 0. 08 0. 06 Limitation of He flow rate Cold box 0. 04 0. 02 with a cryo-plant to be designed at the SNS SCL layout Given the design of the cryogenic plant, the highest overall efficiency is not necessarily achieved when the nominally optimal thermodynamic conditions are reached. Since the cryogenic plant has to run at a fixed load no matter what the actual static and 43 dynamic Managed by UT-Battelle loads from the cryomodules, a more efficient use of the plant would be for the U. S. Department of Energy FNAL Visit, September 30, 2010 at temperatures different from the designed ones.

SCL for the Design Goal • 1 ms beam pulse – 1350 us HVCM

SCL for the Design Goal • 1 ms beam pulse – 1350 us HVCM 1270 us RF (300 us filling + 30 us FB stabilization + 950 us beam) – Shorter filling time (need more RF) 950 us 1000 us • 26 -m. A average current (or 38 -m. A midi-pulse current) at 1 -Ge. V operation – Need more RF available for the design beam current • 1 -Ge. V energy + energy reserve (~40 Me. V) – All cavities in the tunnel in service 940~950 Me. V (no reserve) – SCL HB cavity performances should be improved (+2. 5~3 MV/m) 44 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010 Additional HVCM/HPRF Configuration ; done

Increasing the Beam Energy • Repaired ~12 cryomodules to regain operation of 80 out

Increasing the Beam Energy • Repaired ~12 cryomodules to regain operation of 80 out of 81 cavities – CM 19 removed: had one inoperable cavity (excessive power through HOM); removed both HOM feedthroughs – CM 12 removed: removed 4 HOM feedthroughs on 2 cavities – Tuner repairs performed on ~9 CMs – We have warmed up, individually, ~12 CMs in the past 4 years – Individual cryomodules may be warmed up and accessed due to cryogenic feed via transfer line. • Installed an additional modulator and re-worked klystron topology in order to provide higher klystron voltage (for beam loading and faster cavity filling) 45 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Efforts for SCL performance improvement • Reworks; removing, disassembling, reprocessing, assembling not a realistic

Efforts for SCL performance improvement • Reworks; removing, disassembling, reprocessing, assembling not a realistic approach • Attempted Helium processing did not work due to heavy MP around HOM coupler • Plasma Processing the first attempt gives a promising result. R&D programs are on-going • Spare cryomodule for major repair work of weak cryomodule. Fabrication is on-going 46 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

in-situ plasma processing; first attempt • In-situ plasma processing; First attempt with H 01

in-situ plasma processing; first attempt • In-situ plasma processing; First attempt with H 01 showed very promising results • Set a systematic R&D program to find optimum processing conditions • Hardware preparations are in progress Ionization Chamber Internal Ionization Chamber Phosphor Screen, Camera, Faraday Cup IC 1 IC 2 Cavity D Cavity C Cavity B IC 7 IC 3 IC 4 IC 5 Phosphor Screen & Faraday Cup 47 IC 0 Managed by UT-Battelle for the U. S. Department of Energy Cavity A IC 6 Phosphor Screen & Faraday Cup IC-int FNAL Visit, September 30, 2010

Phosphor screen images before processing Cavity D 12 MV/m Camera exposure; 30 ms Cavity

Phosphor screen images before processing Cavity D 12 MV/m Camera exposure; 30 ms Cavity A 9. 3 MV/m Camera exposure; 30 ms Processed at cold and warm up RGA analysis All kinds of C-H-(O)-(N) R&D for room temperature processing Could be a post additional processing (H 2 removal, oxygen layer removal) 48 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Spare cryomodule • Revisit SNS HB cavity processing – Vertical test data has traditionally

Spare cryomodule • Revisit SNS HB cavity processing – Vertical test data has traditionally not been a good indicator of module performance due mainly to field emission limiting the collective gradients of all installed cavities – Field emission on-set point is more relevant criteria – What else can enhance electron activity, especially FE • Lots of processing/testing for 4 cavities 49 – Additional BCP made performance worse in many cases – Random variations of performance/field emission after processing cycle – Visual inspection tells that end group(reactor grade Nb)/first iris is very rough Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Endgroup Roughness Cells have normal surface finish Rough Surface to the First IRIS 50

Endgroup Roughness Cells have normal surface finish Rough Surface to the First IRIS 50 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Summary of Cavity VTA Performance: Cavity Number Emax (MV/m) Rad at Emax (m. R/hr)

Summary of Cavity VTA Performance: Cavity Number Emax (MV/m) Rad at Emax (m. R/hr) HB 53 17. 6 2. 0 HB 58 17. 2 0. 0 HB 56 17. 5 408 HB 54 13. 0 850 Field Emission Tunnel Data RF Only 20 Seconds 51 Managed by UT-Battelle for the U. S. Department of Energy Multipacting FNAL Visit, September 30, 2010 Combination

Spare Cryomodule field emission, pressure vessel, other minor improvement (HOM, cooling, etc) 52 Managed

Spare Cryomodule field emission, pressure vessel, other minor improvement (HOM, cooling, etc) 52 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Power Upgrade Project • Cavity – Field emission onset is more important – End

Power Upgrade Project • Cavity – Field emission onset is more important – End group material; high RRR • Coupler – Inner conductor; improve thermal conduction • HOM coupler – Remove • Pressure vessel 53 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Lessons learned, experiences on design vs. real world • • Performances, Cost, vs. Stability/Availability

Lessons learned, experiences on design vs. real world • • Performances, Cost, vs. Stability/Availability ‘Ideal’ vs. ‘Practically better’ General vs. Machine specific Predictable vs. Unpredictable – Unexpected problems will arise. More complex systems lead to more troubles. • R&D devices vs. Devices for operational machine – To address a specific problem good chance to generate other problems – Typically designers are not operators and vice-versa • Simpler is always better as long as the consequence is acceptable. • Balanced performances lead to the most efficient system. – Overdesign for something while overlooking something else – Limited by the scarcest resource; Law of the minimum • Identify what are the practically important parameters. • Have rooms for failures, system degradation, and unknowns. • Establish ‘reasonably’ conservative physics/engineering margin 54 Managed by UT-Battelle and systems overly optimistic/pessimistic for the U. S. avoid Department of designing Energy FNALusing Visit, September 30, 2010 assumptions.

Thank you for your attention! 55 Managed by UT-Battelle for the U. S. Department

Thank you for your attention! 55 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

supplementary 56 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit,

supplementary 56 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Overall RF characteristic curves 57 Managed by UT-Battelle for the U. S. Department of

Overall RF characteristic curves 57 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010 Presentation_name

Klystron power (HPM readings) at saturation vs. HVCM voltage 22 k. W~25 k. W

Klystron power (HPM readings) at saturation vs. HVCM voltage 22 k. W~25 k. W of RF at saturation/k. V of HVCM 58 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Gradient Limitations from “Collective Effects” • Electrons from Field Emission and Multipacting – Steady

Gradient Limitations from “Collective Effects” • Electrons from Field Emission and Multipacting – Steady state electron activity (and sudden bursts) affects other cavities Beam pipe Temperature Flange T Coupler or Outer T • Electron impact location depends on relative phase and amplitude of adjacent cavities • Leads to gas activity and heating with subsequent end-group quench and/or reaches intermediate temperature region (520 k); H 2 evaporation and redistribution of gas which changes cavity and coupler conditions individual limits; 19. 5, 17, 14. 5 MV/m • Example for CM 13: collective limits; 14. 5, 15, 10. 5 MV/m a b c Linac 08, Victoria Canada 59 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010 d

Collective effects FE; heating vs. relative phase and amplitude b cavity phase a cavity

Collective effects FE; heating vs. relative phase and amplitude b cavity phase a cavity beam pipe a 60 Managed by UT-Battelle for the U. S. Department of Energy b FNAL Visit, September 30, 2010

Radiation signals with RF only Radiation Signals Radiation (arb. unit) 13 a; 14. 5

Radiation signals with RF only Radiation Signals Radiation (arb. unit) 13 a; 14. 5 MV/m 13 b; 15 MV/m 13 c; 15 MV/m 13 d; 10. 5 MV/m 15 a; 19 MV/m 15 b; 17 MV/m 15 c; 21. 5 MV/m (1 unit=10 us) 61 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Accelerating gradients distributions 62 Managed by UT-Battelle for the U. S. Department of Energy

Accelerating gradients distributions 62 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Cryogenic loads (II) Qo~4 e 9 Qo~2. 5 e 9 Qo~1 e 10 Set

Cryogenic loads (II) Qo~4 e 9 Qo~2. 5 e 9 Qo~1 e 10 Set 1; Below FE threshold average~9 MV/m Set 2; 80 % of individual limits averate~13. 8 MV/m Set 3; 88 % of collective limits average~12. 8 MV/m 63 Managed by UT-Battelle for the U. S. Department of Energy Set 3 Set 1 Set 2 900 us 1300 us (300+1000) (300+600) 30 Hz 15 Hz 30 Hz Total dynamic heat loads due to different sources FNAL Visit, September 30, 2010

CW, Pulse (BCS and cooling) Tb=4. 2 K, f=805 MHz, niobium thickness=4 mm (Ti=4.

CW, Pulse (BCS and cooling) Tb=4. 2 K, f=805 MHz, niobium thickness=4 mm (Ti=4. 6 K) 150 m. T Reaches film boiling regime (Ts=4. 53 K) 130 m. T (Ti=4. 56 K, Ts=4. 5 K) CW operation at 4. 2 K, 805 MHz Meet film boiling regime (quench) We tested all cavities at both 2 and 4. 5 The performances are exactly same 64 Managed by UT-Battelle for the U. S. Department of Energy Pulsed operation at 60 Hz, 4. 2 K, 805 MHz No limitation up to or close to the critical field (Rs enhancement at close to K critical field is not concerned) (due to relative low operating frequency, pulsed nature) FNAL Visit, September 30, 2010

Plasma cleaning Ion, molecule (radical), electron contaminants Base material • Ablation – Soft –

Plasma cleaning Ion, molecule (radical), electron contaminants Base material • Ablation – Soft – Etching wettability 65 Managed by UT-Battelle for the U. S. Department of Energy before after • Activation • Crosslinking • Deposition FNAL Visit, September 30, 2010

R&D tools SRF cavity FPC Flange Surface analysis TM 020 Test cavity 3. 4

R&D tools SRF cavity FPC Flange Surface analysis TM 020 Test cavity 3. 4 GHz, TM 020 mode Ep/Bp=1. 12 (MV/m)/m. T Ex. Ep=50 MV/m, Bp=56 m. T Pdiss=36 W at 4. 2 K OD; 150 mm FPC Flange Demountable witness plate -Cold test w/ dual mode (CW or pulse) -Plasma processing Microwave Plasma processor 66 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010 3 -cell cavity

Beam induced trip At normal beam At errant beam Beam pipe temperature w/o beam

Beam induced trip At normal beam At errant beam Beam pipe temperature w/o beam Beam trucation 2. Dark current 1. Errant Beam and RF truncation at upstream 67 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

SCL tuning; beam operation • Beam Energy −Have operated with output energies of 1010,

SCL tuning; beam operation • Beam Energy −Have operated with output energies of 1010, 952, 930, 880, 860, 850, 550 Me. V. −Routine operation has been near 860 -930 Me. V • Tune-up: −It is faster to establish 81 phase/amplitude setpoints in SCL than for the 10 normal conducting setpoints • Flexibility −One of the main benefits of a superconducting linac for proton beams is operational flexibility −We have taken advantage of the flexibility of individually powered superconducting cavities to “tune around” cavities with reduced gradients, etc. −Have operated with as many as 20 cavities turned off in initial tune-up. 68 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Beam loss • Still not fully understood – Halo, Intra beam scattering, etc (multiple

Beam loss • Still not fully understood – Halo, Intra beam scattering, etc (multiple sources) – Normal production; mismatched tuning gives less beam loss • Operation expert’s touch after initial physics tuning • quads ~40 % lower than design Warm Linac vacuum improvements 69 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

Activation decay We finished 1 MW production run 6/29/10. Residual activations in SCL 2

Activation decay We finished 1 MW production run 6/29/10. Residual activations in SCL 2 days after 25 -30 mrem/hr 6 days after 10 mrem/hr Decay around SCL; very fast 70 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010

SCL Activation History NOT Loss limited • Over the last year the SCL activation

SCL Activation History NOT Loss limited • Over the last year the SCL activation is not increasing, even though the accelerated charge increased – Reduced beam loss helps 71 Managed by UT-Battelle for the U. S. Department of Energy FNAL Visit, September 30, 2010