the main injector program
DESCRIPTION
Electron Cloud Measurements at the Fermilab Main Injector Bob Zwaska Fermilab ECloud07 Workshop April 9, 2007. The Main Injector Program. Provides high power, 120 GeV proton beam 80 kW for antiproton production 180 kW for neutrino production - PowerPoint PPT PresentationTRANSCRIPT
1
Electron Cloud Measurements
at the Fermilab Main Injector
Bob Zwaska
Fermilab
ECloud07 Workshop
April 9, 2007
2
The Main Injector Program
(Double) Batch 1 (PBar)
Batch 2
Batch 3
Batch 4
Batch 5
Batch 6
Booster
Main Injector
• Provides high power, 120 GeV proton beam 80 kW for antiproton production 180 kW for neutrino production
• Takes 6 or 7 batches from the 8 GeV Booster @ 15 Hz 4-5 × 1012 protons per Booster batch
• Total cycle time ≥ 1.4 s + batches/15
NuMI
3
Main Injector Operation• 53 MHz beam
• H=588
• 84-500 bunches
6-10 x 1010 protons/bunch
• Bunch length: 0.2-1.5 m
• Transverse size : 1-5 mm
• Ramps 8 – 120 GeV
0.8 s ramp period
• Passes through transition
• 3-D dampers needed for operation
Resistive wall instability
No evidence of e-p
• Linear growth rate scaling
• Operation limited by fractional loss
Losses < 10%
Maximum charge is secondary
4
Upgrade Plans at Fermilab• Medium term Proton Intensity upgrades
Intended for neutrino program (at first)
• Proton Plan (in progress, done by ~ 2008)
Use slip stacking in Main Injector to increase
proton bunch intensity
• NOvA-ANU (planned for ~2011)
Increase cycling rate of MI by using Recycler
for stacking
• SNuMI (early planning)
Increase proton bunch intensity by using
accumulator for stacking
• HINS (Proton Driver, on hold)
Increase proton bunch intensity through new
8 GeV Linac
5
Evolution of Proton Intensities
• Early plans were to go straight from Proton Plan to HINS Start to get big bunch intensities, and worry about electron cloud
• More recently, upgrade path has lengthened First leg, using the Recycler, does not significantly increase bunch intensity
Other legs still involve some increase
• Miguel Furman did initial simulations of the MI w/ Proton Driver Instigated study program at Fermilab
More calculations from LBL (other talks)
6
First Simulation Input• Simulations suggested that MI might be near a threshold for electron cloud formation
4-5 orders or magnitude increase of cloud density with a doubling of bunch intensity
• Leads to a program of studies: Try to find evidence of a cloud with present MI
Expand simulations
Look at secondary emission in the MI
M. Furman (LBL) FERMILAB-PUB-05-258-AD
7
Dynamic Pressure Rise
See fast rise over the course of a cycle (1s)
The control system induces delay
Occurs only at location of uncoated ceramic
Ion Pump Current
Ceramic beam pipes
Beam Intensity
9
50 Hz Pump
• Higher bandwidth pump
• Saw more structure
Pressure increases with
injections
Increases and decreases during
cycle
0
20
40
60
80
100
120
140
160
180
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8
Time (s)
Pres
sure
Rise
(nto
rr)
Pressure Difference
Inferred Gas Load
20_02
0 84 168 252 336 420 504 588
1.0 × 1011 / bunch0.5 × 1011 / bunch
Type of pump installed at two locations
10
Electron Probe• Retarding Field Analyzer
Borrowed from Argonne
Installed in drift region
• Have a lot of interferenceMagnet bus (grounds)
RF & beam signals (RF noise)
• Being used as an electron counterNot biasing retarder
Filtered output current
Collector
Retarder
11
Cycle Measurement• DC signal seen to spike at middle of cycle
Around the time of transition
• Rapid increase of signal occurs into accelerationDip occurs at transitionMaximum occurs shortly after transitionElectron count decreases toward the end of the cycle
-0.005
0
0.005
0.01
0.015
0.02
0.025
0.03
0 0.2 0.4 0.6 0.8 1 1.2
Time (s)
Cu
rren
t (u
A)
12
Collected results• Large number of cycles sampled
at maximum current
• Clear turn-on at higher intensities
• Noise is bad due to amplifier/MADC system
• 0.2 uA ~ 1% neutralization
• Expect new measurements with 11-batch structure
More high intensity bunches
13
Closer look at Transition• Cloud increases rapidly as size decreases
• Decreases temporarily at minimum bunch lengthWasn’t expected, but repeatable
-0.005
0
0.005
0.01
0.015
0.02
0.025
0.50 0.60 0.70 0.80 0.90
Time (s)
Cu
rren
t (u
A)
14
Another look at Transition• Better filtering/amplifying allow a
closer look Introduces time delay
• Some cloud before transition
• Biggest effect after The dip definitely occurs
• Bunch length dependence looks complicated
Naïve expectation was that shortest bunch length gave highest electron current
• Perhaps due to electron energy or beam pipe geometry (Furman)
15
Secondary Emission Measurement• Measured at SLAC’s facility with actual
MI beam pipe
(Bob Kirby)
• On average, 1.9-2 electrons produced per
incident 400 eV electron on MI pipe
Difference is conditioning
• SEY maximum is far beyond that used in
simulation
POSINST needs more like 1.3-1.5 for
reasonable simulation results
16
Future Measurements• Improve MI detector installation
Better shielded cables and groundsBetter electronics/DAQ
• Real-time bunch-by-bunch tune measurementAchieved by manipulating damper system
• Running sums of beam oscillations
• Well suited for FPGA
May see coherent shifts
• Plan to install new detectors in Booster & RR
• Enameled coatings for high resistivity electrodesFritz Caspers ideaLooking into getting MI pipe coated and installed
17
Summary• Measurements of electron cloud formation in MI
Vacuum pressure rise & Direct electron detection• Suggest few % neutralization
• No Instabilities from electrons
• Dip of electron current at transitionPerhaps due to SEY/geometry effects
• Simulations suggest possibility of thresholdSomewhat consistent with observed turn-onHowever, disconnect on SEYMain Injector upgrades may push us past threshold
• However, none of the approved upgrades do so
• Planning to continue measurementsTest new, higher intensity beamsNew instrumentation