Beam

1
Beam Line Status
2
Topics to be Addressed
4.
4. COBRA End-Cap Insertion Drive System
Status
3.
3. COBRA/BTS Fringe Field Beam alignment
influence

• Degrader
• Commissioning Run
• Results

1.
2.
2. COBRA He-atmosphere
5. ? - Beam Test BTS
5.
6.
. Target System
3
Degrader Run Status

• Total 5 weeks planned Many Problems
  encountered several Surprises
• However some
  interesting facts learned !!!
• Goal
• first time measurement of Beam in COBRA with
  Degrader
• System deployed at the centre of BTS
• understand misalignment problem seen Dec. 2005
• Complications
• First time 6cm Target E employed during MEG
  Commissioning time
• Lost more than 2 weeks of real beam time
• 11 days due to accelerator
• 2 days due to controller problems 3-D
  scanner
• 1 day control computer problems BTS
• 1 day Separator vacuum interlock problems
• Measurements stopped 4 last days lost due to
  interference COBRA stray
• field with other Users beam lines µSR ?M3
  (LTF, GPS) ?E3 µCap-Expt.

4
1st Surprise Missing Rate from 6 cm Target!
R4cm(0.550.05)R6cm (1.8) Measured
??? L. Simons et al (Pions!!!) from geometry
alone would expect 0.67 (1.5)
EXPECTED
Very PROVISIONAL !!! Measured R6cm 1.24
R4cm With slits open However - at 1.8mA 6cm
Target 1.1109 e/s at 4cm Target 7.7108
e/s at factor 1.38 Naïve Model could
explain missing µ rate Surface µ ? Target
Surface e ? Target Volume
Target E 4/6 cm
Projected Intensity dist. (surface)
Low energy ?-production X-sections ? rel. stop
density factors back face/side face/front face
3.3/2.5/1.7
If interpretation Correct ? 6 cm Target BAD for
MEG Dont gain µ have 1.4 more background e
5
2nd Surprise Beam Misalignment Cause!

• Bfield measurements with triple-axis Tesla meter
  BTS showed
• BTS Bfield asymmetry at symmetric distances from
  axis of max. 10G (below axis)
• Equivalent to extra Dipole field
• symmetry points above/below axis for equal
  Bfield 30 cm displaced (therefore
• not error in measurement)
• Area Floor exhibits Remanence Hysterisis
  (remembers if BTS ve/-ve polarity)
• fields very reproducible, max. value on
  Area Floor
• ? Shows iron under the floor !!! which causes
  field lines to be diverted alters the
• symmetry of the solenoidal field at a point
  which is important for focusing
• Further field measurements after DC-test
  with COBRA BTS ON !!!

• Enquired about Hall floor- plans should exist
  lay-out for 40t/m2
• 40 cm thick layer of steel reinforced concrete
• steel layer 30 cm thick starts about 10 cm
  down
• high-quality steel but NOT STAINLESS !!!

6
3rd Surprise Muons Prematurely Range-out!
Expected 100 transmission to centre
COBRA, 50 to end COBRA After degrader
21 MeV/c entry to COBRA
Measured Mean Range at COBRA z -900 mm
R 1460 mm He Equiv. ? 235
µm CH2 Extra Material Thickness TMAT 900 mm He
Equiv. or 145 µm CH2 OR ? 9 Air Contamination
Know that air back diffusion
via leaks problematic as well as
suspect laminar flow Mixing!
test measurement after DC-Test
Measure Range Curve
post BTS to test Momentum
hypothesis
18MeV/c
100
TMAT
50
R 1460 mm He
? 18 MeV/c in He
7
Beam Test Conclusions

• more than 2 weeks of real beam time lost mainly
  due to the accelerator
• 6 cm target proved problematic since beam wasnt
  as expected
• took time to investigate
• possible explanation for lack of increase in µ
  rate from 6 cm Target
• if true 6 cm Target No good for MEG
  signal/noise(e) bad
• magnetic field anomaly found (Iron in floor)
  causes BTS field asymmetry beam
• misalignment (further investigation needed)
• good He circulation crucial for MEG possible
  cause of our muons ranging-out
• range curve post degrader BTS
  should answer this

• Need extra Beam Time (4 weeks) with 4 cm Target
  Degrader
• Only possible after end July (4cm Target)
  start 4cm Target unstable low
• Current MEGAPIE
• Only possible after COBRA stray field influence
  on other beams solved
• To Not Delay MEG - has to be when End-Caps
  mounted however problem
• no magnet measuring machine possible therefore
  NEW APD array Detector
• NEEDED (presented Tokyo Meeting)

8
Question of Muons
Ranging-out
9
COBRA He-Atmosphere
Measure Profiles _at_ Centre COBRA ?X 11.8 mm ?Y
12.0 X0 4mm offset Y0 on axis Rate 8107 µ/s
at 1.8mA, 6cm Target 64 of muons reach
centre !!!
Muons Range-out prematurely
WHY?
Checked

• Too much material in beam?
• Degrader too thick? ?
• New beam window gt190 microns
• Mylar ?
• Air contamination in He !!!
• Momentum too low?
• 6cm Target (transverse offset) ???
• AHW41 Bending magnet ?
• measured momentum spectrum

Checked
10
Beam Materials Momentum

• Degrader 33 measurements per foil made ?
• New Mylar Window - 16 measurements of
• sample of same foil made ?
• Beam Momentum - Integral Differential
  Range Curve
• measured post BTS using 50µm 100 µm
• 
  Mylar foils

Mylar foils Holder
APD Holder
11
Momentum Measurement
Low threshold
High threshold
45.5 mm Air 20 µm Al foil

• Counts µ only (Landau!)
• possible threshold dependence

• Counts µe
• no threshold dependence
• Michel MS same for all
• measurements

Mylar ?RLL? 355 µm ?RUL? 389 µm
?Tµ? (2230 60)keV ?Pµ? (21.8
0.3)MeV/c 3.8 higher than expected, Possible
with 6cm Tg ! Gives lateral shift p change
BEAM MOMENTUM OK !!!
12
COBRA He-atmosphere
2 Measurements used as cross-check

• TU-1530 He-Monitor (Japan)
• Range 0-100 He
• accuracy 1
• Probe part magnetic

• Sonic Gas Monitor SGM (home-made)
• Calibrated Range 92-100 He
• precision 0.3
• microphone speaker magnetic

13
He Monitor Cross Calibration
TU-153 ? 3.5
Measured Concn
SGM ? 0.2
Gas Rack (mixer)
True He-mixture
He
TU-153 Monitor needs correction within 92-100
Range of ? 3.5
Air
14
COBRA He-Measurements
TU-153 sample He via inserted tube Sampling
points A SGM B z 2085 mm C z 705
mm D z 45 mm E z - 355 mm
Pos Comm Run DC Run B 97
93 C 96 92 D 90
89 E 91 89
P r o v i s i o n a l
3 to 9 Air
7 to 11 Air

• He-gradient, worst US !!!
• explains ranging-out of Muons
• He gas distribution too simple
• Care with final gas system !!!

15
Beam Misalignment BTS COBRA
Influence
16
Beam Misalignment/Fringe Field Problem
Initial field measurements during this run with
BTS ONLY showed ? iron under the floor !!!
which causes field lines to be diverted alters
the symmetry of the solenoidal field at a
point which is important for focusing
Measurements
extended to Final BTS settings COBRA
Series of measurements done at US DS faces of
BTS with BTS alone BTS COBRA Asymmetry (beam
pipe dia.) BTS alone US 6 G, C 7G, DS 5G
BTS COBRA US 6G, C 0.6G, DS 29G
17
Radial BTS Symmetry (No COBRA)
BTS Measured radial Symmetry distributions US/DS
at beam pipe Diameter I -200A v. Simple
c-of-g interpretation Magnetic axis
centre US r2.1 mm, ?292.5 Field Asymmetry
11G DS r 6.0 mm, ?247.5 Field Asymmetry
33 G
Bot
18
Radial COBRA Asymmetry BTSCOBRA
COBRA Measured radial symmetry distribution US at
beam pipe diameter IBTS -203A,
ICOBRA360/320A v. Simple c-of-g
interpretation Magnetic axis centre
US r1.7 mm, ?240
asymmetry 55G Problem to be studied by PSI
Magnet Group !!!
Influence on µ-Beam COBRA Beam Centroid
Excursion
COBRA centre
COBRA centre
19
COBRA End-Cap
Insertion Drive System
20
COBRA US End-Cap System
US End-Cap schedule Bieri Engineering
manufacture costs 55 kCHf delivery to PSI
THIS WEEK (2 weeks late)
21
Insertion System
Detailed FEM study
View from Inside COBRA

• Gas-tight to He-side CH2/EVAL window
• normally connected to motor-driven accelerator
• beam tube
• frictional hand-drive via electric
  drill/crank-handle

Electric-drill or hand drive
22
COBRA DS End-Cap Insertion Drive Systems

• Complication encountered with DS End-Cap
  Insertion Drive System
• Offer received from Bieri Engineering 200kCHf
  !!!
• successful negotiations with PSI Management for
  extra money
• MEG project raised to priority 1 again hence
  PSI workshops can take-over
• assembly testing of complete system Bieri
  price now 140 kCHf
• Delivery schedule End-August DS End-Cap
  (as planned but v. tight)
• Mid-September
  Insertion Drive System

23
BTS ?-Beam Test
24
BTS Pion Beam Test

• 1st MEG ?-beam Studies in 2004
• part of momentum spectrum study
• 25-33 MeV/c
• dedicated runs at 56 MeV/c 103 MeV/c
• CEX run in ?E5 at 112 MeV/c Oct. 2004
• ALL BEFORE BTS ARRIVED!!!
• Problem BTS cannot be excited to transmit
• Momenta gtgt 70 MeV/c since
• maximum IBTS 270 A
• exceeds allowed force on COBRA coils

Results ?- Integral Spot
Rates in MHz for 1,8mA Proton Current 4cm
Target E Measured UPSTREAM of BTS position
Normalized to Momentum Slit Settings
FS41L/R 250/280 FS43L/R 240/220
Measured US BTS
Solution - should be able to transmit 56 Mev/c
particles (228 MeV/c) with Good optics
56 MeV/c R? 7.6 106 ?-/s slits open
R? 7.2 105 ?-/s slits70/70
25
BTS ?-Beam Test cont.

• BTS test done last week
• Problem encountered Hamamatsu APD
• used for µ (no scint. but utilize
  Nuclear Counter Effect)
• has no pulse-ht. resolution for ?- CANNOT
  DISTINGUISH e- ?-
• measured at 56 MeV/C 107 MeV/c with APD
  Pill Counter (scintillator)
• see pions electrons with pill-counter BUT
  CANNOT USE WITH BTS BFIELD
• HOWEVER
• COULD TRANSMIT 56 MeV/c PARTICLES as expected

BTS Excitation Curve For 56 MeV/c particles
Question What are expected low-energy Pion
Beam Rates at centre of COBRA?
26
BTS ?-Beam Test cont.
Expected low-energy Pion Beam Rates at centre
COBRA for 1.8 mA Proton Beam 4 cm Tg. Taking
decay-rate into account
Expected Pion Beam Rates Centre COBRA
70 MeV/c ? 1.6MHz at 1.8mA IPROT

• CONCLUSION
• APDs with scintillators needed for Expt.
• Cross-System of 13 APDs must be built
• before final Commissioning with 4cm Tg
• max. ?- momentum for good optics
• 70 MeV/c !!!
• expected rate (slits open) 1.6 MHz at COBRA
  centre

27
Target System UCI
28
Target System Mechanical Requirements

• Substantial Progress made with Target System
  since last Review !!!
• Supported from DC Support Structure
• externally surveyed introduced with DCs
• possibility to move target for End-Cap Insertion
  System introduction (C-W, LH2,)
• ? target parking
• Mechanically stable reproducible positioning

DC Support Structure
Target movement
New method of Parking using Translation rather
than Rotation
29
Target System Characteristics

• Present Target Characteristics
• Ellipse (210 x 70)mm Polyester foil 175 µm
• freely suspended by support pins from a
• thin Rohacell support frame at 22 to axis
• (differential expansion)
• frame attached by Rohacell support stems
• mounted on v. thin movable rods
• Driven by pneumatic drive

• Current Status UCI
• prototype system
• successfully tested
• Final System
• All parts machined
• Assembly testing about
• to start
• target foil material angle
• still under study

Pneumatic Drive
DC Support
Rohacell
Movement
30
Prototype Target Performance

• Thin film (175 micron) target material to be
  determined
• soft polyethylene too difficult to maintain
  flat
• Various polyester, polystyrene, hard
  polyethylene materials possible
• Implementation
• Target flatness controlled by Rohacell frame
  clamping two frames together allows control of
  flatness
• Hanging film between frames
• allows for differential expansion
• without deformation of film
• Distance between frames controlled
• by washers at screw locations
• Final frame cut precisely with high
• speed CNC router
• Nylon screws/nuts used to reduce mass

31
Prototype Target Performance cont.

• Flatness measured by reflected laser off target
  surface and measuring reflected angle as laser
  spot is scanned across target.
  Z(x,y) Z(0,0) ? (dz/dx)dx ?(dz/dy)dy
• Target measured to be flat to less
  than /-100 microns

Target Size Study
Measured 45 target ? 88 stops Slanted target
gives leakage due to MS
Relatively insensitive to vertical size down to
5.7cm Relatively insensitive to length down to
19 cm HOWEVER Thickness of 175 microns
required Final Parameters slope sense still
under study
32
Schedule

• US End-Cap
• Delivery US COBRA End-Cap end June
• US End-Cap preparations mounting PSI workshops
  6WD installation after US TC
• US End-Cap installation 5WD Beg. Sept.
• Target System
• Production End July
• Target assembly installation 2W
• DS End-Cap Insertion Drive System
• Delivery DS COBRA End-Cap End Aug. Mid Sept.
• Delivery Insertion Drive System Mid Sept.
• DS End-Cap preparations mounting PSI workshops
  6WD installation after DS TC
• Insertion Drive System mounting testing PSI
  workshops 6WD
• DS End-Cap Insertion Drive System
  installation 10WD End. Sept.
• Beam Commissioning (degrader 4cm Tg.)
• Beam Line setup survey 5WD post US End-Cap
  Beg. Sept.
• BTS cryo-connections pump cool-down 8WD