The Front End Test Stand at RAL

1
The Front End Test Stand at RAL
Ajit Kurup for the FETS Collaboration IAP
Winterseminar, Riezlern 4 10th March 2007
2
The FETS Collaboration
3
FETS Layout

• FETS main components
• High brightness H- ion source.
• Magnetic Low Energy Beam Transport (LEBT).

• High current, high duty factor Radio Frequency
  Quadrupole (RFQ).
• Very high speed beam chopper.
• Comprehensive diagnostics.

4
Ion Source
Development Goals

• Increase Pulse Length 200µs to 1.5ms ?
• Increase Output Current 35mA to 70mA ?
• Reduce Emittance
• Maximise Lifetime

78 mA H- current 500 µs extract pulse 50 Hz
repetition rate
5
Laser Diagnostic
Non-destructive emittance and profile measurement
device
Scan the laser across the beam in x and y
direction to get transverse profile.
6
Laser Diagnostic
Linear travel 150mm (1?m res.) Rotary res.
0.1mrad
Vacuum pumping tank after ion source
Amplifiers and power supplies
Motion controller
Encoders
Linear stage
Rotary stage
7
Pepperpot Diagnostic

• Current Allison-type scanners give high
  resolution emittance measurements, but at fixed
  z-position and too far from ion source.
• X and Y emittance also uncorrelated, with no idea
  of X Y profile.
• Correlated, 4-D profile (x, y, x, y) required
  for accurate simulations.
• Pepperpot reduces resolution to make correlated
  4-D measurement.
• Moving stage allows measurement at different
  z-locations space charge information.

8
MK I Pepperpot Setup
9
MK I Results
X emittance
False colour data image using P43 scintillator
Y emittance
10
MK I Problems
P43

• Screen too small only see full beam at small
  z-postion.
• Poor quality holes in tungsten (size, shape,
  spacing).
• Destructive testing of scintillators ?
• Fast (down to 500ns exposure).
• High light output.
• Survives beam (lt1 micron stopping distance).
• Poor mechanical stability.
• Mounted at an angle

Al coating
profile with quartz and no pepperpot
plastic scintillator
ruby and Al plate
11
MK II Pepperpot Design

• Better support structure.
• Cooling for pepperpot head.
• Second mount for profile measurements.
• Improved DAQ and data analysis.
• Fast camera.

• Larger screen 41x41 holes, 120mm x 120mm, 50
  micron holes.
• Switch to pure and Ce-doped quartz
• Pure survives beam, but slow.
• Cerium-doped quartz is fast, high light output,
  but survival time unknown.

Tungsten mesh
Pepperpot head
12
RFQ

• 60mA H- beam
• Accelerate from 65keV to 3MeV.
• Input emittance is 0.25? mm mrad
• Transmission efficiency is 95.
• Initial design done by Alan Letchford.
• Consider both 4 rod and 4 vane designs and build
  cold models.
• A few pros and cons

13
Tracking Studies
Beam distribution at RFQ input using a waterbag
generated beam after tracking from the ion source
exit through the 3 solenoid LEBT. ex,rms 0.33
pmmmrad ey,rms 0.33 pmmmrad
Input distribution using measurements from the
pepperpot after tracking through the 3 solenoid
LEBT. ex,rms 1.21 pmmmrad ey,rms 0.93 pmmmrad
Presented at LINAC06
14
Tracking Studies(2)
Particle distribution after the RFQ using the
generated input distribution. ex,rms 0.35
pmmmrad ey,rms 0.35 pmmmrad Transmission 80
(ion source ? rfq)
Particle distribution after the RFQ using the
measured input distribution. ex,rms 0.62
pmmmrad ey,rms 0.62 pmmmrad Transmission
40 (ion source ? rfq)
Presented at LINAC06
15
4 Vane Cold Model Simulations
Results presented at EPAC06
16
4 Vane Simulations - Update
0.4m long Cold Model
1m long section
Investigate the effect of the end flanges in
simulations and measurement on the cold model
CST Studio 2006B
17
4 Vane Coupling Power In
Waveguide to Coax transition
Need to find the optimal way to split the power
Coupling into the RFQ using coax to loop.
Waveguide to iris coupler also being investigated
18
First 4 rod simulations
Surface current distribution shows the currents
are concentrated near the join between the stem
and the rod.
Results presented at EPAC06
19
4 rod simulations
CST Studio 2006B
Temperature Distribution
Thermal Losses
Static thermal analysis taking into account only
conduction through the copper rods and stems.
Background temperature was 25C and boundaries
were open.
Surface currents normalised to an average power
of 100kW.
20
4 rod simulations(2)
Investigate different geometries near the
rod-stem interface with the aim to smoothen out
surface current (and hence thermal loss)
distribution.
Temperature Distribution
Surface currents normalised to an average power
of 100kW.
Thermal Losses
21
Bead Pull Diagnostic
ISIS 4 rod RFQ Cold Model
22
Cold Model Manufacturing
New major-minor vane design and improved undercut
design
Old vane design
Machining at IC
23
Beam Chopper and MEBT
Scheme C
24
Beam Chopper and MEBT
Scheme A
MEBT Schemes
25
Summary and Plans

• Ion Source
• Improve emittance and lifetime
• LEBT
• 3 solenoid MAFIA simulations done. Engineering
  of the solenoids is next.
• RFQ
• 4 Vane
• Investigate ways to shift dipole modes.
• Input power coupling.
• 4 Rod
• Investigate cooling solutions.
• Chopper and MEBT
• FPG nearly met spec. SPG development beginning.
• Cavity and quadrupole design in progress.
• Diagnostics
• Manufacturing of MKII Pepperpot in progress.
• Laser profile first measurements end of year.
• Laser emittance first design phase.

26
Timescale
RD phase Design Construction
phase Installation and Commissioning phase