Pr

1
Cold BPM for TTF2

• Tesla prototype
• - low beam impedance
• cooling to 2K without strain

- Low beam coupling impedance reduces the beam
break-up forces and minimizes the cryogenic
heat-load due to resonances. - The (axial)
geometry is favorable to cooling to 2K without
strain. - The dimensions are small. - The design
is adapted to UHV dust-free conditions. - The
mechanics is relatively simple to machine
(lathe?precision of axial sym.) Ability
to measure sum signal and dark current
2
WIDE-BAND MEASUREMENT

• Antennae mechanically and electrically connected
  to opposite wall of the cavity
• very low external Q

1 antennae fully pushed 100 MHz bandwidth 2
antennae withdrawn
Then the BPM bandwidth is determined by the
Bessel filter downstream
on TTF 4 or 8 MHz
3
TTF1
f 78 beam pipe 8 mm gap 50 mm cavity
length 140 mm total length with flanges 650
MHz demountable Severe tolerances were applied
on R1, R2, and the perpendicularity of the
assembling surface (2/100). Concentricity
actually measured better than 20 ?m.
When cooling down to 2K - the cylindrical shape
of the cavity, and the outer position of the
antennae, are perfectly preserved - the room t
calibration is still valid (out of resonance
measurement).
4
RESULTS ON TTF1

• 5 reentrant BPM installed on BPM,
• one at 2K inside the capture cavity cryostat.

1COL1 BW 8 MW measurement range /- 3
mm detected signal FWHM 130 ns
1 Delta signal 2 Sum signal
From noise (15 mV) and sensitivity (1.5 V/mm)
levels estimated resolution _at_ 0.8 nC 10 µm
Only valid if isolation S/D lt 50 dB over whole
bandwidth
Extrapolations (caution !) - resolution beam
charge - resolution sqrt ( BW )
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22/01/02 Reentrant BPM for TTF2 Fabrication and
mounting procedure      
Reentrant BPM for TTF2 Fabrication and mounting
procedure    Fabrication of the BPM cavity
The 2 parts of the cavity are assembled by EB
welding Leak test Fabrication
of the feedthroughs. At Saclay Fabrication
of the part flange with bellow. (Shorten the
bellow) Firing of the flangebellow At
DESY Cu coating of the flangebellow
Firing (900 ?C) of the BPM cavity Welding
of the flangebellow to the BPM cavity. At
DESY RF calibration. At Saclay   Welding
to quadrupole beam tube, (TIG welding from
inside, with tool providing centering and
azimuthal positioning). At DESY
Cleaning of the BPM cavity. Cleaning of the
feedthroughs. At DESY Mounting onto
quadrupole, (Centering of the BPM w.r.t. the
quad is made with an external part, which is
fixed by a few TIG welding points) At DESY
 
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Cold bpm for ttf2 - status

• - Firing 1200C
• Cu coated bellow (Fluhman)
• RF calibration on testbench (rod simulates beam)
• Chemistry
• TIG welded (from inside) to quad beam pipe
• Will be installed in ACC1

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CALIBRATION
8
CHECK AFTER MOUNTING
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PROPOSED PARAMETERS FOR A BPM _at_ TESLAto be
discussed

• The ratio (meas. range)/resolution cannot exceed
  a few 102.

measurement frequency 900 MHz Bessel filter
bandwidth 50 MHz detected signal FWHM 20
ns position resolution _at_ 4nC/bunch 1 µm time
resolution 20 ns
working at 2K
To be studied - isolation of the hybrid
coupler - digitized processing after frequency
downconversion to 200 MHz.
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  R and D on rf-cavity BPM inside a
cryomodule in the SRFTECH Joint Research
Activity.   (SRFTECH , Superconducting
Radio-frequency Technology, Co-ordinator T.
Garvey )     testing of one such BPM in a TTF2
module, and possibly the design of a new
electronics.   Milestones Mid-2004 (As soon
as TTF2 commisionning with beam is started)
results of the prototype installed in the cold
module performance with analog electronics and
cryogenic losses. Beg-2006 Commissionning of BPM
with new digital electronics.       If approved
this program will start beg. of 2004.
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outlook
BPM based on a cylindrical reentrant RF cavity
equipped with 4 weakly coupled antennae. The
associated wideband electronics allows 100 ns
time-domain response without too much degradation
of the resolution (in the case of the very short
TESLA bunches).
Possible program for a new R D
An improvement in the resolution, flexibility
and cost of the BPM is needed to meet the TESLA
requirements. The goals for the new R D are  
- To increase the resolution to 10 µm while
keeping a fast time response. This will will be
obtained by 2 improvements - optimization of the
rf cavity shape to have a better common mode
rejection, - design and fabrication of a high
isolation hybrid coupler.
The parameters required for TESLA are a 10 µm
resolution and a time response as low as
possible.   - To adapt the cavity mechanics to
the adjacent new superconducting quadrupole
developed by CIEMAT/DFFPE, Madrid. The alignment
tolerance is 100 µm.
 
- To provide a more flexible operation. This
will be obtained with the design and fabrication
of a new electronics based on digital signal
processing. It will benefit from the low cost
components developed by the telecommunication
industry.  
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Transparency D. Nölle
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Dark Current Monitor - design Optimised to
measure the monopole mode signal at 1.3GHz.
However we keep the 4-antenna design for 2
reasons - the sensitivity and homogeneity of the
dark current measurement is increased - it can be
used as a BPM later, by adding adequate
electronics. Dipole mode frequency 2.6 GHz.
antenna
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Dark Current Monitor laboratory test
Fmono 1.3 GHz Fdip 2.6 GHz
  An aluminium prototype has been fabricated to
study the optimum antenna design. - Network
analyser - testbench
Alu prototype
Electronics (analog) - One unit (refurbished) is
avalaible - Need to build 1 (or 2?) more