tesla meeting frascati 27/05/03 c. magne cold bpm for ttf2 tesla prototype - low beam impedance -...

Tesla Meeting Frascati 27/05/03 C. Magne

Cold BPM for TTF2Tesla 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 (latheprecision of axial sym.)

Ability to measure sum signal and dark current


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2 : antennae withdrawn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:

filter mono dipole

on TTF: 4 or 8 MHz


78 beam pipe8 mm gap50 mm cavity length140 mm total length with flanges 650 MHz

demountableSevere 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).

TTF1


RESULTS ON TTF1

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

1COL1 : BW = 8 MWmeasurement range : +/- 3 mmdetected signal: FWHM = 130 ns

1: Delta signal2: Sum signal

From noise (15 mV) and sensitivity (1.5 V/mm) levels:

estimated resolution @ 0.8 nC = 10 µm

Extrapolations (caution !) :- resolution ~ beam charge- resolution ~ sqrt ( BW )

Only valid if isolation S/D < 50 dBover whole bandwidth


Reentrant BPM for TTF2Fabrication 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 flange+bellow At DESY Cu coating of the flange+bellow

Firing (900 C) of the BPM cavity Welding of the flange+bellow 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


- Firing 1200°C

• 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

Cold bpm for ttf2 - status

-20

-15

-10

-5

0

5

10

15

20

-20 -15 -10 -5 0 5 10 15 20

distortion

y(-30.5dB)

y(-34.0dB)

y(-40.8dB)

y(-70dB)

y(-40.8dB)

y(-34.0dB)

y(-30.5dB)

y

A

A

A

A

A

A

x

X (mm)

Y (mm)

RF calibration - mapping


-400

-300

-200

-100

0

100

200

300

400

-20 -15 -10 -5 0 5 10 15 20

bpm_ttf2_y 23/10/02

Dy /mV

H

y /mm

CALIBRATION

50

HP8510A Network analyser


HP8510A Network analyser

50

50

CHECK AFTER MOUNTING

r l u

l-24.3 dB

-41.6°deg.

u-17.01-25.6°

-16.95-23.3°

d-17.07-25.5°

-17.07-24°

-24.33-42°


PROPOSED PARAMETERS FOR A BPM @ TESLAto be discussed

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

To be studied:

- isolation of the hybrid coupler- digitized processing after frequency downconversion to 200 MHz.

measurement frequency 900 MHzBessel filter bandwidth 50 MHzdetected signal FWHM 20 ns

position resolution @ 4nC/bunch 1 µmtime resolution 20 ns

working at 2K


“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.


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.

outlookBPM 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).


Transparency D. Nölle


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


Dark Current Monitor – laboratory test

Fmono= 1.3 GHz

Fdip = 2.6 GHz

Alu prototype

An aluminium prototype has been fabricated to study the optimum antenna design.

- Network analyser- testbench

Electronics (analog):

- One unit (refurbished) is avalaible

- Need to build 1 (or 2?) more

tesla meeting frascati 27/05/03 c. magne cold bpm for ttf2 tesla prototype - low beam impedance -...

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