NLC - The Next Linear Collider Project

Tuesday, June 25, 2002 Marc Ross – ISG8

Author NameDate

Slide #2

Beam Tilt MonitorMarc Ross ISG 8– SLACJune 26, 2002

CLIC J/NLC TESLA

Why measure tilt?• Most emittance dilution effects introduce a first order

y – z or x – z correlation(also E – z is very interesting)

• Profile monitors are ineffective at measuring small correlations– Measures projection – and that with at best 5% (SLC ~10%)– Very sparsely located

• A ‘tilt’ (y – z) monitor with 1 mrad resolution allows rapid tuning of linac

• Important for IP • Two methods proposed:

– Transverse deflecting structure (RF streak)– Cavity BPM

NLC linac should not be tuned as SLC was!

Author NameDate

Slide #3

Beam Tilt MonitorMarc Ross ISG 8– SLACJune 26, 2002

CLIC J/NLC TESLA

Transverse deflection Old idea – 1965 ‘LOLA IV’Testing in linac sector 29

Brute forceCalibratedExpensiveExcellent resolution

SLAC LCLS – Krejcik/Emma (EPAC 02)SLAC/DESY TTF2

Krejcik / Emma EPAC 2002

Krejcik / Emma EPAC 2002

Krejcik / Emma EPAC 2002

Author NameDate

Slide #8

Beam Tilt MonitorMarc Ross ISG 8– SLACJune 26, 2002

CLIC J/NLC TESLA

Response of Cavity BPMto Point Charge

S. Smith – Snowmass 2001

Q

�

)sin()( taqtV ���

Response of BPM to Tilted BunchCentered in Cavity

q

2sincos

2)

2(sin

22)

2(sin

22)( ttt tqatqatqatV ��

���

���

��

�����

Treat as pair of macroparticles:

���

�tq/2

���

q/2

Tilted bunch

)sin()( taqtVy ���• Point charge offset by �

• Centered, extended bunch tilted at slope ���t

• Tilt signal is in quadratureto displacement

• The amplitude due to a tilt of ��� is down by a factor of:with respect to that of a displacement of �(~bunch length / Cavity Period )

2sincos

2)( t

t tqatV ���

��

TVV tt

y

t

24����

��

Example

• Bunch length �t = 200 �m/c = 0.67 ps • Tilt tolerance d = 200 nm• Cavity Frequency F = 11.424 GHz• Ratio of tilt to position sensitivity ½�f�t = 0.012• A bunch tilt of 200 nm / 200 �m (1 mrad) yields as much signal

as a beam offset of 0.012 * 200 nm = 2.4nm• Need BPM resolution of ~ 2 nm to measure this tilt

• Challenging!– Getting resolution– Separating tilt from position

• Use higher cavity frequency?

Need 1 mrad tilt sensitivity for linac tuning

Angled trajectories

��y res/�y ~ 5%��y’ res/�y’ ~ 10x

Relative normalized precisionBeam position/beam traj angle

• A trajectory that is not parallel to the cavity axis also introduces a quadrature signal (in phase with ‘tilt’ signal)

• Projected ‘dipole’ sensitivity is increased by �z/cavity length– ~ 50

Cavity BPMFFTB (Shintake) ATF ext line (Vogel) X-band (Naito)

f 5.712 6.426 11.424 (GHz)position resolution 20 200 200 (nm)Vt/Vy (200um sig_z) 0.6% 0.7% 1.2% (.5 pi sig_t f)achieved 'projected dipole resolution' (200um sig_z) 3.3 29.7 16.7 umachieved 'tilt' angle resolution 17 149 84 mradachieved 'trajectory angle resolution' 3 26 30 uradcavity 'length' 15 15 8 mm

�

ATF �z ~ 8mm gives expected tilt resolution ~ 0.1mrad

�Wave cavity BPM X-band

12 mm bore

Naito/Li

Very good resolution possible – 25 nm achieved in FFTB few nm possible by limiting spatial dynamic range

ATF Cavity BPM – V. Vogel / H. Hayano ATF extraction lineC-band cavityL = 12mm, Radius = 26mm, f = 6426MHz, �=46.6mmMovers – x, y, pitch (y-z)

Author NameDate

Slide #15

Beam Tilt MonitorMarc Ross ISG 8– SLACJune 26, 2002

CLIC J/NLC TESLA

ReferenceCavity

BPMcavity C-band

Amplifiers15dB gain

X

X

X

Splitter

6410MHzsource

StriplineBPM

4:1 combinerX4

Scope, 250Ms/s4 channel, external trigger500 samples/ch

20MHz BW limit

Ch1

Ch2

Ch3 (Y)

Ch4 (X)

Tilt monitor electronicsJ. Frisch

Author NameDate

Slide #16

Beam Tilt MonitorMarc Ross ISG 8– SLACJune 26, 2002

CLIC J/NLC TESLA

Raw ‘mixed –down’ scope data from cavity BPM

Phase and amplitude wrt ref are extracted

(I and Q)

Author NameDate

Slide #17

Beam Tilt MonitorMarc Ross ISG 8– SLACJune 26, 2002

CLIC J/NLC TESLA

If there is a large offset in one plane, and little in the other, we see beating between modes

(nominally cylindrically symmetric cavity)

Author NameDate

Slide #18

Beam Tilt MonitorMarc Ross ISG 8– SLACJune 26, 2002

CLIC J/NLC TESLA

I Q response as the cavity is moved vertically using mover

The angle is arbitrary (phase offset between ref and BPM cavity)

A ‘monopole’ beam with an axial trajectory should give a (0,0) response at some point

Author NameDate

Slide #19

Beam Tilt MonitorMarc Ross ISG 8– SLACJune 26, 2002

CLIC J/NLC TESLA

Use the cavity ‘tilter’ to observe response to tilted trajectories

(Beam ‘tilter’ was not ready during this test – May 2002)

Compare 35 urad with 26 in table estimate

Author NameDate

Slide #20

Beam Tilt MonitorMarc Ross ISG 8– SLACJune 26, 2002

CLIC J/NLC TESLA

SLD at SLC – the innermost vacuum chamber is a crude cavity BPM

Author NameDate

Slide #21

Beam Tilt MonitorMarc Ross ISG 8– SLACJune 26, 2002

CLIC J/NLC TESLA

Plans• Collaboration with LBNL for cavity BPM ‘tiltmeter’

– AFRD and UCB Physics Department– Possible use at LBL ‘Femtosecond Light Source’– LDRD application submitted for 2003 funding

• Tests at ATF in November 2002• Couple with tests of deflecting structure – TTF2

• Cavity BPM is a ubiquitous device and can serve many functions –• calibration and modeling (PT)• beam ‘angle’ monitor• structure manifold BPM’s