1 27 Sep 05 Discussion of anti-DID ( “DIDNT” ? ) A.Seryi September 27, 2005

2 27 Sep 05 Motivation Normal polarity of Detector Integrated Dipole (DID) allows to compensate locally the effect of crossing the solenoid field for the incoming beam, while the field seen by outgoing beam (and low energy pairs) about doubles Reverse polarity of Detector Integrated Dipole (anti-DID) would effectively zero the crossing angle for outgoing beam (and pairs) but would double it for incoming beam Doubling the effective crossing angle for incoming beam may create too much synchrotron radiation size growth (which depend as  SR  5/2 ) Smaller initial crossing angle would ease the use of anti-DID

3 27 Sep 05  sr ~0.3nm (20mrad)  sr ~5nm (20mrad) IP position =0  sr ~ 20mrad IP position free SR in SiD (without DID) No IP orbit correction Both Y and Y’ are zeroed by FD quads offsets (very bad case) Only Y’ at IP is zeroed by QD0 offset Pictures correspond to old (before 2005) SiD field

4 27 Sep 05 Old SiD:  sr =0.3nm (20mrad) 2005 SiD:  sr =0.22nm (20mrad) at IP y= -20.7um, y’= urad Old and 2005 SiD New SiD field is shorter and SR effect is smaller

5 27 Sep 05 with DID or anti-DID Will now include DID or anti-DID In addition to bare SiD, will consider three cases: –DID, both Y and Y’ at IP are zeroed (by QD0 offset and DID) –anti-DID, only Y at IP is zeroed (by QD0) –anti-DID, only Y’ at IP is zeroed (by QD0) Not considered (known will be very bad): –anti-DID, both Y and Y’ at IP are zeroed (by QD0 and QF1) Will calculate and compare –SR size growth, IP coordinates –Post-IP field and post-IP dY, dY’ for outgoing beam Will use 20mrad, then recalculate for 14mrad

6 27 Sep 05  sr =0.19nm (20mrad) y‘ and y at IP are zeroed DID, both Y & Y’ at IP are zeroed SR growth about the same as for bare SiD Post IP field is about doubled by DID IP

7 27 Sep 05  sr =1.6nm (20mrad) y at IP is zeroed, y‘ = -185 urad anti-DID, only Y at IP is zeroed SR effect for incoming beam increased, but may be tolerable even at 20mrad: –For 5nm beam SR effects reduce Luminosity by 5% ( 5/(5^2+1.6^2)^0.5 = ) The effective crossing angle for outgoing beam reduced significantly (zeroed?)

8 27 Sep 05  sr =5.4nm (20mrad) y‘ at IP is zeroed, y = 860 um anti-DID, only Y’ at IP is zeroed SR effects are too big (L reduced to 67%) and would not be tolerable at 20mrad Compensation of post-IP field is the same as in previous case (i.e. very good) Effects of IP offset need to be studied (e+ and e- incoming beamlines are offset (energy dependent), collimation may be affected (especially at low E), etc.)

9 27 Sep 05 Y,  m Y’,  rad  SR, nm L, %Y,  m Y’,  rad  SR, nm L, % Bare SiD DID, y=y’= anti-DID, y= anti-DID, y’= mrad & 14mrad x-ing With 14mrad crossing, can use anti-DID and effectively zero the crossing angle for outgoing pairs –can zero Y at IP for ~no Luminosity cost –can zero Y’ for small Luminosity cost For 20mrad, full strength anti-DID would cause larger Lumi loss, but certainly can use anti-DID with ~50% strength to halve the effective x-ing angle for pairs If IP y’ does not have to be zeroed, all this is much easier

10 27 Sep 05 Conclusion Anti-DID can be used to zero or reduce effective crossing angle for outgoing beam (and pairs) At 14mrad we have much more flexibility, since SR effects are much smaller It is also easier if y’ at IP would not need to be zeroed –flexibility of polarization measurements upstream and downstream need to be considered